Business Data Communications and Networking, 14th Edition By Jerry FitzGerald Solution Manual

Business Data Communications and Networking, 14th Edition By Jerry FitzGerald

CHAPTER 1 INTRODUCTION TO DATA COMMUNICATIONS Chapter Summary This chapter introduces the students to the concept of data communications in business. It describes why it is important to study data communications and introduces you to the three fundamental questions that this book answers. Next, it discusses the basic types and components of a data communication network. Also, it examines the importance of a network model based on layers. Finally, it describes the three key trends in the future of networking and the importance of cyber security.

Learning Objectives • • • • • • • •

Be aware of the three fundamental questions this book answers Be aware of the applications of data communications networks Be aware of how data communications fit within the discipline of MIS Be familiar with the major components of and types of networks Understand the role of network layers Be familiar with the role of network standards Be aware of cyber security issues Be aware of three key trends in communications and networking

Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

Key Terms American National Standards Institute (ANSI) Application layer Attacks Backbone network (BN) Bring Your On Device (BYOD) Browser-based Cable Circuit Client Cyber security Data link layer Extranet File server Hardware layer Institute of Electrical and Electronics Engineers (IEEE) International Telecommunications UnionTelecommunications Group (ITU-T) Internet Engineering Task Force (IETF) Internet model Internet of Things (IoT) Internet service provider (ISP)

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Internetwork layers Intranet Layers Local area network (LAN) Mail server Native apps Network of Things (NoT) Network layer Open Systems Interconnection Reference model (OSI model) Peer-to-peer networks Physical layer Protocol Protocol Data Unit (PDU) Protocol stack Request for Comment (RFC) Router Server Standards Switch Transport layer Web server Wide area networks (WAN) Wireless access point

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

Chapter Outline 1.1 Introduction 1.2 Data Communications Networks 1.2.1 Components of a Network 1.2.2 Types of Networks 1.3 Network Models 1.3.1 Open Systems Interconnection Reference Model 1.3.2 Internet Model 1.3.3 Message Transmission Using Layers 1.4 Network Standards 1.4.1 The Importance of Standards 1.4.2 The Standards-Making Process 1.4.3 Common Standards 1.5 Future Trends 1.5.1 Wireless LAN and BYOD 1.5.2 The Internet of Things 1.5.3 Massively Online 1.6 Implications for Cyber Security Summary

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

Answers to Textbook Exercises Answers to End-of-Chapter Questions 1. How can data communication networks affect businesses?

Data communication networks can affect businesses by being the foundations for distributed systems in which information system applications are divided among a network of computers. Data communication networks facilitate more efficient use of computers and improve the day-to-day control of a business by providing faster information flow, aiding strategic competitive advantage. They also provide message transfer services to allow computer users to talk to one another via electronic mail.

2. How do data communications networks support the four core capabilities of MIS? The four core areas are: 1) storing and retrieving data, 2) analyzing and visualizing data, 3) automating data operations, and 4) protecting data. Storing and retrieving data is handled using database. There are many different kinds of databases. The most frequently used database in organizations is an SQL database. Analyzing and visualizing data is handled by retrieving the data from a database and importing it into a software program like Excel, Tableau, or PowerBI so that these business questions can be answered using a variety of techniques Automating data operations we have a wide variety of IT we can buy or build using a variety of programming languages. For protecting data, organizations must spend resources to protect their data and ensuring the confidentiality, integrity, and availability of the data.

In order for the IT strategy to implement the core capabilities, data communications and networking infrastructure must be available.

3. Discuss three important applications of data communications networks in business and personal use.

Three important applications of data communication networks in business and personal use include email, videoconferencing, and the Internet.

4. How do LANs differ from WANs, and BNs? A Local Area Network (LAN) is a group of microcomputers or terminals located in the same general area. A Backbone Network (BN) is a large central network that connects most everything on a single company site. A Metropolitan Area Network (MAN) encompasses a city or county area. A Wide Area Network (WAN) spans cities, states, or national boundaries. Typically, MANs and WANs used leased facilities, while LANs and BNs are often located internally in an organization and used owned facilities.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 5. What is a circuit?

The circuit is the pathway through which the messages travel. It can be made up of a copper wire, although fiber optic cable and wireless transmission are becoming more common. A circuit can also pass across many types of physical facilities such as copper wire or fiber optic cable, but the single end-to-end connection, no matter what the equipment, is referred to as the circuit. There are many devices along the circuit’s path that perform special functions such as hubs, switches, routers, and gateways.

6. What is a client?

The client is the input or output hardware device at the other end of a communication circuit.

It typically provides remote users with access to the network and the data and software on the server.

7. What is a server?

The server stores data or software that can be accessed by the clients, or remote users of a hardware input or output device. In client-server computing, several servers may work together over the network to support the business application.

8. What is a router?

A special-purpose computer whose primary job is to find the best route for these packets to their final destination.

9. There are three computers that make the Internet work. Name them and describe their similarities and differences.

There are three computers that make networks what they are. These are the client, the server, and the router. The client initiates a communication with the server by sending a request to the server. Once the server receives the request, it processes it, and responds with a response.

The router makes this connection possible.

10. Why are network layers important?

Communication networks are often broken into a series of layers, each of which can be defined separately, to enable vendors to develop software and hardware that can work together in the overall network. These layers enable simplicity in development and also in the comprehension of complex networks. In the end, the strategy of using more simplistic network layers allows vastly different kinds of equipment to be able to have connectivity over a common platform or network, using protocols and standards that are applicable to each narrow slice of the network.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 11. Describe the seven layers in the OSI network model and what they do.

The application layer is the application software used by the network user. The presentation layer formats the data for presentation to the user by accommodating different interfaces on different terminals or computers so the application program need not worry about them. The session layer is responsible for initiating, maintaining, and terminating each logical session between end users. The transport layer deals with end-to-end issues, such as procedures for entering and departing from the network, by establishing, maintaining, and terminating logical connections for the transfer of data between the original sender and the final destination of the message. The network layer takes the message generated by the application layer and if necessary, breaks it into several smaller messages. It then addresses the message(s) and determines their route through the network, and records message accounting information before passing it to the data link layer. The data link layer formats the message to indicate where it starts and ends, decides when to transmit it over the physical media, and detects and corrects any errors that occur in transmission. The physical layer is the physical connection between the sender and receiver, including the hardware devices (e.g., computers, terminals, and modems) and physical media (e.g., cables, and satellites).

12. Describe the five layers in the Internet network model and what they do.

The application layer is the application software used by the network user. The transport layer deals with end-to-end issues, such as procedures for entering and departing from the network, by establishing, maintaining, and terminating logical connections for the transfer of data between the original sender and the final destination of the message. The network layer takes the message generated by the application layer and if necessary, breaks it into several smaller messages. It then addresses the message(s) and determines their route through the network, and records message accounting information before passing it to the data link layer.

The data link layer formats the message to indicate where it starts and ends, decides when to transmit it over the physical media, and detects and corrects any errors that occur in transmission. The physical layer is the physical connection between the sender and receiver, including the hardware devices (e.g., computers, terminals, and modems) and physical media (e.g., cables, and satellites).

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 13. Explain how a message is transmitted from one computer to another using layers.

The application layer is the application software used by the network user. The transport layer is responsible for obtaining the address of the end user (if needed), breaking a large data transmission into smaller packets (if needed), ensuring that all the packets have been received, eliminating duplicate packets, and performing flow control to ensure that no computer is overwhelmed by the number of messages it receives. The network layer takes the message generated by the application layer and if necessary, breaks it into several smaller messages. It then addresses the message(s) and determines their route through the network, and records message accounting information before passing it to the data link layer. The data link layer formats the message to indicate where it starts and ends, decides when to transmit it over the physical media, and detects and corrects any errors that occur in transmission. The physical layer is the physical connection between the sender and receiver, including the hardware devices (e.g., computers, terminals, and modems) and physical media (e.g., cables, and satellites).

14. Describe the three stages of standardization.

The formal standardization process has three stages: specification, identification of choices, and acceptance. The specification stage consists of developing a nomenclature and identifying the problems to be addressed. In the identification of choices stage, those working on the standard identify the various solutions and choose the optimum solution from among the alternatives. Acceptance, which is the most difficult stage, consists of defining the solution and getting recognized industry leaders to agree on a single, uniform solution.

ISO standards development is pursued at the national and international levels. Authorized national technical committees can be designated as Technical Advisory Groups (TAGs) to international subcommittees or workgroups.

Examples of national-level standards bodies (with the legal authority for national standards development and articulation with ISO) are: Standards Designation ANSI SCC DGN

Name of National Standards Body (ISO Member) American National Standards Institute Standards Council of Canada Dirección General de Normas

BSI JISC

British Standards Institution Japanese Industrial Standards Committee Association française de normalisation Bureau of Indian Standards China State Bureau of Quality and Technical Supervision

AFNOR BIS CSBTS

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Web Site

Nation

www.ansi.org www.scc.ca www.economia.gob. mx/normas www.bsi-global.com www.jisc.org

USA Canada Mexico

www.afnor.fr www.bis.org.in www.csbts.cn.net

France India China

UK Japan

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova GOST R

SNV DIN

State Committee of the Russian Federation for Standardization and Metrology Swiss Association for Standardization (Schweizerische Normen-Vereinigung) Deutsches Institut für Normung

www.gost.ru

Russian Federation

www.snv.ch

Switzerland

www.din.de

Germany

15. How are Internet standards developed?

The Internet Engineering Task Force (IETF; www.ietf.org) sets the standards that govern how much of the Internet will operate. Developing a standard usually takes 1-2 years.

Usually, a standard begins as a protocol developed by a vendor. When a protocol is proposed for standardization, IETF forms a working group of technical experts to study it. The working group examines the protocol to identify potential problems and possible extensions and improvements, and then issues a report to IETF. If the report is favorable, the IETF issues a Request for Comment (RFC) that describes the proposed standard and solicits comments from the entire world. Once no additional changes have been identified, it becomes a Proposed Standard. Once at least two vendors have developed software based on it, and it has proven successful in operation, the Proposed Standard is changed to a Draft Standard. This is usually the final specification, although some protocols have been elevated to Internet Standards, which usually signifies a mature standard not likely to change. There is a correlation of IETF RFCs to ISO standards.

16. Describe two important data communications standards-making bodies. How do they differ?

The International Organization for Standardization (ISO) makes technical recommendations about data communication interfaces. The Telecommunications group (ITU-T) is the technical standards-setting organization of the United Nations International Telecommunications Union (ITU). Postal Telephone and Telegraphs (PTTs) are telephone companies outside of the United States. ITU-T establishes recommendations for use by PTTs, other common carriers, and hardware and software vendors. Although a complicated series of acronyms, it is useful to point out that the ISO created the OSI model!

Information technology standards contribute to data communications. In the USA, the National Committee for Information Technology Standards (NCITS) has responsibility (under ANSI) for multimedia (MPEG/JPEG), intercommunication among computing devices and information systems (including the Information Infrastructure, SCSI-2 interfaces, Geographic Information Systems), storage media (hard drives, removable cartridges), database (including SQL3), security, and programming languages (such as C++). The NCITS T3 committee on Open Distributed Processing (ODP) is the US Technical Advisory Group (TAG) to JTC 1/SC 6/WG 7 (Subcommittee 6, Workgroup 7). JTC 1 is the ISO/IEC Joint Technical Committee 1 on Information Technology. Among NCITS/T3's current projects are: Abstract Syntax Notation One (ASN.1), the OSI Directory Services (and protocols), routing information exchange protocols, multicasting (all of considerable interest to the telecommunications industry.) T3 has US TAG responsibility for codes and character sets.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova IEEE plays an important standards role for data communications, particularly in LAN technology protocols.

Note that the HTML specifications state that HTML uses the ISO 8859-1 (Latin 1) character set.

17. What is the purpose of a data communications standard?

The use of standards makes it much easier to develop software and hardware that link different networks because software and hardware can be developed one layer at a time. The software or hardware defined by the standard at one network layer can be easily updated, as long as the interface between that layer and the ones around it remains unchanged.

18. Discuss three trends in communications and networking.

First, pervasive networking will change how and where we work and with whom we do business. Pervasive networking means that we will have high speed communications networks everywhere, and that virtually any device will be able to communicate with any other device in the world. Prices for these networks will drop and the globalization of world economies will continue to accelerate. Second, the integration of voice, video, and data onto the same networks will greatly simplify networks and enable anyone to access any media at any point. Third, the rise in these pervasive, integrated networks will mean a significant increase the availability of information and new information services. It is likely that application service providers will evolve that act as information utilities.

19. Why has the Internet model replaced the OSI model?

The Internet model is simpler (effectively collapsing the top three layers of the OSI model into a single model) and easier to remember and understand. Further, the ISO OSI Reference Model is the result of a formal standardization process and is technical in its presentation.

By contrast, the Internet model is appropriate for those within the networking community with practical needs related to implementing the Internet and networking.

However, only a few years ago the Internet model was commonly understood to have only four layers. Today, the transport layer is now separately identified in the Internet model, yielding an important, fifth layer for comprehension. This evolution in presentation may show that at least one technical distinction from the OSI model is now considered practical as the scope, volume of traffic, and complexity of networking (and of the Internet) grows.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 20. In the 1980s, when we wrote the first edition of this book, there were many, many more protocols in common use at the data link, network, and transport layers than there are today.

Why do you think the number of commonly used protocols at these layers has declined? Do you think this trend will continue? What are the implications for those who design and operate networks?

Today there is convergence around the non-proprietary use of TCP/IP as the protocol of choice for all networks. For the most part, network software is designed to interface with networks using this protocol. By non-proprietary, this means that TCP/IP is an interoperable protocol portable to any manufacturer's hardware. All manufacturers are developing their products to use TCP/IP as their protocol of choice. This is of great benefit for those operating networks because they do not have to deal with the incompatibilities of various proprietary networks. In the past, network equipment such as IBM’s SNA and Novell’s Netware products had retained proprietary protocols that did not interface with as much ease as today’s more compatible and TCP/IP based products. The decline of the number of competing protocols is related to the emergence of TCP/IP as the universal connector, along with the rise in competition and subsequently better price availability from those vendors who market to this protocol, thus ensuring the viability of this standard for a long time to come for network managers.

21. The number of standardized protocols in use at the application layer has significantly increased from the 1980s to today. Why? Do you think this trend will continue? What are the implications for those who design and operate networks?

The biggest reason that there are more standardized protocols at the application layer is related to the predominant use of the Web and its standardized graphic interface (HTTP, DHCP, for example). In a way, many new protocols ride on top of TCP/IP networks, and some of these new protocols have been developed to enable the retrofitting of new technologies on top of an older networking architecture. On the other hand some proprietary protocols connected with such models as IBM's SNA and DECNet have declined in significance while the importance of Internet-related protocols has grown, 22. How many bits (not bytes) are there in a 10 page text document? Hint: There are approximately 350 words on a double-spaced page. We need 8 bits to encode each character.

First, some assumptions must be made. Assume each word averages seven letters and there is one space between each word. Next assume we are using 8-bit ASCII. Multiply 350 words by 8 bytes (7 letters plus a space) to get 2,800 bytes per page.

Multiply 2,800 by 10 pages to get 28,000 Multiply 28,000 bytes by 8 bits per byte to get 224,000 bits

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 23. What are three cyber security issues?

Students can provide a wide range of answers to this question. Possibilities from the chapter include threats via wireless networks, BYOD devices, IoT, and the massive amount of data online.

24. What is the Internet of Things (IoT)? What are the benefits and risks?

The Internet of Things is the connection of everyday things (refrigerators, watches, TVs, gaming systems, etc that are interconnected seamlessly, without human intervention.

The benefits of IoT include improved consumer satisfaction, ease of use, and improved information availability. Risks include an increased number of devices online that could be used in attacks and dependence on devices that are possibly remotely controlled by criminals.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova Exercises A. Investigate the latest cyber security threats. What services and/or data were affected by these threats? What was done to recover from this situation?

Student answers will vary. One likely response is ransomware.

B. It turns out that not all industries are equally sensitive to cyber-attacks. There are multiple industries that belong to the “critical infrastructure”. Investigate which industries belong to the critical infrastructure, why they are part of it, and what laws govern this group of industries regarding cyber security.

Student answers will vary. One class of likely answers include utilities, such as the electric grid, natural gas, and water. Another class of answers include industries subject to HIPAA and other federal laws. (Your college is subject to FERPA so it too is a possible answer.)

C. Discuss the issue of communications monopolies and open competition with an economics instructor and relate his or her comments to your data communication class.

Student answers will vary.

D. Find a college or university offering a specialized degree in telecommunications or data communications and describe the program.

Student answers will vary.

E. Investigate the IoT. What IoT devices are you most interested in? Why? Student answers will vary. The Internet of things (IoT) is growing rapidly so students have a wide variety of devices to choose from. Basically, anything in the home that can be controlled by an app is part of the IoT. F. Investigate the networks in your school or organization. Describe the important LANs and BNs in use (but do not describe the specific clients, servers, or devices on them).

Student answers will vary. Keep in mind that your school likely has a number of networks.

These might include faculty/administrative, student, learning management system, and WIFI. G. Visit the Internet Engineering Task (IETF) website (www.ietf.org). Describe one standard that is in the RFC stage.

Student answers will vary. You can find more information about RFC’s at https://www.ietf.org/about/participate/get-started/getting-started-appendix/ and https://www.rfc-editor.org/retrieve/. The site does not make it easy to find an answer to this question and the answer varies over time.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova H. Discuss how the revolution/evolution of communications and networking is likely to affect how you will work and live in the future.

Student answers will vary.

I. Investigate the pros and cons of developing native apps versus taking a browser-based approach.

Native apps require an app to be developed for each application that an employee might be using for every potential device that the employee might use. These can be more powerful and better fitted for the device on which they are being used. However, they can take a long time to develop; especially if they have to run on a wide variety of platforms. Discuss with the students any native apps they might use.

The browser-based approach (often referred to as responsive design using HTML5) doesn’t create an app but rather requires employees to access the application through a Web browser.

These only have to be developed once, regardless of the number of platforms but they are limited in appearance and power by the browser.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova Mini-Cases I. Global Consultants What advice would you give Mr. Adams? (...given two de facto standards for financial software, neither of which is completely satisfactory as neither one supports both required financial analysis tasks adequately.)

One solution would be to choose a software source adhering to the de facto standards of either Group A or Group B and attempt to negotiate the development of a new and satisfactory version of the financial analysis task deemed inadequate. This likely would not work because no firm could be found that would agree to develop a new version of its software or because Global Consultants would be expected to bear high development costs to meet its specific need. Most software companies would be unwilling to interrupt or significantly modify a software development schedule for the sake of a single client. .

Thus, if no software source can be found that will undertake the needed development for reasonable cost, the practical solution may be for Global Consultants to undertake a ground up development project of new software that will meet all needs. This could be done internally or by hiring a consultant firm (outsourcing). This approach could be evaluated in light of the firm’s strategic plan, and, if the new software is highly successful for GC, it might become a marketable product for the firm.

II.

Atlas Advertising

What types of standard protocols and technologies do you think they are using at each layer?

Students should refer to Figure 1.5 to address the issues raised with this mini-case.

III.

Consolidated Supplies

Should Consolidated Supplies replace all the networking equipment in all the warehouses now, should it wait until newer networking technologies are available, or should it upgrade some of the warehouses this year, some next year, and some the year after, so that some warehouses will benefit from the expected future improvements in networking technologies?

Students should consider the history of information systems when thinking about this issue.

Rapid changes in technology will continue to make the decision about when to implement new technologies a difficult one for businesses. The solution must be one that fits well with the nature of the organization itself and its corporate, long term goals. If Consolidated Supplies is in an aggressive acquisition mode and involved in a rapidly changing, high tech industry, perhaps a more aggressive upgrade of the network would be appropriate. If Consolidated Supplies is in a market niche that does not face deep market changes and offshore competition for its continued success, and is less concerned about the role of technology in their immediate strategy, then the

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova firm may have the luxury of waiting out a round of technological change in the interest of allowing the future improvements to reach the marketplace.

IV.

Asia Importers

What are the potential benefits and challenges that Asia Importers should consider in making the decision about whether or not to move to one integrated service?

An integrated service will enable Ms. Wong to consolidate her bills and technical support with a single company. This single source of contact would be of benefit to Asia Importers by streamlining services and technological sourcing. However, a potential disadvantage of the single source approach is that the sole vendor would then manage more of Asia Importers’ technical infrastructure, leaving the firm with some vulnerability due to single sourcing. If the vendor proves unreliable or inefficient, this will affect a greater portion of Asia Importers’ business than if the vendor was only servicing one or another technology.

Additional Content Teaching Notes I usually spend 1 hour of class time on this chapter.

My goals in teaching this chapter are to introduce the basic concepts of data communications and to motivate the importance of learning this material for the students. I usually focus on the network layer model approach because this sets the stage for everything that follows in the book.

I take time to trace how a message starts in the application layer and moves through the other layers, each of which adds a packet to the message. This helps to give the students a conceptual underpinning as to how the rest of the course will be laid out. I then refer to this introduction across the course as each new layer is explored in depth later on. I then trace how the message flows upward in the receiver. Together with this chapter, I cover binary representation and the number system topics outlined in the preface. Binary is sometimes a review for students, but not always, so it is useful to have all students have the same level of understanding.

I usually caution the students that this material is complex and difficult to learn, and that it is best approached in three ways: 1) first, treat it as if one is learning a foreign language, and try to absorb the material by not letting oneself become overwhelmed or to get too far behind- a little bit each day is a much better approach to learning about networks. 2) If one does not grasp it all immediately, they are not to worry, but to come at it again and again from several sessions, using several different learning styles- reading, lectures, labs, slides and conversations in class. 3) The students are well served by being sure to attend as many classes as possible, and to skim the material before the lectures, as well as read the chapters in depth after the lectures. The student who tries to learn it all on their own will struggle, but the student who keeps up will really enjoy learning all about this new and interesting topic.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova I pull up a jobs website, and explore several current job offers to show the students how interesting networking jobs can be- and it doesn’t hurt for them to learn about the potential salaries in this area, either!

The future trends section should really be emphasized. These issues are important relative to the personal and business impacts that they provide. These also provide instructors with an effective way to engage the students in a discussion.

War Stories Microsoft Internet Explorer and HTML Standards (could also fit in Chapter 2) (Objective: illustrate the importance of standards) In early 1996, when we were developing our Web-groupware software (now a commercial product called Consensus @nyWARE (www.softbicycle.com) we discovered that Microsoft's IE would not work with our software. IE did not support the full HTML 3.0 standard in forms processing. All the form information was returned in reverse order from the standard. Since IE was a marginal product at the time and since our project was a research project, we decided not to bother rewriting our software to support IE. I received an email message from an IE user mentioning that they had discovered that IE would not work with our software and asking if we knew why. I didn't really read the note very carefully. I explained the problem and told them they should use Netscape and forget about IE …

It turned out that the user was Microsoft's chief software architect for IE. Microsoft quickly confirmed that the problem was indeed their non-support for the standard.

However, they ultimately decided not to support the standard, thus requiring developers to change the way they write code (must use the form value tags, not position in the file returned from the forms).

Other topics to cover here in terms of war stories for illustrating the importance of networks is to talk about current standards with which the students are familiar- MP3 vs. ripped iPod files, or Blue Ray CD’s vs. the new High Def standards. I ask them what technology standards they use each and every day, and write these on the board. Some prompting will uncover the standards that are in the chapter- TCP/IP and HTML, and then this can be a good place to re-introduce Figure 1.4.

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CHAPTER 2 APPLICATION LAYER Chapter Summary The Application Layer (also called layer 5) is the software that enables the user to perform useful work. The software at the application layer is the reason for having the network because it is this software that provides the business value. This chapter examines the five fundamental types of application architectures used at the application layer (host-based, client-based, client-server, cloud-based, peer to peer). It then looks at the Internet and the primary software application packages it enables: the Web, email, Telnet, and instant messaging.

Learning Objectives • • • •

Understand host-based, client-based, client–server, and cloud-based application architectures Understand how the Web works Understand how email works Be aware of how Telnet and instant messaging work

Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

Key Terms Application architecture Body Cloud-based architecture Data access logic Distributed computing model H.320 Header HTTP response

Application logic Client-based architectures Cloud computing Data storage Distribution list H.323 Host-based architectures hybrid cloud strategy

Hypertext Transfer Protocol (HTTP) Internet

Infrastructure as a Service (IaaS) Internet Message Access Protocol (IMAP) Middleware Multitenancy

Mail user agent Multipurpose Internet Mail Extension (MIME) Peer-to-peer Post Office Protocol (POP) Pure strategy Request line Response status Services logic Software as a service (SaaS) Telnet Three-tier architecture Videoconferencing Web server

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Architectures Presentation logic Request body Response body Scalability Simple Mail Transfer Protocol (SMTP) SQL injection Thick client Two-tier architecture Web browser

Application security Client–server architectures Cloud providers Desktop videoconferencing Email Hardware as a Service (HaaS) HTTP request Hypertext Markup Language (HTML) nstant messaging (IM) Mail transfer agent MPEG-2 N-tier architecture Platform as a Service (PaaS) Protocol Request header Response header Server farm SMTP header Storage area network Thin client Uniform resource locator (URL) Webcasting

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

Chapter Outline 2.1 Introduction 2.2 Application Architectures 2.2.1 Host-Based Architectures 2.2.2 Client-Based Architectures 2.2.3 Client–Server Architectures 2.2.4 Cloud Computing Architectures 2.2.5 Peer-to-Peer Architectures 2.2.6 Choosing Architectures 2.3 World Wide Web 2.3.1 How the Web Works 2.3.2 Inside an HTTP Request 2.3.3 Inside an HTTP Response 2.4 Electronic Mail 2.4.1 How Email Works 2.4.2 Inside an SMTP Packet 2.4.3 Attachments in Multipurpose Internet Mail Extension 2.5 Other Applications 2.5.1 Telnet 2.5.2 Videoconferencing 2.6 Implications for Cyber Security Summary

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

Answers to Textbook Exercises Answers to End-of-Chapter Questions 1. What are the different types of application architectures?

Host-based (all processing done on host system and all data on host with terminals providing access), client-based (with processing done on client and all data stored on server), clientserver (balanced processing; usually host provides data access and storage while the client provides application and presentation logic), cloud-based and peer-to-peer.

2. Describe the five basic functions of an application software package.

1.

Data storage

2.

Data access logic

3.

Application logic

4.

Presentation logic

5.

Services logic

Most application programs require data to be stored and retrieved, whether it is a small file such as a memo produced by a word processor or a large database such as an organization’s accounting records.

This is the processing required to access data, which often means database queries in SQL. This is sometimes called business logic). It can be simple or complex, depending on the application.

The presentation of information to the user and the acceptance of the user’s commands.

The provision of services to other applications (e.g., application program interfaces (API).

3. What are the advantages and disadvantages of host-based networks versus client-server networks?

• • Advantages

• • •

Disadvantages •

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Host-based Centralized security Integrated architecture from single vendor Simpler, centralized installation Having all processing on host may lead to overload Cost of software and upgrades; expensive infrastructure Terminal totally dependent on server

• • • • • •

Client-server Balanced processing demands Lower cost; inexpensive infrastructure Can use software and hardware from different vendors Scalability Problems with using software and/or hardware from different vendors More complex installation or updating (although automated installation software helps greatly in this area).

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 4. What is middleware and what does it do?

Middleware manages client-server message transfer and shields application software from impacts of hardware changes. Middleware provides standard communication between products of different vendors through translation.

5. Suppose your organization was contemplating switching from a host-based architecture to client-server. What problems would you foresee?

Infrastructure supporting cabling hardware and software will need to be redesigned to support the client-server approach to the architecture. Someone would need to be designated to manage what would now become the local area network, so there may be a personnel impact. Security would be one area of concern, since processing can be done on individual workstations. There may be somewhat greater complexity of upgrades, although newer software is reducing the impact of this kind of problem.

6. Which is less expensive: host-based networks or client-server networks? Explain.

Client-server networks are less expensive because in a competitive market involving multiple vendors, software and hardware upgrades cost substantially less. Upgrades for host-based networks are generally very expensive, and occur in what is generally termed a “step function,” meaning requiring large, discrete steps in expenditure. LANs have the ability to be deployed with a smoother cost curve in less severe increments.

7. Compare and contrast two-tiered, three-tiered, and n-tiered client server architectures. What are the technical differences, and what advantages and disadvantages do each offer?

Two-tiered architectures have only clients and servers.

Three-tiered architectures typical separate (1) presentation logic, (2) application logic, and (3) and data access logic and storage.

In n-tiered architecture more than one tier may be used to support application logic, typically due to a Web server tier being included.

Three-tiered or n-tiered architectures place a greater load on the network, but balances server load better and is more scalable.

8. How does a thin client differ from a thick client?

Thick clients support all or most application logic while thin clients support little or no application logic. Development and maintenance costs for more complex thick-client environments can be higher than for thin clients.

9. What are the benefits of cloud computing?

Benefits include gaining access to experts to manage the cloud, potentially lower costs, scalability, and pay-as-you-g0.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 10. Compare and contrast the three cloud computing models.

11. For what is HTTP used? What are its major parts?

The standard protocol for communication between a Web browser and a Web server is Hypertext Transfer Protocol (HTTP). An HTTP request from a Web browser to a Web server has three parts. Only the first part is required; the other two are optional.

• The request line, which starts with a command (e.g., GET), provides the URL, and ends with the HTTP version number that the browser understands.

• The request header, which contains a variety of optional information such as the Web browser being used (e.g., Internet Explorer), the date, and a userid and password for use if the Web page is password-protected.

• The request body, which contains information sent to the server, such as information from a form.

The format of an HTTP response from the server to the browser is very similar to the browser request. It has three parts, but only the last part is required; the first two are optional: • The response status, which contains the HTTP version number the server has used, a status code (e.g., 200 means OK, 404 means page not found), and reason phrase (a text description of the status code) • The response header, which contains a variety of optional information such as the Web server being used (e.g., Apache), the date, the exact URL of the page in the response body, and the format used for the body (e.g., HTML) • The response body, which is the Web page itself.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 12. For what is HTML used?

HTML is the language in which web pages are created. The response body of an HTTP response can be in any format, such as text, Microsoft Word, Adobe PDF, or a host of other formats, but the most commonly used format is HTML. The major parts of HTML are the heading (denoted by the <head> tag) and the body (denoted by the <body> tag) of the response.

13. Describe how a Web browser and Web server work together to send a Web page to a user.

In order to get a page from the Web, the user must type the Internet Uniform Resource Locator (URL) for the page he or she wants, or click on a link that provides the URL. The URL specifies the Internet address of the Web server and the directory and name of the specific page wanted.

In order for the requests from the Web browser to be understood by the Web server, they must use the same standard protocol. The standard protocol for communication between a Web browser and a Web server is Hypertext Transfer Protocol (HTTP).

14. Can a mail sender use a two-tier architecture to send mail to a receiver using a three-tier architecture? Explain.

Yes. With e-mail, users with the two-tier architecture will use the user agent software to interface with their email server, which will send out web based, SMTP packets to the far end receiver’s server computer with mail server software. The server at the far end will issue an IMAP or SMTP packet to the receiver’s server computer, which will then arrive at the receiver when they ask for the email with an HTTP request to the web based email application. Thus, a 2-tiered system easily interfaces with a three-tiered architecture over the internet using the appropriate protocols.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 15. Describe how mail user agents and message transfer agents work together to transfer mail messages.

The sender of an e-mail uses a user agent (an application layer software package) to write the email message. The user agent sends the message to a mail server that runs a special application layer software package called a message transfer agent. These agents read the envelope and then send the message through the network (possibly through dozens of mail transfer agents) until the message arrives at the receiver’s mail server. The mail transfer agent on this server then stores the message in the receiver’s mailbox on the server. When the receiver next accesses his or her e-mail, the user agent on his or her client computer contacts the mail transfer agent on the mail server and asks for the contents of the user’s mailbox. The mail transfer agent sends the email message to the client computer, which the user reads with the user agent.

16. What roles do SMTP, POP, and IMAP play in sending and receiving e-mail on the Internet?

SMTP defines how message transfer agents operate and how they format messages sent to other message transfer agents. The SMTP standard covers message transmission between message transfer agents (i.e., mail server to mail server). A different standard called Post Office Protocol (POP) defines how user agents operate and how messages to and from mail transfer agents are formatted. POP is gradually being replaced by a newer standard called Internet Mail Access Protocol (IMAP). While there are several important technical differences between POP and IMAP, the most noticeable difference is that before a user can read a mail message with a POP user agent, the e-mail message must be copied to the client computer’s hard disk and deleted from the mail server. With IMAP, e-mail messages can remain stored on the mail server after they are read.

17. What are the major parts of an e-mail message?

The major parts of an e-mail message are: • The header, which lists source and destination e-mail addresses (possibly in text form (e.g., “Susan Smith”) as well as the address itself (e.g., smiths@robert-morris.edu)), date, subject, and so on.

• The body, which is the message itself.

18. What is Telnet, and why is it useful?

Telnet enables users on one computer to login into other computers on the Internet. Once Telnet makes the connection from the client to the server, a user can login into the server or host computer in the same way as that person would if they dialed in with a modem; the user must know the account name and password of an authorized user. Telnet enables a person to connect to a remote computer without incurring long distance telephone charges.

Telnet can be useful because it enables access to servers or host computers without sitting at the dedicated computer’s keyboard. Most network managers use Telnet to work on their organization’s servers, rather than physically sitting in front of them and using the keyboards.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 19. What is cloud computing?

With cloud computing, a company contracts with another firm to provide software services over the Internet, rather than installing the software on its own servers. The company no longer buys and manages its own servers and software, but instead pays a monthly subscription fee or a fee based on how much they use the application.

20. Explain how videoconferencing works.

Videoconferencing provides real-time transmission of video and audio signals to enable people in two or more locations to have a meeting. Special audio microphones and speakers are used to capture and play audio signals. The audio and video signals are combined into one signal that is transmitted through a WAN or the Internet to people at the other location.

21. Which of the common application architectures for e-mail (two-tier client-server, Web-based) is "best"? Explain.

The best architecture for email can depend on how one wants to use e-mail. If a person wants to be able to access their e-mail from anywhere, then Web-based is best. If the person wants professional backup and storage within an organization, then two-tier client-server is best. If the person wants storage of e-mail strictly under their control and they also want to be able to access their e-mail files off-line when there is a network service interruption, then host-based is best.

Employers may choose to use client-server architecture for email access within the organization and Web-based architecture for access to the same system for those times when employees are outside the company (at home, at another business, or on travel).

22. Some experts argue that thin-client client-server architectures are really host-based architectures in disguise and suffer from the same old problems. Do you agree? Explain.

While thin client have substantially less application logic than thick client, they have sufficient application logic (as, for example, a Web browser possibly with Java applets) to participate in a client-server relationship. The older host-based terminals did not even have this much application logic. While thin-client use today reflects some level of return to a more centralized approach, the client is likely served by multiple servers (and even multiple tiers), rather than a single large host server as in the past. Thus, the two approaches are similar, but not exact, from a technological design perspective.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova Exercises A. Investigate the use of the major architectures by a local organization (e.g., your university).

Which architecture(s) does it use most often and what does it see itself doing in the future?

Why? Answers will vary.

B. What are the costs of thin-client versus thick-client architectures? Search the Web for at least two different studies and be sure to report your sources. What are the likely reasons for the differences between the two?

Answers will vary.

C. Investigate which companies are the most reliable cloud computing providers for small business.

Answers will vary but the two most likely to show up in answers are Amazon (AWS), Google, and IBM. D. What application architecture does your university use for email? Explain.

The answer will depend on your university.

E. Investigate the options for having your private cloud as an individual. Hint: Try the Apple website.

Answers will vary. If the desire is to have cloud storage, then Microsoft, Apple, and Dropbox are the more likely answers; although, there are a host of other companies offering cloud storage. For cloud computing, the answers will be similar to those for small businesses, as discussed above.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova Mini-Cases I. Deals-R-Us Brokers (Part 1) Fred's information systems department has presented him with two alternatives for developing the new tools. The first alternative will have a special tool developed in C++ that clients will download onto their computers to run. The tool will communicate with the DRUB server to select data to analyze. The second alternative will have the C++ program running on the server; the client will use his or her browser to interact with the server. a) Classify the two alternatives in terms of what type of application architecture they use. b) Outline the pros and cons of the two alternatives and make a recommendation to Fred about which is better.

The alternatives are shown in the text as Figures 2-2 (client-based) and 2-3 (two-tier clientserver).

Client-based is simple; however all data must travel to the client for processing, thus giving the potential for speed delays over the network.

Client-server provides processing on the server, which could be an advantage if the data to be processed also resides on the server; yet, because it involves heterogeneous software, this can be a significant disadvantage in terms of interoperability.

II. Deals-R-Us Brokers (Part 2) Dears-R-Us Brokers has decided to install a new e-mail package. One vendor is offering an SMTP-based two-tier client server architecture. The second vendor is offering a Web-based email architecture. Fred doesn't understand either one, but thinks the Web-based one should be better because, in his words "the Web is the future." a) Briefly explain to Fred, in layman's terms, the differences between the two. b) Outline the pros and cons of the two alternatives and make a recommendation to Fred about which is better. a) If they host the email in-house using Microsoft Exchange Server, this means that they purchase a physical computer to use as a mail server and install Microsoft Server as the operating system. Then, they will need to install the Microsoft Exchange Server software which will allow the server to be used as a mail server. The network administrator at DRUB can then configure and manage the email user accounts, etc himself. The second solution is to use one of the cloud-based providers and completely outsource the company email. Two examples are Gmail and GoDaddy. With each of these services, the DRUB will pay a monthly fee for one of the providers to configure and manage the mail servers for them. b) Each of these options has their advantages and disadvantages. A few of these include: In-house advantages: control, potentially lower cost In-house disadvantages: more work to do, potentially less expertise available .

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova Outsourcing advantage: potentially lower cost, better service, less work to do in-house Outsourcing disadvantages: loss of control, potentially higher costs III. Accurate Accounting Accurate Accounting managing partner Diego Lopez asks: Why can’t IM work as simply as email? Will the new videoconferencing software and hardware work as simply as e-mail, or will it be IM all over again? Prepare a response to his questions.

E-mail standards enable it to be used easily between companies. Lack of IM standards means that several competing protocols exist. This problem will be overcome as commercial interests push for standardization or development of middleware that enables disparate systems to talk to one another. The same pattern of innovation will likely happen that is typical of all new technologies. At present, there are large corporate concerns over the security aspects of externally based IM software deployments within an organization’s boundaries, limiting the use of IM packages in some organizations until these concerns are mitigated.

IV. Ling Galleries How can the Internet help gallery owner Hoard Ling with his two new galleries?

There are a variety of ways the Internet could help Mr. Ling. He could develop a website where his paintings would be featured and some additional information about the artist would be displayed for potential buyers to learn and explore more about the works. Further, the website could include an e-commerce function whereby visitors would be able to order prints of paintings they like. The site could help Mr. Ling track customer tastes so that he can better understand the types of paintings that sell well, thus allowing the business to develop while matching future production to the strongest market for the paintings.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova Additional Content Teaching Notes I usually spend 3 hours of class time on this chapter.

I also include hands-on labs on (1) HTML (using Microsoft Word, Front Page, or Dreamweaver) to ensure that all students can create their own web pages and (2) FTP (using both a graphicinterface FTP application and command line FTP access) to ensure that students can transfer files. Sometimes I include a hands-on Web and e-mail lab as well.

I have several goals when I teach this chapter. First, I want students to get a sense of the history of the Internet beyond what they already know. Most of my students think the Internet has always been there. The “traditional” history given in Introduction to Computing courses usually mentions that the Internet started in the late 1960s. This is true, but can be misleading; it implies the Internet has always been an important network. I try to show how small it was at first and illustrate that that it was only one of several possible networks that could have “won.” I also try to impress upon them the extremely rapid growth in the past few years. You might want to update the timeline with more recent statistics on the number of Internet users.

I have two goals for the Internet applications section. First, I want students to become familiar with the Web, SMTP, FTP, and telnet, although for most students this is remedial. Starting with this material, however, helps students to understand the importance and relevance of the course – everyone wants to learn more about the Internet.

The Internet applications discussion is also a good place to explain exactly what is meant by standards and layers from Chapter 1. The HTTP/SMTP standards help students understand why we need standards and most importantly that there are standards at all layers in the network model. This underscores the concept that each layer is distinct and has a packet within a packet within a packet, something I have always found that students have difficulty understanding. In my opinion, this concept is more important than having them memorize the contents and format of each type of packet, although I require them to be able to explain the parts of the packet and what each does.

Electronic commerce is an important topic. Most students want to learn about it, and many have been exposed to it in prior classes. I cover enough to help them sort out what is going on the Web with respect to the use of the Internet to operate the back end of businesses using electronic commerce. I also try to link the material to their marketing or economics courses. We discuss aspects of purchasing goods over the internet, and I also ask them if they have purchased anything over the web, used instant messaging or else used desktop videoteleconferencing. Most students have done so, and they are interested in this chapter because it begins their understanding of the nuts and bolts of how web pages and web site forms might be transmitted over networks.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova War Stories Electronic Commerce and Prices (Objective: Illustrate the implications of electronic commerce for today’s businesses; The potential is immense).

A friend of mine recently decided to get a car loan for a new car. After checking out Edmund’s (www.edmunds.com) for information, he clicked on the link to a car loan firm. The loan quote was 7.70%. He then called his bank and USAA (a large financial organization well known for offering cheap loans to U.S. veterans). Neither could match the loan rate, although USAA came the closet at 7.85%. Neither would match the Internet rate, even though he had extensive ties to both. It turns out the company offering the low rates on the Internet was actually his bank, doing business under a different name. Electronic commerce has vast implications for business, and this chapter is about the technical underpinnings of how this information moves around the internet.

E-mail I usually describe my first experiences with e-mail, which were before the days of the Internet.

You may also have some good e-mail war stories. The objective is to reinforce the changes in technologies; the Internet hasn’t always been dominant. Sometimes I cite an alternative e-mail technology, the US Veterans Affairs (VA) FORUM, the VA's national electronic mail system.

Electronic discussions, conferences, distribution of VA directives, news, and computer programs are its primary functions. FORUM disseminates information across any communications medium and also hosts several national databases. Because VA FORUM works according to email threads, it has been extensively used to document the process of software development in the VA health care system.

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CHAPTER 3 PHYSICAL LAYER Chapter Summary The physical layer (also called layer 1) is the physical connection between the computers and/or devices in the network. This chapter examines how the physical layer operates. It describes the most commonly used media for network circuits and explains the basic technical concepts of how data is actually transmitted through the media. Three different types of transmission are described: digital transmission of digital computer data; analog transmission of digital computer data; and digital transmission of analog voice data. You do not need an engineering-level understanding of the topics to be an effective user and manager of data communication applications. It is important, however, that you understand the basic concepts, so this chapter is somewhat technical.

Learning Objectives • • • • • •

Be familiar with the different types of network circuits and media Understand the digital transmission of digital data Understand the analog transmission of digital data Understand the digital transmission of analog data Be familiar with analog and digital modems Be familiar with multiplexing

Key Terms Adaptive differential pulse code modulation (ADPCM) Amplitude shift keying (ASK) Bandwidth Bit rate Circuit configuration Codec Data rate Fiber-optic cable Frequency shift keying (FSK) Guided media Kilo Hertz (kHz) Logical circuit Microwave transmission Multiplexing Phase modulation (PM)

American Standard Code for Information Interchange (ASCII) Amplitude

Amplitude modulation (AM)

Baud rate Bits per second (bps) Circuit Coding scheme Digital subscriber line Frequency division multiplexing (FDM) Frequency Half-duplex transmission Lempel–Ziv encoding Malware Modem Parallel transmission Phase shift keying (PSK)

Bipolar Carrier wave Coaxial cable Data compression Digital transmission Frequency modulation (FM)

Analog transmission

Full-duplex transmission ISO 8859 Local loop Manchester encoding Multipoint circuit Phase Physical circuit

Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova Plain old telephone service (POTS) Pulse code modulation (PCM) Radio transmission Serial transmission

Point-to-point circuit

Polarity

Quadrature amplitude modulation (QAM) Retrain time Simplex transmission

Quantizing error

Switch

Symbol rate

Turnaround time Unipolar Voice over Internet Protocol (VoIP)

Twisted pair cable USB drive Wavelength division multiplexing (WDM)

Satellite transmission Statistical time division multiplexing (STDM) time-division multiplexing (TDM) Unicode V.44

Chapter Outline 3.1 Introduction 3.2 Circuits 3.2.1 Circuit Configuration 3.2.2 Data Flow 3.2.3 Multiplexing 3.3 Communication Media 3.3.1 Twisted Pair Cable 3.3.2 Coaxial Cable 3.3.3 Fiber-Optic Cable 3.3.4 Radio 3.3.5 Microwave 3.3.6 Satellite 3.3.7 Media Selection 3.4 Digital Transmission of Digital Data 3.4.1 Coding 3.4.2 Transmission Modes 3.4.3 Digital Transmission 3.4.4 How Ethernet Transmits Data 3.5 Analog Transmission of Digital Data 3.5.1 Modulation 3.5.2 Capacity of a Circuit 3.5.3 How Modems Transmit Data 3.6 Digital Transmission of Analog Data 3.6.1 Translating from Analog to Digital 3.6.2 How Telephones Transmit Voice Data 3.6.3 How Instant Messenger Transmits Voice Data 3.6.4 Voice over Internet Protocol (VoIP) 3.7 Implications for Cyber Security Summary

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova

Answers to Textbook Exercises 1. How does a multipoint circuit differ from a point-to-point circuit?

A point-to-point configuration is so named because it goes from one point to another (e.g., one computer to another computer). These circuits sometimes are called dedicated circuits because they are dedicated to the use of these two computers. In a multipoint configuration (also called a shared circuit), many computers are connected on the same circuit. This means that each must share the circuit with the others, much like a party line in telephone communications. The disadvantage is that only one computer can use the circuit at a time.

Multipoint configurations are cheaper than point-to-point configurations.

2. Describe the three types of data flows.

The three types of data flows are simplex, half-duplex and full duplex. Simplex is one-way transmission, such as that in radio or TV transmission. Half duplex is two-way transmission, but you can transmit in only one direction at a time. A half-duplex communication link is similar to a walkie-talkie link; only one computer can transmit at a time. With full duplex transmission, you can transmit in both directions simultaneously, with no turnaround time.

3. Describe three types of guided media.

Guided media are those in which the message flows through a physical media such as a twisted pair wire, coaxial cable, or fiber optic cable; the media “guides” the signal.

One of the most commonly used types of guided media is twisted pair wire, insulated or unshielded twisted pairs (UTP) of wires that can be packed quite close together. Bundles of several thousand wire pairs are placed under city streets and in large buildings. Twisted pair wire is usually twisted to minimize the electromagnetic interference between one pair and any other pair in the bundle.

Coaxial cable is another type of commonly used guided media. Coaxial cable has a copper core (the inner conductor) with an outer cylindrical shell for insulation. The outer shield, just under the shell, is the second conductor. Coaxial cables have very little distortion and are less prone to interference, they tend to have low error rates.

Fiber optics, is becoming much more widely used for many applications, and its use is continuing to expand. Instead of carrying telecommunication signals in the traditional electrical form, this technology utilizes high-speed streams of light pulses from lasers or LEDs (light emitting diodes) that carry information inside hair-thin strands of glass or plastic called optical fibers.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova 4. Describe four types of wireless media.

Wireless media are those in which the message is broadcast through the air, such as radio, infrared, microwave, or satellite.

One of the most commonly used forms of wireless media is radio. Radio data transmission uses the same basic principles as standard radio transmission. Each device or computer on the network has a radio receiver/transmitter that uses a specific frequency range that does not interfere with commercial radio stations. The transmitters are very low power, designed to transmit a signal up to 500 feet and are often built into portable or handheld computers.

Infrared transmission uses low frequency light waves (below the visible spectrum) to carry the data through the air on a direct line-of-sight path between two points. This technology is similar to the technology used in infrared TV remote controls. It is prone to interference, particularly from heavy rain, smoke, and fog that obscure the light transmission. Infrared is not very common, but it is sometimes used to transmit data from building to building.

A microwave is an extremely high frequency radio communication beam that is transmitted over a direct line-of-sight path between any two points. As its name implies, a microwave signal is an extremely short wavelength. Microwave radio transmissions perform the same functions as cables. Similar to visible light waves, microwave signals can be focused into narrow, powerful beams that can be projected over long distances.

Transmission via satellite is similar to transmission via microwave except, instead of transmitting to another nearby microwave dish antenna, it transmits to a satellite 22,300 miles in space.

5. How does analog data differ from digital data?

Computers produce digital data that are binary, either on or off. In contrast, telephones produce analog data whose electrical signals are shaped like the sound waves they transfer. Analog data are signals that vary continuously within a range of values (e.g., temperature is analog).

6. Clearly explain the differences among analog data, analog transmission, digital data, and digital transmission.

Data can be transmitted through a circuit in the same form they are produced. Most computers, for example, transmit their data through digital circuits to printers and other attached devices.

Likewise, analog voice data can be transmitted through telephone networks in analog form. In general, networks designed primarily to transmit digital computer data tend to use digital transmission, and networks designed primarily to transmit analog voice data tend to use analog transmission (at least for some parts of the transmission).

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova 7. Explain why most telephone company circuits are now digital.

Most telephone company circuits are now digital because digital transmission is “better” than analog transmission. Specifically, digital transmission offers several key benefits over analog transmission: • • • • •

Digital transmission produces fewer errors than analog transmission. Because the transmitted data is binary (only two distinct values), it is easier to detect and correct errors.

Digital transmission is more efficient. Time division multiplexing (TDM) is more efficient than frequency division multiplexing (FDM) because TDM requires no guardbands. TDM is commonly used for digital transmission, while FDM is used for analog transmission.

Digital transmission permits higher maximum transmission rates. Fiber optic cable, for example, is designed for digital transmission.

Digital transmission is more secure because it is easier to encrypt.

Digital transmission is less expensive than analog in many instances.

Finally, and most importantly, integrating voice, video and data on the same circuit is far simpler with digital transmission.

8. What is coding?

Coding is the representation of one set of symbols by another set of symbols. In data communications, this coding is a specific arrangement of binary 0s and 1s used to represent letters, numbers, and other symbols that have meaning.

9. Briefly describe three important coding schemes.

There are three predominant coding schemes in use today. United States of America Standard Code for Information Interchange (USASCII), or more commonly ASCII, is the most popular code for data communications and is the standard code on most terminals and microcomputers.

There are two types of ASCII; one is a 7-bit code that has 128 valid character combinations, and the other is an 8-bit code that has 256 combinations. Extended Binary Coded Decimal Interchange Code (EBCDIC) is IBM's standard information code. This code has 8 bits, giving 256 valid character combinations.

10. How is data transmitted in parallel?

Parallel mode is the way the internal transfer of binary data takes place inside a computer. If the internal structure of the computer is 8-bit, then all eight bits of the data element are transferred between main memory and the central processing unit simultaneously on 8 separate connections. The same is true of computers that use a 32-bit structure; all 32 bits are transferred simultaneously on 32 connections.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova 11. What feature distinguishes serial mode from parallel mode?

Serial mode is distinguished from parallel mode by the time cycle in which the bits are transmitted. Parallel implies that all bits of a character are transmitted, followed by a time delay, and then all bits of the next character are transmitted, followed by a time delay. Serial implies that characters are sent one bit at a time, with each bit followed by a time delay. Put another way, parallel is character-by-character and serial is bit-by-bit.

12. How does bipolar signaling differ from unipolar signaling? Why is Manchester encoding more popular than either?

With unipolar signaling, the voltage is always positive or negative (like a dc current). In bipolar signaling, the 1’s and 0’s vary from a plus voltage to a minus voltage (like an ac current). In general, bipolar signaling experiences fewer errors than unipolar signaling because the signals are more distinct.

Manchester encoding is a special type of unipolar signaling in which the signal is changed from a high to low or from low-to-high in the middle of the signal. A change from high to low is used to represent a 1 (or a 0), while the opposite (a change low to high) is used to represent a 0 (or a 1). Manchester encoding is less susceptible to having errors go undetected, because if there is no transition in mid-signal the receiver knows that an error must have occurred.

13. What are three important characteristics of a sound wave?

Sounds waves have three important characteristics. The first is the height of the wave, called amplitude. Our ears detect amplitude as the loudness or volume of sound. The second characteristic is the length of the wave, usually expressed as the number of waves per second or frequency. Frequency is expressed in hertz (Hz). Our ears detect frequency as the pitch of the sound. Human hearing ranges from about 20 hertz to about 14,000 hertz, although some people can hear up to 20,000 hertz. The third characteristic is the phase, refers to the direction in which the wave begins.

14. What is bandwidth? What is the bandwidth in a traditional North American telephone circuit?

Bandwidth refers to a range of frequencies. It is the difference between the highest and the lowest frequencies in a band; thus the bandwidth of human voice is from 20 Hz to 14,000 Hz or 13,880 Hz. The bandwidth of a voice grade telephone circuit is from 0 to 4000 Hz, or 4000 Hz; however, not all of this is available for use by telephone or data communications equipment. To start, there is a 300-hertz guardband at the bottom of the bandwidth and a 700-hertz guardband at the top. These prevent data transmissions from interfering with other transmissions when these circuits are multiplexed using frequency division multiplexing. This leaves the bandwidth from 300 to 3300 hertz or a total of 3000 Hz for voice or data transmission.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova 15. Describe how data could be transmitted using amplitude modulation.

With amplitude modulation (AM) (also called amplitude shift keying (ASK)), the amplitude or height of the wave is changed. One amplitude is defined to be zero, and another amplitude is defined to be a one.

16. Describe how data could be transmitted using frequency modulation.

Frequency modulation (FM) (also called frequency shift keying (FSK)), is a modulation technique whereby each 0 or 1 is represented by a number of waves per second (i.e., a different frequency). In this case, the amplitude does not vary. One frequency (i.e., a certain number of waves per second) is defined to be a one, and a different frequency (a different number of waves per second) is defined to be a one.

17. Describe how data could be transmitted using phase modulation.

Phase modulation (PM) (also called phase shift keying (PSK)), is the most difficult to understand. Phase refers to the direction in which the wave begins. Until now, the waves we have shown start by moving up and to the right (this is called a 0º phase wave). Waves can also start down and to the right. This is called a phase of 180º. With phase modulation, one phase is defined to be a zero and the other phase is defined to be a one.

18. Describe how data could be transmitted using a combination of modulation techniques.

It is possible to use amplitude modulation, frequency modulation, and phase modulation techniques on the same circuit. For example, we could combine amplitude modulation with four defined amplitudes (capable of sending two bits) with frequency modulation with four defined frequencies (capable of sending two bits) to enable us to send four bits on the same symbol.

19. Is the bit rate the same as the symbol rate? Explain.

The terms bit rate (i.e., the number bits per second transmitted) and baud rate are used incorrectly much of the time. They often are used interchangeably, but they are not the same. In reality, the network designer or network user is interested in bits per second because it is the bits that are assembled into characters, characters into words and, thus, business information.

Because of the confusion over the term baud rate among the general public, ITU-T now recommends the term baud rate be replaced by the term symbol rate. The bit rate and the symbol rate (or baud rate) are the same only when one bit is sent on each symbol. For example, if we use amplitude modulation with two amplitudes, we send one bit on one symbol. Here the bit rate equals the symbol rate. However, if we use QAM, we can send four bits on every symbol; the bit rate would be four times the symbol rate.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova 20. What is a modem?

Modem is an acronym for MOdulator/DEModulator. A modem takes the digital electrical pulses received from a computer, terminal, or microcomputer and converts them into a continuous analog signal that is needed for transmission over an analog voice grade circuit.

Modems are either internal (i.e., inside the computer) or external (i.e., connected to the computer by a cable).

21. What is quadrature amplitude modulation (QAM)?

One popular technique is quadrature amplitude modulation (QAM). QAM involves splitting the symbol into eight different phases (three bits) and two different amplitudes (one bit), for a total of 16 different possible values. Thus, one symbol in QAM can represent four bits.

22. What is 64- QAM? If we use 64-QAM, the bit rate is six times the symbol rate. A circuit with a 10 MHz bandwidth using 64-QAM can provide up to 60 Mbps.

23. What factors affect transmission speed?

The factors that affect the transmission speed are the number of bits per signal sample and the number of samples per second.

24. What is oversampling?

For voice digitization, one typically samples at twice the highest frequency transmitted, or a minimum of 8,000 times a second. Sampling more frequently than this will improve signal quality. For example, CDs sample at 44,100 times a second and use 16 bits per sample to produce almost error-free music.

25. Why is data compression so useful?

Data compression can increase throughput of data over a communication link literally by compressing the data. A 2:1 compression ratio means that for every two characters in the original signal, only one is needed in the compressed signal (e.g., if the original signal contained 1000 bytes, only 500 would needed in the compressed signal).

In 1996, ITU-T revised the V.34 standard to include a higher data rate 33.6 Kbps. This revision is popularly known as V.34+. The faster data rate is accomplished by using a new form of TCM that averages 9.8 bits per symbol (symbol rate remains at 3429).

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova 26. What data compression standard uses Lempel-Ziv encoding? Describe how it works.

V.42bis, the ISO standard for data compression, uses Lempel-Ziv encoding. As a message is being transmitted, Lempel-Ziv encoding builds a dictionary of two, three, and four character combinations that occur in the message. Any time the same character pattern reoccurs in the message, the index to the dictionary entry is transmitted rather than sending the actual data.

V.42bis compression can be added to almost any modem standard; thus a V.32 modem providing a data rate of 14,400 bps, could provide a data rate of 57,600 bps when upgraded to use V.42bis.

27. Explain how pulse code modulation (PCM) works.

Analog voice data must be translated into a series of binary digits before they can be transmitted. With PAM-based methods, the amplitude of the sound wave is sampled at regular intervals, and translated into a binary number. The most commonly used type of PAM is Pulse Code Modulation (PCM). With PCM, the input voice signal is sampled 8000 times per second.

Each time the input voice signal is sampled, eight bits are generated. Therefore, the transmission speed on the digital circuit must be 64,000 bits per second (8 bits per sample x 8,000 samples per second) in order to transmit a voice signal when it is in digital form.

28. What is quantizing error?

Quantizing error is the difference between the replicated analog signal and its original form, shown with jagged “steps” rather than the original, smooth flow. Voice transmissions using digitized signals that have a great deal of quantizing error will sound metallic or machinelike to the human ear.

29. What is the term used to describe the placing of two or more signals on a single circuit?

Multiplexing is the term used to describe the placing of two or more signals on a single circuit.

30. What is the purpose of multiplexing?

A multiplexer puts two or more simultaneous transmissions on a single communication circuit.

Multiplexing a voice telephone call means that two or more separate conversations are sent simultaneously over one communication circuit between two different cities. Multiplexing a data communication network means that two or more messages are sent simultaneously over one communication circuit. In general, no person or device is aware of the multiplexer; it is “transparent.”

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova 31. How does DSL (digital subscriber line) work?

DSL allows for simultaneous transmission of voice (phone calls), data going to the Internet (called upstream data), and data coming to your house from the Internet (called downstream data). With DSL, a DSL modem is installed at the customer’s home or office, and another DSL modem is installed at the telephone company switch closet. The modem is first an FDM device that splits the physical circuit into three logical circuits (phone, upstream data, and downstream data). TDM is then used within the two data channels to provide a set of one or more individual channels that can be used to carry different data. A combination of amplitude and phase modulation is used in the data circuits to provide the desired data rate.

32. Of the different types of multiplexing, what distinguishes a. Frequency division multiplexing (FDM)?

Frequency division multiplexing can be described as dividing the circuit “horizontally” so that many signals can travel a single communication circuit simultaneously. The circuit is divided into a series of separate channels, each transmitting on a different frequency, much like series of different radio or TV stations. All signals exist in the media at the same time, but because they are on different frequencies, they do not interfere with each other. b. Time division multiplexing (TDM)?

Time division multiplexing shares a communication circuit among two or more terminals by having them take turns, dividing the circuit “vertically.” In TDM, one character is taken from each terminal in turn, transmitted down the circuit, and delivered to the appropriate device at the far end. Time on the circuit is allocated even when data are not be transmitted, so that some capacity is wasted when terminals are idle. c. Statistical time division multiplexing (STDM)?

Statistical time division multiplexing is the exception to the rule that the capacity of the multiplexed circuit must equal the sum of the circuits it combines. STDM allows more terminals or computers to be connected to a circuit than FDM or TDM. STDM is called statistical because selecting the transmission speed for the multiplexed circuit is based on a statistical analysis of the usage requirements of the circuits to be multiplexed. STDM is like TDM, except that each frame has a terminal address and no blanks are sent.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova d. Wavelength division multiplexing (WDM)?

Wavelength division multiplexing is a version of FDM used in fiber optic cables. WDM works by using lasers to transmit different frequencies of light (i.e., colors) through the same fiber optic cable; each channel is assigned a different frequency so that the light generated by one laser does not interfere with the light produced by another. WDM permits up to 40 simultaneous circuits each transmitting up to 10 Gbps, giving a total network capacity in one fiber optic cable of 400 Gbps (i.e., 400 billion bits per second).

33. What is the function of inverse multiplexing (IMUX)?

Inverse multiplexing (IMUX) combines several low speed circuits to make them appear as one high-speed circuit to the user.

34. If you were buying a multiplexer, why would you choose either TDM or FDM? Why? If buying a multiplexer, you would choose TDM over FDM. In general, TDM is preferred to FDM, because it provides higher data transmission speeds and because TDM multiplexers are cheaper. Time division multiplexing generally is more efficient than frequency division multiplexing, because it does not need guardbands. Guardbands use “space” on the circuit that otherwise could be used to transmit data. It is not uncommon to have time division multiplexers that share a line among 32 different low speed terminals. It is easy to change the number of channels in a time division multiplexer. Time division multiplexers generally are less costly to maintain.

35. Some experts argue that MODEMs may soon become obsolete. Do you agree? Why or why not?

The traditional context of MODEM no doubt has become obsolete. We no longer can consider a MODEM a device that connects two computers by merely modulating and demodulating transmission signals over the Public Switched Network at speeds ranging up to 56Kbps. This type of MODEM now must be evaluated in light of newer technologies such as xDSL MODEMs and Cable MODEMs each of which generates, propagates and transmits signals at far greater speeds. In addition we must evaluate the traditional MODEMs as well in light of newer protocols and compression techniques which have greatly improved overall bandwidth and throughput with the traditional types of MODEMs. In short, though many new forms of MODEMs and MODEM supported technology have come in to play, the traditional MODEM continues to be a cost-effective and flexible means of networking if your bandwidth requirements remain under the 56Kbps threshold.

36. What is the maximum capacity of an analog circuit with a bandwidth of 4,000 Hz using QAM? Under perfect circumstances, the maximum symbol rate is about 4,000 symbols per second. If we were to use QAM (4 bits per symbol), the maximum data rate would be 4 bits per symbol X 4,000 symbols per second = 16,000 bps.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova 37. What is the maximum data rate of an analog circuit with a 10 MHz bandwidth using 64-QAM and V.44?

A circuit with a 10 MHz bandwidth using 64-QAM can provide up to 60 Mbps. A V.44 modem can provide as much as 6:1 compression ratio, depending on the type of data sent. Thus, the maximum data rate of 64-QAM with compression is 360 Mbps.

38. What is the capacity of a digital circuit with a symbol rate of 10 MHz using Manchester encoding?

B=s*n B = (10 MHz) * 1 bit per symbol Capacity is 10 Mbps 39. What is the symbol rate of a digital circuit providing 100 Mbps if it uses bipolar NRz signaling?

B=s*n 100 Mbps = s * 1 bit per symbol Symbol rate is 100 Mhz 40. What is VoIP? Voice over IP is commonly used to transmit phone conversations over the digital networks.

VoIP uses digital phones with built-in codecs to convert analog to digital.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova

Exercises A. Investigate the costs of dumb terminals, network computers, minimally equipped personal computers, and top-of-the-line personal computers. Many equipment manufacturers and resellers are on the Web, so it’s a good place to start looking.

Student answers will vary.

B. Investigate the different types of cabling used in your organization and where they are used (e.g., LAN, backbone network).

Student answers will vary.

C. Investigate different types of satellite communication services that are provided today.

Student answers will vary.

D. Draw how the bit pattern 01101100 would be sent using a. Single-bit AM With AM, one amplitude is the symbol defined to be 0, and another amplitude is the symbol defined to be a 1. b. Single-bit FM FM is a modulation technique whereby each 0 or 1 is represented by a number of waves per second. The amplitude does not vary. c. Single-bit PM Phase refers to the direction in which the wave begins. Waves can start up or down moving to the right. With phase modulation, one phase symbol is defined to be a 0 and the other phase symbol is defined to be a 1. d. Two-bit AM (i.e., four amplitude levels) With AM, multiple amplitudes are used to define each of the two bits. e. Two-bit FM (i.e., four frequencies) With FM, multiple frequencies are used to define each of the two bits.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova f. Two-bit PM (i.e., four different phases) Two bits could be sent on the same symbol by defining four different frequencies, one for 11, one for 10, and so on. g. Single-bit AM combined with single-bit FM Amplitudes would be combined with different frequencies. h. Single-bit AM combined with single-bit PM Amplitudes would be combined with different phases. i. Two-bit AM combined with two-bit PM Amplitudes would be combined with different phases.

E. If you had to download a 20-page paper of 400k (bytes) from your professor, approximately how long would it take to transfer it over the following circuits? Assume that control characters add an extra 10% to the message.

With 10 percent overhead, you are actually downloading 440k. Speeds can be calculated using the online calculator at https://downloadtimecalculator.com/. To calculate manually, you must first convert the file size (440k) in bites to bits by multiplying times eight. So, 440𝑘 × 8 = 3,520𝑏𝑖𝑡𝑠. You then divided by the speed to get the number of seconds. a. Dial-up modem at 33.6 Kbps 3,520 = 104.7 𝑠𝑒𝑐𝑜𝑛𝑑𝑠.

33.6 This converts to 1:47 or one minute 47 seconds. b. Cable modem at 384 Kbps 3,520 = 9.17 𝑠𝑒𝑐𝑜𝑛𝑑𝑠.

384 c. Cable modem at 1.5 Mbps 3,520 = 2.35 𝑠𝑒𝑐𝑜𝑛𝑑𝑠.

1,500

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova d. If the modem includes V.44 data compression with a 6:1 data compression ratio, what is the data rate in bits per second you would actually see in choice c?

Assuming the compression did not add any additional characters, then using 6:1 compression would reduce the times to one sixth of the times shown above.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova

Minicases I. Eureka! (Part 1) Eureka staff answers the phone and respond to requests entered on the Eureka! Web site. Much of their work is spent on the phone and on computers searching on the Internet. They have just leased a new office building and are about to wire it. What media would you suggest they install in their office and why?

If you are comfortable with prefacing a discussion on “wiring” a new office building with a talk about IEEE 802.11 wireless Local Area Networking, it may add value to the class, clarify some questions which many students may be hearing about companies not needing to wire building anymore and sharpen your focus on the main topic which is wiring the building to support networking.

Certainly today all if not most companies in this scenario will pre-wire their new workspaces to support modular, multimedia connectivity. That translates into CATEGORY 5 (CAT-5) or better (i.e. 5E, 6) with RJ-45 faceplates supporting connections for data and voice.

II. Eureka! (Part 2) What type of connections should they consider from their offices to the outside world, in terms of phone and Internet? Outline the pros and cons of each alternative below and make a recommendation. They have four alternatives: 1. Should they use standard voice lines, but use DSL for their data ($60 per month per line for both services)?

Option 2 requires a individual DSL line, DSL MODEM, connection cable(s) and DSL software on each and every computer to network data this way. Higher cost. Each telephone requires an individual trunk line. Higher bandwidth speeds would be an advantage with each DSL line.

2. Should they separate their voice and data needs using standard analog services for voice but finding some advanced digital transmission services for data ($40 per month for each voice line and $300 per month for a circuit with 1.5 Mbps of data)?

Option 3 requires an individual dedicated circuit, Channel Service Unit (CSU), Router, connection cables and software configuration. But if the company has a Local Area Network in place, they can share much higher bandwidth speeds with any computer connected to this LAN. Each telephone requires an individual trunk line. Unit costs would be proportional, though voice line costs would be the same the company could leverage the data line costs to show that after 5-6 computer connection, the company would save money on the data side and achieve much higher bandwidth thresholds with a large degree of scalability.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova 3. Should the company search for all digital services for both voice and data ($60 per month for an all-digital circuit that provides two PCM phone lines that can be used for two voice calls, one voice call and one data call at 64 Kbps, or one data call at 128 Kbps)?

The context here outlines the use of a BRI (i.e. ISDN) connection. Specifically, a BRI service with 2B channels, each channel providing 64Kbps. With the correct terminating hardware in place, the BRI could support both data and voice up to 128Kbps.

III.

Eureka! (Part 3)

Eureka! Is a telephone and Internet-based concierge service that specializes in obtaining things that are hard to find (e.g., Super Bowl tickets, first-edition books from the 1500s, Faberge eggs).

It currently employees 60 staff members who work 24 hours per day (over three shifts). Staff members answer phone calls and respond to requests entered on the Eureka! Web site. Currently, each staff member has a desktop PC with two monitors and a twisted pair connection (Cat5e) that offers speeds up to 100Mbps. Some employees made a suggestion to the CEO of Eureka! to upgrade their connection to a fiber-optic cable that can provide speeds up to 1Gbps. What do you think about this idea? How easy (difficult) it is to change wiring from twisted pair to fiber-optic?

Can we use the same network card in the PCs or do we need to change them? How much would this change cost?

Speed to the desktop depends on many factors, including the speed from the ISP to the company network, and then the speed to the individual desktops. If the speed is upgraded from the ISP to the company network using fiber, but the Cat5e to the desktops isn’t upgraded, the maximum speed to the desktops will still not exceed 100Mbps. In order to increase the speed to the desktop, both sets of circuits must be upgraded.

Changing from twisted pair to fiber-optic requires that not only the cabling be changed, but may also require network cards and other equipment to be changed. These other devices may have fiber ports, depending on their age. Costs will certainly increase, but how much depends on current prices.

IV.

Speedy Package

1.) Assuming that each label is 1000 bytes long, how long does it take to transmit one label over the cell network, assuming that the cell phone network operates at 144 kbps (144,000 bits per second and that there are 8 bits in a byte)? 2.) If Speedy were to upgrade to the new, faster digital phone network that transmits data at 200 Kbps (200,000 bits per second) how long would it take to transmit?

144,000/8 = 18,000 bytes/second 1,000/18,000 = .056 seconds 200,000/8 = 25,000 bytes/second 1,000 /25,000 = .04 seconds .

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V.

Boingo

Reread Management Focus 3.2. What other alternatives can travelers consider? How is Boingo different from other companies offering hot-spots, such as T-Mobile or AT&T? Travelers can also consider using mobile hotspots from their cellular providers such as AT&T and Verizon. Boingo is different, because they actually offer wireless service within the airports and coffee shops with IEEE802.11 service rather than via a cellular tower.

Additional Content Teaching Notes Generally preconceptions about what analog and digital transmission are vary greatly among undergraduate students. For this reason it is necessary to spend at least about 3-4 hours covering this chapter.

Make sure at first that the students understand the dual characteristic state of what constitutes a circuit- the concepts of logical and physical. Circuits are probably the most important aspect of comprehending the physical layer. A circuit can be viewed and generally is viewed as a wire or a cable. This is the physical aspect of the circuit. There is also a logical aspect of a circuit. It is not just how long, wide or what type of cable; it is also what it is that propagates through the cable.

When I discuss circuits and media, I try to remember to hand around twisted pair cable, coax cable and fiber optic cable. I also try to link the media to common media with which the student are familiar: twisted pair to telephone cable, coax to cable TV cable, radio to cell phones, and infrared to TV controllers. If you can illustrate circuits in this or similar ways, coverage of the physical characteristics of circuits will not be as complex.

On the other hand, covering the logical aspects of circuits will form a greater part of this chapter.

So allow yourself ample time to define, explore and discuss analog and digital and how the two are mixed to optimize different forms of transmission.

Coverage on MODEMs, CODECs and Multiplexers rounds out the chapter and illustrates both the physical and logical aspects of circuits.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova War Stories Every network, including those using wireless connectivity must have electrical power to function. The physical layer of the network is highly dependent on electrical power. During Desert Storm the network supporting COMNAVSURFLANT in Norfolk, Virginia was completely down for about 5 hours one day at the height of the first Persian Gulf war. This network supported 290 network users that were housed in 7 different buildings on the Naval Station at Norfolk. These users were responsible for expediting the shipment of replacement parts in support of the Atlantic Fleet Operations including those Navy and Marine Units on the ground in the Gulf region.

SURFLANT as they called it, was a campus-like network environment. Inside the buildings they used twisted-pair cabling to connect the client PCs to multi-port HUBs located in the floor closet spaces. The HUBs were interconnected within the building closets using coaxial cable. The HUB stacks in each building were all connected across the naval station via multi-mode fiber-optic cable.

As the War progressed in the Gulf, a terrible storm hit the east coast of the U.S. on this day in January of 1991. Lightning struck the main power station at Naval Station Norfolk. All electricity was out across the base. Needless to say none of the network hardware, except those devices running on backup (battery) power was operating. To complicate matters further, when the power did come back on, power surges occurred at several locations around the network.

These surges were responsible for burning out the circuit boards on four network interface cards (NICs) and one multi-port HUB. This resulted in all of the users connected via that HUB to be down until the bad HUB could be replaced. In addition the client PCs housing the four bad NICs, which were connected via other HUBs still operating were down until the NICs could be replaced. All of the circuits were fine but as you can see how we terminate and power circuits becomes a critical network management factor at the physical layer.

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CHAPTER 4 DATA LINK LAYER Chapter Summary The data link layer (also called layer 2) is responsible for moving a message from one computer or network device to the next computer or network device in the overall path from sender or receiver. It controls the way messages are sent on the physical media. Both the sender and receiver have to agree on the rules, or protocols, that govern how they will communicate with each other. A data link protocol determines who can transmit at what time, where a message begins and ends, and how a receiver recognizes and corrects a transmission error. In this chapter, we discuss these processes as well as several important sources of errors.

Learning Objectives • • • • •

Understand the role of the data link layer Become familiar with two basic approaches to controlling access to the media Become familiar with common sources of error and their prevention Understand three common error detection and correction methods Become familiar with several commonly used data link protocols

Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova

Key Terms

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Access request Asynchronous transmission

Acknowledgment (ACK) Attenuation

Burst error Continuous ARQ Cyclic redundancy check (CRC) Error detection Ethernet (IEEE 802.3) Frame High-level data link control (HDLC) Information bits Link Access ProtocolBalanced (LAP-B) Media access control

Checksum Controlled access Echo

Amplifiers Automatic Repeat reQuest (ARQ) Contention Cross-talk Efficiency

Error prevention Even parity Gaussian noise Hub polling

Error rates Forward error correction Hamming code Impulse noise

Intermodulation noise Logical link control [LLC]

Line noise Sublayer MAC address

MAC address filtering

Media access control [MAC] sublayer MAC address spoofing

Odd parity Parity check Repeater Start bit Synchronous transmission Transmission efficiency

Overhead bits Point-to-Point Protocol (PPP) Roll-call polling Stop bit Throughput White noise

Negative acknowledgment (NAK) Parity bit Polling Sliding window Synchronization Token passing

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova

Chapter Outline 4.1 Introduction 4.2 Media Access Control 4.2.1 Contention 4.2.2 Controlled Access 4.2.3 Relative Performance 4.3 Error Control 4.3.1 Sources of Errors 4.3.2 Error Prevention 4.3.3 Error Detection 4.3.4 Error Correction via Retransmission 4.3.5 Forward Error Correction 4.3.6 Error Control in Practice 4.4 Data Link Protocols 4.4.1 Asynchronous Transmission 4.4.2 Synchronous Transmission 4.5 Transmission Efficiency 4.6 Implications for Cyber Security Summary

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova

Answers to Textbook Exercises Answers to End-of-Chapter Questions

1. What does the data link layer do?

The data link layer controls the way messages are sent on the physical media. The data link layer handles three functions: media access control, message delineation, and error control.

The data link layer accepts messages from the network layer and controls the hardware that actually transmits them. The data link layer is responsible for getting a message from one computer to another without errors. The data link layer also accepts streams of bits from the physical layer and organizes them into coherent messages that it passes to the network layer.

2. What is media access control, and why is it important?

Media access control handles when the message gets sent. Media access control becomes important when several computers share the same communication circuit, such as a point-topoint configuration with a half-duplex line that requires computers to take turns, or a multipoint configuration in which several computers share the same circuit. Here, it is critical to ensure that no two computers attempt to transmit data at the same time -- or if they do, there must be a way to recover from the problem. Media access control is critical in local area networks.

3. Under what conditions is media access control unimportant?

With point-to-point full duplex configurations, media access control is unnecessary because there are only two computers on the circuit and full duplex permits either computer to transmit at any time. There is no media access control.

4. Compare and contrast roll-call polling, hub polling (or token passing), and contention.

With roll call polling, the front end processor works consecutively through a list of clients, first polling terminal 1, then terminal 2, and so on, until all are polled. Roll call polling can be modified to select clients in priority so that some get polled more often than others. For example, one could increase the priority of terminal 1 by using a polling sequence such as 1, 2, 3, 1, 4, 5, 1, 6, 7, 1, 8, 9.

Hub polling is often used in LAN multipoint configurations (i.e., token ring) that do not have a central host computer. One computer starts the poll and passes it to the next computer on the multipoint circuit, which sends its message and passes the poll to the next. That computer then passes the poll to the next, and so on, until it reaches the first computer, which restarts the process again.

Contention is the opposite of controlled access. Computers wait until the circuit is free (i.e., no other computers are transmitting), and then transmit whenever they have data to send.

Contention is commonly used in Ethernet local area networks. .

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5. Which is better, controlled access or contention? Explain.

The key consideration for which is better is throughput -- which approach will permit the largest amount of user data to be transmitted through the network. In most of the 1990s, contention approaches worked better than controlled approaches for small networks that have low usage. In this case, each computer can transmit when necessary, without waiting for permission. In high volume networks, where many computers want to transmit at the same time, the well-controlled circuit originally prevented collisions and delivered better throughput in such networks. Today contention-based systems have been improved to the point where they deliver substantially better throughput and are competitive because of hardware cost considerations.

6. Define two fundamental types of errors.

There are two fundamental types of errors: human errors and network errors. Human errors, such as a mistake in typing a number, usually are controlled through the application program.

Network errors, such as those that occur during transmission, are controlled by the network hardware and software. There are two categories of network errors: corrupted data (data that have been changed) and lost data.

7. Errors normally appear in _____, which is when more than one data bit is changed by the errorcausing condition.

Errors normally appear in bursts, which is when more than one data bit is changed by the errorcausing condition.

8. Is there any difference in the error rates of lower-speed lines and of higher-speed lines?

Yes, normally lower speed lines have higher error rates because (1) leased lines can be conditioned to prevent noise, but dial-up lines cannot and (2) dial-up lines have less stable transmission parameters.

9. Briefly define noise.

Noise consists of undesirable electrical signals, or, in the instance of fiber optic cable, undesirable light. Noise is typically introduced by equipment or natural disturbances, and it can seriously degrade the performance of a communication circuit. Noise manifests itself as extra bits, missing bits, or bits that have been "flipped," (i.e., changed from 1 to 0 or vice versa).

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova 10. Describe four types of noise. Which one is likely to pose the greatest problem to network managers?

The following list summarizes the major sources of error. The first six are the most important; the last three are more common in analog rather that digital circuits.

Line outages are a catastrophic cause of errors and incomplete transmission. Occasionally, a communication circuit fails for a brief period. This type of failure may be caused by faulty telephone end office equipment, storms, loss of the carrier signal, and any other failure that causes a short circuit. When constructing and designing redundant networks that are fault survivable, this is usually called designing for the “farmer with a back hoe” problem.

White noise or Gaussian noise (the familiar background hiss or static on radios and telephones) is caused by the thermal agitation of electrons and therefore is inescapable. Even if the equipment was perfect and the wires were perfectly insulated from any and all external interference, there still would be some white noise. White noise usually is not a problem unless it becomes so strong that it obliterates the transmission. In this case, the strength of the electrical signal is increased so it overpowers the white noise; in technical terms, we increase the signal to noise ratio.

Impulse noise (sometimes called spikes) is the primary source of errors in data communications.

Some of the sources of impulse noise are voltage changes in adjacent lines, lightning flashes during thunderstorms, fluorescent lights, and poor connections in circuits.

Cross-talk occurs when one circuit picks up signals in another. It occurs between pairs of wires that are carrying separate signals, in multiplexed links carrying many discrete signals, or in microwave links in which one antenna picks up a minute reflection from another antenna.

Cross-talk between lines increases with increased communication distance, increased proximity of the two wires, increased signal strength, and higher frequency signals. Wet or damp weather can also increase cross-talk. Like white noise, cross-talk has such a low signal strength that it normally is not bothersome.

Echoes can cause errors. Echoes are caused by poor connections that cause the signal to reflect back to the transmitting equipment. If the strength of the echo is strong enough to be detected, it causes errors. Echoes, like cross-talk and white noise, have such a low signal strength that they normally are not bothersome. In networks, echo suppressors are devices that reduce the potential for this type of error. Echoes can also occur in fiber optic cables when connections between cables are not properly aligned.

Attenuation is the loss of power a signal suffers as it travels from the transmitting computer to the receiving computer. Some power is absorbed by the medium or is lost before it reaches the receiver. This power loss is a function of the transmission method and circuit medium. High frequencies lose power more rapidly than low frequencies during transmission, so the received signal can thus be distorted by unequal loss of its component frequencies. Attenuation increases as frequency increases or as the diameter of the wire decreases, or as the distance of the transmission increases. Repeaters can be used in a digital environment to correct for .

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova attenuation due to distance, where amplifiers can be used to boost diminishing or attenuating analog signals over longer distances. A repeater will perfectly replicate the incoming, distorted digital signal and send it on deeper into the network as if new. An amplifier will boost an attenuating analog signal, but also boost the error noise in the signal as it does so.

Fewer repeaters are necessary as compared to amplifiers to correct for attenuation, thus helping to make digital more cost effective when compared to analog transmission in controlling for noise.

Intermodulation noise is a special type of cross-talk. The signals from two circuits combine to form a new signal that falls into a frequency band reserved for another signal. On a multiplexed line, many different signals are amplified together, and slight variations in the adjustment of the equipment can cause intermodulation noise. A maladjusted modem may transmit a strong frequency tone when not transmitting data, thus producing this type of noise.

Jitter may affect the accuracy of the data being transmitted because minute variations in amplitude, phase, and frequency always occur. The generation of a pure carrier signal in an analog circuit is impossible. The signal may be impaired by continuous and rapid gain and/or phase changes. This jitter may be random or periodic.

Harmonic distortion usually is caused by an amplifier on a circuit that does not correctly represent its output with what was delivered to it on the input side.

Phase hits are short-term shifts "out of phase," with the possibility of a shift back into phase.

11. How do amplifiers differ from repeaters?

An amplifier takes the incoming signal, increases its strength, and retransmits it on the next section of the circuit. They are typically used on analog circuits such as the telephone company’s voice circuits. On analog circuits, it is important to recognize that the noise and distortion are also amplified, along with the signal.

Repeaters are commonly used on digital circuits. A repeater receives the incoming signal, translates it into a digital message, and retransmits the message. Because the message is recreated at each repeater, noise and distortion from the previous circuit are not amplified.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova 12. What are three ways of reducing errors and the types of noise they affect?

Shielding (protecting wires by covering them with an insulating coating) is one of the best ways to prevent impulse noise, cross-talk and intermodulation noise.

Moving cables away from sources of noise (especially power sources) can also reduce impulse noise cross-talk and intermodulation noise. For impulse noise, this means avoiding lights and heavy machinery. Locating communication cables away from power cables is always a good idea. For cross-talk, this means physically separating the cables from other communication cables.

Cross-talk and intermodulation noise is often caused by improper multiplexing. Changing multiplexing techniques (e.g., from FDM to TDM), or changing the frequencies or size of the guardbands in frequency division multiplexing can help.

Many types of noise (e.g., echoes, white noise, jitter, harmonic distortion) can be caused by poorly maintained equipment or poor connections and splices among cables. The solution here is obvious: tune the transmission equipment and redo the connections.

To avoid attenuation, telephone circuits have repeaters or amplifiers spaced throughout their length.

13. Describe three approaches to detecting errors, including how they work, the probability of detecting an error, and any other benefits or limitations.

Three common error detection methods are parity checking, longitudinal redundancy checking, and polynomial checking (particularly checksum and cyclic redundancy checking).

One of the oldest and simplest error detection methods is parity. With this technique, one additional bit is added to each byte in the message. The value of this additional parity bit is based on the number of 1’s in each byte transmitted. This parity bit is set to make the total number of ones in the byte (including the parity bit) either an even number or an odd number.

Any single error (a switch of a 1 to a 0 or vice versa) will be detected by parity, but it cannot determine which bit was in error. But, if two bits are switched, the parity check will not detect any error. Parity can detect errors only when an odd number of bits have been switched; any even number of errors cancel each other out. Therefore, the probability of detecting an error, given that one has occurred, is only about 50 percent. Many networks today do not use parity because of its low error detection rate.

Polynomial checking adds a character or series of characters to the end of the message based on a mathematical algorithm. With the checksum technique, a checksum (typically one byte) is added to the end of the message. The checksum is calculated by adding the decimal value of each character in the message, dividing the sum by 255, and using the remainder as the checksum. The receiver calculates its own checksum in the same way and compares it with the transmitted checksum. If the two values are equal, the message is presumed to contain no errors.

Use of checksum detects close to 95 percent of the errors for multiple bit burst errors. The most .

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova popular polynomial error checking scheme is cyclical redundancy check (see the answer to # 16 below for more discussion). The probability of detecting an error is nearly 100% or, in some cases, 100%.

14. Briefly describe how even parity and odd parity work.

Even parity is when the seven bits of an ASCII character have an even (2, 4, or 6) number of 1s, and therefore a 0 is placed in the eighth parity position. Odd parity is when the seven bits of an ASCII character have an odd (1, 3, 5, or 7) number of 1s, and therefore a 1 is placed in the eighth parity position.

15. Briefly describe how checksum works.

Checksum error checking adds a checksum (typically 1 byte) is added to the end of the message.

The checksum is calculated by adding the decimal value of each character in the message, dividing the sum by 255, and then using the remainder as the checksum. The same approach is used at the receiving end. If the receiver gets the same result, the block has been received correctly.

16. How does CRC work?

Cyclical redundancy check (CRC) adds 8, 16, 24 or 32 bits to the message. With CRC, a message is treated as one long binary number, P. Before transmission, the data link layer (or hardware device) divides P by a fixed binary number, G, resulting in a whole number, Q, and a remainder, R/G. So, P/G = Q + R/G. For example, if P = 58 and G = 8, then Q = 7 and R = 2. G is chosen so that the remainder R will be either 8 bits, 16 bits, 24 bits, or 32 bits.

The remainder, R, is appended to the message as the error checking characters before transmission. The receiving hardware divides the received message by the same G, which generates an R. The receiving hardware checks to ascertain whether the received R agrees with the locally generated R. If it does not, the message is assumed to be in error.

17. How does forward error correction work? How is it different from other error-correction methods?

Forward error correction uses codes containing sufficient redundancy to prevent errors by detecting and correcting them at the receiving end without retransmission of the original message. The redundancy, or extra bits required, varies with different schemes. It ranges from a small percentage of extra bits to 100 percent redundancy, with the number of error detecting bits roughly equaling the number of data bits.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova 18. Under what circumstances is forward error-correction desirable?

Forward error correction is commonly used in satellite transmission. A round trip from the Earth station to the satellite and back includes a significant delay. Error rates can fluctuate depending on the condition of equipment, sun spots, or the weather. Indeed, some weather conditions make it impossible to transmit without some errors, making forward error correction essential.

Compared to satellite equipment costs, the additional cost of forward error correction is insignificant.

19. Briefly describe how continuous ARQ works.

With continuous ARQ, the sender does not wait for an acknowledgment after sending a message; it immediately sends the next one. While the messages are being transmitted, the sender examines the stream of returning acknowledgments. If it receives an NAK, the sender retransmits the needed messages. Continuous ARQ is by definition a full duplex transmission technique, because both the sender and the receiver are transmitting simultaneously (the sender is sending messages, and the receiver is sending ACKs and NAKs).

20. Which is the simplest (least sophisticated) protocol described in this chapter? How does it work?

Students could make an argument for SDLC, HDLC, or PPP. Each of these are similar in many ways.

Each SDLC frame begins and ends with a special bit pattern (01111110), known as the flag. The address field identifies the destination. The length of the address field is usually 8 bits but can be set at 16 bits; all computers on the same network must use the same length. The control field identifies the kind of frame that is being transmitted, either information or supervisory. An information frame is used for the transfer and reception of messages, frame numbering of contiguous frames, and the like. A supervisory frame is used to transmit acknowledgments (ACKs and NAKs). The message field is of variable length and is the user’s message. The frame check sequence field is a 32-bit CRC code (some older versions use a 16-bit CRC).

High-Level Data Link Control High-level data link control (HDLC) is a formal standard developed by the ISO often used in WANs. HDLC is essentially the same as SDLC, except that the address and control fields can be longer.

The PPP frame starts with a flag and has a 1-byte address (which is not used on point-topoint circuits). The control field is typically not used. The protocol field indicates what type of data packet the frame contains (e.g., an IP packet). The data field is variable in length and may be up to 1,500 bytes. The frame check sequence is usually a CRC-16 but can be a CRC32. The frame ends with a flag.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova 21. Describe the frame layouts for SDLC, Ethernet, and PPP. Each SDLC frame begins and ends with a special bit pattern, known as the flag. The address field identifies the destination. The length of the address field is usually 8 bits but can be set at 16 bits; all computers on the same network must use the same length. The control field identifies the kind of frame that is being transmitted, either information or supervisory. An information frame is used for the transfer and reception of messages, frame numbering of contiguous frames, and the like. A supervisory frame is used to transmit acknowledgments (ACKs and NAKs). The message field is of variable length and is the user's message. The frame check sequence field is a 16-bit or 32-bit cyclical redundancy checking (CRC) code.

For a typical Ethernet packet, the destination address specifies the receiver, while the source address specifies the sender. The length indicates the length in 8-bit bytes of the message portion of the packet. The LLC control and SNAP control are used to pass control information between the sender and receiver. These are often used to indicate the type of network layer protocol the packet contains (e.g., TCP/IP or IPX/SPX as described in Chapter 6). The maximum length of the message is 1492 bytes. The packet ends with a CRC-32 frame check sequence used for error detection.

The PPP frame is similar to the SDLC frame. The frame starts with a flag and has a one-byte address. It also contains a control field which is rarely used. The protocol field indicates what type of data is contained. The message portion is variable in length and may be up to 1,500 bytes long. The frame check sequence is either CRC-16 or -32. The frame ends with a flag.

22. What is transmission efficiency?

Transmission efficiency is defined as the total number of information bits (i.e., bits in the message sent by the user) divided by the total bits in transmission (i.e., information bits plus overhead bits).

23. How do information bits differ from overhead bits?

Information bits are those used to convey the user’s meaning. Overhead bits are used for purposes such as error checking, and marking the start and end of characters and packets.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova 24. Are stop bits necessary in asynchronous transmission? Explain using a diagram.

Stop bits in asynchronous transmission are necessary to return the state of the transmission medium to the idle state (such as +3v in Figure 4-9). The signal must return to the idle state in order for the start bit to be recognized as such.

Start Bit 0

7-bit ASCII data 1

1

1

0

1

0

0

Parity Stop bit bit 1 1

Idle

Idle

25. During the 1990s, there was intense competition between two technologies (10 Mbps Ethernet and 16 Mbps token ring) for the LAN market. Ethernet was promoted by a consortium of vendors while token ring was primarily an IBM product, even though it was standardized.

Ethernet won, and no one talks about token ring anymore. Token ring used a hub-polling-based approach. Outline a number of reasons why Ethernet might have won. Hint: the reasons were both technical and business.

• • • • •

Ethernet tended to be faster Ethernet tended to be less expensive Ethernet ran across telephone-grade unshielded copper wires Soderblom demanded royalties from Token Ring venders Cisco dropped out of efforts to develop high-speed Token Ring (1998)

26. Under what conditions does a data link layer protocol need an address?

At some point in the networking process, the device’s data link layer must be addressed by the layer 3 protocol, no matter what the particular data link layer protocol that is running on the network.

27. Are large frame sizes better than small frame sizes? Explain.

Selecting the right frame size can have a great effect on performance. There is an optimal frame size that is not so small that packets have low efficiency by carrying too little information for too much overhead, nor so large as to incur the risk of more errors and thus longer and more frequent retransmission. The optimal frame size is dependent on the specific application and the pattern of messages it generates.

28. What media access control technique does your class use?

Each class will have a different answer.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova 29. Show how the word “HI” would be sent using asynchronous transmission using even parity (make assumptions about the bit patterns needed). Show how it would be sent using Ethernet.

H → 0100 1000 I → 0100 1001 Adding single bit, even parity: H → 0100 1000 0 I → 0100 1001 1 Thus, asynchronous with 0 start bit, 1 stop bit: 0 0 0100 1000 0 1 0 0100 1001 1 1 Ethernet packet would have frame with data inserted within it as follows: 7 byte preamble 1 byte frame start 6 bytes destination 6 bytes source 4 bytes VLAN (optional) 2 bytes length 1 byte control information (DSAP) 1 byte control information (SSAP) 1-2 bytes control Data: H → 0100 1000 I → 0100 1001 Frame check sequence

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova Exercises A. Draw how a series of four separate messages would be successfully sent from one computer to another if the first message were transferred without error, the second were initially transmitted with an error, the third were initially lost, and the ACK for the fourth were initially lost.

Computer 1 Computer 1 Computer 1 Computer 1 Computer 1 Computer 1 Computer 1 Computer 1

       

Message1 Message2 Resend request Message2 Message3 Resend request Message3 Message4

       

Computer 2 Computer 2 Computer 2 Computer 2 Computer 2 Computer 2 Computer 2 Computer 2

Message successful Error Message successful Lost packet detected Message successful ACK lost

For Message4, most likely no resending is required. Directly after the lost ACK, the host started sending data. That data, like all TCP packets, will have an ACK number so the recipient would get an ACK from the TCP packets.

B. How efficient would a 6-bit code be in asynchronous transmission if it had 1 parity bit, 1 start bit, and 2 stop bits? (Some old equipment uses 2 stop bits.)

A total of 6 + 1 + 1 + 2 = 10 bits is being used to transmit 6 pits of information so the 6 efficiency is 10 = 60 𝑝𝑒𝑟𝑐𝑒𝑛𝑡. That is not every efficient.

C. What is the transmission rate of information bits (TRIB) if you use ASCII (8 bits plus 1 parity bit), a 1,000-character frame, 56 Kbps modem transmission speed, 20 control characters per frame, an error rate of 1%, and a 30-millisecond turnaround time? What is the TRIB if you add a half-second delay to the turnaround time because of satellite delay?

First Part 𝐾(𝑀 − 𝐶)(1 − 𝑃) 𝑇𝑅𝐼𝐵 = (𝑀⁄𝑅 ) + 𝑇 8(𝑏𝑖𝑡𝑠⁄𝑐ℎ𝑎𝑟) × (1,000 − 20) 𝑐ℎ𝑎𝑟 × (1 − 0.01) = = 40,700 𝑏𝑖𝑡𝑠⁄𝑠𝑒𝑐 1,000 𝑐ℎ𝑎𝑟 ( ⁄6,222 𝑐𝑎𝑟/𝑠𝑒𝑐 ) + 0.03 𝑠𝑒𝑐 Second Part The only difference is we add 0.50 sec to T 8(𝑏𝑖𝑡𝑠⁄𝑐ℎ𝑎𝑟 ) × (1,000 − 20) 𝑐ℎ𝑎𝑟 × (1 − 0.01) 𝑇𝑅𝐼𝐵 = = 11,200 𝑏𝑖𝑡𝑠⁄𝑠𝑒𝑐 1,000 𝑐ℎ𝑎𝑟 ( ⁄6,222 𝑐𝑎𝑟/𝑠𝑒𝑐 ) + (0.50 + 0.03 𝑠𝑒𝑐) .

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova

D. Search the Web to find a software vendor that sells a package that supports each of the following protocols: SDLC, HDLC, Ethernet, and PPP (i.e., one package that supports SDLC, another [or the same] for HDLC, and so on).

Student answers will vary.

E. Investigate the network at your organization (or a service offered by an IXC) to find out the average error rates.

Answers will vary by location.

F. What is the efficiency if a 100-byte file is transmitted using Ethernet? A 10,000-byte file?

Using the default Ethernet frame size of 1,518 bytes with a maximum transmission unit (MTU) of 1,500 bytes: 𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦100 =

100 = 6.59% 1,518 10,000

A 10,000 byte file must be broken down into 1,500 = 6.67 → 7 𝑓𝑟𝑎𝑚𝑒𝑠 10,000 𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦10,000 = = 94.11% 1,518 × 7 G. What is the propagation delay on a circuit using a LEO satellite orbiting 500 miles above the earth if the speed of the signal is 186,000 miles per second? If the satellite is 22,000 miles above the earth?

500 = 0.0026882 𝑠𝑒𝑐𝑜𝑛𝑑 = 2.6882 𝑚𝑖𝑙𝑙𝑖𝑠𝑒𝑐𝑜𝑛𝑑𝑠 186,000 22,000 = 0.1183 𝑠𝑒𝑐𝑜𝑛𝑑 = 118.3 𝑚𝑖𝑙𝑙𝑖𝑠𝑒𝑐𝑜𝑛𝑑𝑠 186,000 H. Suppose that you are going to connect the computers in your house or apartment. What media would you use? Why? Would this change if you were building a new house?

Student answers will vary depending on broadband availability in your area.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova Mini-Cases I. Smith, Smith, Smith, and Smith Smith, Smith, Smith, and Smith is a regional accounting firm that is building a new headquarters building. The building will have a backbone network that connects eight LANs (two on each floor).

They are very concerned with network errors. What advice would you give them in the design of the building and network cable planning that would help reduce network errors?

Building and network cable planning should take into account the recommended maximum lengths for media and protocols, avoid running network cable alongside power cable, include adequate shielding in specifying cable, keep cable away from lights and heavy machinery, and include adequate repeaters or amplifiers.

II. Worldwide Charity Worldwide Charity is a charitable organization whose mission is to improve education in developing countries. What data link layer protocols should WC staff use for file transfer? What range of frame sizes is likely to be used?

Recommended is Zmodem, because it has a powerful error detection method (CRC-32) with continuous ARQ. Note that Zmodem dynamically adjusts packet size to communication circuit conditions to increase efficiency.

III.

Industrial Products

What would you suggest Clarence Hung do to investigate why the network is reported to be slow over the past week?

He should check to see if any new computers have been added to the network, which may result in collisions if the system uses a contention approach to control network access.

IV.

Alpha Corp.

1. Without considering transmission efficiency, how large an Internet connection would you recommend in terms of bits per second (assuming that each byte is 8 bits in length)?

Since transmission efficiency is not a consideration, one could get by with V.92 modem at 56 Kbps; however keep in mind this would be very slow. If given the choice, avoid the potential problem, consider SDLC. 2. Assuming they use a synchronous data link layer protocol with an efficiency of about 90%, how large an Internet connection would you recommend?

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova You would need an Internet connection that could handle 2,000 and 4,000 bytes. This number should be sufficient; however, if you would like to fine tune the exact number of bits, a system manager can use the TRIB calculation.

TRIB = Number of information bits accepted, divided by, the total time required to get the bits accepted 3. Suppose Alpa wants to be sure that its Internet connection will provide sufficient capacity for the next 2 years, how large an Internet connection would you recommend?

Alpa is transmitting large sums of data every hour; thus, a Zmodem might be used as it can handle a message length up to 1,024 bites. Migrating to a different protocol might also prove efficient, as the general rule is that the larger the message field, the more efficient the protocol.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova

Additional Content Teaching Notes I start by revisiting the network model introduced in Chapter 1 to help students put this material in context.

I spend time making sure the students understand what media access control is. This section will be revisited in detail in Chapter 6 on LANs and I want the students to have a good foundation. I just try to get the issue of controlling access to the media on the table at this point.

In my teaching on error control, my goal is to ensure that students understand the cause of errors, how to detect them (parity, LRC, CRC) and how to correct them. I do not cover forward error correction except to discuss it is possible. Likewise, I focus only on the most straightforward sources of error (white noise, impulse noise, cross-talk, echo, and attenuation); I do not discuss the others. I do examples for parity and LRC and discuss the idea behind CRC. I do several examples of error correction by retransmission. I build a simple diagram and explain the roles of ACKs and NAKs. I then ask what happens if a message is lost (and let them discover the need for timeouts). I ask what happens if an ACK is lost (and let them discover the need for buffers and message numbers). I ask what happens if a NAK is lost (and let them discover that we really don’t need NAKs, they just make the network faster).

I discuss each of the packets for the various data link layer protocols. My goal is to drive home the point that there is such a thing as packets at each level, that each protocol is different, and that many protocols are similar in structure (how they mark the start and end of a packet, where error control information and addresses are). I integrate the discussion of efficiency into each protocol by calculating its efficiency and asking the class how to improve it. I also introduce the idea that too large packets are a bad idea by asking why we don’t have XMODEM-1meg. It is intuitive that this would be a bad idea and helps students understand why large packets aren’t always the best.

Vivid examples help students understand media access control. We talk about conversation at social gatherings or parties as contention-based and discuss how people handle situations where more than one person begins to talk at the same time (like Ethernet). We talk about events where parliamentary procedure is used ("You now have the floor!") as using controlled access, like hub polling or Token Ring. In this way students realize they understood these concepts long before enrolling in a data communications course! Students are encouraged to observe "CSMA/CD" at parties (now they can fulfill a data communications assignment and go to a party at the same time!) and controlled access in Congress on C-SPAN.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 13e by Fitzgerald/Dennis/Durcikova War Stories Squirrels and Impulse Noise (Objective: illustrate the difficulties caused by impulse noise) Recently our campus radio station received FCC approval to broadcast using a stronger signal.

Immediately after they started broadcasting, the campus backbone network became unusable. It was filled with impulse noise. It took 2 days to link the impulse noise to the radio station, and when the radio station returned to its usual broadcast signal the problem disappeared.

However, this was only the first step in the problem. The radio station wanted to broadcast at full strength and there was no good reason for the stronger broadcast to affect the backbone in this way. After two weeks of effort, the problem was discovered. A short section of the backbone ran above ground between two buildings. It turns out that this specific brand of outdoor cable we used was particularly tasty to squirrels. They had eaten the outer insulating coating off of the cable, making it act like an antennae to receive the radio signals. The cable was replaced with a steel-coated armored cable and things worked fine when the radio station returned to its stronger signal.

Shielding Against Impulse Noise (Objective: another example of impulse noise problems) When I was an undergraduate, I worked during the summers in Halifax Nova Scotia for Sperry Univac (a then-important computer manufacturer, now Unisys). One of our clients was Power Corp, a large electrical utility with a computer room on the 7th floor of a downtown skyscraper.

Every second Friday at about 4:00pm the computer network would suffer a short-duration (2-5 seconds) impulse noise hit that caused considerable problems.

It took a long time to identify that the noise was occurring at regular intervals, and even longer to identify the source. Halifax is the major east coast base of the Royal Canadian Navy, whose ships at the time were on a two-week rotation ending every second Friday. Just as they rounded the point into the harbor, the lead ship would blip its high power radar into the harbor and directly into our building, causing the network outage.

Obviously, asking the navy to stop was not a viable option. Instead, we coated that side of the computer room wall with aluminum foil to act as a shield. It worked fine, but looked rather silly.

I have learned from one of my students that there is a company that now sells this type of insulating material for exactly this type of problem, and that the panels look like ordinary cubicle walls, not something out of the Apollo missions.

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CHAPTER 5 NETWORK AND TRANSPORT LAYERS Chapter Summary The network layers and transport layer are responsible for moving messages from end to end in a network. They are so closely tied together that they are usually discussed together. The transport layer (layer 4) performs three functions: linking the application layer to the network, segmenting (breaking long messages into smaller packets for transmission), and session management (establishing an end-to-end connection between the sender and receiver). The network layer (layer 3) performs two functions: routing (determining the next computer to which the message should be sent to reach the final destination) and addressing (finding the address of that next computer). There are several standard transport and network layer protocols that specify how packets are to be organized, in the same way that there are standards for data link layer packets.

However, only one protocol is in widespread use today: Transmission Control Protocol/Internet Protocol (TCP/IP), the protocol used on the Internet. This chapter takes a detailed look at how TCP/IP works.

Learning Objectives After reading this chapter, students should be able to: • be aware of the TCP/IP protocols • be familiar with linking to the application layer, segmenting, and session • management • be familiar with addressing • be familiar with routing • understand how TCP/IP works

Key Terms Access Control List (ACL) Address resolution Application layer address ARP cache Autonomous systems Border Gateway Protocol (BGP) Broadcast message Cisco Internetwork Operating Systems (IOS) Connectionless messaging Console port Data link layer address Destination port address Domain Name Service (DNS)

Acknowledgment (ACK) Address Resolution Protocol (ARP) Authoritative name server Automatic Repeat reQuest (ARQ) Auxiliary port Border router Centralized routing Classless addressing Connection-oriented messaging Continuous ARQ Designated router Distance vector dynamic routing Dynamic addressing

Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova Dynamic Host Configuration Protocol (DHCP) Enhanced Interior Gateway Routing Protocol (EIGRP) Flow control Go-Back-N ARQ Interface Interior routing protocol Internet address classes Internet Corporation for Assigned Names and Numbers (ICANN) Link Access Protocol for Modems [LAP-M] Loopback Multicast message Negative acknowledgment (NAK) Network layer address Port address Quality of Service (QoS) Real-Time Transport Protocol (RTP) Resolving name server Root server Routing Segment Selective-Repeat ARQ Sliding window Static routing Subnet Top-level domain (TLD) Unicast message

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Dynamic routing Exterior routing protocol Gateway Hop Interior Gateway Routing Protocol (IGRP) Intermediate System to Intermediate System (IS-IS) Internet Control Message Protocol (ICMP) Internet Group Management Protocol (IGMP) Link state dynamic routing Multicasting Name server Network interface port Open Shortest Path First (OSPF) Private IPv4 address space Real-Time Streaming Protocol (RTSP) Reserved addresses Resource Reservation Protocol (RSVP) Router ROUTING Information Protocol (RIP) Segmenting Session Source port address Stop-and-wait ARQ Subnet mask Transmission Control Protocol/Internet Protocol (TCP/IP) User Datagram Protocol (UDP)

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

Chapter Outline 5.1 Introduction 5.2 Transport and Network Layer Protocols 5.2.1 Transmission Control Protocol (TCP) 5.2.2 Internet Protocol (IP) 5.3 Transport Layer Functions 5.3.1 Linking to the Application Layer 5.3.2 Segmenting 5.3.3 Session Management 5.4 Addressing 5.4.1 Assigning Addresses 5.4.2 Address Resolution 5.5 Routing 5.5.1 Types of Routing 5.5.2 Routing Protocols 5.5.3 Multicasting 5.5.4 The Anatomy of a Router 5.6 TCP/IP Example 5.6.1 Known Addresses 5.6.2 Unknown Addresses 5.6.3 TCP Connections 5.6.4 TCP/IP and Network Layers 5.7 Implications for Cyber Security Summary

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

Answers to Textbook Exercises Answers to End-of-Chapter Questions 1. What does the transport layer do?

The transport layer links application software in the application layer with the network and is responsible for the end-to-end delivery of the message. The transport layer sits between the application layer and the network layer. The transport layer accepts messages from the application layer and packetizes them. Packetizing means to take one outgoing message from the application layer and break it into a set of smaller packets for transmission through the network. Conversely, it also means to take the incoming set of smaller packets form the network layer and reassemble them into one message for the application layer.

2. What does the network layer do?

The network layer performs three important functions: addressing, routing, and breaking long messages into smaller packets for transmission by the data link layer. The network layer sits between the application layer and the data link layer. The network layer accepts messages from the application layer and formats and addresses them for transmission by the data link layer. The network layer also accepts individual messages from the data link layer and organizes them into coherent messages that it passes to the application layer.

3. What are the parts of TCP/IP and what do they do? Who is the primary user of TCP/IP? TCP performs packetizing: breaking the data into smaller packets, numbering them, ensuring each packet is reliably delivered, and putting them in the proper order at the destination. IP performs routing and addressing. IP software is used at each of the intervening computers through which the message passes; it is IP that routes the message to the final destination. The TCP software only needs to be active at the sender and the receiver, because TCP is only involved when data comes from or goes to the application layer.

TCP/IP is the network layer protocol now used on the Internet. It is also the world’s most popular network layer protocol, used by almost 70 percent of all backbone, metropolitan, and wide area networks. TCP/IP is commonly combined with Ethernet.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 4. Compare and contrast the three types of addresses used in a network.

When users work with application software, they typically use the application layer address (e.g., entering an Internet address into a browsers, such as www.cba.uga.edu). When a user types an Internet address into a Web browser, the request is passed to the network layer as part of an application layer packet formatted using the HTTP standard.

The network layer software translates this application layer address into a network layer address.

The network layer protocol used on the Internet is TCP/IP, so this Web address (www.cba.uga.edu) is translated into an TCP/IP address (usually just called an IP address for short) which is four bytes long when using IPv4 (e.g., 128.192.78.5).

The network layer then determines the best route through the network to the final destination.

Based on this routing, the network layer identifies the data link layer address of the next computer to which the message should be sent. If the data link layer is running Ethernet, then the network layer IP address would be translated into an Ethernet address (e.g., 00-0F-00-8114-00).

5. How is TCP different from UDP? TCP is a connection-oriented protocol. UDP is a connection-less protocol. What are the differences between connectionless and connection-oriented routing?

Connection-oriented routing sets up a virtual circuit between the sender and receiver. In this case, a temporary virtual circuit is defined between the sender and receiver. The network layer makes one routing decision when the connection is established, and all packets follow the same route. All packets in the same message arrive at the destination in the same order in which they were sent. In this case, packets only need to contain information about the stream to which it belongs; sequence numbers are not needed, although many connection-oriented protocols include a sequence number to ensure that all packets are actually received.

Connection-oriented routing has greater overhead than connectionless routing, because the sender must first “open” the circuit by sending a control packet that instructs all the intervening devices to establish the circuit routing. Likewise, when the transmission is complete, the sender must “close” the circuit. Connection-oriented protocols also tend to have more overhead bits in each packet.

Connectionless routing means each packet is treated separately and makes its own way through the network. It is possible that different packets will take different routes through the network depending upon the type of routing used and the amount of traffic. Because packets following different routes may travel at different speeds, they may arrive out of sequence at their destination. The sender’s network layer therefore puts a sequence number on each packet, in addition to information about the message stream to which the packet belongs. The network layer must reassemble them in the correct order before passing the message to the application layer.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 6. How does TCP establish a session?

TCP sets up a virtual circuit between the sender and the receiver. The transport layer software sends a special packet (called a SYN, or synchronization characters) to the receiver requesting that a connection be established. The receiver either accepts or rejects the connection, and together, they settle on the packet sizes the connection will use. Once the connection is established, the packets flow between the sender and the receiver, following the same route through the network.

7. What is a subnet and why do networks need them?

Each organization must assign the IP addresses it has received to specific computers on its networks. In general, IP addresses are assigned so that all computers on the same local area network have a similar addresses. For example, suppose a university has just received a set of Class B addresses starting with 128.184.x.x. It is customary to assign all the computers in the same LAN numbers that start with the same first three digits, so the Business School LAN might be assigned 128.184.56.x while the Computer Science LAN might be assigned 128.184.55.x (see Figure 6-8). Likewise, all the other LANs at the university and the backbone network that connects them, would have a different set of numbers. Each of these LANs are called a TCP/IP subnet because they are logically grouped together by IP number. Knowing whether a computer is on your subnet or not it very important for message routing.

8. What is a subnet mask?

While it is customary to use the last byte of the IP address to indicate different subnets, it is not required. Any portion of the IP address can be designated as a subnet by using a subnet mask.

Every computer in a TCP/IP network is given a subnet mask to enable it to determine which computers are on the same subnet (i.e., LAN) as it is, and which computers are outside of its subnet. The subnet mask is a number that each routing device on a network can use to compare the routing packet to in order to determine if the packet stays in that portion or the network, or should be routed on to the next portion of the network.

For example, a network could be configured so that the first two bytes indicated a subnet (e.g., 128.184.x.x) so all computers would be given a subnet mask giving the first two bytes as the subnet indicator. This would mean that a computer with an IP address of 128.184.22.33 would be on the same subnet as 128.184.78.90, and that the message stays within that network. On the other hand, if the subnet comparison shows that the message is not on that particular subnet, then the routing device will move the packets on in their journey.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 9. How does dynamic addressing work?

With dynamic addressing, a server is designated to supply a network layer address to a computer each time the computer connects to the network. This is commonly done for client computers, but usually not done for servers.

Instead of providing a network layer address in a configuration file, a special software package is installed on the client that instructs it to contact bootp or DHCP servers using data link layer addresses. This message asks the servers to assign the requesting computer a unique network layer address. The server runs a corresponding bootp or DHCP software package that responds to these requests and sends a message back to the client giving it its network layer address (and its subnet mask).

10. What benefits and problems does dynamic addressing provide?

The bootp or DHCP server can be configured to assign the same network layer address to the computer each time it requests an address (based on its data link layer address), or it can lease the address to the computer by picking the “next available” network layer address from a list of authorized addresses. Addresses can be leased for as long as the computer is connected to the network or for a specified time limit (e.g., two hours). When the lease expires, the client computer must contact the bootp or DHCP server to get a new address. Address leasing is commonly used by Internet service providers (ISPs) for dial-up users.

Dynamic addressing greatly simplifies network management in non-dial-up networks too. With dynamic addressing, address changes need to be done only to the bootp or DHCP server, not each individual computer. The next time each computer connects to the network or whenever the address lease expires, it automatically gets the new address.

11. What is address resolution?

In order to send a message, the sender must be able to translate the application layer address (or server name) of the destination into a network layer address and in turn translate that into a data link layer address. This process is called address resolution. There are many different approaches to address resolution that range from completely decentralized (each computer is responsible for knowing all addresses) to completely centralized (there is one computer that knows all addresses).

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 12. How does TCP/IP perform address resolution for network layer addresses?

Server name resolution is the translation of application layer addresses into network layer addresses (e.g., translating an Internet address such as www.cba.uga.edu into an IP address such as 128.192.98.3). This is done using the Domain Name Service (DNS). Throughout the Internet there are a series of computers called name servers that provide DNS services. These name servers run special address databases that store thousands of Internet addresses and their corresponding IP addresses. These name servers are in effect the "directory assistance" computers for the Internet. Any time a computer does not know the IP number for a computer, it sends a message to the name server requesting the IP number.

When TCP/IP needs to translate an application layer address into an IP address, it sends a special TCP-level packet to the nearest DNS server. This packet asks the DNS server to send the requesting computer the IP address that matches the Internet address provided. If the DNS server has a matching name in its database, it sends back a special TCP packet with the correct IP address. If that DNS server does not have that Internet address in its database, it will issue the same request to another DNS server elsewhere on the Internet.

Once your computer receives an IP address it is stored in a server address table. This way, if you ever need to access the same computer again, your computer does not need to contact a DNS server. Most server address tables are routinely deleted whenever you turn off your computer.

13. How does TCP/IP perform address resolution for data link layer addresses?

To send a message to a computer in its network, a computer must know the correct data link layer address. In this case, the TCP/IP software sends a broadcast message to all computers in its subnet. A broadcast message, as the name suggests, is received and processed by all computers in the same LAN (which is usually designed to match the IP subnet). The message is a specially formatted TCP-level request using Address Resolution Protocol (ARP) that says “Whoever is IP address xxx.xxx.xxx.xxx, please send me your data link layer address.”

The TCP software in the computer with that IP address then responds with its data link layer address. The sender transmits its message using that data link layer address. The sender also stores the data link layer address in its address table for future use.

14. What is routing?

Routing is the process of determining the route or path through the network that a message will travel from the sending computer to the receiving computer. Every computer that performs routing has a routing table developed by the network manager that specifies how messages will travel through the network.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 15. How does decentralized routing differ from centralized routing?

With centralized routing, all routing decisions are made by one central host computer.

Centralized routing is used typically only in host-based networks and in this case, routing decisions are rather simple. All computers are connected to the central computer by individual point-to-point circuits, so any message received is simply retransmitted on the point-to-point circuit connected to the destination.

Decentralized routing allows all computers in the network make their own routing decisions following a formal routing protocol. In MANs and WANs, the routing table for each computer is developed by its individual network manager. Most decentralized routing protocols are selfadjusting, meaning that they can automatically adapt to changes in the network configuration (e.g., adding and deleting computers and circuits).

16. What are the differences between connectionless and connection-oriented routing?

Connectionless routing means each packet is treated separately and makes its own way through the network. It is possible that different packets will take different routes through the network depending upon the type of routing used and the amount of traffic. Because packets following different routes may travel at different speeds, they may arrive out of sequence at their destination. The sender’s network layer therefore puts a sequence number on each packet, in addition to information about the message stream to which the packet belongs. The network layer must reassemble them in the correct order before passing the message to the application layer.

Connection-oriented routing sets up a virtual circuit between the sender and receiver. In this case, a temporary virtual circuit is defined between the sender and receiver. The network layer makes one routing decision when the connection is established, and all packets follow the same route. All packets in the same message arrive at the destination in the same order in which they were sent. In this case, packets only need to contain information about the stream to which it belongs; sequence numbers are not needed, although many connection-oriented protocols include a sequence number to ensure that all packets are actually received.

Connection-oriented routing has greater overhead than connectionless routing, because the sender must first “open” the circuit by sending a control packet that instructs all the intervening devices to establish the circuit routing. Likewise, when the transmission is complete, the sender must “close” the circuit. Connection-oriented protocols also tend to have more overhead bits in each packet.

17. What is a session?

A session can be thought of as a conversation between two computers. When the sender wants to send a message, it first establishes a session with the destination computer. The sender then sends the data packets in order until all data has been sent. Then the session is ended.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 18. What is QoS routing and why is it useful?

Quality of service (QoS) routing is a special type of connection-oriented dynamic routing in which different messages or packets are assigned different priorities. For example, videoconferencing requires fast delivery of packet to ensure that the images and voices appear smooth and continuous; they are very time-dependent, because delays in routing will seriously affect the quality of the service provided. Email can have a low QoS, as it is not critical that it be delivered immediately to the destination.

19. Compare and contrast unicast, broadcast, and multicast messages.

The most common type of message in a network is the usual transmission between two computers. One computer sends a message to another computer (e.g., a client requesting a Web page). This is called a unicast message. In the situation of a broadcast message, the message is sent to all computers on a specific LAN or subnet. A third type of message called a multicast message is used to send the same message to a group of computers.

20. Explain how multicasting works.

Computers wishing to participate in a multicast (e.g., for videoconferencing) send a message to the sending computer or some other computer performing routing along the way using a special type of TCP-level packet called Internet Group Management Protocol (IGMP). Each multicast group is assigned a special Class D IP address to identify the group. Any computer performing routing knows to route all multicast messages with this Class D IP address onto the subnet that contains the requesting computer. The routing computer sets the data link layer address on multicast messages to a matching multicast data link layer address. Each requesting computer must inform its data link layer software to process incoming messages with this multicast data link layer address. When the multicast session ends (e.g., the videoconference is over), the client computer sends another IGMP message to the organizing computer or the computer performing routing to remove it from the multicast group.

21. Explain how the client computer in Figure 5-16 (128.192.98.xx) would obtain the data link layer address of its subnet gateway.

When a computer is installed on a TCP/IP network (or dials into a TCP/IP network), it knows the IP address of its subnet gateway. This information can be provided by a configuration file or via a bootp or DHCP server. However, the computer does not know the subnet gateway’s Ethernet address (data link layer address). Therefore, TCP would broadcast an ARP request to all computers on its subnet, requesting that the computer whose IP address is 128.192.98.1 to respond with its Ethernet address.

All computers on the subnet would process this request, but only the subnet gateway would respond with an ARP packet giving its Ethernet address. The network layer software on the client would then store this address in its data link layer address table.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 22. Why does HTTP use TCP and DNS use UDP? HTTP at the application layer would pass its message packet with overhead, including the Internet address of the destination, to the transport layer where TCP software would complete packetization at the Transport layer and hand it off to the Network layer.

Domain Name Services, the Domain Name Server (aka DNS) is primarily responsible for translating IP Addresses into valid Domain Names and translating valid Domain Names into IP addresses. UDP is a connection-less transport layer protocol. DNS would pass either a Domain Name or an IP address along with its packet(s) to the Transport layer for forwarding to the Network layer to be routed to the destination.

23. How does static routing differ from dynamic routing? When would you use static routing?

When would you use dynamic routing?

With static routing, the routing table is developed by the network manager, and changes only when computers are added to or removed from the network. For example, if the computer recognizes that a circuit is broken or unusable (e.g., after the data link layer retry limit has been exceeded without receiving an acknowledgment), the computer will update the routing table to indicate the failed circuit. If an alternate route is available, it will be used for all subsequent messages. Otherwise, messages will be stored until the circuit is repaired. When new computers are added to the network, they announce their presence to the other computers, who automatically add them into their routing tables. Static routing is commonly used in networks that have few routing options. For example, most LANs are connected to the backbone network in only one place. There is only one route from the LAN to the backbone, so static routing is used.

Dynamic routing (or adaptive routing) is used when there are multiple routes through a network and it is important to select the best route. Dynamic routing attempts to improve network performance by routing messages over the fastest possible route, away from busy circuits and busy computers. An initial routing table is developed by the network manager, but is continuously updated by the computers themselves to reflect changing network conditions, such as network traffic. Routers can monitor outgoing messages to see how long they take to transmit and how long it takes for the receiving computer to acknowledge them. Based on this monitoring the router can effectuate table updating.

24. What type of routing does a TCP/IP client use? What type of routing does a TCP/IP gateway use? Explain.

The TCP/IP client uses static routing because the client must always point to a single gateway router. The TCP/IP gateway router uses dynamic routing because typically it must process multiple requests for routing beyond the single segment that it physically supports.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 25. What is the transmission efficiency of a 10-byte Web request sent using HTTP, TCP/IP, and Ethernet? Assume the HTTP packet has 100 bytes in addition to the 10-byte URL. Hint: Remember from Chapter 4 that efficiency = user data/total transmission size.

Total user data Total transmission size Efficiency

= 10 bytes = 192 bytes = User Data / Total transmission size→ 10/192 = .05

26. What is the transmission efficiency of a 1,000-byte file sent in response to a web request HTTP, TCP/IP, and Ethernet? Assume the HTTP packet has 100 bytes in addition to the 1000-byte file.

Hint: Remember from Chapter 4, that efficiency = user data / total transmission size.

Total user data Total transmission size Efficiency

= 1000 bytes = 1171 bytes = User Data / Total transmission size→ 1000/1171 = .85

27. What is the transmission efficiency of a 5,000-byte file sent in response to a web request HTTP, TCP/IP, and Ethernet? Assume the HTTP packet has 100 bytes in addition to the 5000-byte file.

Assume that the maximum packet size is 1200 bytes Hint: Remember from Chapter 4, that efficiency = user data / total transmission size.

User data = 1200 bytes Transmission size = 1223 bytes Efficiency = 1200/1223 = .98

→ (.98) * 4 = 3.92

User data = 271 bytes Transmission size = 1223 bytes Efficiency = 271/1223 = .22 Total transmission efficiency = (3.92 + .22) / 5 = .828 → .83 28. Describe the anatomy of a router. How does a router differ from a computer?

A router consists of a CPU, memory, and ports or interfaces. A router differs from a computer because they are diskless and they do not come with a monitor, keyboard or mouse.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova Exercises A. Would you recommend dynamic addressing for your organization? Why? Without dynamic addressing, any time a computer is moved or its network is assigned a new address, the software on each individual computer must be updated. This is not difficult, but it is very time-consuming because someone must go from office to office, editing files on each individual computer.

Dynamic addressing avoids this problem. With this approach, a server is designated to supply a network layer address to a computer each time the computer connects to the network. This is commonly done for client computers but usually not for servers.

B. Look at your network layer software (either on a LAN or dial-in) and see what options are set—but don’t change them! You can do this by using the RUN command to run winipcfg.

How do these match the fundamental addressing and routing concepts discussed in this chapter?

Please note that not all computers will have winipcfg.exe installed. Even if it is installed, the path statement may not point to its subdirectory. So, students many have issues running the program.

C. Suppose that a client computer (128.192.98.130) in Building B in Figure 5-17 requests a large Web page from the Web server 2 in the Data Center (www2.anyorg.com). Assume that the client computer has just been turned on and does not know any addresses other than those in its configuration tables. Assume that all gateways and Web servers know all network layer and data link layer addresses. a. Explain what messages would be sent and how they would flow through the network to deliver the Web page request to the server.

This is explained in Section 5.6.1. b. Explain what messages would be sent and how they would flow through the network as the Web server sent the requested page to the client.

This is explained in Section 5.6.1. c. Describe, but do not explain in detail, what would happen if the Web page contained several graphic images (e.g., GIF [Graphics Interchange Format] or JPEG [Joint Photographic Experts Group] files).

A GIF, JPEG, or JPG image is inserted into a webpage using the <IMG SCR=“file”> tag.

When the browser encounters this, it requests the file from the server.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova D. Network Solutions provides a service to find who owns domain names and IP addresses. Go to www.networksolutions.com/whois. Find the owner of Realize that any or all of these could change at any time. As of this writing, Whois provides no information on any of these domains and IP addresses. a. books.com This domain redirects to Barnes & Noble. b. TV.com According to Wikipedia, it is owned by CBS Interactive (ViacomCBS). c. 74.128.18.22 According to whois365.com, this is owned by arin.net. d. 129.79.78.188 This domain has been retired and redirects to Enterprise Linux Web Hosting at Indiana University.

E. What is the subnet portion of the IP address and what is the subnet mask for the following: A subnet mask is the 32-bit combination used to describe which part of an IPv4 address refers to the network/subnet and which part refers to the host/node. There is a table of values at https://www.cloudaccess.net/cloud-control-panel-ccp/157-dns-management/322-subnetmasks-reference-table.html.

a. 12.1.0.0/16 b. 12.1.0.0/24 c. 12.1.0.0/20 d. 12.1.0.0/28

Class A 255.255.0.0 255.255.255.0 255.255.240.0 255.255.255.240

Class B 255.255.0.0 255.255.255.0 255.255.240.0 255.255.255.240

Class C NA 255.255.255.128 NA 255.255.255.240

F. You might be wondering how the first bytes for each address range were picked. Why do you think Class A’s first byte is 1–126, Class B’s byte is 128–191, and Class C’s byte is 192– 223?

Class A addresses are used for networks that have more than 65,536 hosts. Class B addresses are used for networks that have between 256 and 65,536 hosts. Class C addresses are used for networks with less than 254 hosts.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova Mini-cases I. Central University How would you assign the IP addresses to the various subnets? You will have to make some assumptions to answer both questions below, so be sure to state your assumptions.

Let’s assume, the university would be getting a legal Class B IP address range. Further assume that there would be a unit or department responsible for managing IP address assignment, operation and maintenance.

One approach would be to employ sub-netting in a manner that assigns the third OCTET to the individual colleges, staff departments and dormitories. The remaining OCTET can be used to facilitate IP address assignment to individual hosts within the resulting address range.

How would you control the process by which IP addresses are assigned to individual computers?

Assuming the university had a server or server process in place in support of each subnet, they could run dynamic host configuration protocol to assign IP addresses automatically to individual computers on startup. In this way the need for visiting each computer to maintain IP address assignment is eliminated.

II.

Connectus

Connectus currently uses RIP as its routing protocol, but is considering moving to OSPF. Should it stay with RIP or move to OSPF? Why? Migrating from RIP to the OSPF protocol is the right choice. Although RIP is supported by TCP/IP and IPX/SPX, OSPF is much more efficient and is much more flexible. As an ISP provider, Connectus must be able to support and route high levels of traffic utilizing the shortest path. Thus, Open Shortest Path First (OSPF).

III.

Old Army

Old Army currently uses RIP as its routing protocol, but is considering moving to OSPF. Should it stay with RIP or move to OSPF? Why? Old Army should continue using the RIP protocol, as their 1000 stores are maintained through a hub and spoke environment. Since Old Army utilize their LAN and WAN for internal purposes (i.e. batch transaction, financial, inventory, and email) the need is somewhat consistent and really does not warrant the OSPF flexibility. Thus, moving to the OSPF would be an over kill and the added functionality would not be used.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova IV.

General Stores

General Stores currently uses RIP as its routing protocol, but is considering moving to OSPF. Should it stay with RIP or move to OSPF? Why? Answer: General Stores should migrate to the OSPF protocol. The General Stores network is used for their internal business processes (i.e. payroll, inventory, and email); however, they also use it for external use (i.e. credit card processing) and they are considering adding telephone traffic. With the external functionality, the General Stores will need to migrate to a protocol that will support its growth.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

Additional Content Teaching Notes This chapter combines coverage of two of the more significant layers of the OSI Model, Network and Transport layers, including addressing and the major aspects of Routing. For these reasons it is necessary to spend about 4-6 hours covering this chapter.

My goal in teaching about network layer protocols is to drive home (again) the fact that there are different packets used by the different software at the different layers in a network and to show that network layer addresses are used at this layer, not data link layer addresses.

Moreover, it is important to distinguish that IPv4 is dominant, but within a few years IPv6 will likely enter widespread use. This is an area that bears watching.

Internet addressing is the start of understanding how all the upper layers of the OSI Model fit together so I spend a lot of time on it – subnets, and address resolution in particular, and possibly network address translation if one has time. Routing gets less time.

I spend a good hour going through a series of detailed examples of how TCP/IP works. In my opinion, the “protocol wars” are over and TCP/IP has won, so I devote a lot of time to it. The Internet is always a source of interest to the students so they are motivated to learn this material.

I view this section as one of the most important in the entire course

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CHAPTER 6 NETWORK DESIGN Chapter Summary This chapter starts the next section of the book, which focuses on how we design networks. We usually design networks in six network architecture components: Local Area Networks (LANs), Building Backbone Networks, Campus Backbones that connect buildings, Wide Area Networks (WANs) that connect campuses, Internet access, and Data Centers. Network design is an interactive process in which the designer examines users’ needs, develops an initial set of technology designs, assesses their cost, and then revisits the needs analysis until the final network design emerges.

Learning Objectives • • • • •

Understand the seven network architecture components Describe the overall process of designing and implementing a network Describe techniques for developing a logical network design Describe techniques for developing a physical network design Understand network design principles

Key Terms Access layer Building backbone network Capacity planning Core layer Desirable requirements Enterprise campuses Internet access Mandatory requirements

Baseline Building-block process Circuit loading Cost assessment Distribution layer Enterprise edge Logical network design Needs analysis

Physical network design Technology design

Request for proposal (RFP) Traditional network design process Wish-list requirements

Wide area network (WAN)

Bottleneck Campus backbone Common carrier Data center e-Commerce edge Geographic scope Local area network (LAN) Network architecture component Simulation Turnpike effect

Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

Chapter Outline 6.1 Introduction 6.1.1 Network Architecture Components 6.1.2 The Traditional Network Design Process 6.1.3 The Building-Block Network Design Process 6.2 Needs Analysis 6.2.1 Network Architecture Component 6.2.2 Application Systems 6.2.3 Network Users 6.2.4 Categorizing Network Needs 6.2.5 Deliverables 6.3 Technology Design 6.3.1 Designing Clients and Servers 6.3.2 Designing Circuits 6.3.3 Network Design Tools 6.3.4 Deliverables 6.4 Cost Assessment 6.4.1 Request for Proposal 6.4.2 Selling the Proposal to Management 6.4.3 Deliverables 6.5 Implications for Cyber Security Summary

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

Answers to Textbook Exercises Answers to End-of-Chapter Questions 1. What are the keys to designing a successful data communications network?

A thorough needs analysis, developing one or more physical network designs, designing to operate and maintain with minimal staff intervention.

2. How does the traditional approach to network design differ from the building-block approach?

Traditional network designs used a very structured approach for the analysis and design. This by default built in limitations to the growth and need to change network designs as the needs of the organization and technology itself changed.

3. Describe the three major steps in the current network design.

Needs analysis, technology design and cost assessment.

4. What is the most important principle in designing networks?

Completing a thorough needs analysis that takes into consideration the needs of the organization over the short and long-term. From this analysis then a logical network design can be developed to ensure that the network can satisfy all needs over time.

5. Why is it important to analyze needs in terms of both application systems and users?

You want to make sure the network can support the bandwidth and other operational characteristics required by the user applications.

6. Describe the key parts of the technology design step.

It examines the available technologies and assesses which options will meet the users' needs.

The designer makes some estimates about the network needs of each category of user and circuits in terms of current technology and matches needs to technologies.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 7. How can a network design tool help in network design?

Network design tools can perform a number of functions to help in the technology design process.

Other network design tools can discover the existing network; that is, once installed on the network, they will explore the network to draw a network diagram. For example, simulation is used to model the behavior of the communication network.

Network modeling and design tools can perform a number of functions to help in the technology design process. With most tools, the first step is to enter a map or model of the existing network or proposed network design. Some modeling tools require the user to create the network map from scratch. That is, the user must enter all of the network components by hand, placing each server, client computer, and circuit on the map and defining what each.

Other tools can "discover" the existing network. In this case, the user provides some starting point; the modeling software explores the network and automatically draws the map itself.

Once the map is complete, the next step is to add information about the expected network traffic and see if the network can support the level of traffic that is expected. Simulation is used to model the behavior of the communication network. Once the simulation is complete, the user can examine the results to see the estimated response times and throughput. It is important to note that these network design tools only provide estimates, which may vary from the actual results. At this point the user can change the network design in an attempt to eliminate bottlenecks and re-run the simulation.

Good modeling tools not only produce simulation results, but also highlight potential trouble spots (e.g., servers, circuits, or devices that experienced long response times). The very best tools offer suggestions on how to overcome the problems that the simulation identified (e.g., network segmentation, increasing from T1 to T3).

8. On what should the design plan be based?

The design plan should be based on the geographic scope of the network, the number of users and applications, the current and future network needs of the various network segments, and the costs of the network and maintaining the network.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 9. What is an RFP, and why do companies use them?

While some network components can be purchased "off-the-shelf," most organizations develop a request for proposal (RFP) before making large network purchases. RFPs specify what equipment, software, and services are desired. They also ask vendors to provide their best prices. Some RFPs are very specific about what items are to be provided in what time frame. In other cases, items are defined as mandatory, important, or desirable, or several scenarios are provided and the vendor is asked to propose the best solution. In a few cases, RFPs specify what is required and the vendors are asked to propose their own network designs. Once the vendors have submitted their proposals, the organization evaluates them against specified criteria and selects the winner(s). Depending upon the scope and complexity of the network, it is sometimes necessary to redesign the network based on the information in the vendor’s proposals.

The RFP process helps the company to refine and determine what to purchase. It establishes a formal process that becomes well-documented and as a result leaves the company with not only a rationale for what has been purchased but documented proof of how the company arrived at its conclusions as to what vendors would be awarded contract(s) from the company.

10. What are the key parts of an RFP? The following contains the key parts in an RFP: Background Information • • • •

Organizational profile Overview of current network Overview of new network Goals of new network

Network Requirements • • • • •

Choice sets of possible network designs (hardware, software, circuits) Mandatory, desirable, and wish list items Security and control requirements Response time requirements Guidelines for proposing new network designs

Service Requirements • • • •

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Implementation time plan Training courses and materials Support services (e.g., spare parts on site) Reliability and performance guarantees

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova Bidding Process • • • •

Time schedule for the bidding process Ground rules Bid evaluation criteria Availability of additional information

Information required from vendor • • • •

Vendor corporate profile Experience with similar networks Hardware and software benchmarks Reference list

11. What are some major problems that can cause network designs to fail?

Some major problems that can cause network designs to fail can be categorized by the steps of the building block design approach.

Technology design problems • •

buying the wrong equipment or services; often the right technology but the wrong products or features vendor misrepresentation; the products and/or services did not work as promised

Needs analysis problems • •

requirements were incomplete or inaccurate a significant change in business requirements as the network was installed.

Overall problems with the design process •

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lack of network design skills internally; did not use external consultants or systems integrators external network consultants or systems integrators who bungle the project

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 12. What is a network baseline, and when is it established?

Most network design projects today are network upgrades, rather than the design of entirely new networks. In this case, there is already a good understanding of the existing traffic in the network, and most importantly, the rate of growth of network traffic. In this case, it is important to gain an understanding of the current operations (application systems and messages).

The needs analysis step provides a network baseline against which future design requirements can be gauged. It should provide a clear picture of the present sequence of operations, processing times, work volumes, current communication network (if one exists), existing costs, and user/management needs. Whether the network is a new network or a network upgrade, the primary objective of this stage is to define the geographic scope of the network and the users and applications that will use the network.

13. What issues are important to consider in explaining a network design to senior management?

One of the main problems in network design is obtaining the support of senior management.

In their mind, the network is simply a cost center, something on which the organization is spending a lot of money with little apparent change. The network keeps on running just as it did the year before.

The key to gaining senior management acceptance of the network design lies in speaking their language (cost, network growth, and reliability), not the language of the technology (Ethernet, ATM, and DSL). It is pointless to talk about upgrades from 10 Mbps to 100 Mbps on the backbone, because this terminology is meaningless to them. A more compelling argument is to discuss the growth in network use.

Likewise, a focus on network reliability is an easily understandable issue. For example, if the network supports a mission critical system such as order processing or moving point-of-sale data from retail stores to corporate offices, it is clear from a business perspective that the network must be available and performing properly, or the organization will lose revenue.

14. What is the turnpike effect, and why is it important in network design?

The turnpike effect results when the network is used to a greater amount than was anticipated because it is available, is very efficient, and provides new services. The growth factor for network use may vary from 5 to 50 percent and, in some cases, exceed 100 percent for high growth organizations. It is important in network design because not only is usage is higher than anticipated, which slows response time, but also because the types of messages may be different from those for which the network was originally designed.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 15. What are the seven network architecture components?

The seven network architecture components are LANs, building backbones, campus backbones, WANs, Internet access, e-commerce edge and data centers.

16. What is the difference between a building backbone and a campus backbone, and what are the implications for the design of each?

A building backbone distributes network traffic to and from the LANs. The building backbone typically uses the same basic technology that we use in the LAN (a network switch) but usually we buy faster switches because the building backbone carries more network traffic than a LAN. A campus backbone connects all the buildings on one campus. Some vendors call this the Core Layer.

The campus backbone is usually faster than the backbones we use inside buildings because it typically carries more traffic than they do. We use routers or layer 3 switches that do routing when we design the campus.

The cost of each can be significant as they each consist of high-speed fiber optic cable and hardware such as switches and routers. In designing each one though, we can provide an infrastructure that provides for efficient movement of data across the entire network.

17. What are typical speeds for the LAN, building backbone, and campus backbone? Why? LAN – 1 Gbps Building backbone – 10 Gbps Campus backbone – 40 Gbps In most cases, because network traffic is consolidated onto the broader networks, the building backbone is one speed level above the LAN and the campus backbone speed is one speed level about the building backbone.

18. What is a bottleneck, and why do network managers care about them?

A bottleneck is a place where performance of an entire system is limited by capacity at some point in a network. Bottlenecks can exist on physical circuits or networking devices.

Managers care about them because these are points that can be fixed or upgraded and after doing so, the network performance becomes improved.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 19. Is it important to have the fastest wireless LAN technology in your apartment? What about in the library of your school? Explain.

It is not necessarily important to have the fastest wireless LAN technology in your apartment because that technology may be faster than your Internet access to your apartment. For example, if you have 10 Mbps Internet access to your apartment, a 54 Mbps access point in your apartment is still limited to 10 Mbps downloads from the Internet. The 54 Mbps access within the apartment is only good for connections between networking devices within the apartment.

The answer is similar as it applies to the library within your school. As long as the traffic stays within the library, a fast wireless network is beneficial.

20. Why do you think some organizations were slow to adopt a building-block approach to network design?

They were slow because this approach requires network managers to speak the language of upper management (cost, network growth, reliability) rather than the language of technology (Ethernet, ATM, and DSL).

21. For what types of networks are network design tools most important? Why? Large, complex networks require the use of network design tools. The many devices on such systems and the variety of services requested by users requires that network managers organize and manage the process using system management software.

Answers to End-of-Chapter Exercises

A. What factors might cause peak loads in a network? How can a network designer determine if they are important, and how are they taken into account when designing a data communications network?

Many different factors could place a peak load on a network. Perhaps the biggest one is time.

Many networks are slower during the day than at night due to more users. The underlying cause is the system handling a higher load that it was designed to handle. Another factor could be over-utilized devices such as routers and switches. Naturally, faulty device can cause this. Finally, a commonly overlooked possibility is a security attack. Proper sizing of the network and devices, along with robust security protocols, can prevent many of these.

B. Collect information about two network design tools and compare and contrast what they can and cannot do.

Answers will vary.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

Mini-Cases I. Computer Dynamics Computer Dynamics is a microcomputer software development company that has a 300computer network. The company is located in three adjacent five-story buildings in an office park, with about 100 computers in each building. The LANs in each building are similar, but one building has the data center on the second floor. There are no other office locations. The current network is poorly designed for its current needs and must be completely replaced. Develop a logical design for this enterprise campus that considers the seven network architecture components. There are no other campuses, so you can omit WAN access. You will need to make some assumptions, so be sure to document your assumptions and explain why you have designed the network in this way.

Refer to Figure 6-1 for a good example of a typical configuration for a network of this type.

The LAN would typically be designed as a physical star topology connecting the computers on each floor with UTP cabling to a switch. A wireless network is recommended in each building in addition to the wired network. Based on the size of the buildings, number of users, and the fact that a wired network is already in place, the company could get by with 802.11n access points on odd numbered floors (3 per building). These would probably provide enough wireless access to support the users.

The switch(es) on each floor would connect to the main switch on the first floor of each building, which would then connect to a router in that building. The connections among the switches would be fiber.

It is recommended to use multi-mode fiber optic cable to connect all three buildings to the others. One of the three buildings would be designated as the main building, as it contains the data center on the second floor. Each of the respective building LANs would connect into a device like a data switch that had a fiber uplink port. At the main building, the other two buildings would be terminated via the other end of the fiber into ports on the main campus data switch.

Any needs for connectivity to the outside, for example the Internet, could be supported by connecting the gateway router directly into a port on the main data switch. The router could connect to a CSU which brought into the campus network a high-speed circuit. In this design everyone on campus could have Internet connectivity and also connect to any server or printer physically located at any of the other buildings.

The data center would contain the e-commerce edge. This would consist of at least the web server that allows potential and existing customers to view their website.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova II. Drop and Forge Drop and Forge is a small manufacturing firm with 60 computers on their network. Describe the network you would recommend and how it would be configured. The goal is to build a new network that will support the company’s needs for the next three years with few additional investments. Be sure to include the devices and type of network circuits you would use. You will need to make some assumptions, so be sure to document your assumptions and explain why you have designed the network in this way.

For this situation, if we assume that all of the computers, including servers, can support the installation of a 10/100Mbps Ethernet card, the recommended approach for this company’s network needs would be to install Switched Ethernet switches and a supportive new cable plant that can run Ethernet. For example a Category 5 cable plant. Each of the computers would need to have installed a 10/100Mbps Ethernet NIC. Each computer would connect via CAT 5 to a port on the nearest switch. Each switch connected to a main switch in each building. The two main switches in the buildings would be connected together.

III. AdviceNet AdviceNet is a consulting firm with offices in Toronto, New York, Los Angeles, Dallas, and Atlanta. The firm currently uses the Internet to transmit data, but its needs are growing and it is concerned over the security of the Internet. The firm wants to establish its own private WAN. Consultants in all offices are frustrated at the current 1.5Mbps circuits they use for Internet access, so the firm believes that it needs faster data transmission capabilities. The firm has no records of data transmission, but it believes that the New York and Toronto offices send and receive the most data. The New York office is the primary headquarters and has the enterprise data center. Develop a logical design for the New York enterprise campus that considers the seven network architecture components. Describe the assumptions you have made.

A logical design may be as follows. The assumptions will vary depending on the student.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

3rd Floor – West Typical

Building Backbone

2nd Floor – West Typical

3rd Floor – East Typical

1st Floor – West High-speed Contains the e-commerce edge

2nd Floor – East Typical

1st Floor – East High-speed Contains Enterprise Data Center

Campus Core Backbone

IV. Accurate Accounting Accurate Accounting is a regional accounting firm that has 15 local offices throughout Georgia, Florida, and the Carolinas. The company is constructing a new office building for use as its main headquarters. The building will have two floors with a total of 40 offices, each with a desktop computer. Develop a logical design for the Atlanta headquarters enterprise campus that considers the seven network architecture components. You will need to make some assumptions, so be sure to document your assumptions and explain why you have designed the network in this way.

Student answers will vary considerably based on their assumptions and preferences. A logical design could look similar to the one in Minicase III or Figure 6-4.

In order to link all of the computers in the main headquarters together, you could install an Ethernet 10/100/1000Base-T 48 port switch. Due to the size of the building, each PC should be able to connect to this switch with a UTP Cat 5e cable. A couple of wireless 802.11n access points could be installed as well to provide wireless access.

The equipment for the WAN connectivity will be based on the preferences of the network manager and the circuit options available.

It should be assumed that traffic management, security, and other software will be purchased as the budget allows.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova V. Donald's Distributing Donald’s Distributing is a regional trucking firm that is constructing a new office building (its only office). The network has 80 desktop computers and 2 servers. Develop a logical design for the enterprise campus that considers the seven network architecture components. You will need to make some assumptions, so be sure to document your assumptions and explain why you have designed the network in this way.

Student answers will vary considerably based on their assumptions and preferences. A logical design could look similar to the one in Minicase III or Figure 6-4.

In order to link all of the computers in the main headquarters together, you could install a couple of Ethernet 10/100/1000Base-T 48 port switches in the MDF. Due to the size of the building, each PC should be able to connect to one of these switches with a UTP Cat 5e cable. A couple of wireless 802.11n access points could be installed as well to provide wireless access.

The equipment for the Internet access will be based on the preferences of the network manager and the circuit options available.

The network will also need a router (the specific one, again depending on preferences of the network manager).

It should be assumed that traffic management, security, and other software would be purchased as the budget allows.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

Additional Content Teaching Notes I usually only spend 1-3 hours on this, plus I give the students a project to do.

The most commonly used design process was the “building block” approach described in this chapter. One of the major reasons for this is that network technology has changed dramatically in the last 5 years. For this reason, the Internet related fundamentals have been extrapolated from this chapter and housed into their own dedicated Chapter (Chapter 10) and the complete design process elements have been incorporated into this chapter on design.

The goals in this chapter are to provide a checklist of steps to help students in designing networks and to outline the pros and cons of several commonly used networks. The building block process is a very “clean” and simple approach that I have seen used. The biggest difference between it and the traditional approach is that it assumes that network demand will grow and therefore makes no attempt to accurately understand current network demand.

However, I have added a great deal of information on the design process itself. This includes: Needs Analysis, Technology Design form circuits to servers and Cost Assessment from RFP to Deliverables. Many of the concepts are abstract such as “logical design.” You will find that students will need more visual information to comprehend network design.

War Stories (Objective: illustrate the futility of trying to accurately predict growth) In the mid-1980s when I was on the faculty of Queen’s University in Canada, the mainframe and its network were very slow. Most faculty did not give course assignments because of the problems. The university then upgraded its network. The upgrade cost several million dollars. It was predicted to last five years before another upgrade would be necessary. Then the turnpike effect kicked in. Faculty began to use the network in their courses and demand grew. The network was saturated in 2 years.

A new upgrade was done and again the networking group predicted it would last for 5 years.

This time it was only 18 months before the network was saturated.

I would like to say that this is an isolated incident, but I have seen the same pattern at many organizations. Network designers often badly underestimate the growth in network demand. New applications add to this turnpike effect, as upgrades are saturated due to not only growth in existing usage patterns, but also due to the addition of new and more data intensive applications.

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CHAPTER 7 WIRED AND WIRELESS LOCAL AREA NETWORKS Chapter Summary This chapter examines the three major network architecture components that use Local Area Networks (LANs): the LANs that provide network access to users, the data center, and the ecommerce edge. We focus on the LANs that provide network access to users, as these are more common. This chapter draws together the concepts from the first section of the book on fundamental concepts to describe how wired and wireless LANs work. We first summarize the major components of LANs and then describe the two most commonly used LAN technologies: wired and wireless Ethernet. The chapter ends with a discussion of how to design LANs and how to improve LAN performance.

Learning Objectives • • • • •

Understand the major components of LANs Understand the best practice recommendations for LAN design Be able to design wired Ethernet LANs Be able to design wireless Ethernet LANs Be able to improve LAN performance

Key Terms Access point (AP) Association Bottleneck Cable plan Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) Channel Collision Collision domain Directional antenna Domain controller Ethernet Forwarding table Frame IEEE 802.3 Latency Lightweight directory access protocol (LDAP) Load balancing switch MAC address filtering

Active Directory Service (ADS) Beacon frame Bus topology Cabling Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Clear to send (CTS) Collision detection (CD) Cut-through switching Distributed coordination function (DCF) Dual-band AP Fiber-optic cable Fragment-free switching Hub IEEE 802.11 Layer 2 switch Load balancer Logical topology Managed APs

Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova Network-attached storage (NAS) Network operating system (NOS) Network segmentation Omnidirectional antenna Physical carrier sense method Point coordination function (PCF) Power over Ethernet (POE) Probe frame Request to send (RTS) Shielded twisted-pair (STP) Small-office, home-office (SOHO) Store-and-forward switching Switched Ethernet Topology Unshielded twisted-pair Virtual carrier sense Wireless Ethernet Wi-Fi Controller (WPA) Wired Equivalent Privacy Wireless LAN (WLAN), 10Base-T 1000Base-T 1GbE 40GbE 802.11ac 802.11n

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Network interface card (NIC) Network profile Network server Overlay network Physical topology Port Powerline networking Redundant array of inexpensive disks (RAID) Server virtualization Site survey Storage area network (SAN) Switch Symmetric multiprocessing (SMP) Twisted-pair cable (UTP) cable Wardriving (Wi-Fi) Wi-Fi Protected Access WiGig (WEP) 180 100Base-T 10/100/1000 Ethernet 10GbE 100GbE 802.11ax

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

Chapter Outline 7.1 Introduction 7.2 LAN Components 7.2.1 Network Interface Cards 7.2.2 Network Circuits 7.2.3 Network Hubs, Switches, and Access Points 7.2.4 Network Operating Systems 7.3 Wired Ethernet 7.3.1 Topology 7.3.2 Media Access Control 7.3.3 Types of Ethernet 7.4 Wireless Ethernet 7.4.1 Topology 7.4.2 Media Access Control 7.4.3 Wireless Ethernet Frame Layout 7.4.4 Types of Wireless Ethernet 7.4.5 Security 7.5 The Best Practice LAN Design 7.5.1 Designing User Access with Wired Ethernet 7.5.2 Designing User Access with Wireless Ethernet 7.5.3 Designing the Data Center 7.5.4 Designing the e-Commerce Edge 7.5.5 Designing the SOHO Environment 7.6 Improving LAN Performance 7.6.1 Improving Server Performance 7.6.2 Improving Circuit Capacity 7.6.3 Reducing Network Demand 7.7 Implications for Cyber Security Summary

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

Answers to Textbook Exercises Answers to End-of-Chapter Questions

1. Define local area network.

A local area network is a group of microcomputers, or other workstation devices, located within a small or confined area and are connected by a common cable. A LAN can be part of a larger backbone network connected to other LANs, a host mainframe, or public networks.

2. Describe at least three types of servers.

A LAN can have many different types of dedicated servers. Four common types are file servers, database servers, print servers, and communication servers. File servers allow many users to share the same set of files on a common, shared disk drive. A database server usually is more powerful than a file server. It not only provides shared access to the files on the server, but also can perform database processing on those files associated with client-server computing. The key benefit of database servers is that they reduce the amount of data moved between the server and the client workstation. They can also minimize data loss and prevent widespread data inconsistencies if the system fails.

Print servers handle print requests on the LAN. By offloading the management of printing from the main LAN file server or database server, or print servers helps reduce the load on them and increase network efficiency in much the same way that front-end processors improve the efficiency of mainframe computers. Communications servers are dedicated to performing communication processing. There are three fundamental types: fax servers, modem servers, and access servers.

Fax servers manage a pool of fax-boards that enable LAN users to send or receive faxes. Access servers and modem servers allow users to dial into and out of the LAN by telephone. Dialing into the LAN is accomplished with an access server, whereas dialing out is accomplished with a modem server.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

3. Describe the basic components of a wired LAN. The basic components of a wired LAN are the NICs, circuits, access points, and network operating system.

The network interface card (NIC) allows the computer to be physically connected to the network cable, which provides the physical layer connection among the computers in the network.

The circuits are the cables that connect devices together. In a LAN, these cables are generally twisted pair from the client to the hub or server. Outside the building, fiber optic is generally used.

Network hubs and switches serve two purposes. First, they provide an easy way to connect network cables. In general, network cables can be directly connected by splicing two cables together. Second, many hubs and switches act as repeaters or amplifiers. Signals can travel only so far in a network cable before they attenuate and can no longer be recognized.

The network operating system (NOS) is the software that controls the network. Every NOS provides two sets of software: one that runs on the network server(s), and one that runs on the network client(s). The server version of the NOS provides the software that performs the functions associated with the data link, network, and application layers and usually the computer’s own operating system. The client version of the NOS provides the software that performs the functions associated with the data link and the network layers, and must interact with the application software and the computer’s own operating system.

4. Describe the basic components of a wireless LAN. The basic components of a wireless LAN are the NICs, circuits, access points, and network operating system.

The network interface card (NIC) allows the computer to be physically connected to the network cable, which provides the physical layer connection among the computers in the network.

The “circuit” is the air that connects the wireless clients to the access points. Between the access points and the switches or servers, twisted pair cable is typically utilized.

A wireless access point performs the same functions as a hub or switch in a wired environment.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova The network operating system (NOS) is the software that controls the network. Every NOS provides two sets of software: one that runs on the network server(s), and one that runs on the network client(s). The server version of the NOS provides the software that performs the functions associated with the data link, network, and application layers and usually the computer’s own operating system. The client version of the NOS provides the software that performs the functions associated with the data link and the network layers, and must interact with the application software and the computer’s own operating system.

5. What types of cables are commonly used in wired LANs? It is very common to see LANs built using traditional twisted pair cables (e.g., Cat 5, Cat 5e).

6. Compare and contrast category 5 UTP, category 5e UTP, and category 5 STP.

Category

Type

Max. Data Rate (Mbps)

Often Used By

5e 5 5

UTP UTP STP

100 100 100

1,000Base-T Ethernet 100Base-T Ethernet 100Base-T Ethernet

Cost ($/foot) .10 .07 .18

7. What is a cable plan and why would you want one?

A cable plan is a plan for the network layout, including how much cable is used, where the cables are, how many and where hubs are located, how many ports are available, what local city fire codes must be followed, and what are the identification labels of the cable. Most buildings under construction today have a separate LAN cable plan as they do for telephone cables and electrical cables. The same is true for older buildings in which new LAN cabling is being installed. It is common to install 20 to 50 percent more cable than you actually need to make future expansion simple.

With today’s explosion in LAN use, it is critical to plan for the effective installation and use of LAN cabling. The cheapest time to install network is during the construction of the building; adding cable to an existing building can cost significantly more. Indeed, the costs to install cable (i.e., paying those doing the installation and additional construction) are usually substantially more than the cost of the cable itself, making it expensive to re-install the cable if the cable plan does not meet the organization’s needs.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 8. What does a NOS do? What are the major software parts of a NOS? The network operating system (NOS) is the software that controls the network. Every NOS provides two sets of software: one that runs on the network server(s), and one that runs on the network client(s). The server version of the NOS provides the software that performs the functions associated with the data link, network, and application layers and usually the computer’s own operating system. The client version of the NOS provides the software that performs the functions associated with the data link and the network layers, and must interact with the application software and the computer’s own operating system.

9. How does wired Ethernet work?

Ethernet is the most commonly used LAN in the world, accounting for almost 70 percent of all LANs. Ethernet uses a bus topology and a contention-based technique media access technique called Carrier Sense Multiple Access with Collision Detection (CSMA/CD). Many different types of Ethernet use different network cabling (e.g., 10Base-2, 10Base-5, 10Base-T, and 10Broad-36).

10. How does a logical topology differ from a physical topology?

A logical topology illustrates how the network operates with the various protocols that may be running. A single network can have multiple protocols. A physical topology illustrates exactly where all the hardware and cabling are ‘physically’ located and connected.

11. Briefly describe how CSMA/CD works.

CSMA/CD, like all contention-based techniques, is very simple in concept: wait until the bus is free (sense for carrier) and then transmit. Computers wait until no other devices are transmitting, and then transmit their data. As long as no other computer attempts to transmit at the same time, everything is fine. However, it is possible that two computers located some distance from one another can both listen to the circuit, find it empty, and begin to simultaneously. This simultaneous transmission is called a collision. The two messages collide and destroy each other.

The solution to this is to listen while transmitting, better known as collision detection (CD). If the NIC detects any signal other than its own, it presumes that a collision has occurred, and sends a jamming signal. All computers stop transmitting and wait for the circuit to become free before trying to retransmit. The problem is that the computers, which caused the collision, could attempt to retransmit at the same time. To prevent this, each computer waits a random amount of time after the colliding message disappears before attempting to retransmit.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 12. Explain the terms 100Base-T, 1000Base-T, 100Base-F,10GbE, and 10/100/1000 Ethernet.

Historically, the original Ethernet specification was a 10 Mbps data rate using baseband signaling on thick coaxial cable, called 10Base5 (or “Thicknet”), capable of running 500 meters between hubs. Following 10Base5 was 10Base2 or thinnet as we used to say. Thinnet or RG-58 coaxial cable, similar to what is used for cable TV was considerably cheaper and easier to work with, although it was limited to 185 meters between hubs. The 10Base-2 standard was often called “Cheapnet.”

When twisted pair cabling was standardized for supporting Ethernet (app. 1988) the T replaced the 2 to represent “twisted-pair”. Twisted pair is the most commonly used cable type for Ethernet. 10BaseT breaks down as 10 Mbps, baseband, and the “T” means it uses twisted pair wiring (actually unshielded twisted pair). The 10Base-T standard revolutionized Ethernet, and made it the most popular type of LAN in the world.

Eventually the 10BaseT standard was improved to support Fast Ethernet or 100BaseT that breaks down as 100Mbps baseband over twisted-pair cable and 100BaseF over fiber. This eventually was improved even further to 1000BaseT or 1 Billion BITs per second baseband.

There is currently a revised standard evolving which makes Ethernet even faster. It is known as the 10GbE or 10 Billion BITs per second Ethernet. Though proven to work it has yet to reach the marketplace. However, it would be astute to consider that it will be here in the near future.

Finally, 10/100Mbps Ethernet refers to the standard that can autosense which speed it needs to run at between the two speeds of 10Mbos or 100Mbps. It comes down to the type of NIC running at the individual node and the type of switch port that the node connects into. It is commonplace to run 10/100Mbps switches in LAN operating environments where there are older NICs already operating and no real business case requirements for upgrading these nodes.

13. How do Ethernet switches know where to send the frames they receive? Describe how switches gather and use this knowledge.

Ethernet switches operate on the destination MAC address of each packet processed to determine which port to pass on each packet presented for transmission.

Ethernet switches learn and store in memory in the form of a forwarding table, the specific port location of each MAC address for every device connected to any of its ports.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 14. Compare and contrast cut-through, store and forward, and fragment-free switching.

With cut through switching, the switch begins to transmit the incoming packet on the proper outgoing circuit as soon as it has read the destination address in the packet.

With store and forward switching the switch does not begin transmitting the outgoing packet until it has received the entire incoming packet and has checked to make sure it contains no errors.

Fragment-free switching lies between the extremes of cut through and store and forward switching. With fragment-free switching, the first 64 bytes and if all the header data appears correct, the switch presumes the rest of the packet is error free and begins transmitting.

15. Compare and contrast the two types of antennas.

A directional antenna projects a signal only in one direction. Because the signal is concentrated in a narrower, focused area, it is a stronger signal and carries further. More popular is the omnidirectional antenna, which broadcasts in all directions except directly above itself.

16. How does Wi-Fi perform media access control?

Media access control uses Carrier Sense Multiple Access with Collision Avoidance, or CSMA/CA, which is similar to the media access control used in Ethernet LANs. The computers “listen” before they transmit, and if there is not a collision, all is well. Wi-Fi does attempt to avoid a collision more than regular Ethernet LANs do, however, by using two techniques called Distributed Coordination Function and Point Coordination Function (refer to questions 12 and 13 for detailed descriptions of these two access control methods).

17. How does Wi-Fi differ from shared Ethernet in terms of topology, media access control, and error control, Ethernet frame?

Wi-Fi is very similar to shared Ethernet in terms of the logical and physical topologies. The Wi-Fi approach uses a logical bus and a physical star arrangement, just like shared Ethernet.

On the shared bus in Wi-Fi, the computers must take turns transmitting, which is not always so in shared Ethernet. For error control, Wi-Fi has a hidden node problem, where some computers may not sense contention, and may therefore transmit when they should not, so Wi-Fi uses a slightly different technique for contention to try and cut down on collisions.

18. Explain how CSMA/CA DCF works.

This technology relies on the ability of computers to physically listen before they transmit.

With DCF, each frame in CSMA/CA is sent using stop and wait ARQ, and it is designed in such a way so that no other computer begins transmitting while the waiting period is going on.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 19. Explain how CSMA/CA PCF works.

Using PCF (also called the virtual carrier sense method), works in traditional Ethernet, and because every computer on thee shared circuit receives every transmission on the shared circuit. There can be a “hidden node problem” with CSMA/CA PCF because some computers at the edge of the network may not sense every transmission, increasing the likelihood of collisions.

20. Explain how association works in WLAN. Searching for an available AP is called scanning and NIC can engage in either active or passive scanning. During active scanning, a NIC transmits a special frame called probe frame on all active channels on its frequency range. When an AP receives a probe frame, it responds with a probe response that contains all the necessary information for a NIC to associate with it. A NIC can receive several probe responses from different APs. It is up to the NIC to choose with which AP to associate. This usually depends on the speed rather than distance from an access point. Once a NIC associates with an access point, they start exchanging packets over the channel that is specified by the access point.

During passive scanning, the NIC listens on all channels for a special frame called beacon frame that is sent out by an access point. The beacon frame contains all the necessary information for a NIC to associate with it. Once a NIC detects this beacon frame, it can decide to associate with it and start communication on the frequency channel set by the access point.

21. What is the best practice recommendation for wired LAN design?

The best recommendations are based primarily on evaluating the trade-off between effective data rates and costs. Sometimes it is also interesting to evaluate LAN vs. WLAN as part of the process.

22. What are the best practice recommendations for WLAN design?

The best recommendations are based primarily on evaluating the trade-off between effective data rates and costs. Sometimes it is also interesting to evaluate LAN vs. WLAN as part of the process.

23. What is a site survey, and why is it important?

The site survey determines the feasibility of the desired coverage, the potential source of interference, the current locations of the wired network into which the WSAN will connect, and an estimate of the number of APs required to provide coverage.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 24. How do you decide how many APs are needed and where they should be placed for best performance?

The network manager will make a determination based off four factors: nominal data rates, error rates, efficiency of the data link layer protocols used, and efficiency of the media access control protocols.

25. How does the design of the data center differ from the design of the LANs intended to provide user access to the network?

Data centers are designed to house significant number of servers since this is where most of the data on a network comes from or goes to. Thus, the data center needs significant physical space and a significant amount of circuit capacity added to handle the data flow. The data center must also be built with other devices like load balancers and virtual servers, which the LAN does not have. Due to the physical space requirements and the large amount of data transferred, the design of the data center is different from that of a LAN for user access.

26. What are three special purpose devices you might find in a data center and what do they do?

Three special purpose devices that the data center may contain include a load balancer, virtual servers, and storage area networks. The load balancer acts as a router at the front of the server farm to distribute any processing to an appropriate server. Logical servers are logically separate servers (e.g., a Web server, an email server, and a file server) on the same physical computer. The virtual servers run on the same physical computer but appear completely separate to the network. Lastly, the storage area network are LANs devoted solely to data storage.

27. What is a bottleneck and how can you locate one?

In order to improve performance, the administrator must locate the bottleneck, the part of the network that is restricting the data flow. Generally, the bottleneck will lie in one of two places.

The first is the network server. In this case, the client computers have no difficulty sending requests to the network server, but the server lacks sufficient capacity to process all the requests it receives in a timely manner. The second location is the network circuit. The network server can easily process all the client requests it receives, but the network circuit lacks enough capacity to transmit all the requests to server. It is also possible that the bottleneck could also lie in the client computers themselves (e.g., they are receiving data to fast for them to process it), but this is extremely unlikely.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 28. Describe three ways to improve network performance on the server.

Improving server performance can be approached from two directions simultaneously: software and hardware.

Software methods include changing the NOS and fine-tuning the NOS. Hardware methods include adding a second server and upgrading the server’s hardware.

29. Describe three ways to improve network performance on circuits.

Circuit performance can be improved by using faster technologies, by adding more circuits, and by segmenting the network into several separate LANs by adding more switches or access points.

30. Many of the wired and wireless LANs share the same or similar components (e.g., error control). Why? Wired and wireless LANs share the same or similar components because they are both generally based on the same Ethernet protocol. Thus, although some hardware components are different, the underlying foundation is the similar.

31. As WLANs become more powerful, what are the implications for networks of the future?

Will wired LANS still be common or will we eliminate wired offices?

Networks of the future will continue to become increasingly wireless due to the increased speed and portability wireless offers. Wired LANs will continue to be common partly due to better security and reliability. The best practice networks of the future will continue to be wired networks with added wireless capabilities.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova Answers to End-of-Chapter Exercises

A. Survey the LANs used in your organization. Are they wireless or wired? Why? Answers will vary. Most likely, the LAN will use a combination of wireless and wired.

B. Document one LAN (or LAN segment) in detail. What devices are attached, what cabling is used, and what is the topology? What does the cable plan look like?

Answers will vary.

C. You have been hired by a small company to install a simple LAN for its 18 Windows computers. Develop a simple LAN and determine the total cost; that is, select the cables, hubs/switches, and so on, and price them. Assume that the company has no network today and that the office is small enough that you don’t need to worry about cable length.

Answers will vary.

Mini-Cases

I. Designing a New Ethernet a) Let's assume that the smallest possible message is 64 bytes. If we use 100Base-T, how long (in feet or meters) is a 64-byte message? Hint: you can assume that the electricity in the cable travels at approximately the speed of light (186,000 miles per second).

This is a challenging question designed to get the students to think what is actually going on inside the cable. The length of a message can be calculated as its length in bits divided by the speed of the cable which results in how many nanoseconds it takes to transmit. This times the speed of light give the length in feet. Specifically: 64 bytes x 8 bits/byte__ = 0.0000052 seconds 100 million bits per second 0.0000052 seconds * 186,000 miles per second = .9672 miles or about 5,100 feet b) If we use 10 GbE, how long (in feet or meters) is a 64 -byte message?

10 GBE is 1000 times faster than 10Base-T, so the length is about 51 feet (or 15.5 meters). c) The answer in part b is the maximum distance any single cable could run from a switch to one computer in a switched Ethernet LAN. How would you overcome the problem implied by this?

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova A message must be longer than the cable connecting two devices because if it is not, there could be a collision in the “middle” of the cable and neither device would detect it. With 10Base-T, we have a message that is longer than any cable we would care to make, but with 10GbE, we have a problem: cables can be no longer than 15 meters if we have messages as short as 64 bytes. This problem was addressed in the gigabit Ethernet specification by raising the minimum packet size to 512 bytes. In other words, no matter what it contains, all packets in gigabit Ethernet are a minimum of 512 bytes (or about 120 meters long), which means that the maximum cable length is 100 meters.

If data rates continue to increase, to say, 100 GbE, then we will have the same problem again, and the minimum packet size will have to increase to about 5K (which may significantly affect throughput) or we will have to change the fundamental Ethernet media access control protocol.

II. Pat's Petunias You have been called in as a network consultant by your cousin Pat who operates a successful mail-order flower business. She is moving to a new office and wants to install a network for her telephone operators, who take phone calls and enter orders into the system. The number of operators working varies depending on the time of day and day of the week. On slow shifts, there are usually only 10 operators, whereas at peak times, here are 50. She has bids from different companies to install (1) a shared Ethernet 100Base-T network, or (2) a switched Ethernet 100Base-T network. She wants you to give her some sense of the relative performance of the alternatives so the can compare that with their different costs.

What would you recommend?

Shared 100Base-T is cheaper but all collisions would be shared by all devices connected to the network. This would have a negative effect on overall network performance. Switched 100Base-T would provide much better performance because there would be far less collisions and much greater speed.

III.

Eureka!

Eureka has just leased a new office and are about to wire it. They have bids from different companies to install (a) 100Base-T network, or (c) a WI-FI network. What would you recommend? Why? The 100BaseT solution is probably plenty for this application. The wireless network would provide good performance assuming they install enough wireless access points for the number of users. So, either option a or b would be good.

As Eureka scales to more staff members and additional services to customers it will need a robust system to accommodate the web traffic. It is in the firm’s interest to develop an infrastructure that will be able to handle that growth.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

IV.

Tom’s Home Automation

Should he continue to offer wiring services, which often cost $50 per room) or is wireless a better direction? What type of LAN would you recommend? Why? Student answers may vary.

I would recommend that he continue to offer wired services. Although many users are wanting wireless due to the large number of wireless devices in use today, there is a lot to be said for wired connection because they always work and the speeds will be similar. For devices such as networked TVs, gaming systems (i.e. PS3, Wii, etc), and desktop systems, the wired connections are arguably better. In these cases, the cat 5 or cat 5e is adequate for the data transfer rates common to home users. I would also recommend a switch because these are more commonly sold in retail stores (as opposed to hubs). He can also recommend to the users to install wireless, because it is beneficial as well.

V. Sally’s Shoes Sally wants to network the computer with a LAN. What sort of LAN design would you recommend? Draw a picture.

Sally should use a simple, 10Base-T Ethernet or at most a 100Base-T network solution. The network can use either peer to peer or a dedicated server, but a dedicated server would be preferable for the long run. Cost will be an overriding concern, as this is probably a small business.

VI. South West State University With a wireless network installed in the library of South West State University, how should they protect the network performance?

The network is suffering with a perfectly normal overload of users, so a good solution would be to segment the wireless LAN by adding more APs, as well as to explore more careful channel allocation to give better coverage. The university should try to accommodate the users in this fashion.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova VII. Household Wireless Is your sister’s new house going to need any special wiring?

The sister will need to have a reliable and fast network for work reasons in the evening.

Although a wired network might provide this, a wireless LAN would add convenience, and possibly worth the additional expense. Based on my own experiences, I suggest adding the Ethernet cable during the construction because it doesn’t cost very much at that point. Then add the $40 switch and the three desktop computers are ready to be networked. The wired networks are very stable and fast.

Since they already have a laptop, I would also add an access point so that they could be wireless with the laptop anywhere in the house.

VIII. Ubiquitous Office How many access points would you buy for the Ubiquitous Office? Where would you place them?

Depending on the bandwidth you require, the answers may vary. Using 802.11g with 54 Mbps (although they may consider 802.11n as well), you could install five access points to provide coverage throughout the office building.

As with any wireless networking, a site survey will need to be conducted with testing in each office to insure that each office has enough signal strength.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova IX. ABC Warehouse How many access points would you buy for the Ubiquitous Office? Where would you place them?

Depending on the bandwidth you require, the answers may vary. Using 802.11g with 5 Mbps, you could install 12 access points to provide coverage throughout the building. With a Z (length of one side of a square) of 60 feet for 5Mbps with obstacles, you would need two rows of six access points.

As with any wireless networking, a site survey will need to be conducted with testing in each office to insure that each office has enough signal strength.

10'-0"

35'-0"

X. Metro Motel How many access points would you buy for the Ubiquitous Office? Where would you place them?

Depending on the bandwidth you require, the answers may vary. Using 802.11g with 5 Mbps, you could install four access points per floor for a total of 16 in the building to provide coverage throughout the building. With a Z (length of one side of a square) of 60 feet for 5Mbps with obstacles, you would need one row of four access points per floor.

As with any wireless networking, a site survey will need to be conducted with testing in each office to insure that each office has enough signal strength.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

Additional Content Teaching Notes This Chapter will require 5-6 hours of class time.

My goals in this chapter are to ensure that the students understand the basic components of wired and wireless LANs and to ensure that they understand Ethernet. Many students already have a good understanding of LAN components, but many do not, so I discuss these in some detail to ensure an even understanding on the topics. But I warn those with experience that they will be bored. I also talk a bit about the need to develop a cable plant diagram and how such a tool can be used to operate and maintain a LAN. The focus on Ethernet and switched Ethernet in this chapter is because Ethernet-based LANs have replaced token ring for the most part, although a very few organizations to a still use token ring.

The chapter contains technical detail on how the three major WLAN technologies work, but frankly it is not necessary to go overboard on teaching the technical details of this chapter. I just focus on the basics, plus the key elements of WLAN design and improving performance.

Because WLANs have increased in significance and are more likely to come under the student’s job descriptions in the future, it is important that they understand the connection between a wired LAN and the concept of using a WLAN in an overlay arrangement in organizations.

Improving performance is a good topic to reinforce some of the basic concepts and also can provide a practical checklist for students interviewing or entering the job market. Toward the end of the chapter I summarize some concepts in this subject matter. This chapter is an important part of the management of networks, and covers some practical aspects to managing networks.

The section comparing the different types of Ethernet is technically somewhat challenging, but is a good way to help students put together the concepts in the previous chapters and show how they shape the fundamental performance of networks.

A Technical focus box highlights the fact that Ethernet as deployed today typically does not use error control, although error control is built-in.

War Stories In 1988 I accepted the awesome challenge of building a campus-like Local Area Network for the Bureau of Mines, Pittsburgh Energy Technology Center (PETC). The center was located in the South Hills of Pittsburgh and occupied a 252-acre campus of 28 buildings used in various aspects of health and safety research. There were a total of 394 people working at PETC, as we referred to it. At the time, the center had no means of networking beyond that of 9600bps MODEMs. We had a VAX Cluster of six Digital Equipment Corporation (DEC) processors, two IBM mainframes and three PRIME mainframe computers.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova All the processing was centralized mainframe with the users either dialing in via MODEM or actually being hardwired directly into the back plane of these processors running at 9600bps. For users exceeding the distance limitations of twisted-pair copper wiring, a pair of devices known as “line drivers” were used to amplify and forward the signaling up to the processor’s back plane.

There was a need to integrate newer applications running under newer processor technologies among several of the groups in the various buildings. Cost economies dictated that an Ethernet based network was needed in order to provide high-speed connectivity and support resource sharing across all buildings on the campus over the long-term.

Over the course of the next 6 years I was to play the principal role of managing the design, installation, operation and evolution of this campus-like environment to an Ethernet-based LAN running not only the systems mentioned above, but also adding on in many of the physically dispersed buildings: four SUN subnets running the SUN-OS and Solaris Operating Systems, six Novell Netware subnets running Netware versions 2.x up through the first ever Netware 4.x Server Operating System in the Pittsburgh Region and eventually the WINDOWS NT Operating System. As the network evolved users from any building on campus that was networked could be given authorized access by the Network Administrator to any of the servers or processors located in any of the other buildings networked on campus.

My staff consisted of three Network Technician’s who completed much of the physical layer requirements. When cabling projects were too large for staff, I would contract out with nearby cabling plant installation companies. Staff also included 2 Client-Server Programmers who were responsible for installing and configuring server and client PC/workstations and network related software, 2 Computer Operators who were primarily responsible for the centralized mainframe computers, and 2 Network Specialists who were cross-trained to support the help desk and perform Network Administrator functions. As the network evolved and the end-user groups acquired their own client-server systems, these groups hired people to support their end systems within their groups and to coordinate operations with the larger network.

PETC became known for establishing some of the first multi-protocol stack client PCs that could actually do many client-server applications without having to reboot and reload specific protocol types. For example on startup, the client PC could load TCP/UDP/IP, IPX/SPX, IBM-3270 for connectivity to the processors or servers. We also loaded on some PCs, Xerox Network Services (XNS) and Local Area Transport (LAT) protocols for connectivity to terminal servers that connected to the back plane of the VAX processors→ for those users who for whatever reasons could not be completely connected to the evolving Ethernet. For instance, when their PC would not support installation of a NIC or they could not be rewired to connect to a HUB or Switch.

We eventually integrated Internet and a Wide Area Network interfaces into PETC’s LAN. PETC became the Internet gateway site for 17 other sites nationwide. Though wireless Ethernet did not arrive prior to the end of my tenure, I am sure I would have integrated this technology into PETC’s architecture had I remained there. However, I needed to move on to start my own company in the growing areas of Networking & Telecommunications. However, PETC became a notable site in the region for demonstrating the promise of Local Area Networking and clientserver computing over a physically distributed environment. .

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova War Story Wireless Snooping (Objective: Illustrate the dangers of low security wireless) A friend of mine took his laptop with a wireless sniffer to a public access point in a local store.

The store provided free wireless Internet access – no signing up for access, no buying daypasses or annual contracts – just plain and simple free access. Anyone could bring their laptop in and use the Internet.

My friend did not connect into the network, but simply used the sniffer to monitor traffic flowing between the access point and the laptops that customers brought in to work on as they sipped their coffee. After a couple of hours, he had collected many thousands of packets as he sat there, watching the traffic flow. Some of the packets were encrypted. Some were not. He poked through the non-encrypted packets and found a dozen or so that contained user logins to Web sites. The web sites failed to use proper encryption for the login and thus he had usernames and passwords for supposedly private Web sites. One was a free e-mail site, so he now had access to the individual’s e-mail and could read, erase or send e-mail as this person.

And to this point, he had broken no laws. Monitoring public radio broadcasts – even data packets – is not a crime. As long as you take no active measures, it is the same as listening to a radio.

At this point, he started using his decryption software to see if he could break the encrypted packets, because they likely contained the most “interesting” stuff. When he did this action, he crossed the line and started to break the law, and I asked him not to tell me any more.

Wardriving (Objective: Illustrate the dangers of low security wireless) A friend of mine went wardriving around our small college town (Bloomington IN) in January 2004. He found about 130 wireless access points as he drove around town. About 40% of them had no security and another 40% used SSID. Only about 20% used WEP or WPA. He was planning to try to break into unsecured or SSID-protected networks, but there were so many that he gave up trying – it was just too simple.

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CHAPTER 8 BACKBONE NETWORKS Chapter Summary This chapter examines backbone networks (BNs) that are used in the distribution layer (withinbuilding backbones) and the core layer (campus backbones). We discuss the three primary backbone architectures and the recommended best practice design guidelines on when to use them. The chapter ends with a discussion of how to improve BN performance and of the future of BNs.

Learning Objectives • • • • • •

Understand the Internetworking devices used in BNs Understand the switched backbone architecture Understand the routed backbone architecture Understand virtual LAN architecture Understand the best practice recommendations for backbone design Be aware of ways to improve BN performance

Key Terms Access control list (ACL) IEEE 802.1q Main distribution facility (MDF) Multiswitch VLAN Rack Single-switch VLAN Switches VLAN ID VLAN tag

Chassis switch Layer 2 switches Modules Patch cables Routed backbones router Switched backbones Virtual LAN (VLAN) VLAN switches VLAN trunks

Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

Chapter Outline 8.1 Introduction 8.2 Switched Backbones 8.3 Routed Backbones 8.4 Virtual LANs 8.4.1 Benefits of VLANs 8.4.2 How VLANs Work 8.5 The Best Practice Backbone Design 8.6 Improving Backbone Performance 8.6.1 Improving Device Performance 8.6.2 Improving Circuit Capacity 8.6.3 Reducing Network Demand 8.7 Implications for Cyber Security Summary

Answers to Textbook Exercises Answers to End-of-Chapter Questions

1. How does a layer-2 switch differ from a router?

Layer 2 switches operate by using the data link layer address or MAC address to forward packets between network segments. They connect the same or different types of cable. Layer2 switches (or workgroup switches) operate at the Data Link layer, and typically provide ports for a small set of 16 to 24 computers. Layer-2 switches enable all ports to be in use simultaneously by managing paired combinations of ports as separate point-to-point circuits.

Layer-2 switches "learn" addresses; a layer-2 switch builds a forwarding table after it is first turned on. To learn addresses, a layer-2 switch retransmits to all ports (except to the one from which it was received) only for a packet with a destination address not already in the forwarding table. The resulting ACK from the destination computer (that recognized its address) is then used by the layer-2 switch to add the new port number and address to the forwarding table.

Routers operate at the network layer. They connect two different TCP/IP subnets. Routers strip off the data link layer packet, process the network layer packet, and forward only those messages that need to go to other networks based on their network layer address. In general, they perform more processing on each message than switches and therefore operate more slowly.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 2. How does a layer-2 switch differ from a VLAN? Layer 2 switches operate by using the data link layer address or MAC address to forward packets between network segments. They connect the same or different types of cable. Layer2 switches (or workgroup switches) operate at the Data Link layer, and typically provide ports for a small set of 16 to 24 computers. Layer-2 switches enable all ports to be in use simultaneously by managing paired combinations of ports as separate point-to-point circuits.

Layer-2 switches "learn" addresses; a layer-2 switch builds a forwarding table after it is first turned on. To learn addresses, a layer-2 switch retransmits to all ports (except to the one from which it was received) only for a packet with a destination address not already in the forwarding table. The resulting ACK from the destination computer (that recognized its address) is then used by the layer-2 switch to add the new port number and address to the forwarding table.

VLAN switches work a little differently. When a VLAN switch receives a frame that is destined for another computer in the same subnet on the same VLAN switch, the switch acts as a traditional layer-2 switch: it forwards the frame unchanged to the correct computer.

VLAN switches use Ethernets 802.1q’s tagging to move frames from one switch to another.

When a VLAN switch receives an Ethernet frame that needs to go to a computer on another VLAN switch, it changes the Ethernet frame by inserting the VLAN ID number and a priority code into the VLAN tag field.

3. How does a router differ from a VLAN? VLAN switches can create multiple subnets, so they act like routers, except the subnets are inside the switch, not between switches. Therefore, broadcast messages sent by computers in one VLAN segment are sent only to the computers on the same VLAN. 4. Under what circumstances would you use a switched backbone?

Switched backbones can be used in situations where the network administrators wants to spread the traffic around the network more efficiently. In addition, it also provides an architecture where network capacity is no longer tied to the physical location of the computers, as computers in 5. Under what circumstances would you want to use a routed backbone?

Routed backbones are good for connecting different buildings on the same enterprise campus backbone network. The primary advantage of the routed backbone is that it clearly segments each part of the network connected to the backbone. Each segment has its own subnet addresses that can be managed by a different network manager. Broadcast messages stay within each subnet and do not move to other parts of the network.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 6. Under what circumstances would you use a VLAN backbone?

A VLAN backbone is useful when you want to put computers that are in different geographic locations in the same subnet. In addition, VLANs make it much simpler to manage the broadcast traffic and provide a better opportunity to prioritize traffic on the network.

7. Explain how routed backbones work.

Routed backbones move packets along the backbone based on their network layer address (i.e., layer 3 address). The most common form of routed backbone uses a bus topology (e.g., using Ethernet 100Base-T). Routed backbones can be used at the core or distribution layers.

At the core layer, routed backbones are sometimes called subnetted backbones or hierarchical backbones and are most commonly used to connect different buildings within the same campus network.

At the distribution layer, a routed backbone uses routers or layer 3 switches to connect a series of LANs (access layer) to a single shared media backbone network. Each of the LANs are a separate subnet. Message traffic stays within each subnet unless it specifically needs to leave the subnet to travel elsewhere on the network, in which case the network layer address (e.g., TCP/IP) is used to move the packet.

8. In Figure 8-5, would the network still work if we removed the routers in each building and just had one core router? What would be the advantages and disadvantages of doing this?

The network would still work, although the traffic on the network would be significantly increased due to the creation of one large LAN instead of three subnets. The advantages of this would be slightly lower costs due to only purchasing one router instead of four and less maintenance and management. Each of these advantages are minor, and certainly not work the additional traffic on the network.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 9. Explain how switched backbones work.

Switched backbone networks use a star topology with one device, usually a switch, at its center.

The traditional backbone circuit and set of routers or bridges is replaced by one switch and a set of circuits to each LAN. The collapsed backbone has more cable, but fewer devices. There is no backbone cable. The “backbone” exists only in the switch, which is why this is called a collapsed backbone. The original collapsed backbone technology uses layer-2 switches and suffers some disadvantage due to the load of data link layer overhead message traffic and limitations on network segmentation. As this weakness has been recognized, collapsed backbone technology is adapting by evolving to the use of layer-3 switches to overcome these problems. The result is better performance and improved network management capabilities for switched backbone networks.

Collapsed backbones are probably the most common type of backbone network used in the distribution layer (i.e., within a building). Most new building backbone networks designed today use collapsed backbones. They also are making their way into the core layer as the campus backbone, but routed backbones remain common.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 10. What are the key advantages and disadvantages of routed and switched backbones?

Advantages Disadvantages Routed • Clear segmentation of parts of the • Slower performance as routing takes backbones network connected to the backbone as more time than bridging or switching. each network has a subnet address • Management and/or software and can be managed separately. overhead costs due to need to establish subnet addressing and provide reconfiguration when computers are moved (or support dynamic addressing).

Switched • Performance is improved. With the • Because data link layer addresses are backbones traditional backbone network, the used to move packets, there is more backbone circuit was shared among broadcast traffic flowing through the many LANs; each had to take turns network and it is harder to isolate and sending messages. With the collapsed separately manage the individually backbone, each connection into the attached LANs. Layer 3 switches can switch is a separate point-to-point use the network layer address, so circuit. The switch enables future collapsed backbones built with simultaneous access, so that several layer 3 will not suffer from this LANs can send messages to other problem.

LANs at the same time. Throughput • Collapsed backbones use more cable, is increased significantly, often by and the cable must be run longer 200% to 600%, depending upon the distances, which often means that number of attached LANs and the fiber optic cables must be used. traffic pattern.

• If the switch fails, so does the entire • Since there are far fewer networking backbone network. If the reliability of devices in the network, this reduces the switch has the same reliability as costs and greatly simplifies network the reliability of the routers, then there management. All the key backbone is less chance of an failure (because devices are in the same physical there are fewer devices to fail). location, and all traffic must flow For most organizations, the relatively through the switch. If something goes minor disadvantages of cable wrong or if new cabling is needed, it requirements and impacts of potential can all be done in one place. switch failure are outweighed by the • Software reconfiguration replaces benefits offered by collapsed backbones. hardware reconfiguration.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 11. Compare and contrast rack-based and chassis-switch based switched backbones.

The rack-based collapsed backbone has the advantage of placing all network equipment in one place for easy maintenance and upgrade, but does require more cable. In most cases, the cost of the cable itself is only a small part of the overall cost to install the network, so the cost is greatly outweighed by the simplicity of maintenance and the flexibility it provides for future upgrades. The room containing the rack of equipment is sometimes called the main distribution facility (MDF) or central distribution facility (CDF). The cables from all computers and devices in the area served by the MDF (often hundreds of cables) are run into the MDF room. Once in the run they are connected into the various devices. The devices in the rack are connected among themselves using very short cables called patch cables. With rack-based equipment, it becomes simple to move computers from one LAN to another. This convenience is used to spread the traffic around the network more efficiently so that network capacity is no longer tied to the physical location of the computers. Computers in the same physical area can be connected into very different network segments conveniently in the MDF. A chassis switch enables users to plug modules directly into the switch. Each module is a certain type of network device. The key advantage of chassis switches is their flexibility. It becomes simple to add new modules with additional ports as the LAN grows, and to upgrade the switch to use new technologies. For example, if you want to add gigabit Ethernet or ATM you simply lay the cable and insert the appropriate module into the switch.

12. What is a module and why are modules important?

A module is any of certain types of network devices that can be plugged directly into a chassis switch. Since a chassis switch must be able to support simultaneous activities of all connected module, each switch has an internal capacity (in Mbps) which limits the maximum number of modules that can be accepted by the switch. Modules can be switches, hubs, or routers.

13. Explain how single-switch VLANs work.

In a single switch VLAN the VLAN operates only inside one switch. The computers on the VLAN are connected into the one switch and assigned by software into different VLANs. The network manager uses special software to assign the dozens or even hundreds of computers attached to the switch to different VLAN segments. The VLAN segments function in the same way as physical LAN segments; the computers in the same VLAN act as though they are connected to the same physical switch or hub.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 14. Explain how multiswitch VLANs work.

A multi-switch VLAN works the same way as a single switch VLAN, except that several switches are used to build the VLANs. The switches must be able to send packets among themselves in a way that identifies the VLAN to which the packet belongs. There are two approaches to this: packet encapsulation and modifying the Ethernet packet.

•

In the encapsulation approach, a proprietary protocol encapsulates the packet. When a packet needs to go from one VLAN switch to another VLAN switch, the first switch puts a new VLAN packet around the outside of the Ethernet packet. The VLAN packet contains the VLAN information and is used to move the packet from switch to switch within the VLAN network..

When the packet arrives at the final destination switch, the VLAN packet is stripped off and the unchanged Ethernet packet inside is sent to the destination computer.

•

In the modification approach, the Ethernet packet itself is to modified to carry the VLAN information. 16-bytes of VLAN information (according to emerging standard IEEE 802.1q) are added to the standard Ethernet (IEEE 802.3) packet. The additional VLAN information is used to move the packet from switch to switch within the VLAN network. The original Ethernet packet is restored from the modified packet at the final destination switch and then sent to the destination computer.

15. What is IEEE 802.1q?

IEEE 802.1q is an emerging standard that inserts 16-bytes of VLAN information into the normal IEEE 802.3 Ethernet packet. When a packet needs to go from one VLAN switch to another VLAN switch, the first switch replaces the incoming Ethernet packet with an 802.1q packet that contains all the information in the original 802.3 Ethernet packet, plus 16-bytes of VLAN information. The additional VLAN information is used to move the packet from switch to switch within the VLAN network. When the packet arrives at the final destination switch, the IEEE 802.1q packet is stripped off and replaced with a new Ethernet packet that is identical to the one with which it entered the VLAN. 16. What are the advantages and disadvantages of VLANs? Advantages: • • •

VLANs are often faster and provide greater opportunities to manage the flow of traffic on the LAN and BN than do the traditional LAN and routed BN architecture.

Allow the ability to prioritize traffic They allow computers in separate geographic locations to be placed on the same LAN.

Disadvantages: • •

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However, VLANs are significantly more complex, so they usually are used only for large networks.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 17. How can you improve the performance of a BN? Improving the performance of backbone networks is similar to improving LAN performance.

First, find the bottleneck, and then solve it (or more accurately, move the bottleneck somewhere else). You can improve the performance of the network by improving the computers and other devices in the network, by upgrading the circuits between computers, and by changing the demand placed on the network.

Network performance can be improved by: • • • • • •

upgrading the computers and other devices in the network by using static rather than dynamic routing if there are few routes through the network by reducing switch-to-switch traffic in networks without standard protocols by using the same protocols in the backbone network as in the attached LANs by encapsulating rather than translating between different protocols by increasing the memory in backbone devices

Performance can also be improved by adding additional circuits to increase capacity, by going to a switched network, and by increasing the circuits on high traffic circuits. In addition, performance can be enhanced by reducing demand or by restricting applications that use lots of network capacity, and by using switches that filter certain broadcast messages.

18. Why are broadcast messages important?

Some application software packages and network operating system modules written for use on LANs broadcast status messages to all computers on the LAN (but not necessarily all computers served by a BN). For example, broadcast messages inform users when printers are out of paper, or when the network manager is about to shut down the server. These types of messages require filtering in a backbone network if their broadcast scope should be restricted to a particular LAN or segment.

19. What are the preferred architectures used in each part of the backbone?

Answers can vary depending on preferences, but suggestions include: Access – switched backbones Distribution layer – Virtual LAN Core layer – routed backbones

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 20. Some experts are predicting that Ethernet will move into the WAN. What do you think?

The new Ethernet/IP packet networks have become dominant for high-traffic networks (2 Mbps to 1Gbps), even though SONET and ATM remain preferred for some requirements. Since WAN required a network with high network capacity, I believe that Ethernet will move into the WAN into the near future.

End of Chapter Exercises

A. Survey the BNs used in your organization. Is the campus core backbone different from the distribution backbones used in the buildings? Why? Answers will vary.

B. Document one BN in detail. What devices are attached, what cabling is used, and what is the topology? What networks does the backbone connect?

Answers will vary.

C. You have been hired by a small company to install a backbone to connect four 100base-T Ethernet LANs (each using one 24-port hub) and to provide a connection to the Internet.

Develop a simple backbone and determine the total cost (i.e., select the backbone technology and price it, select the cabling and price it, select the devices and price them, and so on).

Prices are available at www.datacommwarehouse.com, but use any source that is convenient.

For simplicity, assume that category 5, category 5e, category 6, and fiber-optic cable have a fixed cost per circuit to buy and install, regardless of distance, $50, $60, $120, and $300, respectively.

Answers will vary.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova Mini-Cases

I. Pat’s Engineering Works Pat’s Engineering Works is a small company that specializes in complex engineering consulting projects. The company is moving into new offices and want you to design their network. They have a staff of eight engineers (which is expected to grow to 12 over the next five years), plus another eight management and clerical employees who also need network connections, but whose needs are less intense. Design the network. Be sure to include a diagram.

The recommended design should be based on the Rack-based collapsed backbone network design or on the VLAN-based collapsed backbone network design.

II. Hospitality Hotel Hospitality Hotel is a luxury hotel that whose guests are mostly business travelers. To improve its quality of service, it has decided to install network connections in each of its 600 guest rooms and 12 conference meeting rooms. Your task is to design the network for the public network and decide how to connect the two networks together. Be sure to include a diagram.

The recommended design should be based on the Rack-based collapsed backbone network design shown in the text. Each floor should have a layer-2 switch. Each conference room should "home run" to the main closet switch. All floors should use an uplink port to interconnect to the main switch.

The two networks should be connected together with a router in between the two networks. This will allow the networks to be connected so that traffic can pass from one to the other, but the router can also keep “local traffic local,” thus reducing traffic on the network.

III. Indiana University Reread Management Focus 8-1. What other alternatives do you think Indiana University considered? Why do you think they did what they did?

They probably also considered a routed backbone and a virtual LAN. Either of these could offer some advantages, but the switched design is a good design that allows for flexibility in design.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova IV. Shangri-La Reread Management Focus 8-2. What other alternatives do you think the Shangri-La Resort considered? Why do you think they did what they did?

The other alternatives could be numerous. They probably considered both routed and switched backbone architectures as well. Although the VLAN is more costly, it does provide much more efficiency, especially under heavy loads.

V. Chicago Consulting You are the network manager for a consulting firm that needs to install a backbone to connect four 100Base-T Ethernet LANs (each using a 24-port switch). Develop a simple backbone and determine the total cost (i.e., select the device and price it). Prices are available at www.cdw.com, but you can use any source that is convenient.

The answers can vary depending on the design by the student. A routed backbone architecture (similar to Figure 8-5) would be a good option to consider.

VI. Western Trucking Western Trucking operates a large fleet of trucks that deliver shipments for commercial shippers such as food stores, retailers, and wholesalers. Their main headquarters building and secondary building are shown in Figure 8-10. They want to upgrade to a faster network. Design a new network for them, including the specific backbone and LAN technologies to be used. Assume that the main office building is 170 feet by 100 feet in size and that the secondary building is 100 feet by 50 feet. The two buildings are 100 feet apart.

I would install a collapsed backbone network using a star topology with a Gigabit Ethernet switch at the center. This backbone would support a series of LAN’s (as needed). In this new architecture, all circuits, routers, and bridges are replaced by one switch.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

Additional Content Teaching Notes I cover most material evenly, but I omit the selecting backbone networks section. I no longer cover FDDI and token ring as they are faded technologies, but I may mention these briefly in class to let the students know about these technologies just in case they encounter these older approaches in a job somewhere.

Fast Ethernet, gigabit Ethernet and switched networks are the new “hot” technologies so I spend a significant amount of time on them.

I also spend some amount of time on ATM. It is quite different from the other technologies we have examined and students have a harder time understanding it. It is useful for them to understand the concepts of an edge switch.

Gigabit Ethernet and switch technologies (especially layer-3 and layer-4 switches) are the least mature of the technologies in this chapter. They will probably need careful watching to stay current.

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CHAPTER 9 WIDE AREA NETWORKS Chapter Summary The wide area network (WAN) is a key part of the enterprise edge. Most organizations do not build their own WAN communication circuits, preferring instead to lease them from common carriers or to use the Internet. This chapter focuses on the WAN architectures and telecommunications services offered by common carriers for use in enterprise WANs, not the underlying technology that the carriers use to provide them. We discuss the three principal types of WAN services that are available: dedicated-circuit services, packet-switched services, and virtual private network (VPN) services. We conclude by discussing how to improve WAN performance and how to select services to build WANs.

Learning Objectives • • • • •

Understand dedicated-circuit services and architectures Understand packet-switched services and architectures Understand Internet-based VPN services and architectures Understand the best practice recommendations for WAN design Be familiar with how to improve WAN performance

Key Terms Access VPN Channel service unit/data service unit (CSU/DSU) Common carrier Data plane Discard eligible (DE) Encapsulating Security Payload (ESP) Federal Communications Commission (FCC) Frame relay Interexchange carrier (IXC) Intranet VPN L2TP Layer 2 VPN Local exchange carrier (LEC) Maximum allowable rate (MAR) Multiprotocol label switching (MPLS) Orchestration plane Packet-switched services

Canadian Radio-Television and Telecommunications Commission (CRTC) Committed information rate (CIR) Control plane Dedicated-circuit services Ethernet services Extranet VPN Fractional T1 (FT1) Full-mesh architecture Internet service provider (ISP) IPSec Latency Layer 3 VPN Management plane Mesh architecture Packet assembly/disassembly device (PAD) Packet services Partial-mesh architecture

Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova Permanent virtual circuits (PVC) Public utilities commission (PUC) Software Defined WAN (SDWAN) Switched virtual circuits (SVCs) Synchronous optical network (SONET) T1 and T2 circuits Virtual private network (VPN) VPN software

Point of presence (POP) Ring architecture Star architecture Synchronous digital hierarchy (SDH) T-carrier circuit T3 and T4 circuits VPN gateway Wide area networks (WANs)

Chapter Outline 9.1 Introduction 9.2 Dedicated-Circuit Networks 9.2.1 Basic Architecture 9.2.2 T-Carrier Services 9.2.3 SONET Services 9.3 Packet-Switched Networks 9.3.1 Basic Architecture 9.3.2 Frame Relay Services 9.3.3 MPLS Services 9.3.4 Ethernet Services 9.4 Virtual Private Networks 9.4.1 Basic Architecture 9.4.2 VPN Types 9.4.3 How VPNs Work 9.5 The Best Practice WAN Design 9.5.1 Software Defined WAN 9.5.2 Choosing WAN Circuits 9.6 Improving WAN Performance 9.6.1 Improving Device Performance 9.6.2 Improving Circuit Capacity 9.6.3 Reducing Network Demand 9.7 Implications for Cyber Security Summary

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

Answers to Textbook Exercises Answers to End-of-Chapter Questions

1. What are common carriers, local exchange carriers, and interexchange carriers?

A common carrier is a private company that sells or leases communication services and facilities to the public. Common carriers are profit-oriented, and their primary products are services for voice and data transmissions, both over traditional wired circuits as well as cellular services. Common carriers often supply a broad range of computer-based services, such as the manufacturing and marketing of specialized communication hardware and software. Common carriers that provide local telephone services are commonly called local exchange carriers (LEC), while carriers that provide long distance services (e.g., Sprint) are commonly called interexchange carriers (IXC). As the LECs move into the long distance market and IXCs move into the local telephone market, this distinction may disappear.

2. Who regulates common carriers and how is it done?

Most countries have a federal government agency that regulates data and voice communications. In the United States, the agency is the Federal Communications Commission (FCC); in Canada, it is the Canadian Radio-Television and Telecommunications Commission (CRTC). Each state or province also has its own public utilities commission (PUC) to regulate communications within its borders. The FCC regulates interstate and international communications to and from the United States. State Public Utilities Commissions (PUCs) regulate intrastate communications within their states. Regulation is achieved based on tariffs filed and approved (or disapproved) by the FCC and PUCs. The FCC/CRTC differs from the state PUCs in the following way: •

The FCC has regulatory powers to compel common carriers to conform to the Federal Communications Act of 1934 and its revisions. It regulates the tariffs for interLATA and international (calls to and from the United States) communications. These usually are referred to as long distance communications.

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A state PUC sets the rules and regulates the tariffs for all communications in its individual state boundary.

Note to the instructor: There may be some overlap between federal and state jurisdictions because you can have both intraLATA and interLATA communications take place entirely within one state.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 3. How do Ethernet services work in the WAN? Companies offering Ethernet services have laid their own gigabit Ethernet fiber-optic networks in large cities. When an organization signs up for service, the packet network company installs new fiber-optic cables from their citywide backbone into the organization’s office complex and connects it to an Ethernet switch. The organization simply plugs its network into its Ethernet switch and begins using the service. All traffic entering the packet network must be Ethernet, using IP.

4. Compare and contrast dedicated-circuit services, and packet-switched services.

With dedicated circuit networks, a circuit is established between the two communicating computers. This circuit provides a guaranteed data transmission capability that was available for use by only those two computers and is assigned solely to that transmission. No other transmission is possible until the circuit is closed. In contrast, packet switched services enable multiple connections to exist simultaneously between computers over the same physical circuit or even over different physical circuits.

With a dedicated circuit network, you lease circuits from common carriers for their exclusive use twenty-four hours per day, seven days per week. All connections are point to point, from one building in one city to another building in the same or a different city. The carrier installs the circuit connections at the two end-points of the circuit and makes the connection between them. The circuits still run through the common carrier's cloud, but the network behaves as if you have your own physical circuits running from one point to another: •

Dedicated circuits are billed at a flat fee per month and the user has unlimited use of the circuit.

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Once you sign a contract, making changes can be expensive because it means rewiring the buildings and signing a new contract with the carrier. Therefore, dedicated circuits require more care in network design than switched circuits in terms of both locations and the amount of capacity you purchase.

With packet switched services, the user again buys a connection into the common carrier cloud). The user pays a fixed fee for the connection into the network. This depends upon the type and capacity of the service. They are then is charged for the number of packets transmitted.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 5. Is a WAN that uses dedicated circuits easier or harder to design than one that uses packetswitched circuits? Explain.

A WAN using dedicated circuits is harder to design than one that uses packet-switched circuits. With dedicated circuits, once you sign a contract, making changes can be expensive because it means rewiring the buildings and signing a new contract with the carrier.

Dedicated circuits therefore require more care in network design than using packet-switched circuits. In addition, packet-switched networks enable packets from separate messages with different destinations to be interleaved for transmission, unlike dedicated circuits.

6. Compare and contrast ring architecture, star architecture, and mesh architecture.

A ring architecture connects all computers in a closed loop, with each computer linked to the next. The circuits are full duplex circuits. Computers in the ring may send data in one direction or the other depending upon which direction is the shortest to the destination.

Properties of the ring architecture (assuming a double ring structure): •

Messages can take a long time to travel from the sender to the receiver. Considering there are only two routes from any one computer to another, if one part of the circuit or any one computer becomes overloaded, traffic delays can build up very quickly.

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The double-ring structure offers redundancy. If a circuit fails, messages can travel to their destinations in the opposite direction (probably with a time and distance penalty). If the network is operating close to its capacity, this will dramatically increase transmission times because the traffic on the remaining part of the network may come close to doubling (because all traffic originally routed in the direction of the failed link will now be routed in the opposite direction through the longest way around the ring).

A star architecture connects all computers to one central computer that routes messages to the appropriate computer. Properties of the star architecture:

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•

It is easy to manage because the central computer receives and routes all messages in the network.

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It can be faster than the ring network since, in general any message needs to travel through fewer circuits to reach its destination than is the case in the ring network).

However, the star topology is the most susceptible to traffic problems because the central computer must process all messages on the network. The central computer must have sufficient capacity to handle traffic peaks or it may become overloaded and network performance will suffer.

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In general, the failure of any one circuit or computer affects only the one computer on that circuit.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova •

If the central computer fails, the entire network fails because all traffic must flow through it. It is critical that the central computer be extremely reliable.

In a mesh architecture (usually implemented as partial mesh architecture), every computer may be connected to any other computer. Typically many, but not all, computers are connected. Properties of the mesh architecture: • The effects of the loss of computers or circuits in a mesh network depend entirely upon the circuits available in the network. If there are many possible routes through the network, the loss of one or even several circuits or computers may have few effects beyond the specific computers involved. However, if there are only few circuits in the network, the loss of even one circuit or computer may seriously impair the network.

•

In general, mesh networks combine the performance benefits of both ring networks and star networks. Mesh networks usually provide relative short routes through the network (compared to ring networks) and provide many possible routes through the network to prevent any one circuit or computer from becoming overloaded when there is a lot of traffic (compared to star networks in which all traffic goes through one computer).

•

Since mesh networks use decentralized routing, each computer in the network performs its own routing. This requires more processing by each computer in the network than in star or ring networks as well as the "overhead" transmission of network status information (e.g., how busy each computer is), reducing network capacity.

7. What are the most commonly used T carrier services? What data rates do they provide?

T-Carrier Designation T-1 T-2 T-3 T-3

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DS Designation DS-0 DS-1 DS-2 DS-3 DS-4

Speed 64 Kbps 1.544 Mbps 6.312 Mbps 33.375 Mbps 274.176Mbps

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 8. Distinguish among T-1, T-2, T-3, and T-4 circuits.

A T-1 circuit (sometimes called a DS-1 circuit) provides a data rate of 1.544 Mbps. T-1 circuits can be used to transmit data, but often are used to transmit both data and voice. In this case, a time division multiplexer (TDM) provides 24 64 Kbps circuits. Digitized voice using pulse code modulation (PCM) requires a 64 Kbps circuit so a T-1 circuit enables 24 simultaneous voice channels.

A T-2 circuit transmits data at a rate of 6.312 Mbps. Basically; it is a multiplexed bundle of four T-1 circuits. A T-3 circuit allows transmission at a rate of 44.376 Mbps, although most articles refer to this rate as 45 megabits per second. This is equal to the capacity of 28 T-1 circuits. T-3 circuits are becoming popular as the transmission medium for corporate WANs because of their higher data rates. At low speed, these T-3 circuits can be used as 672 different 64 Kbps channels or voice channels. A T-4 circuit transmits at 274.176 Mbps, which is equal to the capacity of 178 T-1 circuits. Obviously, an organization using either T3 or T-4 circuits must have a tremendous need to transmit very large quantities of data.

9. Describe SONET. How does it differ from SDH? The synchronous optical network (SONET) has been accepted by the U.S. standards agency (ANSI). It was accepted as a standard for optical transmission at gigabit per second speeds.

The international telecommunications standards agency (ITU-T) also recently standardized a version of SONET under the name of synchronous digital hierarchy (SDH). SONET and SDH are very similar and can be easily interconnected. The SONET standard includes more data rates than the SDH standard. As with T carrier services, a CSU/DSU is needed to connect the user's network into the SONET/SDH circuit.

SONET transmission speeds begin at the OC-1 level (optical carrier level 1) of 51.84 Mbps.

Each succeeding rate in the SONET fiber hierarchy is defined as a multiple of OC-1, with SONET data rates defined as high as OC-192 or about 10 Gbps. Each level above OC-1 is created by multiplexing. Although not yet available in all locations, SONET/SDH is available in most large cities worldwide.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 10. How do packet-switching services differ from other wide area networks services?

Packet switched services are quite different from the other types of network services. For each of these three, dialed circuit services, dedicated circuit services, and circuit switched services, a physical circuit was established between the two communicating computers. This circuit provided a guaranteed data transmission capability that was available for use by only those two computers.

In contrast, packet switched services enable multiple connections to exist simultaneously between computers. With packet switched services, the user again buys a connection into the common carrier network. The user pays a fixed fee for the connection into the network. They are then charged for the number of packets transmitted.

11. Where does packetizing take place?

Splitting messages into individual packets (packetizing) takes place at a packet assembly/disassembly device (PAD), which can be owned and operated by the customer or by the common carrier.

The PAD converts the sender's data into the network layer and data link layer packets used by the packet network and sends them through the packet switched network. At the other end, another PAD reassembles the packets back into the network layer and data link layer protocols expected by the destination and delivers it to the appropriate computer. This "packetizing" and re-assembly is almost instantaneous, and data are transmitted continuously.

The PAD can translate between different data link layer protocols between the sender and the destination (e.g., Ethernet at the sender and token ring at the receiver). It may also provide conversion from one code to another (i.e., ASCII to EBCDIC).

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 12. Compare and contrast frame relay and Ethernet services.

Frame relay differs from traditional networks in three important ways. First, frame relay operates only at the data link layer. Frame relay, like other packet switched networks takes the incoming packets from the user network and converts them to its own packet structure for internal transmission. Frame relay uses variable length packets, which adapt to the size of the incoming packet (up to 8K).

Second, frame relay networks do not perform error control. Virtually all other types of networks perform error checking at each computer in the network. Any errors in transmission are corrected immediately, so that the network layer and application software can assume error-free transmission. However, this error control is one of the most time consuming processes in a network. Most networks today are relatively error-free, so frame relay networks do not ensure error-free delivery of the packets (they do perform error checking, but simply discard packets with errors; they do not generate NAKs and ask for retransmission). It is up to the software at the source and destination to perform error correction and to control for lost messages. Since the user's data link packet remains intact, it is simple for the devices at the edge of the frame relay network to check the error control information in the user's data link layer packet to ensure that no errors have occurred and to request transmission of damaged or lost packets.

A third major difference is that frame relay defines two connection data rates that are negotiated per connection and for each virtual circuit as it is established. The committed information rate (CIR) is the data rate the circuit must guarantee to transmit. If the network accepts the connection, it guarantees to provide that level of service. Most connections also specify a maximum allowable rate (MAR), which is the maximum rate that the frame relay network will attempt to provide, over and above the CIR. The circuit will attempt to transmit all packets up to the MAR, but all packets that exceed the CIR are marked as discard eligible (DE). If the network becomes overloaded, DE packets are discarded. So while can transmit faster than the CIR, they do so at a risk of lost packets.

Ethernet service networks bypass the PSTN; companies offering Ethernet/IP packet networks have laid their own gigabit Ethernet fiber optic networks in large cities. When an organization signs up for service, the packet network company installs new fiber optic cables from their citywide WAN backbone into the organization's office complex and connect it to an Ethernet switch. The organization simply plus their network into their Ethernet switch and begins using the service. All traffic entering the packet network must be Ethernet using IP. Since most organizations today use Ethernet and IP in the LAN and BN environment, Ethernet/IP avoids the need to translate or encapsulate to generate addresses for LAN or BN traffic and gains in throughput. It avoids complexity, meaning that companies do not have to add staff knowledgeable in the different WAN protocols, software, and hardware these technologies require. This technology is offered by relatively new startup companies like Yipes.com.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 13. Which likely to be the longer-term winner, MPLS or Ethernet services?

Both of these technologies has benefits and an argument could be made for each. As such, student answers will vary. MPLS seems to be a contender because the Internet utilizes TCP/IP. Ethernet has the advantage of being used heavily on LANs, so the protocol conversion does not have to occur.

14. Explain the differences between CIR and MAR. The committed information rate (CIR) is the data rate the circuit must guarantee to transmit.

If the network accepts the connection, it guarantees to provide that level of service. Most connections also specify a maximum allowable rate (MAR), which is the maximum rate that the frame relay network will attempt to provide, over and above the CIR. The circuit will attempt to transmit all packets up to the MAR, but all packets that exceed the CIR are marked as discard eligible (DE). If the network becomes overloaded, DE packets are discarded. So while can transmit faster than the CIR, they do so at a risk of lost packets.

15. How do VPN services differ from common carrier services?

A type of VAN, called a virtual private network (VPN) (or sometimes software-defined network) has emerged. VPNs provide circuits that run over the Internet but appear to the user to be private networks. Internet access is inexpensive compared to the cost of leasing dedicated circuits, circuit switched services, or packet switched services from a common carrier.

Different VPNs provide different services, but most offer packet switching hardware that will communicate via the Internet, or VPN services, which you lease from the VPN in much the same way as leasing a service from a common carrier. These VPN hardware (or services) take your data, encrypt it, and send it through the Internet through a series of “tunnels” -- a virtual circuit through the Internet, which constrains the source and destination to only those within the VPN.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 16. Explain how VPN services work.

A virtual private network (VPN) provides the equivalent of private packet switched network over the public Internet. You establish a series of PVCs that run over the Internet, so that the network acts like a set of dedicated circuits over a private packet network.

With a VPN, you first lease an Internet connection at whatever access rate and access technology you choose for each location you want to connect. For example, you might lease a T-1 circuit from a common carrier that runs from your office to your Internet service provider (ISP). You pay the common carrier for the circuit and the ISP for Internet access. Then you connect a VPN device (a specially designed router or switch) to each Internet access circuit to provide access from your networks to the VPN. The VPN devices enable you to create PVCs through the Internet that are called tunnels.

The VPN device at the sender takes the outgoing packet and encapsulates it with a protocol that is used to move it through the tunnel to the VPN device on the other side (a technology focus box later in this chapter describes this process in more detail). The VPN device at the receiver, strips off the VPN packet, and delivers the packet to the destination network. The VPN is transparent to the users; it appears as though a traditional packet switched network PVC is in used. The VPN is also transparent to the ISP and the Internet as a whole; there is a simply a stream of Internet packets moving across the Internet.

The primary advantages of the VPNs is low cost and flexibility. Because they use the Internet to carry messages, the major cost is Internet access, which is inexpensive compared to the cost of circuit switched services, dedicated circuit services, or packet switched services from a common carrier. Likewise, anywhere you can establish Internet service you can quickly put a VPN. There are two important disadvantages.

First, since traffic on the Internet is unpredictable, sometimes packets travel quickly and at other times, they take a long time to reach their destination.

Second, because the data travels on the Internet, security is always a concern. Most VPN networks encrypt the packet at the source VPN device before it enters the Internet and decrypt the packet at the destination VPN device.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 17. Compare the three types of VPN. Three types of VPN are in common use: intranet VPN, extranet VPN and access VPN. •

An intranet VPN provides virtual circuits between organization offices over the Internet.

Each location has a VPN device that connects the location to another location through the Internet.

•

An extranet VPN is the same as an intranet VPN except that the VPN connects several different organizations, often customers and suppliers, over the Internet.

•

An access VPN enables employees to access an organization's networks from a remote location. Employees have access to the network and all the resources on it in the same way as employees physically located on network. The user connects to a local ISP that supports the VPN service via POTS, ISDN, or other circuit. The VPN device at the ISP accepts the user's login, establishes the tunnel to the VPN device at the organization's office, and begins forwarding packets over the Internet. An access VPN provides a less expensive connection than having a national toll-free 800 number that connects directly into large sets of modems at the organization's office. Compared to a typical ISP-based remote connection, the access VPN is secure connection than simply sending packets over the Internet.

18. How can you improve WAN performance?

Improving the performance of WANs is handled in the same way as improving LAN performance. You begin by checking the devices in the network, by upgrading the circuits between the computers, and by changing the demand placed on the network. Below is the performance checklist for improving WANs. Increase Computer and Device Performance • •

Upgrade devices Change to a more appropriate routing protocol (either static or dynamic)

Increase Circuit Capacity • •

Analyze message traffic and upgrade to faster circuits where needed Check error rates

Reduce Network Demand • • • .

Change user behavior Analyze network needs of all new systems Move data closer to users Page 11

Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

19. Describe three important factors in selecting WAN services.

The three factors used are effective data rates, cost, and reliability. These are all detailed in Figure 9-11.

20. Are Ethernet services a major change in the future of networking or a technology blip?

It is reasonable to expect major changes in the future of networking with Ethernet services.

Several carriers have announced that they intend to stop offering all services except Ethernet and Internet services. With the advent of Ethernet services such as YIPES, this offers a significant approach to networking because it offers a way to "slice" fiber services down to the 1 Mbit level. Thus, the customer can dynamically allocate slices and pay for what is used without the costs of infrastructure change. Further, as organizational LANs heavily use Ethernet and IP in the LAN and BN environment, and the WAN packet network services (X.25, ATM, Frame Relay, and SMDS) use layer-2 protocols, it is likely that Ethernet services would be more attractive. Any LAN or BN traffic must be translated (or encapsulated) into a new protocol and destination addresses generated for the new protocol.

This takes time, slowing network throughput. Thus, the advantage of Ethernet services in networking is that there is no translation prior to transmission, making the service appealing.

Ethernet services will represent a new and very attractive WAN technology in the future.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 21. What is SDWAN and what benefits does it provide?

A Software Defined WAN uses software to control and manage the routers used in the WAN. This enables the network manager to balance the use of the different network services, so that the network makes decisions about cost and reliability in real time as network conditions change.

A SDWAN provides four benefits. First, it provides centralized management–one software system to see the network status and manage all the devices and circuits in the WAN. Second, it reduces costs by balancing network traffic over circuits that have different costs and capacities (this also means that companies can buy cheaper circuits that will only be used if the network gets busy). Third, it provides more visibility over network traffic so network managers can see end-to-end traffic flows to better predict future growth and know what new circuits are needed before traffic slowdowns become a problem. Fourth, SDWANs provide good security because most routers that are compatible with SDWAN software also have built-in VPN capabilities, so they routinely encrypt traffic from router to router in the SDWAN.

22. What is the architecture of an SDWAN? The architecture of an SDWAN has three parts, which are also called planes. The top level is the Management Plane. This software is used to control the network. The second plane is the Control Plane. This software controls the network and makes the decisions. The third plane is the Data Plane. This plane includes the routers that implement the network.

23. Are there any WAN technologies that you would avoid if you were building a network today? Explain.

Of the technologies described in the chapter, frame relay may be one that would be wise to avoid at this time. Many people argue that IP services will replace frame relay by 2022 so it would be wise to avoid it if possible.

24. Suppose you joined a company that had a WAN composed of SONET, T carrier and frame relay services, each selected to match a specific network need for a certain set of circuits. Would you say this was a well-designed network? Explain.

This depends on how suitable the various technologies are for the applications supports.

Today, increasingly, network designers make decisions to reduce costs, gain reliability, and increase performance through network integration, dynamic allocation so that unused capacity much not be paid for, and failover capabilities.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 25. It is said that frame relay services and dedicated-circuit services are somewhat similar from the perspective of the network designer. Why? Both are based on a single connection to the common carrier. Both provide similar transmission speed and reliability.

Answers to End-of-Chapter Exercises

A. Find out the data rates and costs of T carrier services in your area.

Student answers will vary.

B. Find out the data rates and costs of packet-switched and dedicated-circuit services in your area.

Student answers will vary.

C. Investigate the WAN of a company in your area. Draw a network map.

Student answers will vary.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova D. Using Figure 9-9:

a. Suppose that the example used a layer 2 VPN protocol called L2TP. Draw the messages and the packets they would contain.

VPNs operate at either layer 2 or layer 3. A layer 2 VPN uses the layer 2 packet (e.g., Ethernet) to select the VPN tunnel and encapsulates the entire packet, starting with the layer 2 packet. b. Suppose that the Web server was an email server. Draw the messages from the email server to the employee’s computer. Show what packets would be in the message.

Email servers use SMTP to send and receive mail messages. SMTP servers commonly use the Transmission Control Protocol on port number 25. c. Suppose the office connects to its ISP using metro Ethernet. What packets would be in the message from the office router to the ISP? A metropolitan area network (MAN) is based on Ethernet standards. It is commonly used to connect subscribers to a larger service network or the Internet. Businesses can also use metropolitan-area Ethernet to connect their own offices to each other.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova d. Suppose the employee connects to the ISP using a layer 2 protocol called XYZ. What packets would be in the message from the employee’s router to the ISP? A router examines a packet header's destination IP address and compares it against a routing table. It uses the table to determine the packet's best next hop. Routing tables list directions for forwarding data to network destinations.

E. Select one SDWAN vendor and describe the products it offers.

Student answers will vary.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova Mini-Cases I. Cookies Are Us Cookies are Us runs a series of 100 cookie stores across the Midwestern U.S. and central Canada. At the end of each day, the stores sends sales and inventory data to headquarters, which uses the data to ship new inventory and plan marketing campaigns. They have decided to move to a WAN. What type of a WAN architecture and WAN service would you recommend?

Based on limited application requirements, VPN or T-carrier services will work well. Each of these are relatively cheap and will suffice for the file transfers required daily at the headquarters site.

II. MegaCorp MegaCorp is large manufacturing firm that operates 5 factories in Dallas, 4 factories in Los Angeles, and 5 factories in Albany, New York. It operates a tightly connected order management system that coordinates orders, raw materials, and inventory across all 14 factories. What type of a WAN architecture and WAN service would you recommend?

Student answers can vary on this one based on some assumptions that can be made related to the volume of data and current costs. T carrier services would be a good option, as these would provide the necessary bandwidth at a reasonable price. .

III. Sunrise Consultancy Sunrise Consultancy is a medium-sized consulting firm that operates 17 offices around the world (Dallas, Chicago, New York, Atlanta, Miami, Seattle, Los Angeles, San Jose, Toronto, Montreal, London, Paris, Sao Paulo, Singapore, Hong Kong, Sydney, and Bombay). They have been using Internet connections to exchange email and files, but the volume of traffic has increased to the point that they now want to connect the offices via a WAN. Volume is low but expected to grow quickly once they implement a new knowledge management system. What type of a WAN topology and WAN service would you recommend? Why? With Sunrise moving from the Internet to a Wide Area Network (WAN), I would suggest a Cloudbased design, as that will be the simplest method for the network manager to network in the nine independent offices.

IV. Cleveland Transit Reread Management Focus 9-1. What other alternatives do you think Cleveland Transit considered? Why do you think they did what they did?

Cleveland Transit probably considered many of the packet-switched services. One of the main reasons they chose a SONET ring was because of the full-duplex ring which enables communication to continue even in the event of a circuit cut. Resiliency of the network is key due to the 24/7 requirement for the types of services that they require.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova V. Marietta City Schools Reread Management Focus 9-3. What alternatives do you think Marietta City Schools considered? Why do you think they did what they did?

They probably considered many of the packet-switched services as they offer some of the same benefits. They probably selected Ethernet because they probably are using Ethernet on their LANs so no protocol translation is required. In addition, the 1-10 Gbps speeds offer the service they need for the new application types they are considering.

Additional Content Teaching Notes

I cover the material in this chapter evenly, but I omit the selecting WAN services. My primary goal is to have students understand the major differences between the general categories of services and to have some familiarity with the specific services offered. In many ways, dialed services and circuit switched services are the same and I point this out to students. Likewise, the data rates for many services are similar so I point out that most of the internal network “plumbing” uses 64 Kbps PCM circuits and this is why the data rates are similar. The primary differences are the connection features (dedicated, circuit switched, packet switched) and the way in which the services are marketed to the users.

Dedicated circuit services have remained changed over the past few years, especially with the ever-increasing data rates. DSL and its derivatives (e.g., ADSL, VDSL) and competitors (cable modems) have become more mainstream. This is an area to watch. There will be many new developments over the next few years as this technology matures.

War Stories

Installing ISDN (Objective: illustrate the problems with ISDN) A friend of mine who worked for AT&T attended a 2-day seminar on installing ISDN in New York. The entire first day (except for some introductory remarks) was spent watching the instructor call six different organizations to get provisioning information needed to connect the ISDN card to the telephone network and have it talk to the training organization’s server over the ISDN line. I am not joking. After six hours’ worth of phone calls and several incorrect responses to the instructor’s questions requiring additional calls, the computer was finally able to talk with the organization’s server. With stories like this, it is no wonder that organizations are looking toward ADSL rather than ISDN.

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CHAPTER 10 THE INTERNET Chapter Summary This chapter examines the Internet in more detail to explain how it works and why it is a network of networks. The chapter also examines Internet access technologies, such as DSL and cable modem, as well as the possible future of the Internet.

Learning Objectives • • •

Understand the overall design of the Internet Be familiar with DSL, cable modem, and fiber to the home Be familiar with possible future directions of the Internet

Key Terms Asymmetric DSL (ADSL) Broadband technologies Cable modem termination system (CMTS) Data over Cable Service Interface Specification (DOCSIS) Distribution hub DSL modem Gigapop Internet Architecture Board (IAB) Internet Engineering Steering Group (IESG) Internet exchange point (IXP) Internet service provider (ISP) Internet2® Local loop Mobile wireless Next Generation Internet (NGI) Optical network unit (ONU) Point of presence (POP) Request for comment (RFC) Tier 2 ISP

Autonomous system Cable modem Customer premises equipment (CPE) Digital subscriber line (DSL) DSL access multiplexer (DSLAM) Fiber to the home (FTTH) Hybrid fiber coax (HFC) Internet Corporation for Assigned Names and Numbers (ICANN) Internet Engineering Task Force (IETF) Internet Research Task Force (IRTF) Internet Society Line splitter Main distribution facility (MDF) National ISPs Optical-electrical (OE) converter Peering Regional ISP Tier 1 ISP Tier 3 ISP

Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

Chapter Outline 10.1 Introduction 10.2 How the Internet Works 10.2.1 Basic Architecture 10.2.2 Connecting to an ISP 10.2.3 The Internet Today 10.3 Internet Access Technologies 10.3.1 Digital Subscriber Line 10.3.2 Cable Modem 10.3.3 Fiber to the Home 10.4 The Future of the Internet 10.4.1 Internet Governance 10.4.2 Building the Future 10.5 Implications for Cyber Security Summary

© 2011 John Wiley & Sons, Inc.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

Answers to Textbook Exercises Answers to End-of-Chapter Questions

1. What is the basic structure of the Internet?

The Internet is hierarchical in structure. At the top are the very large national Internet service providers like AT&T, Sprint, etc. with regional and local internet service providers reporting up through this hierarchy.

2. Explain how the Internet is a network of networks.

The Internet was originally run by the U.S. National Science Foundation (NSF), but now the NAP’s are commercial enterprises run by various common carriers. These NAP’s are connected to other NAP’s, who have several ISPs attached, who have regional ISPs attached to them, who have consumers attached to them. This spider web branches out into countless networks all over the world. There are agreements between the carriers to enable the exchange of messages, with varying payment mechanisms.

3. What is an IXP? Internet Exchange Points are connection points between Internet Service Providers.

4. What is a POP? A POP is an acronym for “point of presence.” The POP is the place at which the ISP providers services to its customers.

5. Explain one reason why you might experience long response times in getting a Web page from a server in your own city.

If the other organization uses a different local ISP, which in turn uses a different regional ISP, the message may have to travel all the way to the Chicago IXP before it can move between the two separate parts of the Internet.

6. What type of circuits are commonly used to build the Internet today? What type of circuits are commonly used to build Internet 2?

Today, the backbone circuits of the major U.S. national ISPs operate at SONET OC-192 (10 Gbps).

Internet 2 will consist of circuits at least at OC-192 levels, with OC-768 (80 Gbps) and possibly even OC-3072 (160 Gbps) available.

© 2011 John Wiley & Sons, Inc.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 7. Compare and contrast cable modem and DSL. Individuals connect to ISP’s mostly via DSL and cable modems today. The speeds vary between the two technologies, it depends on location, and provider as to which is faster. One of the main differences between the two is that DSL customers have a direct connection back to the end office with point-to-point technology, whereas cable modems use shared multipoint circuits.

8. Explain how DSL works.

DSL requires equipment that is installed at the end of the cable (within the house or office) which allows traditional telephone service (POTS) to take advantage of much higher data transmissions rates via the existing cable in the local loop.

9. How does a DSL modem differ from a DSLAM? A DSL modem produces Ethernet 10Base-T packets so it can be connected directly into a computer or router and hub so that it can serve the needs of a small network. The DSLAM de-multiplexes the data streams and converts them into ATM data, which are then distributed to the ISPs. 10. Explain how ADSL works.

ADSL is the most common type of DSL used today. It uses frequency division multiplexing to create three separate channels over the one local loop circuit. One channel is the traditional voice telephone circuit, the second channel is a relatively high-speed simplex data channel, and the third channel is a slightly slower duplex data channel.

11. Explain how a cable modem works.

The cable modem works very similar to DSL, with one very important difference, DSL is a point-to-point technology, whereas cable modems use shared multipoint circuits. Cable modems must compete with other users for the available capacity. Circuits that have many clients are slower than circuits with fewer circuits.

12. What is an OE converter? A CMTS? An OE is an optical-electrical converter, which converts between the coaxial cable on the customer side and fiber-optic cable on the cable TV company side. The CMTS contains a series of cable modems/multiplexers and converts the data from cable modem protocols into protocols needed for Internet traffic, before passing them to the router connected to an ISP POP.

© 2011 John Wiley & Sons, Inc.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 13. Which is better, cable modem or DSL? Explain.

The speeds for each of these has increased significantly over the past few years. However, cable is typically much faster than DSL. 14. Explain how FTTH works.

The traditional set of hundreds of copper telephone lines that run from the telephone company switch office is replaced by one fiber‐optic cable that is run past each house or office in the neighborhood. Data is transmitted down the signal fiber cable using wavelength division multiplexing (WDM), providing hundreds or thousands of separate channels.

At each subscriber location, a Optical Network Unit (ONU) (also called an Optical Network Terminal (ONT)) acts like a DSL modem or cable modem and converts the signals in the optical network into an Ethernet format. The ONU acts as an Ethernet switch. It can also include a router. FTTH is a dedicated point‐to‐point service like DSL, not a shared multipoint service like cable modem.

15. What are some future technologies that might change how we access the Internet?

The next big technologies are Passive Optical Networking and Internet 2.

16. What are the principal organizations responsible for Internet governance, and what do they do?

There is no one organization that operates the Internet. The closest thing the Internet has to an owner is the Internet Society (ISOC). This is an open membership professional society with more than 175 organizational and 8,000 individual members in over 100 countries. The ISOC mission is to ensure “the open development, evolution and use of the Internet for the benefit of all people.

17. How is the IETF related to the IRFT? The ISOC comprises of four bodies that act together to govern, IETF and IRFT are two of the four.

18. What is the principal American organization working on the future of the Internet?

The Internet Society is an open-membership professional society with about 150 organizational members and 65,000 individual members in more than 100 countries, including corporations, government agencies, and foundations that have created the Internet and its technologies. Because membership is open, anyone, including students, is welcome to join and vote on key issues facing the Internet. Its mission is to ensure “the open development, evolution and use of the Internet for the benefit of all people throughout the world.” It works in three general areas: public policy, education, and standards.

© 2011 John Wiley & Sons, Inc.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 19. What is Internet2®?

Internet2® comprises about 400 universities, corporations, government agencies, and organizations from more than 100 countries with a primary focus to develop advanced networking as well as other innovative technologies for research and education.

20. What is a gigapop?

These are new points-of-presence (POP) that work at gigabit speeds.

21. Today, there is no clear winner in the competition for higher-speed Internet access. What technology or technologies do you think will dominate in 2 years’ time? Why? There is no answer for this, as technology changes day by day; however, I think Internet 2 development is definitely something to watch.

22. Would you be interested in subscribing to 1 Gbps FTTH (i.e., 1 Gbps both up and down) for a monthly price of $150? Why or why not?

This answer depends on the options that you currently have and the amount of uploading and downloading you actually perform. Many locations offer DSL and/or cable access for $30 per month with data rates up to 15 Mbps. Obviously increasing the download rate to 100 Mbps would provide a much faster connection, but at more than double the price.

For those users who use email and do some light browsing, then the increased speed may not provide enough benefit. For those who are heavy users (file sharing, watching movies online, playing games, and such), the increased cost would be well worth it.

23. Many experts predicted that small, local ISPs would disappear as regional and national ISPs began offering local access. This hasn’t happened. Why? There are technology changes made every day, which requires all ISP’s to constant change.

There have been some consolidation recently. However, with all the change underway, what would the larger companies really be purchasing?

© 2011 John Wiley & Sons, Inc.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova Answers to End-of-Chapter Exercises

A. Describe the current network structure of Internet2®.

According to https://whatis.techtarget.com/definition/Internet2: Internet2 is a collaboration among more than 100 U.S. universities to develop networking and advanced applications for learning and research. Since much teaching, learning, and collaborative research may require real-time multimedia and highbandwidth interconnection, a major aspect of Internet2 is adding sufficient network infrastructure to support such applications. But Internet2 also intends to investigate and develop new ways to use the Internet and the Internet2 infrastructure for its educational purposes. Although Internet2 is not envisioned as a future replacement for the Internet, its organizers hope to share their developments with other networks, including the Internet. Internet2 will include and further develop the National Science Foundation's very high-speed Backbone Network Service (vBNS) that currently interconnects research supercomputer centers in the U.S. The involved institutions plan to continue using the existing Internet for "ordinary" services such as e-mail, personal Web access, and newsgroups.

B. Provide the service details (e.g., pricing and data rates) for at least one high-speed Internet access service provider in your area.

Student answers will vary.

C. Some people are wiring their homes for with Cat 5e for 1000Base-T. Suppose a friend who is building a house asks you what—if any—wired network to put inside the house and what Internet access technology to use. What would you recommend?

Student answers will vary. However, expect that most students will recommend a high-speed, future-proof option. One option for this purpose is Cat-6. Students who give this some thought will suggest putting network wiring and jacks in every room, including the garage.

D. Provide service details (e.g., pricing and data rates) for FTTH in your area or a large city such as New York or Los Angeles.

Student answers will vary depending on your area.

E. Report the prices and available connections for one IXP, such as the Seattle IXP. Student answers will vary depending on your area. For consistency, you might want to assign the area for the students to research.

© 2011 John Wiley & Sons, Inc.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova Mini-Cases I. Cathy’s Collectibles Your cousin Cathy runs a part-time business out of her apartment. She buys and sells collectibles such as antique prints, baseball cards, and cartoon cells and has recently discovered the Web with its many auction sites. She has begun buying and selling on the Web by bidding on collectibles at lesser-known sites and selling them at a profit at more well-known sites. She downloads and uploads lots of graphics (pictures of the items she’s buying and selling). She asks you for advice. Figure 10-8 shows some of the available Internet services and their prices.

Explain the differences in these services and make a recommendation.

The differences are mostly related to speed (bandwidth). It really depends on how much time she is willing to spend uploading and downloading. This would be a personal, economic decision for her. Any of the services that offer at least 12 Mbps download and 1.5 Mbps upload will probably be good for her.

One thing to consider is that the advertised cable rates are faster than DSL, since the cable connection is based on a shared circuit, if many other users in the same neighborhood as Cathy are online at the same time, the available bandwidth could decrease significantly to the point where DSL might be better (at least during the parts of the day when many other users are online).

Another issue to consider related to the shared circuit (cable) versus direct connection (DSL) is security. Although this is a lesser issue based on the assumption that the ISP is providing good security, cable is potentially a less-secure option because of the shared circuit.

II.

Surfing Sam

Sam likes to surf the Web for fun, to buy things, and to research for his classes. Figure 10-8 shows some of the available Internet services and their prices. Explain the differences in these services and make a recommendation.

DSL works by using the existing phone line that comes into this house and multiplexing it such that there are three channels: upload, download, and phone. It uses a point-to-point connection back to the end office.

Cable companies offer their service which supplies Internet access over the existing cable system. It is different in that the local service is on a closed loop, so speeds may vary depending on neighborhood use. Security is a minor issue.

FTTH uses fiber-optic cable into the home. The traditional set of hundreds of copper telephone lines that run from the telephone company switch office is replaced by one fiber-optic cable that is run past each house or office in the neighborhood. Data are transmitted down the signal fiber cable using wavelength division multiplexing (WDM), providing hundreds or thousands of separate channels.

© 2011 John Wiley & Sons, Inc.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova WiMax reuses many of the Wi-Fi components and was designed to connect easily into Ethernet LANs. WiMax can be used as a fixed wireless technology to connect a house or an office into the Internet, but its future lies in its ability to connect mobile laptops and smart phones into the Internet.

Sam really is a casual web user; thus, not having any demanding needs. He could go with any of these services.

III.

Cookies Are Us

Cookies Are Us runs a series of 100 cookie stores across the midwestern United States and central Canada. At the end of each day, the stores express-mail a diskette or two of sales and inventory data to headquarters, which uses the data to ship new inventory and plan marketing campaigns. They have decided to move data over a WAN or the Internet. What type of a WAN topology and service (see Chapter 9) or Internet connection would you recommend? Figure 10-8 shows some of the available Internet services and their prices, whereas Figure 9-19 in the previous chapter shows faster circuits that could be used to connect to an ISP for Internet services. You should increase the prices in Figure 9-20 by 50% to get the price that an ISP would charge to provide both the faster circuit and Internet services on it. Why? Since Cookies Are Us is a business and relies on the incoming data to manage the shipment of inventory, the information is critical. I would setup a hub and spoke environment; whereas, all the 100 stores would login to the centralized LAN via the WAN and submit the necessary information directly into the headquarters. With an effort to try and save money, I would recommend going the TCP/IP route and capitalizing on the Internet’s backbone. VPN may be another option to consider too since it is relatively less expensive.

IV.

Organic Foods

Organic Foods operates organic food stores in Toronto. The store operates like a traditional grocery store but offers only organically grown produce and meat, plus a wide array of health food products. Organic Foods sells memberships, and its 3,000 members receive a discount on all products they buy. There are also special member events and sales promotions each month.

Organic Foods wants to open a new Internet site that will enable it to email its members monthly and provide up-to-date information and announcements about new products, sales promotions, and member events on its Web site. It has two options. First, it could develop the software on its own server in its office and connect the office (and the server) to the Internet via DSL, T1, or similar connection from its offices to an ISP. Alternately, it could pay the ISP to host the Web site on its servers and just connect the office to the ISP for Internet service. Figure 10-8 shows some of the available Internet services and their prices, whereas Figure 9-19 in the previous chapter shows faster circuits that could be used to connect to an ISP for Internet services. You should increase the prices in Figure 9-19 by 50% to get the price that an ISP would charge to provide both the faster circuit and Internet services on it. Web hosting would cost $500 to $1,000 per month, depending on the traffic. Which would you recommend, and what size of an Internet connection would you recommend if you choose to host it yourself? Justify your choice.

© 2011 John Wiley & Sons, Inc.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova I would recommend outsourcing the entire Internet site, because if they decide to do everything in house they will be required to purchase new software, hardware, hire new IT employees or consultants, and train their staff. Again, they should outsource this activity and focus on what they are good at (i.e. their core competencies).

They should start outsourcing the bare essentials while they test the model, and as the 3000 members start using the site, they can have the ISP increase bandwidth. Pay as you need it.

© 2011 John Wiley & Sons, Inc.

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CHAPTER 11 NETWORK SECURITY Chapter Summary This chapter describes why networks need security and how to provide it. The first step in any security plan is risk assessment, understanding the key assets that need protection, and assessing the risks to each. A variety of steps can be taken to prevent, detect, and correct security problems due to disruptions, destruction, disaster, and unauthorized access.

Learning Objectives 1.

2.

3.

4.

Be familiar with the major threats to network security Be familiar with how to conduct a risk assessment Understand how to ensure business continuity Understand how to prevent intrusion

Key Terms Accept Advanced Encryption Standard (AES) Anomaly detection Asset Authentication Biometric system Central authentication Ciphertext Continuous data protection (CDP) Cracker DDoS handler Denial-of-service (DoS) attack Disaster recovery drill Disk mirroring Eavesdropping Fault-tolerant server

Access control list (ACL) Adware

Account Algorithm

Antivirus software Asymmetric encryption Availability Brute-force attack Certificate authority (CA) Computer forensics Controls

Application-level firewall Authentication server Backup control Business continuity Certificate Confidentiality Corrective control

Data Encryption Standard (DES) Decryption Desktop management

DDoS agent

Disaster recovery firm Distributed denial-of-service (DDoS) attack Encryption Financial

Disaster recovery plan Demilitarized zone (DMZ)

Defer Detective control

Entrapment Financial impact

Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

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Firewall Host-based IPS Integrity

Hacker Impact score Internet Key Exchange (IKE)

IP Security Protocol (IPSec) IPS sensor Kerberos Legal Misuse detection Network address translation (NAT) Online backup Password manager Phishing Pretty Good Privacy (PGP)

IP spoofing IPSec transport mode Key management Malware Mitigate Network-based IPS

Private key Public key infrastructure (PKI) RC4 Redundant array of independent disks (RAID) Risk assessment Risk score Safety Security hole Sniffer program Something you have Symmetric encryption Traffic analysis Traffic filtering Trojan horse

Productivity Public key

Passphrase Patch Plaintext Preventing unauthorized access Public key encryption Ransomware

Recovery control Reputation

Redundancy Risk assessment frameworks

Risk control strategy Rootkit Secure Sockets Layer (SSL) Security policy Social engineering Something you know Threat scenario Traffic anomaly analyzer Traffic limiting Two-factor authentication

User authentication Worm

User profile Zero-day attack

Risk mitigation RSA Secure switch Share Something you are Spyware Threat Traffic anomaly detector Triple DES (3DES) Uninterruptible power supply (UPS) Virus

Packet-level firewall Password Physical security Preventive control

Honey pot Information warfare Intrusion prevention systems (IPSs) IPS management console IPSec tunnel mode Key Mission-critical application NAT firewall One-time password

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Chapter Outline 11.1 Introduction 11.1.1 Why Networks Need Security 11.1.2 Types of Security Threats 11.1.3 Network Controls 11.2 Risk Assessment 11.2.1 Develop Risk Measurement Criteria 11.2.2 Inventory IT Assets 11.2.3 Identify Threats 11.2.4 Document Existing Controls 11.2.5 Identify Improvements 11.3 Ensuring Business Continuity 11.3.1 Virus Protection 11.3.2 Denial-of-Service Protection 11.3.3 Theft Protection 11.3.4 Device Failure Protection 11.3.5 Disaster Protection 11.4 Intrusion Prevention 11.4.1 Security Policy 11.4.2 Perimeter Security and Firewalls 11.4.3 Server and Client Protection 11.4.4 Encryption 11.4.5 User Authentication 11.4.6 Preventing Social Engineering 11.4.7 Intrusion Prevention Systems 11.4.8 Intrusion Recovery 11.5 Best Practice Recommendations 11.6 Implications for Your Cyber Security Summary

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Answers to Textbook Exercises Answers to End-of-Chapter Questions

1. What factors have brought increased emphasis on network security?

Both business and government were concerned with security long before the need for computer-related security was recognized. They always have been interested in the physical protection of assets through means such as locks, barriers, and guards. The introduction of computer processing, large databases and communication networks has increased the need for security. For many people, security means preventing unauthorized access, such as preventing a hacker from breaking into your computer. Security is more than that, however.

It also includes being able to recover from temporary service problems (e.g., a circuit breaks) or from natural disasters (e.g., fire, earthquake).

The factors that have brought increased emphasis on network security are: • • • • • • •

Numerous legal actions involving officers and directors of organizations Pronouncements by government regulatory agencies requiring controls Losses associated with computer frauds are greater on a per incident basis than those not associated with computers Recent highly publicized cases of viruses and criminally instigated acts of penetration Data is a strategic asset The rise of the Internet with opportunities to connect computers anywhere in the world (increased potential vulnerability of the organization's assets) Highly publicized denial-of-service incidents

2. Briefly outline the steps required to complete a risk assessment.

A. Develop risk measurement criteria B. Inventory IT assets C. Identify threats D. Document existing controls E. Identify improvements

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 3. Name and describe the main impact areas. Who should be responsible for assessing what is meant by low/medium/high impact for each of the impact areas? Explain your answer.

1.

2.

3.

4.

5.

Financial – revenue and expenses Productivity – business operations Reputation – customer perceptions Safety – health of customers and employees Legal – potential for fines and litigation

Business leaders should make the decisions on the impact of each impact area because these are business decisions.

4. What are some of the criteria that can be used to rank security risks?

Importance can be based on number of criteria such as which would have the greatest dollar loss, be the most embarrassing, be the most prone to liability judgments, and have the highest probability of occurrence. The relative importance of a threat to your organization depends upon your business. A bank for example, is more likely to be a target of fraud than a restaurant with an electronic marketing site on the Web. The criteria will also depend on the industry in which the organization works.

Some other criteria that can be used to rank risk in a data communication network are: • • • •

Most damaging, most dangerous, most risky.

Most sensitive, most critical to organization, most likely to cause political problems Most costly to recover, most difficult to recover, most time consuming to recover Greatest delay, most likely to occur

5. What are the most common security threats? What are the most critical? Why? Some of the more common security threats include viruses, theft of equipment, theft of information, device failure, natural disaster, sabotage, and denial of services. The most critical will be the ones for a particular organization that have the highest impact score. This will vary based on the industry, geographic locations, etc.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 6. Explain the purpose of threat scenarios. What are the steps in preparing threat scenarios?

Threat scenarios describe how an asset can be compromised by one specific threat. An asset can be compromised by more than one threat, so it is common to have more than one threat scenario for each asset. The purpose is to begin preparation for mitigation of that threat.

In order to prepare for threat scenarios, the following steps must be followed: 1.

2.

3.

4.

name the asset describe the threat explain the consequence (violation of confidentiality, integrity or availability) estimate the likelihood of this threat happening (high, medium, low)

7. What is the purpose of the risk score and how is it calculated?

Risk scores are used to compare the risk scores among all the different threat scenarios to help us identify the most important risks we face. It is calculated by multiplying the impact score by the likelihood (using 1 for low likelihood, 2 for medium likelihood, and 3 for high likelihood).

8. What are the possible risk control strategies? How do we pick which one to use?

The risk control strategies are to accept the risk, mitigate it, share it, or defer it. Selection of a strategy depends on things such as the impact (positive or negative) of the risk, the likelihood of the event occurring, and the cost.

9. Why is it important to identify improvements that are needed to mitigate risks?

It is important to identify improvements that are needed to mitigate risks because risks are always changing and responses (including technologies) are changing as well.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 10. What is the purpose of a disaster recovery plan? What are the five major elements of a typical disaster recovery plan?

A disaster recovery plan should address various levels of response to a number of possible disasters and should provide for partial or complete recovery of all data, application software, network components, and physical facilities. The most important element of the disaster recovery plan are backup and recovery controls that enable the organization to recover its data and restart its application software should some portion of the network fail.

Major elements of a typical disaster recovery plan are: • • • • •

• • • •

.

The name of the decision-making manager who is in charge of the disaster recovery operation. A second manager should be indicated in case the first manager is unavailable.

Staff assignments and responsibilities during the disaster.

A pre-established list of priorities that states what is to be fixed first.

Location of alternative facilities operated by the company or a professional disaster recovery firm and procedures for switching operations to those facilities using backups of data and software.

Recovery procedures for the data communication facilities (WAN, MAN, BN, and LAN), servers and application systems. This includes information on the location of circuits and devices, whom to contact for information, and the support that can be expected from vendors, along with the name and telephone number of the person to contact.

Action to be taken in case of partial damage, threats such as a bomb threat, fire, water or electrical damage, sabotage, civil disorders, or vendor failures.

Manual processes to be used until the network is functional.

Procedures to ensure adequate updating and testing of the disaster recovery plan Storage of the data, software, and the disaster recovery plan itself in a safe area where they cannot be destroyed by a catastrophe. This area must be accessible, however, to those who need to use the plan.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 11. What is a computer virus? What is ransomware?

A computer virus is an executable computer program that propagates itself (multiplies), uses a carrier (another computer program), may modify itself during replication, is intended to create some unwanted event. Viruses cause unwanted events -- some are harmless (such as nuisance messages), others are serious (such as the destruction of data). Most viruses attach themselves to other programs or to special parts on disks. As those files execute or accessed, the virus spreads. Some viruses change their appearances as they spread, making detection more difficult.

Macro viruses, viruses that are contained in documents or spreadsheet files, can spread when an infected file simply is opened. Macro viruses are the fastest growing type of virus, accounting for more than 75 percent of all virus problems.

Ransomware is a special type of malware that takes a victim’s data hostage and demands a ransom to release it. It usually begins when a user downloads a file containing the ransomware or runs a script on a website. The ransomware encrypts all the files on the victim’s computer with a key unknown to the victim, so he or she cannot access the files. The attacker then demands a ransom that must be paid within a day or two or all the files will be deleted.

12. Explain how a denial-of-service attack works.

A DOS attacks works by an attacker attempting to disrupt the network by flooding it with messages so that the network cannot process messages from normal users. The simplest approach is to flood a Web server, mail server, and so on, with incoming messages. The server attempts to respond to these, but there are so many messages that it cannot.

13. How does a denial-of-service attack differ from a distributed denial-of-service attack?

While the source of a denial-of-service (DoS) attack could be a single computer, a distributed denial-of-service (DDoS) attack could involve hundreds of computers on the Internet simultaneously sending messages to a target site. A DDoS hacker plants DDoS agent software on these computers and then controls the agents with DDoS handler software, which can send instructions to the agent software on the computers controlled by the hacker for purposes of launching a coordinated attack.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 14. What is a disaster recovery firm? When and why would you establish a contract with them?

Disaster recovery firms provide second level support for major disasters. Building a network that has sufficient capacity to recover quickly from a major disaster such as the loss of an entire data center is beyond the resources of most firms. Therefore, contracts with disaster recovery firms are established.

Disaster recovery firms provide a full range of services. At the simplest, they provide secure storage for backups. Full services include a complete networked data center that clients can use when they experience a disaster. Once a company declares a disaster, the disaster recovery firm immediately begins recovery operations using the backups stored on site and can have the organization's entire data network back in operations on the disaster recovery firm's computer systems within hours. Full services are not cheap, but compared to the potentially millions of dollars that can be lost per day from the inability to access critical data and application systems, these systems quickly pay for themselves in time of disaster.

15. What is online backup?

Online backup allows you to back up data to a server across the Internet. Generally, software is installed on the client that allows the user to select which files/folders to backup.

16. People who attempt intrusion can be classified into several different categories. Describe them.

There are four types of intruders who attempt to gain unauthorized access to computer networks. The first are casual computer users who have only a limited knowledge of computer security. They simply cruise along the Internet trying to access any computer they come across. Their unsophisticated techniques are the equivalent of trying doorknobs, and only those networks that leave their front doors unlocked are at risk.

The second type of intruders are experts in security, but whose motivation is the thrill of the hunt. They break into computer networks because they enjoy the challenge. Sometimes they also enjoy showing off for friends or embarrassing the network owners. Fortunately, they usually cause little damage and make little attempt to profit from their exploits.

The third type of intruder is the most dangerous. They are professional hackers who break into corporate or government computer for specific purposes, such as espionage or fraud.

Less than 5 percent of intrusions by these professionals are detected, unless of course, they have been hired to destroy data or disrupt the network.

The fourth type of intruder is also very dangerous. These are organization employees who have legitimate access to the network, but who gain access to information they are not authorized to use. This information could be used for their own personnel gain, sold to competitors, or fraudulently changed to give the employee extra income. Most security break-ins are caused by this type of intruder. .

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With a denial-of-service attack, a hacker attempts to disrupt the network by sending messages to the network that prevent other's messages from being processed. The simplest approach is to flood a server with incoming messages. When an external computer sends a message to a computer connected with a proxy server, it addresses the message to the proxy server. The proxy server receives the incoming message, and determines if the packet should be permitted inside. A proxy server receiving the flood of messages will log the attack and discard the messages (does not permit the messages inside.

17. There are many components in a typical security policy. Describe three important components.

Major elements of a security policy are: • • • • • • • •

The name of the decision-making manager who is in charge of security.

An incident reporting system and a rapid response team that to respond to security breaches in progress.

A risk assessment with priorities as to which components are most important.

Effective controls placed at all major access points into the network to prevent or deter access by external agents.

Effective controls placed within the network to ensure internal users cannot exceed their authorized access.

An acceptable use policy that explains to users what they can and cannot do.

A plan to routinely train users on security policies and build awareness of security risks.

A plan to routinely test and update all security controls that includes monitoring of popular press and vendor reports of security holes.

18. What are the major aspects of intrusion prevention?

The three main aspects of preventing unauthorized access in addition to the security policy: securing the network perimeter, securing the interior of the network, and authenticating users.

19. How do you secure the network perimeter?

There are three basic access points into most organizational networks: from LANs, the Internet, and WLANs. One important element of preventing unauthorized users from accessing an internal LAN is through physical security. A firewall is commonly used to secure an organization’s Internet connection. NAT is a common security measure that can be used as well.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 20. What is physical security and why is it important?

Physical security refers to policies and procedures that are designed to prevent outsiders from gaining access to the organization’s offices, server room, or network equipment facilities.

Good security requires implementing the proper access controls so that only authorized personnel can enter closed areas where servers and network equipment are located or access the network. Network components themselves also have a level of physical security.

Computers can have locks on their power switches or passwords that disable the screen and keyboard.

21. What is eavesdropping in a computer security sense?

Eavesdropping refers to the process of unauthorized tapping into a computer network through local cables that are not secured behind walls or in some other manner.

22. What is a sniffer?

A sniffer program records all messages received for later (unauthorized) analysis. A computer with a sniffer program could then be plugged into an unattended hub or bridge to eavesdrop on all message traffic.

23. What is a firewall?

A firewall is a router, gateway, or special purpose computer that examines packets flowing into and out of a network and restricts access to the organization's network. The network is designed so that a firewall is placed on every network connection between the organization and the Internet. No access is permitted except through the firewall. Some firewalls have the ability to detect and prevent denial-of-service attacks, as well as unauthorized access attempts. Two commonly used types of firewalls are packet level, and application level.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 24. How do the different types of firewalls work?

A packet-level firewall examines the source and destination address of every network packet that passes through it. It only allows packets into or out of the organization’s networks that have acceptable source and destination addresses.

An application level firewall acts as an intermediate host computer between the Internet and the rest of the organization’s networks. Anyone wishing to access the organization’s networks from the Internet most login to this firewall, and can then only access the information they are authorized for based on the firewall account profile they access.

The NAT firewall uses an address table to translate the private IP addresses used inside the organization into proxy IP addresses used on the Internet

25. What is IP spoofing?

IP spoofing means to fool the target computer (and any intervening firewall) into believing that messages from the intruder’s computer are actually coming from an authorized user inside the organization’s network. Spoofing is done by changing the source address on incoming packets from their real address to an address inside the organization’s network.

Seeing a valid internal address, the firewall lets the packets through to their destination. The destination computer believes the packets are from a valid internal user and processes them.

The goal of an intruder using IP spoofing is to send packets to a target computer requesting certain privileges be granted to some user (e.g., setting up a new account for the intruder or changing access permission or password for an existing account). Such a message would not be accepted by the target computer unless it can be fooled into believing that the request is genuine.

26. What is a NAT firewall and how does it work?

The NAT firewall (sometimes referred to as a proxy server) uses an address table to translate the private IP addresses used inside the organization into proxy IP addresses used on the Internet.

When a computer inside the organization accesses a computer on the Internet, the NAT firewall changes the source IP address in the outgoing IP packet to its own address.

When the external computer responds to the request, it addresses the message to the NAT firewall's IP address. The NAT firewall receives the incoming message, and after ensuring that the packet should be permitted inside, changes the destination IP address to the private IP address of the internal computer and changes the TCP port id to the correct port id before transmitting it on the internal network. This way, systems outside the organization never see the actual internal IP addresses, and thus they think there is only one computer on the internal network. .

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27. What is a security hole and how do you fix it?

Many commonly used operating system have major security problems (called security holes) well known to potential intruders; UNIX systems are among the worst. Many security holes have been documented and “patches” are available from vendors to fix them, but network managers may be unaware of all the holes or simply forget to update their systems with new patches regularly.

Many security holes are highly technical; for example, sending a message designed to overflow a network buffer, thereby placing a short command into a very specific memory area that unlocks a user profile. Others are rather simple, but not obvious.

Other security holes are not really holes, but simply policies adopted by computer vendors that open the door for security problems, such as computer systems that come with a variety of pre-installed user accounts.

28. Explain how a Trojan horse works.

Trojans are remote access management consoles that enable users to access a computer and manage it from afar. Trojans are often concealed in other software that unsuspecting users download over the Internet. Music and video files shared on the Internet are common carriers of Trojans. When the user downloads and plays the music file, it plays normally and the attached Trojan software silently installs a small program that enables the attacker to take complete control of the user’s computer, so the user is unaware that anything bad has happened.

29. Compare and contrast symmetric and asymmetric encryption.

A symmetric (or single key) encryption algorithm is one in which the key used to encrypt a message is the same as the one used to decrypt it. Both parties to the transmission must possess the same key for encryption and decryption. The key must be kept secret, leading to a need for key management.

An asymmetric algorithm is one in which the key used to decrypt a message is different from the one used to encrypt it. Public key encryption is the most common for asymmetric encryption. , there are two keys. One key (called the public key) is used to encrypt the message and a second, very different private key is used to decrypt the message. The net result is that if two parties wish to communicate with one another, there is no need to exchange keys beforehand. All public keys are published in a directory. Each knows the other's public key from the listing in the public directory and can communicate encrypted information immediately. The key management problem is reduced to the on-site protection of the private key. .

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30. Describe how symmetric encryption and decryption works.

A symmetric algorithm is an algorithm in which the key used to decrypt a particular bit stream is the same as the one used to encrypt it. Using any other key produces plaintext that appears as random as the ciphertext. No keys are exchanged between the sender and the receiver.

Encryption is the process of disguising information into ciphertext, whereas decryption is the process of restoring it to readable form (plaintext). An encryption system has two parts: the algorithm itself and the key, which personalizes the algorithm by making the transformation of data unique. Two pieces of identical information encrypted with the same algorithm but with different keys produce completely different ciphertexts. When using most encryption systems, communicating parties must share this key. If the algorithm is adequate and the key is kept secret, acquisition of the ciphertext by unauthorized personnel is of no consequence to the communicating parties.

31. Describe how asymmetric encryption and decryption works.

In asymmetric encryption and decryption, there are two keys. One key (called the public key) is used to encrypt the message and a second, very different private key is used to decrypt the message. Public key systems are based on one-way functions. Even though you originally know both the contents of your message and the public encryption key, once it is encrypted by the one-way function, the message cannot be decrypted without the private key. One-way functions, which are relatively easy to calculate in one direction, are impossible to "uncalculate" in the reverse direction.

All public keys are published in a directory. When Organization A wants to send an encrypted message to Organization B, it looks through the directory to find its public key. It then encrypts the message using B's public key. This encrypted message is then send through the network to Organization B, which decrypts the message using its private key.

32. What is key management?

Key management is concerned with dispersing and storing keys carefully. Because the DES algorithm is known publicly, the disclosure of a secret key can mean total compromise of encrypted messages. Managing this system of keys can be challenging, especially with symmetric algorithms.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 33. How does DES differ from 3DES? From AES? DES uses a 56-bit key while 3DES uses a 168-bit key (3 x 56). AES uses the Rijndael algorithm and has key sizes of 128, 192, and 256 bits.

34. Compare and contrast DES and public key encryption.

DES is a symmetric algorithm, which means that the key used to decrypt a particular bit stream is the same as the one used to encrypt it. Using any other key produces plaintext that appears as random as the ciphertext. Because the DES algorithm is known publicly, the disclosure of a secret key can mean total compromise of encrypted messages. Managing this system of keys can be challenging.

Public key encryption is inherently different from secret key systems like DES, because it is asymmetric; there are two keys. One key (called the public key) is used to encrypt the message and a second, very different private key is used to decrypt the message. Public key systems are based on one-way functions. Even though you originally know both the contents of your message and the public encryption key, once it is encrypted by the one-way function, the message cannot be decrypted without the private key. One-way functions, which are relatively easy to calculate in one direction, are impossible to "uncalculate" in the reverse direction. Public key encryption is one of the most secure encryption techniques available, excluding special encryption techniques developed by national security agencies.

Note: DES key length is 56 bits (168 bits for 3DES) while private key length for public key encryption is 512 or 1,024 bits.

The American government has tried to develop a policy to require key escrow. With key escrow, any organization using encryption must register its keys with the government. This enables the government, after receiving a legally authorized search warrant, to decrypt and read any messages sent by that organization. Without key escrow, the government is worried that criminal organizations will use encryption to prevent police agencies from performing legally authorized wiretaps. Free speech advocates are concerned that key encryption will be abused by police agencies who will illegally monitor transactions by otherwise innocent citizens. Key escrow is a good idea if it is used to combat the criminal organizations, but key escrow is not a good idea if it increases “big brother” and abuses our right to free speech.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 35. Explain how authentication works.

Public key encryption permits authentication (or digital signatures). When one user sends a message to another, it is difficult to prove legally who actually sent the message. Legal proof is important in many communications, such as bank transfers and buy/sell orders in currency and stock trading, which normally require legal signatures. Thus, a digital signature or authentication sequence is used as a legal signature on many financial transactions. This signature is usually the name of the signing party plus other key-contents such as unique information from the message (e.g., date, time, or dollar amount). This signature and the other key-contents are encrypted by the sender using the private key. The receiver uses the sender’s public key to decrypt the signature block and compares the result to the name and other key contents in the rest of the message to ensure a match.

36. What is PKI and why is it important?

PKI stands for Public Key Infrastructure. PKI refers to the encryption infrastructure that has developed around the most popular form of asymmetric encryption (also called public key encryption) called RSA. RSA was invented at MIT in 1977. The patent expired on the technology in 2000. Since then, many new companies have entered the market and public key software has dropped in price.

Public key encryption is different from symmetric single key systems. Because pubic key encryption is asymmetric, there are two keys. One key (called the public key) is used to encrypt the message and a second, very different private key is used to decrypt the message.

Public key encryption is one of the most secure encryption techniques available.

37. What is CA? A certificate authority (CA) is a trusted organization that can vouch for the authenticity of the person or organization that is using authentication (e.g., VeriSign). A person wanting to use a CA registers with the CA and must provide some proof of identify. There are several levels of certification, ranging from a simple confirmation from valid email address to a complete police-style background check with an in-person interview. The CA issues a digital certificate that is the requestor's public key encrypted using the CA's private key as proof of identify. This certificate is then attached to the user's email or Web transactions in addition to the authentication information. The receiver then verifies the certificate by decrypting it with the CA's public key -- and must contact the CA to ensure that the user's certificate has not been revoked by the CA.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 38. How does PGP differ from SSL? Pretty Good Privacy (PGP) is freeware public key encryption package developed by Philip Zimmermann that is often used to encrypt e-mail. Users post their public key on Web pages, for example, and anyone wishing to send them an encrypted message simply cuts and pastes the key off the Web page into the PGP software, which encrypts and sends the message.

Secure Sockets Layer (SSL) operates between the application layer software and the transport layer. SSL encrypts outbound packets coming out of the application layer before they reach the transport layer and decrypts inbound packets coming out of the transport layer before they reach the application layer. With SSL, the client and the server start with a handshake for PKI authentication and for the server to provide its public key and preferred encryption technique to the client (usually RC4, DES or 3DES). The client then generates a key for this encryption technique, which is sent to the server encrypted with the server's public key. The rest of the communication then uses this encryption technique and key.

39. How does SSL differ from IPSec? SSL differs from IPSec in that SSL is focused on Web applications, while IPSec can be used with a much wider variety of application layer protocols.

40. What are the three major ways of authenticating users? What are the pros and cons of each approach?

The three major ways to authenticate users is to base account access on something you know, something you have, or something you are.

The most common approach is something you know—usually, a password. Requiring passwords provides mid-level security, at best; it will not stop the professional intruder, but it will slow amateurs.

More and more systems are requiring users to enter a password in conjunction with something they have, such as a smart card. Intruders must have access to both before they can break in.

In high-security applications, a user may be required to present something they are—such as a finger, hand, or retina of their eye for scanning by the system. These biometric systems scan the user to ensure that the user is the sole individual authorized to access the network account.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 41. What are the different types of two-factor authentication methods and how do they work?

Two-factor authentication can work in at least four ways: a. An app is used. Once the user logs in to the system, it sends an alert to an app which asks the user to confirm or deny the login b. A one-time password is sent via email or text to the user to include after their normal password c. In addition to a username and password, a user must also present a biometric confirmation d. In addition to a username and password, a user must also present a card (an ID badge with a magnetic strip)

42. Explain how a biometric system can improve security. What are the problems with it?

In high security applications, a user may be required to present something they are, such as a finger, hand, or the retina of their eye for scanning by the system. These biometric systems scan the user to ensure that user is the sole individual authorized to access the network account. While someone can obtain someone else’s password and access card, it is most difficult to acquire another person’s handprint or eye retina print. While most biometric systems are developed for high security users, several low cost biometric systems to recognize fingerprints are now on the market.

43. Why is the management of user profiles an important aspect of a security policy?

Each user’s profile specifies what data and network resources he or she can access, and the type of access allowed (read only, write, create, delete).

44. What is social engineering? Why does it work so well?

Social engineering refers to breaking security simply by asking. For example, hackers routinely phone unsuspecting users and imitate someone else (e.g., a technician, a boss, a network expert) and ask for a password. Most security experts no longer test for social engineering attacks; they know from experience that social engineering will eventually succeed in any organization and therefore assume that hackers can gain access at will to "normal" user accounts. Training end users not to divulge passwords may not eliminate social engineering attacks, but it may reduce its effectiveness so that hackers give up and move on to easier targets.

A skilled social engineer is like a good con artist, he can manipulate people.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 45. What techniques can be used to reduce the chance that social engineering will be successful?

Most security experts no longer test for social engineering attacks; they know from experience that social engineering will eventually succeed in any organization and therefore assume that attackers can gain access at will to normal user accounts. Training end users not to divulge passwords may not eliminate social engineering attacks, but it may reduce its effectiveness so that hackers give up and move on to easier targets. Acting out social engineering skits in front of users often works very well; when a group of employees sees how they can be manipulated into giving out private information, it becomes more memorable and they tend to become much more careful.

46. What is an IPS? Assuming that prevention efforts will not be sufficient to avoid all intrusions, intrusion prevention systems (IPSs) can be used to monitor networks, circuits, and particular applications and report detected intrusions.

47. How does IPS anomaly detection differ from misuse detection?

Anomaly detection compares monitored activities with a known "normal" set of activities for a stable network environment while misuse detection compares monitored activities with signatures of prior known attacks. Anomaly detection looks for extreme changes in certain kinds of behavior while misuse detection guards against a repeat of prior intrusions.

48. What is computer forensics?

Computer forensics is the use of computer analysis techniques to gather evidence for criminal and/or civil trials and includes the following steps: • • • •

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Identify potential evidence.

Preserve evidence by making backup copies and use those copies for all analysis.

Analyze the evidence.

Prepare a detailed legal report for use in prosecutions.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 49. What is a honey pot?

A honey pot is a server that contains highly interesting fake information available only through illegal intrusion to “bait” or "entrap" the intruder and possibly divert the hacker's attention from the real network assets. The honey pot server has sophisticated tracking software to monitor access to this information that allows the organization and law enforcement officials to trace and document the intruder’s actions. If the hacker is subsequently found to be in possession of information from the honey pot, that fact can be used in prosecution.

50. A few security consultants have said fast Internet and wireless technologies are their best friends. Explain.

If the role of the security consultants is to penetrate security, then broadband and wireless technologies offer important advantages. When guided media are used, physical access or proximity is necessary for interception.

As is mentioned in Chapter 3 of the text (Physical Layer), "wireless media (radio, infrared, microwave, and satellite) are the least secure because their signals are easily intercepted."

Chapter 9 (The Internet) also warns regarding wireless LANs: "Because anyone within range of a WLAN can receive transmissions, eavesdropping a serious threat. IEEE 802.11 encrypts all transmissions using a 40-bit encryption scheme so that only those computers that have the key can decode and read the messages." This chapter documents the limitations of a 40-bit key.

Broadband technologies use broadcast signals. The signal in the medium is a composite (in terms of modulation technique and whatever multiplexing is present) of all the separate communications supported by that circuit at the instant of sampling. Anyone with physical access to the circuit can monitor the composite signal and, as in the case of wireless transmission, eavesdrop. In any broadcast protocol, all computers connected to the medium "hear" all the messages but only act to receive and process the messages with their own addresses (respectively) as the destination. You might encourage students to think of the sound in a room (let us say, at a party or social gathering) as everything transmitted through the medium of air. You can hear many conversations. Typically you only answer when someone says your name (= destination address for the utterance!) However, you might overhear some conversation of interest and decide to eavesdrop, even though the conversation is not intended for your ears. Clearly, the broadcast medium has higher security risks.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 51. Most hackers start their careers breaking into computer systems as teenagers. What can we as a community of computer professionals do to reduce the temptation to become a hacker?

Computer professionals can reduce the temptation to become a hacker by increasing the costs involved in the activity. This can be done by rigorously following and enforcing security measures throughout the organization. In addition, professionals can work with high schools and colleges to identify the most promising computer students and get them involved in more productive organizational tasks and projects.

52. Some experts argue that CERT's posting of security holes on its website causes more security break-ins than it prevents and should be stopped. What are the pros and cons of both sides of this argument? Do you think CERT should continue to post security holes?

While CERT's posting obviously disseminate technical information that could inform someone who wished to exploit vulnerabilities (and thus increase risk to those who do not take advantage of the service), it is necessary to help conscientious security operations reduce risk. I assume the information about the security holes would be disseminated by various means (to interested hackers) even if CERT's postings were not available.

The CERT postings reduce the time it takes for potential victims to identify new security hole threats and respond to them, thus helping to reduce the adverse impacts of viruses and worms which can be quickly propagated around the world through the Internet.

53. What is one of the major risks of downloading unauthorized copies of music files from the Internet (aside from the risk of jail, fines, and lawsuits)?

One of the major risks of downloading files of this nature is the potential to introduce a Trojan Horse into the network.

54. Although it is important to protect all servers, some servers are more important than others.

What server(s) are the most important to protect and why?

To answer this question, return to the risk assessment process and ask which server loss will cause the greatest damage to the organization. Is the highest priority assigned to...?

• • • • • •

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Loss of customer/client information Loss of online access Interruption of or loss of support for activity (manufacturing, health care, etc.)

Invasion of privacy/loss of confidentiality Integrity of accounts Proprietary secrets

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova Answers to End-of-Chapter Exercises A. Conduct a risk assessment of your organization’s networks. Some information may be confidential, so report what you can.

Student answers will vary depending on the specific network.

B. Investigate and report on the activities of CERT (the Computer Emergency Response Team).

Student answers will vary. A good source of information is https://www.sei.cmu.edu/about/divisions/cert/.

C. Investigate the capabilities and costs of a disaster recovery service.

Student answers will vary depending on the company selected and the extent of recovery required.

D. Investigate the capabilities and costs of a firewall.

Student answers will vary depending on the type of firewall and the vendor selected. Note that Windows 10 comes with a built-in and free software firewall so you may wish to provide some guidance to your students regarding the type of firewall to research.

E. Investigate the capabilities and costs of an IPS. IPS is an intrusion prevention system. Student answers will vary depending on the vendor selected.

F. Investigate the capabilities and costs of an encryption package.

Student answers will vary depending on the vendor selected.

G. Investigate the capabilities and costs of an online backup service.

Student answers will vary depending on the vendor selected. Note that there are inexpensive consumer versions of cloud backups so you may wish to specify the type of service to research.

H. Is the DMZ dead? Investigate the use of DMZ in organizations. What lessons can organizations learn from the DMZ mechanism?

DMZ is a physical or logical subnetwork that exposes an organization’s external-facing servers (such as Web Server, DNS Server, and Mail Server) to the Internet. The primary purpose of the DMZ is to provide another layer of security to the LAN. Student answers will vary

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova Mini-Cases I. Belmont State Bank Perform a risk assessment.

The steps of the risk assessment include: 1. Develop risk measurement criteria 2. Inventory IT assets 3. Identify threats 4. Document existing controls 5. Identify improvements Step 1: Student answers can vary considerably in such a large case. Following is a sample of what they may consider.

Impact areas Financial

Priority High

Productivity

Medium

Reputation

Medium

Safety Legal

Low Medium

Low Impact

Medium Impact

High Impact An outsider gains control of a server.

The website is affected by a DOS attack and slows customer web responses A security event that affects our bank is headlined in the news A security breach occurs and all of our customer records are potentially accessed.

Step 2: These can be classified as hardware, circuits, network software, client software, org data, and mission-critical applications.

Step 3: Some of the top threats include viruses, theft of equipment and information, device failure, and natural disaster. .

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

Step 4: Existing controls may include: 1. Disaster recovery plan 2. Halon fire system in server room; sprinklers in the rest of building 3. Not on or below ground level 4. UPS 5. Contract guarantees from interexchange carriers 6. Extra fiber backbone laid in different conduits 7. Virus checking software present and updated 8. Extensive user training about viruses and reminders in monthly newsletter 9. Strong password software 10. Extensive user training about password security and reminders in monthly newsletter 11. Application-layer firewall Step 5: Improvements can include any number of updates to controls. An example would include moving from physical keys to card access or biometrics systems.

II.

Western Bank

Design the key security hardware and software the bank should use.

Student answers will vary considerably for this answer. Questions to consider when developing this plan: What assets are being protected? Consider the hardware, software, and encryption options documented in the chapter. Specify any physical security needed. Compare firewalls and NAT proxy servers. Is there a use for dial-in security in this environment? What level of encryption is needed and for what transmissions? Should the bank have a misuse detection or anomaly detection IDS? Does the bank need a honey pot?

The students’ answers should include numerous levels of security. An answer similar to what is seen in Figure 11.16 would be good, with the web server in the DMZ. III.

Classic Catalog Company, Part 1

Perform a risk assessment.

Student answers will vary, but be similar to those in minicase 1.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova IV.

Classic Catalog Company, Part 2

Outline a brief business continuity plan, including controls to reduce the risks in advance and develop a disaster recovery plan.

Have the students develop a business continuity plan that accounts for natural disasters, theft, viruses, and denial-of-service attacks. Use the elements of a good disaster recovery plan given in the chapter to develop a plan for Classic Catalog. Discuss back up procedures, firewall design, employee password procedures and intrusion preventions for this firm. How will you design the redundancy for the company? Do you recommend any outsourcing in this situation?

V.

Classic Catalog Company, Part 3

Outline a brief security policy and controls that would prohibit unauthorized access.

Have students develop a security policy that defines the assets to be protected and the controls needed to do so. Use the figure in the chapter to design the security policy. Consider the physical layout of the company, relative to its networking choices. Would you recommend wireless? How would you ensure the security of the wireless system? What kinds of controls would you recommend to protect the office computers and warehouse computers?

VI.

Classic Catalog Company, Part 4

What patching policy would you recommend for Classic Catalog?

Patching should be done on a regular, automated basis. Most systems today have the capability to automatically update. These updates should be periodically, manually checked to insure that they complete. In addition, network managers may be required to manually update some systems.

Do you anticipate that there will be any security issues associated with the patching of known network flaws? What is a good managerial approach to reducing the corporation’s risk exposure from patching?

Many applications today include automatic patching or updating. These controls should be turned on to allow this. For those applications and systems that don’t offer automatic updates, a schedule should be developed. For operating systems, patches should be searched for weekly. Depending on the level of importance of other applications, the patching schedule may be more or less often.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova VII.

Personal Password Storage and Protection

To help us not forget our many passwords, several companies provide password managers. Find the top five password manager programs, compare their features and costs, and make a presentation of your findings to your classmates.

Additional Content Teaching Notes I usually spend 4 hours of class time on this chapter.

My goals in this chapter are to discuss specific technologies and approaches to security. Risk assessment sounds more exciting than it really is. I try to express the importance of it on the students, even though it is a bit mundane. Likewise, you could describe some of the organizations that can be hired to test security.

I try to emphasize the need for controls to address risks due to disruption, destruction, and disaster. Most students overlook these because preventing unauthorized access is much sexier and gets more attention from them and from the popular press. Unauthorized access is important, but it is less likely to occur than disruption, destruction, and disaster. Most organizations would cease to function without their networks, so networks are their lifeblood. One disaster that takes out the network can bankrupt the company if there is no recovery plan. I try to ensure that students can differentiate among controls to prevent problems, detect problems, and correct problems. Each is important, but the emphasis is different.

Security to prevent unauthorized access remains a rapidly changing area. Threats from outside have increased as the Internet has become a regular part of most organizations, and are approximately equal to the very real threat from the inside from current or former employees.

Firewalls and proxy servers are interesting discussion topics. I use the section on proxy servers to reinforce the TCP/IP and Internet concepts from earlier chapters. This is a hot area to watch, given the many new security holes discovered in commercial products and news stories about break-ins and worms. Network security in general and firewalls in particular are likely to change over the next few years and bear watching closely. The students can share information about their experiences with different virus check software packages and personal firewalls. A sniffer demonstration (if this can be arranged with help from your campus computer center) dramatically illustrates the vulnerability of data transmissions in networks. Likewise, having two-student role-play a social engineering episode can be very powerful (you could use the Focus box in the text as a pseudo script).

One of the most striking things to me is how the number of security incidents keeps growing.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova I recommend students visit appropriate web sites and discuss what they find there: • • •

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https://www.microsoft.com/en-us/security/ www.cert.org - the CERT® Coordinator Center at the Software Engineering Center, Carnegie Mellon University csrc.nist.gov/ - The National Institutes of Standards and Technology web site on Computer Resource Security

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova War Stories Backups Aren't Fool-Proof (Objective: illustrate the importance of disaster recovery drills) In August 1995, a fire destroyed our building at The University of Georgia. The fifth floor was completely destroyed by fire, and the remaining floors were badly damaged by 1.5 million gallons of water (it took 100 firefighters 8 hours to put out the fire). Our two Web servers were destroyed, but we had off-site backups, exactly as planned.

The first Web server backup was stored on another server in the Computer Science building. The morning after the fire, we got permission from the library to use their Web server. We simply downloaded our directory structure onto their Web sever and changed the University DNS server so that any request for our Web server was answered with the IP address for the library's Web server (we also changed their home page to provide a link to our new home page on their server, along with an explanatory note as to what had happened). The server was back up in less than 24 hours. When our network was restored 5 weeks later, we simply moved everyone back to our new server and changed the University DNS server entry back to our new IP address. No problems.

Break-in on Ginger (Objective: describe a specific security break-in via a security hole) Ginger is a UNIX Web server and mail server in our department that is used by a few faculty and students. One of those students, who ironically was taking my telecom class and doing a group project on network security, decided to break-in to Ginger. We were running an old version of UNIX with a security hole that we didn't know about. It turns out that anyone with an account on the server could access the password file for the entire computer. Even though the file was encrypted, this was still a big security hole.

The student copied the file onto a diskette and took it home. He used Crack, a software tool available on the Internet, to decrypt the password file. Crack is not very efficient, but if you let it run for a few days, it is often successful at decrypting passwords. In this case, it worked. The student was able to get the root password (i.e., the system administrator's password). Fortunately, all he did was poke around, but he could have destroyed the entire system.

Ginger was configured so that no one could log in as root (i.e., the system administrator) without first logging into a regular user account. Ginger was also configured to record all log-ins to the root account and the network administrator routinely checked the log files for unusual activity (which is not often done in most organization). He discovered that someone had logged into the root account after midnight one weekend. He knew he didn't do it and checked with the only other person with root access and discovered that he had not either. A quick check of the log files revealed that the student had logged into the root account from his own account. Had he used someone else's account or erased the file, it still would have been discovered, but would have been much harder to identify the hacker.

When confronted with the evidence, he quickly confessed, and implicated an accomplice (another student). For some unknown reason, the University student disciplinary board was extremely reluctant to prosecute the pair under the University's computer hacking policy. The .

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova only alternative was to notify the FBI and have them prosecuted under the Federal hacking law (a felony) which seemed too extreme. No action was taken.

Break-in on Blaze (Objective: describe a specific security break-in via a bad user password) Blaze is a UNIX Web server and mail server in our department that is used by a most of our faculty and a few students (it got its name after our fire). As part of our routine security detection process we log all telnet accesses and periodically check to see if the accesses seem reasonable.

One check indicated a lot of logins from Romania and Japan to accounts held by two of our faculty. We immediately checked with the account owners and quickly found that they were not in Japan or Romania and had not authorized users from there to access their accounts. The users whose account had been broken into had chosen very poor passwords (e.g., dawgs, the slang name of our football team and an easy word to guess).

We were not completely sure that password guessing had been the means of attack and did not know the extent of the penetration. Therefore, we took the server down, installed the newest version of the operating system (which had patched several security holes in the old version), and recreated all user accounts. We put in a new password security system that forced users to select passwords that were not words in a dictionary. Quite naturally, there was some user resistance but we felt that security concerns outweighed ease of use considerations.

AT&T Network Outage (Objective; illustrate the need for a disaster recovery plan) In early April 1998, AT&T's frame relay network in the United States crashed due to a broadcast storm. The problem started when a technician updated software on one of the 145 Cisco frame relay switches in the AT&T network. The switch software contained a bug that did not prevent a "loopback," a situation in which the switch receives its own broadcast message (you will recall that until recently, broadcast messages were unusual in switched networks, so much of this type of switch software had not been really tested in the field). The switch retransmitted the same broadcast message to other switches, and to itself. It turned out that all of the Cisco switches had the same bug so the entire network suddenly began transmitting and retransmitting the same broadcast message until the network collapsed.

It took more than a day to restore service to customers. For that day, businesses that depended on the network and had no disaster recovery plan could not do business. Many travel agents were unable to make bookings or check their customers' reservations. MasterCard, one of AT&T's largest frame relay customers, had a disaster recovery plan in place and a series of redundant circuits leased from another carrier. When AT&T's network failed, it switched over to the redundant circuits and continued to operate. MasterCard customers noticed only slight delays.

As well as being troublesome and embarrassing, to both Cisco and AT&T, the outage cost AT&T millions of dollars. AT&T had service level agreements (SLA) with most customers guaranteeing 99.99% network availability and promising to restore lost service within four hours.

Because the outage exceeded the SLA, AT&T was required to pay penalties to customers.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova Redundancy is Important, Even in Cabling (Objective: illustrate why redundancy is needed) Our college of business network is composed of networks in three adjacent buildings: Caldwell Hall (a classroom building), Brooks Hall (faculty offices), and Sanford Hall (classrooms). All but one server (file servers, Web servers, and mail servers) were located in Caldwell Hall. The original network design called for all three buildings to be connected to the campus backbone and to be connected to each other via our own college-wide internal backbone (see the figure below). However, due to cost considerations not all segments were actually built.

As Designed

Caldwell Hall

Brooks Hall

As Implemented

Sanford Hall

Campus Backbone

Caldwell Hall

Brooks Hall

Sanford Hall

Campus Backbone

In early 1998, a backhoe cut the cable linking Caldwell Hall to the campus backbone. Suddenly, almost all of our severs were cut off from the Internet and from the rest of the college. The cable was restored in two days, but for those two days, none of the new electronic classrooms in Sanford Hall could access course material on our servers and none of the electronic classrooms in Caldwell Hall could access the Internet. Faculty and staff could only access their email from the classrooms and labs in Caldwell Hall, and even then could only send and receive mail to and from people on the same server.

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CHAPTER 12 NETWORK MANAGEMENT Chapter Summary Network managers perform two key tasks: (1) designing new networks and network upgrades and (2) managing the day-to-day operation of existing networks. The prior chapters have examined network design, so this chapter focuses on day-to-day network management, discussing the things that must be done to ensure that the network functions properly, although we do discuss some special-purpose equipment designed to improve network performance. Our focus is on the network management organization and the basic functions that a network manager must perform to operate a successful network.

Learning Objectives • • • • • •

Understand what is required to manage the day-to-day operation of networks Be familiar with the network management organization Understand configuration management Understand performance and fault management Be familiar with end-user support Be familiar with cost management

Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

Key Terms Agent Alarm storm Availability Cache engine Cluster Content delivery Cost management Downtime Firefighting Managed device Mean time between failures (MTBF) Mean time to repair (MTTR) Network cost of ownership (NCO) Network management software Performance management Problem tracking RMON probes Service-level agreement (SLA) Total cost of ownership (TCO) Trouble ticket

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Akamai Application management software Bandwidth limiter Capacity management Configuration management Content delivery provider Desktop management End user support Help desk Managed network Mean time to diagnose (MTTD) Mean time to respond (MTTR) Network documentation

Alarm Application shaping Bandwidth shaper Charge-back policy Content caching Content engine Device management software Fault management Load balancer Management information base (MIB) Mean time to fix (MTTF) Monitor Network management

Network monitoring

Network operations center (NOC) Policy based management Problem statistics Real TCO Remote monitoring (RMON) Root cause analysis Service farm Simple Network Management System management software Protocol (SNMP) Traffic shaper Traffic shaping Uptime

Virtual server

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

Chapter Outline 12.1 Introduction 12.2 Designing for Network Performance 12.2.1 Managed Networks 12.2.2 Managing Network Traffic 12.2.3 Reducing Network Traffic 12.3 Configuration Management 12.3.1 Configuring the Network and Client Computers 12.3.2 Documenting the Configuration 12.4 Performance and Fault Management 12.4.1 Network Monitoring 12.4.2 Failure Control Function 12.4.3 Performance and Failure Statistics 12.4.4 Improving Performance 12.5 End User Support 12.5.1 Resolving Problems 12.5.2 Providing End User Training 12.6 Cost Management 12.6.1 Sources of Costs 12.6.2 Reducing Costs 12.7 Implications for Cyber Security Summary

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova

Answers to Textbook Exercises Answers to End-of-Chapter Questions

1. What skills does a network manager need?

The books provides the following list: • • • • • • • • • • •

Strong technology skills in a variety of technologies LAN/WAN networking experience working with routers and switches Experience with Internet access solutions, including firewalls and VPN Network architecture design and implementation experience Information security experience Personnel management experience Project management experience Experience working in a team environment Ability to work well in an unstructured environment Excellent problem-solving and analytical skills Effective written and oral communication skills

2. What is firefighting?

Many network managers spend most of their time firefighting -- dealing with breakdowns and immediate problems. If managers do not spend enough time on planning and organizing the network and networking staff, which are needed to predict and prevent problems, they are destined to be reactive rather than proactive in solving problems.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 3. Why is combining voice and data a major organizational challenge?

A major organizational challenge is the prospect of combining the voice communication function with the data and image communication functions. Traditionally, voice communications were handled by a manager in the facilities department who supervised the telephone switchboard systems and coordinated the installation and maintenance of the organization's voice telephone networks. By contrast, data communications traditionally were handled by the IT department because the staff installed their own communication circuits as the need arose, rather than contacting and coordinating with the management staff for voice communications.

This separation of voice and data worked well over the years, but now changing communication technologies are causing enormous pressures to combine these functions.

These pressures are magnified by the high cost of maintaining separate facilities, the low efficiency and productivity of the organization's employees because there are two separate network functions, and the potential political problems within an organization when neither manager wants to relinquish his or her functional duties or job position. A key factor in voice/data integration might turn out to be the elimination of one key management position and the merging of two staffs.

4. Describe what configuration management encompasses.

Configuration management means managing the network’s hardware and software configuration and documenting it (and ensuring it is updated as the configuration changes).

Configuration management is concerned with knowing what hardware and software is where.

One of the most common configuration activities is adding and deleting user accounts. When new users are added to the network, they are usually categorized as being a member of some group of users (e.g., faculty, students, accounting department, personnel department). Each user group has its own access privileges, which define what file servers, directories, and files they can access and provide a standard login script.

Another common activity is updating the software on the client computers attached the network. Every time a new application system is developed or updated (or, for that matter when a new version of networking software is released) each client computer in the organization must be updated.

Configuration documentation includes information about network hardware, network software, user and application profiles, and network documentation. The most basic information about network hardware is a set of network configuration maps that document the number, type, and placement of network circuits (whether organization owned or leased from a common carrier), network servers, network devices (e.g., hubs, routers), and client computers. Documentation for network software includes the network operating system (NOS) and any special purpose network software.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova The third type of documentation is the user and application profiles, which should be provided automatically by the network operating system or additional vendor or third-party software agreements. These should enable the network manager to easily identify the files and directories to which each user has access and their access rights (e.g., read-only, edit, delete).

In addition, other documentation pertaining to the network must be routinely developed and updated. This includes network hardware and software manuals, application software manuals, standards manuals, operations manuals for network staff, vendor contracts and agreements, and licenses for software. The documentation should include details about performance and fault management (e.g., preventive maintenance guidelines and schedules, disaster recovery plan, and diagnostic techniques), end user support (e.g., applications software manuals, vendor support telephone numbers), and cost management (e.g., annual budgets, repair costs for each device). The documentation should also include any legal requirements to comply with local or federal laws, control, or regulatory bodies.

5. People tend to think of software when documentation is mentioned. What is documentation in a network situation?

Documentation in a network situation is mandatory and includes: • • • • • • • • • • • •

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inventory of network hardware and equipment network configuration and maps maintenance records software listings by hardware and network tasks software documentation manuals user names and telephone numbers vendor names and telephone numbers contracts legal requirements operating manuals disaster plan and recovery techniques troubleshooting techniques

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 6. What is desktop management, and why is it important?

Desktop management (DM), sometimes called Electronic Software Delivery (ESD) or automatic software distribution, is one solution to the configuration problem. DM enables network managers to install software on client computers over the network without needing individual access to each client computer. Most DM packages provide application layer software for the network server and all client computers. The server software communicates directly with the DM application software on the clients and can be instructed to download and install certain application packages on each client at some predefined time (e.g., at midnight on Saturday).

DM software greatly reduces the cost of configuration management over the long term because it eliminates the need to update manually each-and-every client computer. It also automatically produces and maintains accurate documentation of all software installed on each client computer and enables network managers to produce a variety of useful reports.

However, DM increases costs in the short term because it costs money (typically $50-100 per client computer) and requires network staff to install manually it on each client computer.

The other problem with DM is that currently there are no standards. Standards are beginning to emerge (e.g., Desktop Management Interface (DMI)), but so far they have not been widely embraced.

7. What is performance and fault management?

Performance management means ensuring the network is operating as efficiently as possible.

Improving network performance is its essence. Several strategies for improving performance were discussed in previous chapters.

Fault management means preventing, detecting, and correcting faults in the network circuits, hardware, and software (e.g., a broken hub or improperly installed software). Fault management and performance management are closely related, because any faults in the network reduce performance. Both require network monitoring, which means keeping track of the operation of network circuits and devices to ensure they are functioning properly and to determine how heavily they are used.

8. What does a help desk do?

Failure control is handled by the network support group (often starting with a help desk) that is called when anything goes wrong in the network. This group has appropriate customer service representatives to record problems, report them to the testing and problem management group, follow up, and generally ensure that the network is back in operation as soon as possible. This group also might be responsible for change scheduling, coordination, and follow-up on any changes, whether they involve hardware, software, or circuits. In other words, this is the user's interface when there is a problem of any kind.

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9. What do trouble tickets report?

Numerous software packages are available for recording fault information. The reports they produce are known as trouble tickets. The software packages assist the help desk personnel so they can type the trouble report immediately into a computerized failure analysis program.

They also automatically produce various statistical reports to track how many failures have occurred for each piece of hardware, circuit, or software package. There are four main reasons for trouble tickets: problem tracking, problem statistics, problem-solving methodology, and management reports.

Trouble tickets report on: • • • • • • • • •

who reported the problem the telephone number of the reporting the problem time and date of the problem (not the time of reporting) location and nature of the problem when the problem was identified why and how the problem happened who is responsible for correcting any outstanding problems what is the status of the problem the priority of the problem

10. Several important statistics related to network uptime and downtime are discussed in this chapter. What are they and why are they important?

The statistics related to network uptime and downtime are: •

•

•

.

mean time to diagnose (MTTD) • measures the efficiency of the in-house testing and problem management personnel • can be used to evaluate the ability of network personnel to isolate and diagnose failure of hardware, software, or circuits and can often be improved by training mean time to respond (MTTR) • indicates how quickly vendors and internal groups respond to emergencies • can lead to a change of vendors or internal management policies, or, at the minimum, can exert severe pressure on vendors who do not respond to problems promptly • can be influenced by showing vendors or internal groups how good or bad their response times have been in the past mean time to fix (MTTF) • measures how long it takes the vendor or internal support group to correct the problem once they arrive on the premises

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova • • •

can be affected by the use of redundant interface equipment, alternate circuit paths, adequate recovery or fallback procedures to earlier versions of software, and the technical expertise of internal or vendor staff mean time to repair • MTTRepair = MTTDiagnose + MTTRespond + MTTFix mean time between failures (MTBF) • indicates the reliability of a network component • developed by equipment vendors to tell customers how frequently their equipment fails (this is the number of hours or days of continuous operation before the component fails) • can be influenced by the original selection of vendor-supplied equipment

Because these mean times affect network availability, their collection is vital if network performance is to be improved. Availability is the percentage of time the network is available to users. It is calculated as the number of hours per month the network is available divided by the total number of hours per month (i.e., 24 hours per day x 30 days/month = 720 hours).

Another set of statistics that should be gathered are those collected daily by the network operations group who employ automated network management software (network monitors and analyzers). These statistics record the normal operation of the network, such as the number of errors (retransmissions) per communication circuit, per terminal, or whatever is appropriate. Statistics also should be collected on the daily volume of transmissions (characters per hour) for each communication link or circuit, each terminal, or whatever is appropriate for the network. It is important to monitor closely utilization rates, the percentage of the theoretical capacity that is being used. These data can identify computers/devices or communication circuits that have higher-than-average error rates, and may be used for predicting future growth patterns and failures. A device or circuit that is approaching maximum utilization obviously needs to be upgraded.

11. What is an SLA? More organizations are beginning to establish service level agreements (SLA) with their common carriers and Internet service providers. An SLA specifies the exact type of performance and fault conditions that the organization will accept. For example, the SLA might state that network availability must be 99 percent or higher and that the MTBF for T1 circuits must be 120 days or more. In many cases, SLA includes maximum allowable response times. Some organizations are also starting to use an SLA internally to clearly define relationships between the networking group and its organizational "customers."

Specifically, it should include at least the following: • • • • • .

Network availability Average round-trip PVC delay PVC throughput MTTR MTTF Page 8

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12. How is network availability calculated?

Network availability is the percentage of time the network is available to users. It is calculated, by using the various mean times, as the number of hours per month the network is available divided by the total number of hours per month (i.e., 24 hours per day x 30 days/month = 720 hours). Availability includes all components of the network that are required for the network to be up and operating (modems, circuits, and so forth).

13. What is problem escalation?

Problem escalation is the increase in severity and scope of a problem caused when the initial problem or error situation is not resolved quickly and efficiently. Staff members who handle escalated problems have specialized skills in certain problem areas or with certain types of software and hardware.

14. What are the primary functions of end user support?

Providing end user support means solving whatever problems users encounter while using the network. There are three main functions within end user support: resolving network faults, resolving software problems, and training.

15. What is TCO? The total cost of ownership (TCO) is a measure of how much it costs per year to keep one computer operating. TCO includes the cost of support staff to attach it to the network, install software, administer the network (e.g., create user ids, backup user data), provide training and technical support, and upgrade hardware and software. It also includes the cost of time "wasted" by the user when problems occur or when the user is attempting to learn new software.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 16. Why is the TCO so high?

While TCO has been accepted by many organizations, other firms argue against the practice of including "wasted" time in the calculation. Some organizations therefore prefer to focus on costing methods that examine only the direct costs of operating the computers, omitting softer costs such as "wasted" time. The most expensive item is personnel (network managers and technicians), which typically accounts for 50 to 70 percent of total costs. The second most expensive cost item is WAN circuits, followed by hardware upgrades and replacement parts. The largest time cost (where staff spend most of their time) is systems management, which includes configuration, fault, and performance management tasks that focus on the network as a whole. The second largest item is end user support.

There is one very important message from this pattern of costs. Since the largest cost item is personnel time, the primary focus of cost management lies in designing networks and developing policies to reduce personnel time, not to reduce hardware cost. Over the long term, it makes more sense to buy equipment that is more expensive if it can reduce the cost of network management.

17. How can network costs be reduced?

Network costs can be reduced by taking these steps: • • • • •

Develop standard hardware and software configurations for client computers and servers Automate as much of the network management function as possible by deploying a solid set of network management tools Reduce the costs of installing new hardware and software by working with vendors Centralize help desks Move to thin client architectures

18. What do network management software systems do and why are they important?

Network management software is designed to provide automated support for some or all of the network management functions. Network management software systems are used to perform some of the functions of monitors and analyzers, identify errors, run diagnostic tests, monitor entire an network, compile statistics, and prepare real-time management reports.

Network management software systems are important because they signify improved or deteriorating conditions.

There are dozens of network management tools available. Some software tools support configuration management, some support performance and fault management, while some attempt to do both. Some tools have modules to support the help desk providing end user support.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 19. What is SNMP and RMON? The most commonly used network management protocol is Simple Network Management Protocol (SNMP). Each SNMP device (e.g., router, switch, server) has an agent that collects information about itself and the messages it processes and stores that information in a database called the management information base (MIB).The network manager’s management station that runs the network management software has access to the MIB. Using this software, the network manager can send control messages to individual devices or groups of devices asking them to report the information stored in their MIB. RMON allows for remote monitoring of equipment. RMON SNMP software enables MIB information to be stored on the device itself or on distributed RMON probes that store MIB information closer to the devices that generate it. The data are not transmitted to the central server until the network manager requests, thus reducing network traffic.

20. Compare and contrast device management software, system management software, and application management software.

Device management software provides information about the specific devices on a network. It enables the network manager to monitor important devices such as servers, routers, and switches, and switches and to report configuration information, traffic volumes, and error conditions for each device.

System management software provides the same configuration, traffic, and error information as device management systems but can analyze the device information to diagnose patterns, not just display individual device problems.

Application management software also builds on the device management software, but instead of monitoring systems, it monitors applications.

21. How does a load balancer work?

A load balancer acts as a traffic manager at the front of the server farm. All requests are directed to the load balancer at its IP address. When a request hits the load balancer, it forwards it to one specific server using the server’s IP address. Sometimes a simple round-robin formula is used, while in other cases, formulas that are more complex track how busy each server actually is.

22. What is server virtualization?

Server virtualization is the process of utilizing one physical server and using special software, creating multiple virtual computers that each run their own separate operating system.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova 23. What is policy-based management?

Policy-based management allows the network manager to use special software to set priority policies for network traffic that take effect when the network becomes busy. It is usually implemented as a combination of hardware and software.

24. What is capacity management?

Capacity management is used to monitor traffic and can slow down traffic from users who consume a lot of network capacity. Capacity management is related to policy-based management but is simpler in that it only looks at the source of the traffic rather than the nature of the traffic.

25. How does content caching differ from content delivery?

Content caching is used to store other people’s Web data closer to your users. Content delivery is the opposite. Rather than storing other people’s web files closer to their own internal users, a content delivery provider stores web files for its clients closer to their potential users.

26. How does network cost of ownership (aka real TCO) differ from total cost of ownership? Which is the most useful measure of network costs from the point of view of the network manager?

Why? The total cost of ownership (TCO) for typical networked PCs is about $7,000 per year per computer, far more than the initial purchase price. The network management cost (omitting "wasted" time) is between $1500 and $3500 per year per computer. The largest single cost item is staff salaries.

27. Many organizations do not have a formal trouble reporting system. Why do you think this is the case?

Typically, size, application diversity and volume of traffic determine whether a formal trouble reporting system is required. All large organizations with heterogeneous type networks require a formal trouble reporting system because the annual cost of maintenance demands it.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova Answers to End-of-Chapter Exercises A. What factors might cause peak loads in a network? How can a network manager determine if they are important, and how are they taken into account when designing a data communications network?

Answers will vary but might include some or all of the following: • • • • • • • •

Too many hosts are in a single broadcast domain Not having adequate bandwidth Adding retransmission hubs Using multicasting Using old or outdated hardware Having poor configuration management Having foreign devices on your network Using Border Gateway Protocol

B. Today’s network managers face a number of demanding problems. Investigate and discuss three major issues.

Answers will vary but might include some or all of the following: • • • • • •

Network security Poor network performance (See Part A) Configuration management (also mentioned in Part A) The Budget Handling the growth of demand for the network Being locked into your existing vendors

C. Research the networking budget in your organization and discuss the major cost areas.

Discuss several ways of reducing costs over the long term.

Student answers will vary.

D. Explore the traffic on the networks managed by the Indiana University NOC as noc.net.internet2.edu. Compare the volume of traffic in two networks and how close to capacity the networks are.

Student answers will vary.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova E. Investigate the latest versions of SNMP and RMON and describe the functions that have been added in the latest version of the standard.

Student answers will vary. Information on SMNP can be found at http://www.snmp.com/protocol/ and https://www.paessler.com/it-explained/snmp.

Information on RMON can be found at https://support.huawei.com/enterprise/en/doc/EDOC1000102433?section=k005.

F. Investigate and report on the purpose, relative advantages, and relative disadvantages of two network management software tools.

Student answers will vary.

G. If a common carrier guarantees 99% reliability, how many hours a year will the circuit be down? How about 99.5%, 99.9%, 99.99%? Improved reliability comes with increased cost.

What is the minimum reliability most firms should consider?

There are 8,760 hours in a year. At 99 percent reliability, you have 1% “unreliability.” That translates into 8,760 × 0.01 = 87.6 hours of downtime. The other values are 99.5% (43.8 hours), 99.9% (8.76 hours), and 99.99% (0.876 hour).

Answers regarding minimum reliability will vary widely. Look for good justification of their selection.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova Mini-Cases

I. City School District, Part 1 City School District is a large, urban school district that operates 27 schools serving 22,000 students from kindergarten through grade 12. All schools are networked into a regional WAN that connects the schools to the district central office and each other. The district has a total of 5,300 client computers. The table below shows the annual costs. Calculate the real TCO (without wasted time).

Budget Item Annual Cost IT staff salaries $7,038,400 Consultants 1,340,900 Software 657,200 Staff training 545,900 Client computers 2,236,600 Servers 355,100 Network 63,600 Supplies and parts 2,114,700 Total Costs = $14,352,400 Client Computers = 5,300 TCO = $2,708 II. City School District, Part 2 Read and complete Minicase I. Examine the TCO by category. Do you think that this TCO indicates a well-run network? What suggestions would you have?

This TCO total indicates a well-run network. Research has estimated that the TCO of a Windows-based client computer averages $7,000/year. The School District TCO of $2,708 is well below that figure.

III. Central Textiles Central Textiles is a clothing manufacturer that operates 16 plants throughout the southern United States and in Latin America. The Information Systems Department, which reports to the vice president of finance, operates the central mainframe and LAN at the headquarters building in Spartanburg, South Carolina, and the WAN that connects all the plants. The LANs in each plant are managed by a separate IT group at each plant that reports to the plant manager (the plant managers report to the vice president of manufacturing).The telephone communications system and long-distance agreements are managed by a telecommunications department in the headquarters that reports to the vice president of finance. The CEO of Central Textiles has come to you asking about whether this is the best arrangement, or whether it would make more sense to integrate the three functions under one new department. Outline the pros and cons of both alternatives. .

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Integrating the three systems under one department would consolidate some of the management issues, and likely would allow for some headcount (cost) reduction. Centralization would also ensure that decisions taken about system upgrades and/or expansions will consider the systems in place in the other areas.

On the other hand, consolidating each system in one department might result in poorer services at the local level. For example, it may take longer for a centralized unit to respond to a trouble ticket on a local LAN than would a decentralized office on site where the problem is occurring.

IV. Indiana University Take another look at Figure 12-1. If this is a typical traffic pattern, how would you suggest that they improve performance?

They could increase performance by adding circuit capacity between devices that have higher circuit utilization.

Additional Content Teaching Notes Plan to spend about 4 hours on this chapter. It is suggested that the course include a network simulation exercise. See this book’s Web Site.

My goals in this chapter are to outline the primary tasks that a network manager must do, as well as to introduce the idea of a managed network. I spend only a little time on the different cultures between LANs and WANs, but I think it is an issue that students entering the work force need to be sensitive to.

Most of the material is fairly straightforward. I use the LAN outage war story below as a lead-in to the need for managed networks. I pose the problem and help the students trace the cause and mentally walk through what they would do without SNMP. Cost management (total cost of ownership (TCO)) has emerged as a crucial issue over the past few years. I spend some time making sure the students understand the TCO measure and tradeoffs in using it. Cost management will continue to be a hot topic that will need to be watched over the next few years. We are likely to see several new technologies emerge that attempt to reduce TCO.

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Instructor’s Manual to Accompany: Business Data Communications and Networking, 14e by Fitzgerald/Dennis/Durcikova War Stories LAN Outage (Objective: illustrate the need for managed networks) During the summer of 1995, I hosted a meeting of 20 senior consultants from CSC that were using our GSS software to perform a major reengineering project for the U.S. Department of Defense. Suddenly, the network crashed, making it impossible for us to work.

The network technicians went to work and tried to find the problem. Unfortunately, we had an unmanaged network, meaning the techs had to do their own trouble shooting. After several hours, it became clear that something was jamming the entire Ethernet LAN -- there was a constant stream of traffic being generated. This suggested that a network card was "jabbering," that is, transmitting constantly. The techs went around turning off all computers one by one until the problem stopped. Once they had identified the computer, it was simple to replace the failed network card and the network was restarted. However, it took 18 hours to find the failed computer. Needless to say, the CSC folks were not impressed.

ESD in the University (Objective: illustrate the practical uses of ESD) One of the constant problems we have had (and I suspect your university has as well), is ensuring that the computers in our labs are not changed by students. Our students were often changing the Windows configurations, adding software and putting wallpaper on the computers that we did not want. We developed our own homegrown solution to reset the computers. We have since switched to a commercial ESD tool, which simplifies upgrades as well as resetting software and configuration files when they are first booted in the morning.

Network Growth versus Staff Growth (Objective: illustrate the crisis in staffing) In 1995, the College of Business at the University of Georgia had 5 servers, 250 client computers, 200 network connections, and 4 electronic classrooms. Today in mid-1998, we have 30 servers, 600 client computers, 2200 network connections (most are designed for use by portable computers) and 25 electronic classrooms.

In 1995, we had nine full-time staff members, while today we have ten. Annual turnover has averaged 30% per year. Simply put, we are having a difficult time keeping up with the network growth. While faculty and staff have lobbied hard for increased network staff, our administration has not committed the needed resources to add staff. As we look around campus here at Georgia, the story is similar to what is occurring in other colleges, although we tend to be a bit more advanced than most. .

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