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p21-36:p26-32.qxd 09/12/2010 13:34 Page 11 Digital Ship Lightweight Ethernet – a new standard for shipboard networks The International Electrotechnical Commission’s TC80 working group has developed a new standard for the use of Ethernet in maritime navigation networks. Nicknamed ‘Lightweight Ethernet’ (LWE), this standard offers a number of potential benefits in the construction of shipboard networks, write Morten Jagd Christensen, Thrane & Thrane, and Ørnulf Jan Rødseth, MARINTEK he International Electrotechnical Commission (IEC) is an organisation responsible for developing standards for electrical, electronic and related technologies. As part of this responsibility, working group 6 (Digital Interfaces) of IEC’s Technical Committee 80 ‘Maritime Navigation and Radiocommunication Equipment and Systems’, has developed a new computer network standard for use of Ethernet in maritime navigation networks. This standard is the result of the collaborative and consensus based work of the participants of the working group, as well as numerous technical comments and proposals from IEC’s national member organisations. The official standard will be named IEC 61162-450 ‘Multiple talkers and multiple listeners - Ethernet interconnection’. Within the working group the nickname ‘Lightweight Ethernet’ (LWE) has been in common use, and this article continues that tradition. Here we will present some background information and selected details from the standard. T Background Ethernet has been in use onboard ships for a long time and various standards have been suggested since before 1995, when IEC TC80 started to work on this issue. The first specification was of a redundant network system based on Ethernet and TCP/IP. This was adopted as an international standard in 2001 and got the designation IEC 61162-400. Unfortunately, the specification proved too complex for the industry to adopt and lack of high quality protocol implementations led to the standard’s silent demise. However, the need for a high capacity and high speed bridge data network was more and more acutely felt, and in 2008 a new work item was approved by IEC TC80 to develop a new Lightweight Ethernet standard. The selection of Ethernet and Internet Protocol (IP) based data transport layers reflects a general trend with a convergence to Ethernet-like technologies everywhere. Today even very small devices can have support for Ethernet at almost negligible cost. Ethernet has been able to quickly respond to the hunger for bandwidth, which is growing as fast as ever, but at the same time has kept a backwards compatibility to lower speeds. Today, identical Ethernet frames can be transported at link speeds from 10Mbps to 10Gbps over electrical and optical cables. Ethernet is also able to supply power with the ‘Power over Ethernet’ (PoE) standards. This feature is a relatively new addition to the Ethernet family that could potentially cut the cabling used for installation in half, compared with the current practice of having separate power and data cables. The IP standards are also ubiquitous in contemporary networked systems, again with extended support even in small embedded computers. The world wide web is powered by IP as are many industrial control systems. IP is also closely related to Ethernet, and the combination of Ethernet and IP is a de facto standard for emerging net- Figure 1 - LWE devices connected to an Ethernet switch worked systems, for home as well as industrial use. Thus, the selection of Ethernet and IP was an obvious choice also for the new navigation network standard. Overall principles and design choices From the outset, there were a number of requirements that needed to be satisfied by the new standard:  Easy to implement: On the order of a few weeks’ work to implement the protocol from scratch  Lightweight: Possible to implement the protocol on embedded computers, e.g., in a GPS receiver Digital Ship December 2010 page 31  Migration: Provide a simple migration path for equipment already using sentences from the existing IEC 61162-1 standard (based on NMEA 0183)  Capacity and scalability: Support existing bridge systems as well as foreseeable capacity and speed requirements for new bridge systems  Increasing complexity: Address increasing complexity in integrated navigation and bridge systems design. This has led to the following design choices for LWE, which mandates the use of:  Single switched Ethernet  UDP datagrams  IP multicast  A function block approach for devices.

Lightweight Ethernet

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