Where network protocols fit in

Applications such as voice, video, and most VDI apps typically use UDP, whereas file transfer and real-time apps often use TCP as the underlying protocol. While TCP has its own flow control, other applications using UDP typically implement their own flow control to control loss detection, retransmissions, Forward Error Correction (FEC), etc

In a typical case, the user’s application traffic traverses multiple network segments (e g , Wi-Fi/cellular, broadband, mid-mile, etc.) before it reaches the application server.

Each network segment may have its own network characteristics with associated network impairments, for example:

● Wireless including Wi-Fi and cellular: Wireless exhibits burst loss from interference, multipath fading, shadowing, and other signal inhibitors. This can result in low bandwidth and poor coverage, which leads to inconsistent throughput, delay, and jitter. (Wireless propagation fundamentals.)

● Broadband includes technologies such as DSL, cable, fiber, Satellite, and wireless (see above): Broadband suffers from a number of issues, including oversubscription, symmetry, rate limiting on certain ports, and “best effort” reliability and uptime.

● Mid-mile: This suffers from ISP/peering issues that impact loss, path selection, latency, and variable delay

Different networks have different issues

The flow control that is implemented at TCP protocol or at the application layer for UDP-based apps is always end-to-end. This means they can only react to what they can measure or predict, such as a packet loss, delay, or jitter across the end-to-end connection. They do not have the knowledge of why certain network impairments impact certain network segments differently. They will not be able to see if the impairment comes from the user being in a crowded hotspot or if it is a broadband oversubscription issue or if it is congestion in the mid-mile due to peering. Many times, by the time the applications or protocols react based on end-to-end measurements or predictions, the condition has changed. Often it is assumed that the impairments are caused by congestion, which may not always be the case, especially in wireless segments.