RTP: Audio and Video for the Internet

Congestion control is a necessary evil. As an application designer, you can ignore it, and your application may even appear to work better if you do. However, you may be affecting other traffic on the network ”perhaps other instances of your own application ”in adverse ways, and you have no way of knowing the relative importance of that traffic. For this reason, and to avoid the possibility of causing congestion collapse, applications should implement some form of congestion control. It is also desirable that the chosen algorithm be approximately fair to TCP traffic, allowing unfairness ”priority ”to be introduced into the network in a controlled manner.

The standards for congestion control are still evolving, so it is difficult to provide a detailed specification for implementers. Nonetheless, it is strongly recommended that unicast applications implement a TCP-friendly rate control algorithm, because these are the best developed. For multicast applications, the choice of congestion control is less clear, but layered coding seems to be the best alternative at present.