7. Early Feedback and Congestion Control

In the previous sections, the FB messages were defined as well as the timing rules according to which to send these messages. The way to react to the feedback received depends on the application using the feedback mechanisms and hence is beyond the scope of this document.

However, across all applications, there is a common requirement for (TCP-friendly) congestion control on the media stream as defined in [1] and [2] when operating in a best-effort network environment.

It should be noted that RTCP feedback itself is insufficient for congestion control purposes as it is likely to operate at much slower timescales than other transport layer feedback mechanisms (that usually operate in the order of RTT). Therefore, additional mechanisms are required to perform proper congestion control.

A congestion control algorithm that shares the available bandwidth reasonably fairly with competing TCP connections, e.g., TFRC [7], MUST be used to determine the data rate for the media stream within the bounds of the RTP sender's and the media session's capabilities if the RTP/AVPF session is transmitted in a best-effort environment.