RTCP receiver report sending interval

Question

What is the sending interval of RTCP Receiver Report? In RFC 3550 I was only able to find computation the RTCP Transmission Interval for the server. But as a client I have no idea about members and senders (or do I?). So I'm a little bit confuse how to calculate the interval or should I send RTCP RR in periods or should I only send RR packet when SR is received?

Answer 1

The RTP and RTCP protocols don't make a distinction between client and server. Both are members within the RTP session and both can send and receive RTP data. Members issue RTCP reports on an interval according to the algorithm in RFC 3550 Section 6.2.

Members issue a compound RTCP report that contains a Receiver Report and optionally a Sender Report if that member has sent any RTP data packets (other report types may be included in the compound report as well). RFC 3550 Section 6.4:

RTP receivers provide reception quality feedback using RTCP report packets which may take one of two forms depending upon whether or not the receiver is also a sender. The only difference between the sender report (SR) and receiver report (RR) forms, besides the packet type code, is that the sender report includes a 20-byte sender information section for use by active senders. The SR is issued if a site has sent any data packets during the interval since issuing the last report or the previous one, otherwise the RR is issued.

Both the client and server are RTP receivers even if your RTP data only flows in one direction. You should be able to observe a sender (your server) creating compound RTCP packets with SR and RR messages. Your client should be sending an RTCP packet with only a RR message

Answer 2

Per RFC 1885 (granted its older than 3550) states this:

The calculated interval between RTCP packets is required to be greater than a minimum of 5 seconds to avoid having bursts of RTCP packets exceed the allowed bandwidth when the number of participants is small and the traffic isn't smoothed according to the law of large numbers.

In practice with WebRTC, I generally see reports about every second for SR and RR.

RFC 1885 Section 6.2