Congestion Control (REMB)¶
Kurento implements the Google Congestion Control algorithm, so it is able to generate and parse both abs-send-time RTP headers and REMB RTCP messages.
It is enabled by by passing the media-level attribute goog-remb in the SDP Offer. For example:
v=0 o=- 0 0 IN IP4 127.0.0.1 s=- c=IN IP4 127.0.0.1 t=0 0 m=video 5004 RTP/AVPF 103 a=rtpmap:103 H264/90000 a=rtcp-fb:103 goog-remb a=sendonly a=ssrc:112233 cname:[email protected]
a=rtcp-fb is an RTCP Feedback Capability Attribute, as defined in RFC 4585.
Also it is important to note that KMS implements REMB propagation between the sender and receiver legs of a connection. This means that when KMS is used as a proxy between a video sender and one or more video receivers, the smallest REMB value from the receivers will be relayed to the sender. This allows the sender to choose a lower bitrate that will accommodate all of the receivers connected to KMS at the other side.
For more context about what is REMB and how it fits in the greater project of RMCAT, please read our Knowledge Base document: Congestion Control (RMCAT).