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Sending Packet Loss Feedback in WebRTC SFUs

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One of the responsibilities of WebRTC SFUs is to receive and send RTCP packets.  RTCP packets include different types of feedback about audio and video streams and one of the most important RTCP packets is the Receiver Report (RR).

RR packets are sent from the receiver of the media stream towards the sender of that media stream.  In case of an SFU the RR are generated and sent from the SFU to the media stream Sender and also from every stream Receiver to the SFU (Figure 1).

The feedback sent inside RR packets include fields to calculate the round-trip-time delay, the jitter and the packet loss introduced by the network.