📝RTCP

RTCP = RTP Control Protocol.

Two types of packets: RTCP Sender/Receiver Report. Typically, one report is sent per second.

Fields:

  • SSRC for each media

  • CNAME — identifier to group medias together

  • timestamps, packet count, jitter estimation (to help with QoS)

RTCP-FB = RTCP Feedback (for congestion control) — optional extensions

  • Google REMB (Receiver Estimated Maximum Bitrate)

    • for dynamic bandwidth adaptation

  • NACK

    • request to resend some packets

  • NACK PLI (Picture Loss Indication)

    • request to resend a new refresh frame

  • CCM FIR (Full Intra Request)

    • request to send a keyframe

These extensions are negotiated in SDP.

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