RTCP = RTP Control Protocol.

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


  • 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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