RTCP Protocol
CategoryInternet Protocol
RTP Control Protocol (RTCP) augments multimedia content transport to allow monitoring of the data delivery in a manner scalable to large multicast networks, to provide minimal transmission control, and to convey information about the participants in an ongoing session.
Media Transmission Control
Voice and Video Delivery Monitoring
RTCP is based on the periodic transmission of control packets to all participants in the media session, using the same distribution mechanism as data packets. The underlying transport protocol must provide multiplexing of the data and control packets — for example, using separate port numbers for RTP and RTCP with UDP.
The primary function of the control protocol is to provide feedback on the quality of the data distribution. The feedback may be directly useful for control of adaptive encodings, but experiments with IP multicasting have shown that it is also critical to get feedback from the receivers to diagnose faults in the media content delivery.
Other RTCP functions include: providing a persistent transport-level identifier — for an RTP source to ensure inter-media synchronization, controlling the rate — in order for RTP to scale up to a large number of participants, and sharing participant identification — for example, to be displayed in the user interface. RTCP serves as a convenient channel to reach all the participants — useful in "loosely controlled" sessions where media endpoints enter and leave without membership control or parameter negotiation.
