RTP Control Protocol (RTCP) is a sister protocol of the Real-time Transport Protocol (RTP). It is defined in RFC 3550. It is based on the periodic transmission of control packets to all participants in the session, using the same distribution mechanism as the data packets. The underlying protocol must provide multiplexing of the data and control packets, for example using separate port numbers with UDP.
RTCP provides feedback on the quality of the data distribution. RTCP carries a persistent transport-level identifier for an RTP source called the canonical name or CNAME, which may be used to associate multiple data streams from a given participant in a set of related RTP sessions, for example to synchronize audio and video.