Real time control protocol

RTP Control Protocol (RTCP) is a sister protocol of the Real-time Transport Protocol (RTP). It is defined in [http://www.ietf.org/rfc/rfc3550.txt RFC 3550] (which obsoletes RFC 1889).

RTCP stands for Real-time Transport Control Protocol, provides out-of-band control information for an RTP flow. It partners RTP in the delivery and packaging of multimedia data, but does not transport any data itself. It is used periodically to transmit control packets to participants in a streaming multimedia session. The primary function of RTCP is to provide feedback on the quality of service being provided by RTP.

It gathers statistics on a media connection and information such as bytes sent, packets sent, lost packets, jitter, feedback and round trip delay. An application may use this information to increase the quality of service perhaps by limiting flow, or maybe using a low compression codec instead of a high compression codec. RTCP is used for QoS reporting.

RTCP itself does not provide any flow encryption or authentication means. SRTCP (Secure RTCP) protocol can be used for that purpose.