RTCP
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.
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Problems and possible further development of RTCP
Deployment of large-scale applications faces unacceptable reporting time delay. For example Video streaming service with bandwidth = 1 Mbps, number of users = <math>10^5</math>, Avarage packet length of Receiver-Report packets <math>PL_RR</math> = 736b. The formula for interval calculation gives the result time <math>TRR = 1963 seconds, i.e. more than half an hour (ommiting compensation that is <math>e-1.5</math>).
Other optimizations are summarized in Realtime control protocol and its improvements for Internet Protocol Television
Mathematical background
Mathematical background could be read in section I. and II.A in paper "Optimization of Large-Scale RTCP Feedback Reporting in Fixed and Mobile Networks".
Further research and development
- Realtime control protocol and its improvements for Internet Protocol Television
- Optimization of Large-Scale RTCP Feedback Reporting in Fixed and Mobile Networks
References
- H. Schulzrinne, S. Casner, R. Frederick, V. Jacobson, “RTP: ATransport Protocol for Real-Time Applications,” RFC 3550, July 2003, ftp://ftp.rfc-editor.org/in-notes/rfc3550.txt
- Optimization of Large-Scale RTCP Feedback Reporting in Fixed and Mobile Networks
