There are two parts to RTP: the data transfer protocol, which was described in Chapter 4, and an associated control protocol, which is described in this chapter. The control protocol, RTCP, provides for periodic reporting of reception quality, participant identification and other source description information, notification on changes in session membership, and the information needed to synchronize media streams. This chapter describes the uses of RTCP, the format of RTCP packets, and the timing rules used to scale RTCP over the full range of session sizes. It also discusses the issues in building a participant database, using the information contained in RTCP packets. |