Components of RTCP


An RTCP implementation has three parts : the packet formats, the timing rules, and the participant database.

There are several types of RTCP packets. The five standard packet types are described in the section titled RTCP Packet Formats later in this chapter, along with the rules by which they must be aggregated into compound packets for transmission. Algorithms by which implementations can check RTCP packets for correctness are described in the section titled Packet Validation.

The compound packets are sent periodically, according to the rules described in the section titled Timing Rules later in this chapter. The interval between packets is known as the reporting interval . All RTCP activity happens in multiples of the reporting interval. In addition to being the time between packets, it is the time over which reception quality statistics are calculated, and the time between updates of source description and lip synchronization information. The interval varies according to the media format in use and the size of the session; typically it is on the order of 5 seconds for small sessions, but it can increase to several minutes for very large groups. Senders are given special consideration in the calculation of the reporting interval, so their source description and lip synchronization information is sent frequently; receivers report less often.

Each implementation is expected to maintain a participant database, based on the information collected from the RTCP packets it receives. This database is used to fill out the reception report packets that have to be sent periodically, but also for lip synchronization between received audio and video streams and to maintain source description information. The privacy concerns inherent in the participant database are mentioned in the section titled Security and Privacy later in this chapter. The Participant Database section, also in this chapter, describes the maintenance of the participant database.



RTP
RTP: Audio and Video for the Internet
ISBN: 0672322498
EAN: 2147483647
Year: 2003
Pages: 108
Authors: Colin Perkins

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