Transport of RTCP Packets

Each RTP session is identified by a network address and a pair of ports: one for RTP data and one for RTCP data. The RTP data port should be even, and the RTCP port should be one above the RTP port. For example, if media data is being sent on UDP port 5004, the control channel will be sent to the same address on UDP port 5005.

As noted in Chapter 4, RTP Data Transfer Protocol, the latest revision of the RTP specification relaxes the requirement that the RTCP port is odd-numbered, and allows nonadjacent RTP and RTCP ports. For compatibility with older implementations , it is still wise to use adjacent ports where possible, with the RTCP data being sent on the higher, odd-numbered, port.

All participants in a session should send compound RTCP packets and, in turn , will receive the compound RTCP packets sent by all other participants. Note that feedback is sent to all participants in a multiparty session: either unicast to a translator, which then redistributes the data, or directly via multicast. The peer-to-peer nature of RTCP gives each participant in a session knowledge of all other participants: their presence, reception quality, and ” optionally ”personal details such as name , e-mail address, location, and phone number.