Guidelines for Choosing an RTP Control Protocol (RTCP) Canonical Name (CNAME) for Hosts with Private IP Addresses
The RTP Control Protocol (RTCP) Canonical Name (CNAME) is a persistent transport-level identifier for an RTP endpoint. While the Synchronisation Source (SSRC) identifier of an RTP endpoint may change if a collision is detected, or when the RTP application is restarted, the CNAME is meant to stay unchanged, so that RTP endpoints can be uniquely identified and associated with their RTP media streams. For proper functionality, CNAMEs should be unique within the participants of an RTP session. The recommendations for choice of the RTCP CNAME provided in RFC 3550 are insufficient to achieve uniqueness in some environments, particularly private IP networks. This memo updates the guidelines in RFC 3550 to allow endpoints to choose unique CNAMEs in these environments.