8. SSRC Identifier Allocation and Use

8.1 Probability of Collision

The SSRC identifier carried in the RTP header and in various fields of RTCP packets is a randomly chosen value meant to be globally unique within a particular RTP session. Although the probability of multiple sources choosing the same 32-bit SSRC identifier is low, all RTP implementations must be prepared to detect collisions and take the appropriate actions to resolve them.

8.2 Collision Resolution and Loop Detection

If a source discovers at any time that another source is using the same SSRC identifier as its own, it must send an RTCP BYE packet for the old identifier and choose another random one.

8.3 Use with Layered Encodings

For layered encodings transmitted on separate RTP sessions using different multicast groups and/or destination transport addresses, a single SSRC identifier space should be used across the sessions of all layers and all participants.

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