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3.1.5.31.2 User agent behavior for a=x-ssrc-range attribute

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When allocating an m=audio or m=video media stream, a user agent SHOULD<58> allocate an appropriate SSRC range.

If a media description in a received SDP message contains an a=x-ssrc-range attribute, the receiving user agent SHOULD configure it's receive stream to expect SSRC values in the range declared by the peer.

If the user agent is an MCU, the SSRC range allocated for a send stream of the media channel SHOULD NOT overlap the SSRC range allocated by the MCU for any other media channel within the same conference. Furthermore, the SSRC ranges allocated by an MCU SHOULD NOT overlap any MSI values it allocates within the conference.

The size of an SSRC range depends on the media type. A size of one (for example, a=x-ssrc-range:1-1) SHOULD be used for an m=audio media description. A range size of 100 (for example, a=x-ssrc-range:101-200) SHOULD be used for an m=video media description.