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Re: [MMUSIC] RID, MID and BUNDLE: Associate received RTP packet with m- line

"Mo Zanaty (mzanaty)" <mzanaty@cisco.com> Thu, 22 October 2015 14:43 UTC

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From: "Mo Zanaty (mzanaty)" <mzanaty@cisco.com>
To: Christer Holmberg <christer.holmberg@ericsson.com>
Thread-Topic: [MMUSIC] RID, MID and BUNDLE: Associate received RTP packet with m- line
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Date: Thu, 22 Oct 2015 14:42:42 +0000
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Subject: Re: [MMUSIC] RID, MID and BUNDLE: Associate received RTP packet with m- line
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MID and RID are both RTCP SDES items that echo SDP identifiers in RTP/RTCP using the generic sdes-hdrext mechanism. Once the identifier value is associated to an RTP stream (identified by its SSRC) via RTCP packets with MID/RID SDES items or RTP packets with MID/RID header extensions, the association can remain in effect without echoing the header extension in every RTP packet.

We should probably add some text to warn implementers not to rely on receiving MID and RID in every RTP packet, and use the last valid association to that SSRC when absent.

Mo

On Oct 22, 2015, at 9:53 AM, Christer Holmberg <christer.holmberg@ericsson.com<mailto:christer.holmberg@ericsson.com>> wrote:

Hi,

Section 7 of the RID draft says:

"Note that 'rid's are only required to be unique within a media
   section ("m-line"); they do not necessarily need to be unique within
   an entire RTP session.  In traditional usage, each media section is
   sent on its own unique 5-tuple, which provides an unambiguous scope.
   Similarly, when using BUNDLE
   [I-D.ietf-mmusic-sdp-bundle-negotiation], MID values associate RTP
   streams uniquely to a single media description."

However, when BUNDLE is used, the MID value (RTP MID header extension) is not guaranteed to be present in every RTP packet. Section 14.1. of BUNDLE says:

"The RTP MID header extension SHOULD be included in some RTP packets
   at the start of the session and whenever the SSRC changes.  It might
   also be useful to include the header extension in RTP packets that
   comprise random access points in the media (e.g., with video
   I-frames)."

So, if the MID value is NOT included, and RTP packets associated with multiple m- lines use the same RIP value and the same PT value, will it be possible to associate the RTP packets to a single media description?

Regards,

Christer

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