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

Christer Holmberg <christer.holmberg@ericsson.com> Thu, 22 October 2015 19:18 UTC

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From: Christer Holmberg <christer.holmberg@ericsson.com>
To: "Mo Zanaty (mzanaty)" <mzanaty@cisco.com>, Adam Roach <adam@nostrum.com>, "mmusic@ietf.org" <mmusic@ietf.org>
Thread-Topic: [MMUSIC] RID, MID and BUNDLE: Associate received RTP packet with m- line
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Date: Thu, 22 Oct 2015 19:18:00 +0000
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Subject: Re: [MMUSIC] RID, MID and BUNDLE: Associate received RTP packet with m- line
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Hi,

>RID (like MID and all SDES items) is limited to 255 octets. No risk of exhaustion, so offerers are free to make them >unique across the whole SDP if they want.

If there is no risk of exhaustion, is there a reason not to MANDATE them to be unique?

Regards,

Christer


On 10/22/15, 3:00 PM, mmusic on behalf of Christer Holmberg <mmusic-bounces@ietf.org<mailto:mmusic-bounces@ietf.org> on behalf of christer.holmberg@ericsson.com<mailto:christer.holmberg@ericsson.com>> wrote:

Hi,

> As long as the recipient has seen both the MID for an SSRC and the RID for an SSRC, then it can perform the proper correlation.


That's what I assumed, and it's the same way BUNDLE works (where you send the RTP MID until you assume the other endpoint has seen the SSRC).

It would probably be a good idea to modify the text in the draft to reflect that.

BTW, is there a reason why the RID value can't be unique for the whole SDP? Is there a risk we'd run out of values? What is the value range that "fits" into the RID RTP header extension?

Regards,

Christer


On 10/22/15 08:53, Christer Holmberg 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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