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Re: [rtcweb] Plan A, respun

Colin Perkins <csp@csperkins.org> Mon, 20 May 2013 11:17 UTC

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From: Colin Perkins <csp@csperkins.org>
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Date: Mon, 20 May 2013 12:17:36 +0100
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To: Adam Roach <adam@nostrum.com>
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Subject: Re: [rtcweb] Plan A, respun
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On 20 May 2013, at 10:45, Adam Roach wrote:
> On 5/18/13 00:10, Martin Thomson wrote:
>> On 16 May 2013 23:31, Harald Alvestrand <harald@alvestrand.no> wrote:
>>> The demuxing is trivial. In fact, I don't think it's even necessary to
>>> describe it as "demux on PT"; you can't allow SSRC collision between two
>>> tracks with different PT anyway.
>> Let's be very, very precise about this.
>> 
>> Demultiplexing is *always* performed based on SSRC.  It's just that
>> correlation with signaling components (the m-line in this case) might
>> use of PT in the absence of prior knowledge of SSRC.
>> 
>> We didn't get this quite right in Plan A.
> 
> Yeah, that's a valid point. It's not really being proposed as a demux point as much as a correlation token. Thanks for clearing that up -- we should definitely clear that up in the next version of the document.


Rather than try to overload the PT, I would suggest we define an explicit correlation token that can be sent. Put something in RTCP SDES and/or RTP header extensions, and in the SDP, to signal what RTP flow corresponds to what m-line.

-- 
Colin Perkins
http://csperkins.org/

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