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Re: [AVTCORE] RTP/TFRC + FEC ?

Olivier Crête <olivier.crete@collabora.co.uk> Tue, 10 May 2011 14:29 UTC

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From: Olivier Crête <olivier.crete@collabora.co.uk>
To: Magnus Westerlund <magnus.westerlund@ericsson.com>
Date: Tue, 10 May 2011 10:19:07 -0400
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Cc: Ladan Gharai <ladan@gharai.org>, "avt@ietf.org" <avt@ietf.org>, Colin Perkins <csp@csperkins.org>
Subject: Re: [AVTCORE] RTP/TFRC + FEC ?
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On Tue, 2011-05-10 at 11:05 +0200, Magnus Westerlund wrote:
> On 2011-05-09 18:57, Ali C. Begen (abegen) wrote:
> 
> >> two streams would get roughly twice the bandwidth of one stream
> >> (and I guess that's not appropriate).
> > 
> > You are right that it is not appropriate but I don't see why TFRC
> > would get roughly twice the bw of one stream if you use two TFRC
> > states. You can easily apply the TFRC limit on the source+FEC, and
> > then try to allocate that bw between the source and FEC.
> > 
> 
> I think this is a comment that the TFRC draft authors should take to
> heart that the document will need to have a discussion on how to
> aggregate multiple SSRCs into a single TFRC flow state.

Actually, aggregating multiple SSRCs into one RTP/TFRC stream is
problematic as TFRC expects to have a linear sequence number. That means
we need to put a TFRC seqnum inside the RTP header extension, can't use
the RTP one. I noticed that Google is already doing something like that
in their we-like-standards-but-not-quite RTP/TFRC implementation in
Google Talk.

-- 
Olivier Crête
olivier.crete@collabora.co.uk
Collabora Ltd

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