Re: [rtcweb] AVPF vs AVP

"Roni Even" <ron.even.tlv@gmail.com> Fri, 16 September 2011 13:02 UTC

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From: "Roni Even" <ron.even.tlv@gmail.com>
To: "'Magnus Westerlund'" <magnus.westerlund@ericsson.com>, <rtcweb@ietf.org>
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Date: Fri, 16 Sep 2011 16:03:34 +0300
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Subject: Re: [rtcweb] AVPF vs AVP
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Magnus,
Maybe we can take the approach from
draft-holmberg-mmusic-sdp-multiplex-negotiation and offer the same m-line
with the same port number twice, one as AVP and one as AVPF and let the
other side chose, he can answer with a port=0 for the profile it does not
want. If the multiplex proposal has backward interoperability than this
proposal also does.

Roni Even

> -----Original Message-----
> From: rtcweb-bounces@ietf.org [mailto:rtcweb-bounces@ietf.org] On
> Behalf Of Magnus Westerlund
> Sent: Wednesday, September 14, 2011 6:09 PM
> To: rtcweb@ietf.org
> Subject: [rtcweb] AVPF vs AVP
> 
> Hi,
> 
> There has been this long thread with the subject partially containing
> "AVPF". I want to clarify something in this context around AVPF. Rather
> than the SRTP question.
> 
> An end-point that is AVPF compliant is in fact interoperable with an
> AVP
> one as long as the trr-int parameter is set reasonably large. A
> parameter value of 1.5-5 seconds (I would recommend 3s) will ensure
> that
> they are in fact compatible. This avoids the risk of any side timing
> out
> the other if the AVP side is using the default 5 s minimum interval.
> 
> Based on this one could in fact have the RTCWEB nodes always use AVPF
> for RTP/RTCP Behavior. The AVPF feedback messages are explicitly
> negotiated and will only be used when agreed on.
> 
> This leaves us with any signaling incompatibilities when talking to a
> legacy device. If one don't want to use cap-neg I see two directions to
> go:
> 
> 1) RTCWEB end-point will always signal AVPF or SAVPF. I signalling
> gateway to legacy will change that by removing the F to AVP or SAVP.
> 
> 2) RTCWEB end-point will always use AVPF but signal it as AVP. It will
> detect the AVPF capabilities of the other end-point based on the
> signaling of the feedback events intended to be used.
> 
> I think 1) is cleaner for the future. 2) might be more pragmatic.
> 
> In both cases I believe there are methods for negotiating a lower
> trr-int than some AVP fallback value to preserve interoperability.
> 
> 
> However, this still don't resolve the question if the "S" should be in
> front of the RTP profile indicator or not. But it might help by
> removing
> the F or not in the profile.
> 
> Cheers
> 
> Magnus Westerlund
> 
> ----------------------------------------------------------------------
> Multimedia Technologies, Ericsson Research EAB/TVM
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