Re: [rtcweb] AVPF vs AVP

Magnus Westerlund <magnus.westerlund@ericsson.com> Thu, 15 September 2011 16:03 UTC

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Date: Thu, 15 Sep 2011 18:06:01 +0200
From: Magnus Westerlund <magnus.westerlund@ericsson.com>
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Subject: Re: [rtcweb] AVPF vs AVP
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On 2011-09-15 16:01, Roni Even wrote:
> Magnus,
> I noticed that you claim that all AVPF feedback messages are explicitly
> negotiated, is this a requirement. At least RTCP-SR-REQ is not negotiated in
> SDP.

You are correct, had not actually noticed that. Fortunately that isn't
an real issue.

First of all the support of AVPF can still be negotiated with the
a=rtcp-fb. Simply the trr-int configuration lets both side show support
of AVPF.

Secondly, for the RTCP-SR-REQ if one uses the header extension to
deliver the synch data then that is explicitly indicated. And if you
ignore or don't understand the request then you simple fall back to
normal synchronization procedures with more delay before completing it.

> 
> As for using AVPF while signaling AVP that will confuse endpoint that so not
> understand this convention and can support AVPF. They will see an offer with
> AVP but with parameters that are not part of AVP. They can respond with AVP
> without the AVPF parameter and behave like AVP endpoints even though they
> support AVPF. This will prevent them from sending AVPF feedback messages.

They can still use AVPF timing rules, even if the other end-point is AVP
only. They only need to restrict themselves from sending feedback messages.

> This may be a problem for what you call "legacy" video conferencing
> endpoint. (I do not like the term legacy here since these are not legacy
> endpoint but AVP/AVPF compliant EPs 

Yes, I agree it is not without issues in that regard.

I would also like to note that if you require AVPF and don't think
talking to AVP only end-points then one really should include the AVPF
in the m= line to prevent fallback.

> 
> I think that if we are not going to use cap-neg we should make it
> historical. 

I kind of agree with that also. But if it constantly fails in the market
I think we have to recognize that and do something else that works better.

Cheers

Magnus Westerlund

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