Re: [MMUSIC] [rtcweb] Quick comments on draft-roach-rtcweb-glareless-add-00

Paul Kyzivat <pkyzivat@alum.mit.edu> Mon, 13 May 2013 14:44 UTC

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Date: Mon, 13 May 2013 10:44:18 -0400
From: Paul Kyzivat <pkyzivat@alum.mit.edu>
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Subject: Re: [MMUSIC] [rtcweb] Quick comments on draft-roach-rtcweb-glareless-add-00
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I'm not going to comment further on the specifics here, since they have 
been well flogged already. But the point of this particular discussion 
was about the likelihood of glare. Stefan's assertion was that O/As 
initiated by one end due to rapid changes in which streams it wants to 
receive will drive up the possibility of glare when the other end wants 
to do an O/A.

I'll just say that if the number of O/As has gone up that much, then 
that was a bad choice of mechanism.

	Thanks,
	Paul

On 5/13/13 10:33 AM, Emil Ivov wrote:
> Hey Stefan,
>
> On 13.05.13, 10:21, Stefan Håkansson LK wrote:
>>> Well the way I remember it SDP O/A was chosen for session negotiation
>>> and that other forms of signalling were explicitly left out of the
>>> charter.
>>
>> I took the result of the discussion and poll at the IETF-84
>> (http://tools.ietf.org/wg/rtcweb/minutes?item=minutes-84-rtcweb.html) as
>> an indication of that SDP O/A should be used for this kind of in-session
>> changes as well.
>
> True, I am not sure we all realized the number of use cases this would
> end up encompassing and how we would end up implementing signalling
> features into SDP.
>
>>>> In this case either to transmit a new imageattr value
>>>
>>> imageattr is great as a declarative parameter indicating capabilities:
>>> "I can't show more than 720p so there's no point to send me more than
>>> that". Using it as a way to switch between thumbnail and HQ videos is
>>> not entire impossible but is not particularly efficient either.
>>
>> To me it looks like a solution that people might feel inclined towards
>> using.
>>
>> But there are others that want to use simulcast, and then pause/resume
>> sending of high and low resolution streams, and that problem is more or
>> less the same when it comes to signaling.
>>
>> And even if we omitted the possibility for a receiver to indicate to the
>> sender (via standardized signaling) that it should pause or resume
>> sending, and instead left that up to an API (at sender side) and
>> proprietary signaling, we still have to have some kind of signaling IMO:
>> the sender can not just stop sending RTP packets, there need to be a
>> signal to the receiver so it understands this
>
> I never implied there should be no signalling. Just that implementing it
> all over SDP O/A leads to unforeseen complexities.
>
> RTCP BYE and/or SSRC expiration would be one option here. Custom
> signalling another.
>
> Cheers,
> Emil
>