Re: [MMUSIC] Scope of RTP payload types in BUNDLE?

"Stach, Thomas" <thomas.stach@siemens-enterprise.com> Mon, 10 June 2013 12:48 UTC

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From: "Stach, Thomas" <thomas.stach@siemens-enterprise.com>
To: Paul Kyzivat <pkyzivat@alum.mit.edu>
Thread-Topic: [MMUSIC] Scope of RTP payload types in BUNDLE?
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Date: Mon, 10 Jun 2013 12:40:41 +0000
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Subject: Re: [MMUSIC] Scope of RTP payload types in BUNDLE?
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> -----Urspr√ľngliche Nachricht-----
> Von: mmusic-bounces@ietf.org [mailto:mmusic-bounces@ietf.org] 
> Im Auftrag von Paul Kyzivat
> Gesendet: Montag, 10. Juni 2013 00:02
> An: Bernard Aboba
> Cc: mmusic@ietf.org
> Betreff: Re: [MMUSIC] Scope of RTP payload types in BUNDLE?
> 
> On 6/9/13 1:48 PM, Bernard Aboba wrote:
> > Paul said:
> >
> >  > There is a big difference between clipping for one 
> second until the 183
> >  > is received, and clipping until the phone is answered 
> and a 200 received.
> >
> > [BA] So you're saying it is sufficient to enable media once a 183 is
> > received, but not before?  I believe that is consistent 
> with the current
> > WebRTC API.   The use case document isn't clear that this is the bar
> > that is being set, though.
> 
> I'm suggesting that in the case of BUNDLE, there be a 
> requirement that 
> media not be sent until an answer is known to have been 
> received by the 
> other end. Sending a reliable 183 and awaiting the PRACK 
> before sending 
> media would satisfy that. Presumably something similar can serve in a 
> pure WebRTC environment.
> 
> That will ensure no clipping.
> 
> The objection I hear to this is that some don't implement PRACK. I'm 
> just saying that we could require support for PRACK with support for 
> BUNDLE. Then that argument becomes bogus.
Just as well, we could require ICE together with BUNDLE and 
re-use how ICE deals with reliability of provisional reponses.
In the RTCWEB this would be a non-issue. 
Environments that don't support ICE could still require PRACK.

Regards
Thomas

> 
> Then we can say that it is ok if something in the answer is 
> needed for 
> the offerer to demux incoming media.
> 
> > One issue is what the WebRTC gateway will do if it gets 
> media before the
> > 183.    If it just forwards it on, then it will be dropped by the
> > browser until the 183 shows up and setRemoteDescription is called.
> > Should it buffer it until the 183 arrives?
> 
> My proposal is that it should not transmit media until it knows the 
> answer has been received. I don't care how it achieves that, but I 
> imagine dropping it would be a good choice.
> 
> Or, if people prefer, we could allow it to be sent, but allow 
> the other 
> end to drop it. But still expect the early answer so that the period 
> when media is lost is brief.
> 
> >  > But I was suggesting that we couple a requirement for 
> PRACK with BUNDLE,
> >  > and say that media should not be sent until the PRACK is 
> received. So
> >  > then there won't be clipping at all.
> >
> > [BA] Personally, I don't see PRACK as being required for BUNDLE, at
> > least in WebRTC uses. However, a WebRTC/SIP gateway probably should
> > support PRACK.
> 
> PRACK wouldn't be required in JSEP. But the equivalent would 
> be expected 
> - a quick ANSWER, before media is sent.
> 
> 	Thanks,
> 	Paul
> 
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