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

Paul Kyzivat <pkyzivat@alum.mit.edu> Mon, 10 June 2013 16:45 UTC

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Date: Mon, 10 Jun 2013 12:45:00 -0400
From: Paul Kyzivat <pkyzivat@alum.mit.edu>
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To: "Stach, Thomas" <thomas.stach@siemens-enterprise.com>
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Subject: Re: [MMUSIC] Scope of RTP payload types in BUNDLE?
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On 6/10/13 8:40 AM, Stach, Thomas wrote:
>> -----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.

The key is to ensure that the offerer gets an answer in a timely way to 
avoid clipping. PRACK is one way. ICE is another. We could require 
either/or.

	Thanks,
	Paul

> 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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