Re: [rtcweb] No Plan

Paul Kyzivat <pkyzivat@alum.mit.edu> Mon, 03 June 2013 20:45 UTC

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Date: Mon, 03 Jun 2013 16:37:30 -0400
From: Paul Kyzivat <pkyzivat@alum.mit.edu>
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To: Emil Ivov <emcho@jitsi.org>
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Subject: Re: [rtcweb] No Plan
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On 6/1/13 1:40 AM, Emil Ivov wrote:
>
>
> On 31.05.13, 22:11, Paul Kyzivat wrote:
>> On 5/31/13 6:51 AM, Emil Ivov wrote:
>>> Hey Paul,
>>>
>>> On 29.05.13, 22:57, Paul Kyzivat wrote:
>>>> Emil,
>>>>
>>>> I'm going to reserve judgment on this pending further discussion.
>>>> I think this *might* work for CLUE, but I want to be certain.
>>>
>>> Sure!
>>>
>>>> I'm concerned with decomposed endpoints that can't manage all the
>>>> streams on the same address/port. They will need multiple independent
>>>> m-lines and/or bundle groups.
>>>
>>> This is obviously open for debate but the general idea of No Plan is
>>> that: Offer/Answer is used for configuring media and RTP stacks and
>>> additional signalling is not the browser's concern.
>>>
>>> Having extra m= lines, particularly when using BUNDLE, is in many ways
>>> just extra signalling.
>>
>> You may be able to argue that adding extra m-lines into an existing
>> bundle is "just extra signaling". But introducing an additional 5-tuple
>> is more substantial. It requires configuring a new RTP stack and media.
>
> Indeed, this would require BUNDLE to work.

I don't understand what that means - what point you are trying to make.

You seem to have some criterion for what requires sdp and what does not. 
And AFAIK you are already assuming bundle works - you are simply using 
it less. As best I can tell, you acknowledge that you need SDP to:
- negotiate a 5-tuple over which media will flow
- specify which types of media can be carried and the codec info
   they may use.

I'm just pointing out that for decomposed endpoints one 5-tuple may not 
be enough. And the need for this might not be known a priori. One side 
may be ready to add another stream for some purpose, and be willing/able 
to use private signaling to negotiate that. But the other side may not 
be able to handle that stream on the same 5-tuple. That in turn may 
result in a need to negotiate SDP changes to establish an additional 
5-tuple that can then be used for that new stream.

	Thanks,
	Paul

> Emil
>
>
>>
>>     Thanks,
>>     Paul
>>
>>> If you'd like for that signalling to be in SDP, I
>>> don't see any problem with it. However it would be best for this extra
>>> layer of SDP signalling to appear at either the application layer or in
>>> a signalling gateway (that is going to be there anyway).
>>>
>>> Does this make sense?
>>>
>>> Emil
>>>
>>>>
>>>> Further questions:
>>>>
>>>> I presume that you expect bandwidth in the SDP to be an aggregate
>>>> per-m-line, with application specific signaling for bandwidth at the
>>>> per-RTP-stream level?
>>>>
>>>>      Thanks,
>>>>      Paul
>>>>
>>>> On 5/29/13 2:59 PM, Emil Ivov wrote:
>>>>> Hey all,
>>>>>
>>>>> Based on many of the discussions that we've had here, as well as many
>>>>> others that we've had offlist, it seemed like a good idea to
>>>>> investigate
>>>>> a negotiation alternative that relies on SDP and Offer/Answer just a
>>>>> little bit less.
>>>>>
>>>>> The following "no plan" draft attempts to present one such approach:
>>>>>
>>>>> http://tools.ietf.org/html/draft-ivov-rtcweb-noplan
>>>>>
>>>>> The draft relies on conventional use of SDP O/A but leaves the
>>>>> intricacies of multi-source scenarios to application-specific
>>>>> signalling, with potentially a little help from RTP.
>>>>>
>>>>> Hopefully, proponents of Plans A and B would find that the
>>>>> interoperability requirements that concerned them can still be met
>>>>> with
>>>>> "no plan". Of course they would have to be addressed by
>>>>> application-specific signalling and/or signalling gateways.
>>>>>
>>>>> Comments are welcome!
>>>>>
>>>>> Cheers,
>>>>> Emil
>>>>>
>>>>
>>>> _______________________________________________
>>>> rtcweb mailing list
>>>> rtcweb@ietf.org
>>>> https://www.ietf.org/mailman/listinfo/rtcweb
>>>> .
>>>>
>>>
>>
>> .
>>
>