Re: [rtcweb] Codec control and SDP offer/answer frequency

Harald Alvestrand <harald@alvestrand.no> Thu, 23 August 2012 20:36 UTC

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Date: Thu, 23 Aug 2012 22:36:38 +0200
From: Harald Alvestrand <harald@alvestrand.no>
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To: Christer Holmberg <christer.holmberg@ericsson.com>
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Cc: "rtcweb@ietf.org" <rtcweb@ietf.org>
Subject: Re: [rtcweb] Codec control and SDP offer/answer frequency
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On 08/23/2012 05:11 PM, Christer Holmberg wrote:
> Hi,
>
>>>>> Also, you would need to describe how the data channel protocol relates to negotiating being done on the signalling plane.
>>>> The format of the signalling channel is defined to be outside the scope of the specification, so it's perfectly legitimate to use the data channel for that purpose - application decision!
>>> Sure, applications can do whatever they want.
>>>
>>> But, I think it would be good to have a standardized mechanisms which works for any application. AFAIK, that was the whole purpose of the discussion in Vancouver.
>>>
>> Since we've settled on using SDP at the UA/Application interface,
> Correct (eventhough someone in Seattle may have a different opinion ;)
>
>> representing the data in SDP is a valid way of describing that interface
>> - thus indeed making it available for use by any application written to that interface.
> Correct.
>
>> The particular worry you raised was how fast applications can do offer/answers - which is dependent on
>> how their signalling channel is implemented, and how many intermediate nodes have to process the data.
> Correct.
>
>> That's what I'm thinking will be different in the Pokerstars example than in a SIP-telephone-gateway example.
> I agree that the impacts are different - but I'd like to have a solution that works in all cases.
>
> So, if I understand you correctly: you suggest that the codec control information is transported using SDP/a=imageattr "internally" (between app and browser), but then people can send it over the wire however they want?
Yes. I believe that's the model we have agreed on.