Re: [rtcweb] SDP Offer/Answer draft-jennings-rtcweb-signaling - More-coming and final answer (Section 5.2.3)

Cullen Jennings <fluffy@cisco.com> Wed, 09 November 2011 14:37 UTC

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From: Cullen Jennings <fluffy@cisco.com>
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Date: Wed, 9 Nov 2011 07:37:41 -0700
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To: Christer Holmberg <christer.holmberg@ericsson.com>
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Subject: Re: [rtcweb] SDP Offer/Answer draft-jennings-rtcweb-signaling - More-coming and final answer (Section 5.2.3)
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On Nov 9, 2011, at 2:14 AM, Christer Holmberg wrote:

> 
> Hi Cullen, 
> 
>>>>> Q2. Are there restrictions when it comes to changing 
>>>>> information in a non-final answer and a final answer? Or, can the final 
>>>>> answer be completely different from previously sent non-final 
>>>>> ANSWERS? In "legacy" O/A there are restrictions.
>>>>> 
>>>> Any answer has to be a valid answer for the offer but other than 
>>>> that, no restrictions, so the final answer can change 
>>>> everything from an earlier one.
>>> 
>>> Is there a reason/use-case/requirement why we need to allow 
>>> that? As far as I know, the reason behind this is ICE.
>>> 
>> There a bunch of use cases but to mention two: In the browser 
>> to browser case, imagine that you start sending audio in the 
>> first answer but need to wait for user feedback to find out 
>> if video can be added or not in the final answer. In a 
>> browser to SIP use case, the early media for 1-800-go-fedex.
> 
> I think that could cause interoperability issues.
> 
> For example, assume that a gateway would map a more-to-come answer to a SIP 18x response.
> 
> Then, if the no-more-to-come answer is different, the gateway can't map it to SIP 200 response - at least not without chaning the SIP dialog identifier.

Seems like it should be able to do this. Lets talk about this in Taipei - I suspect we are just talking past each other and both mean about the same thing. I'm not proposing any change to 3264. 

> 
> Also, if you map a more-to-come answer to a SIP 18x answer, and then receives a new SIP offer, the gateway *cannot* map it to a ROAP offer, as it is still wating waiting for the no-more-to-come answer.
> 
> Regards,
> 
> Christer