Re: [rtcweb] SDP_PRANSWER followed by SDP_OFFER scenario in JSEP

Justin Uberti <juberti@google.com> Tue, 01 May 2012 02:51 UTC

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From: Justin Uberti <juberti@google.com>
Date: Mon, 30 Apr 2012 19:50:56 -0700
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To: "Nataraju A.B" <nataraju.sip@gmail.com>
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Cc: "rtcweb@ietf.org" <rtcweb@ietf.org>
Subject: Re: [rtcweb] SDP_PRANSWER followed by SDP_OFFER scenario in JSEP
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Yes, I was under the impression that SIP enforced this requirement,
although I am probably not aware of all the corner cases. Is there a
real-world scenario where this flow is required?

On Mon, Apr 30, 2012 at 10:55 AM, Nataraju A.B <nataraju.sip@gmail.com>wrote;wrote:

> If the scenario considered is without reliable provisional responses. Then
> the first ANSWER must be in 200-INV and no more O/A allowed during
> INVITE(initial) transaction.
>
> Basic requirement for reliable and unambiguous O/A is -* At any point in
> time there could be only one O/A open. *
>
> Also only one O/A suggested during INVITE(initial) transaction.
>
> For reference, rfc6337, list outs different O/A models...
>
> <rfc6337>
>
>
>             Offer                Answer             RFC    Ini Est Early
>      -------------------------------------------------------------------
>      1. INVITE Req.          2xx INVITE Resp.     RFC 3261  Y   Y    N
>      2. 2xx INVITE Resp.     ACK Req.             RFC 3261  Y   Y    N
>      3. INVITE Req.          1xx-rel INVITE Resp. RFC 3262  Y   Y    N
>      4. 1xx-rel INVITE Resp. PRACK Req.           RFC 3262  Y   Y    N
>      5. PRACK Req.           200 PRACK Resp.      RFC 3262  N   Y    Y
>      6. UPDATE Req.          2xx UPDATE Resp.     RFC 3311  N   Y    Y
>
>           Table 1: Summary of SIP Usage of the Offer/Answer Model
>
> </rfc6337>
>
> Thanks,
> Nataraju A B
>
> On Mon, Apr 30, 2012 at 12:31 PM, Ravindran, Parthasarathi <
> pravindran@sonusnet.com> wrote:
>
>> Justin/Cullen,
>>
>> Could you please explain in case for an SDP_OFFER(1), the remote entity
>> replies with SDP_PRANSWER followed by new SDP_OFFER (2) what is the
>> expected behavior. The exact callflow is as follows:
>>
>>
>> Browser1-------------------------Browser2(SIP-JSEP gateway)
>>    |        SDP_OFFER(1)            |  INV with offer1
>>    |------------------------------->|--->
>>    |       SDP_PRANSWER(1)          |  183 with answer1
>>    |<-------------------------------|<---
>>    |       SDP_OFFER(2)             |   UPDATE with offer2
>>    |<-------------------------------|<---
>>    |       SDP_ANSWER(2?)           |
>>    |--------------------->?
>>
>> The reason for this O/A callflow is due to UPDATE method (RFC 3311)
>> mapping in Browser 2 (SIP-JSEP gateway).
>>
>> Thanks
>> Partha
>>
>> PS: For simplicity, PRACK message exchange is not chosen in SIP side.
>>
>>
>>
>>
>>
>> _______________________________________________
>> rtcweb mailing list
>> rtcweb@ietf.org
>> https://www.ietf.org/mailman/listinfo/rtcweb
>>
>
>
>
> --
> Thanks,
> Nataraju A.B.
>
>