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

"Nataraju A.B" <nataraju.sip@gmail.com> Mon, 30 April 2012 17:55 UTC

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Date: Mon, 30 Apr 2012 23:25:13 +0530
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From: "Nataraju A.B" <nataraju.sip@gmail.com>
To: "Ravindran, Parthasarathi" <pravindran@sonusnet.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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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.

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