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

"Charles Eckel (eckelcu)" <eckelcu@cisco.com> Mon, 30 April 2012 16:22 UTC

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Date: Mon, 30 Apr 2012 09:22:42 -0700
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Thread-Topic: [rtcweb] SDP_PRANSWER followed by SDP_OFFER scenario in JSEP
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From: "Charles Eckel (eckelcu)" <eckelcu@cisco.com>
To: "Ravindran, Parthasarathi" <pravindran@sonusnet.com>, "Justin Uberti" <juberti@google.com>, "Cullen Jennings" <fluffy@iii.ca>
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Cc: rtcweb@ietf.org
Subject: Re: [rtcweb] SDP_PRANSWER followed by SDP_OFFER scenario in JSEP
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Hi Partha,

I believe such a flow illegal, per RFC 3311:

      o  If the UPDATE is being sent before the completion of the INVITE
         transaction, and the initial INVITE contained an offer, the
         UPDATE cannot be sent with an offer unless the callee has
         generated an answer in a reliable provisional response, has
         received a PRACK for that reliable provisional response, has
         not received any requests (PRACK or UPDATE) with offers that it
         has not answered, and has not sent any UPDATE requests
         containing offers that have not been answered.

Cheers,
Charles

> -----Original Message-----
> From: rtcweb-bounces@ietf.org [mailto:rtcweb-bounces@ietf.org] On
> Behalf Of Ravindran, Parthasarathi
> Sent: Monday, April 30, 2012 12:02 AM
> To: Justin Uberti; Cullen Jennings
> Cc: rtcweb@ietf.org
> Subject: [rtcweb] SDP_PRANSWER followed by SDP_OFFER scenario in JSEP
> 
> 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.
> 
> 
> 
> 
> 
> _______________________________________________
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