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List:       sip-implementors
Subject:    Re: [Sip-implementors] PRACK -200 OK / Offer Answer Model
From:       "Serbang, Nabam (Nabam)" <nserbang () avaya ! com>
Date:       2008-12-19 18:36:55
Message-ID: A9CC0EE63801A14DA500BD329B819AD4CC42A4 () 301081ANEX2 ! global ! avaya ! com
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I agree with Paul with addition that If the offer in INVITE has got
answer in 180, SDP in PRACK is optional unless UAC want to change the
media stream.    You can have early dialog even before PRACK transation
is completed.  However, if you have new "m=" lines that is not present
in answer (one came with 180), that means you want to change media
stream. New media streams, after transaction has completed, depends on
reaction of UAS with that new "m=" line. If UAS accepts new "m=" line,
it will present another answer in 200 OK of PRACK else both UAs will be
using earlier negotiated SDP.  PRACK request is for reliability of
provisional responses. As such SDP in PRACK is optional.

 

Thanks and regards
Nabam Serbang




-----Original Message-----
From: sip-implementors-bounces@lists.cs.columbia.edu
[mailto:sip-implementors-bounces@lists.cs.columbia.edu] On Behalf Of
Paul Kyzivat
Sent: Friday, December 19, 2008 11:35 PM
To: pravin.swami@wipro.com
Cc: sip-implementors@lists.cs.columbia.edu
Subject: Re: [Sip-implementors] PRACK -200 OK / Offer Answer Model



pravin.swami@wipro.com wrote:
> HI.. All,
>  
> In the below scenario Is offer /Answer Still required Even if its 
> completed in INV & 180 ??.
>  
> Understanding Early Dialog Establishment is it right way to send PRACK

> request & response without SDP. ??
>  
>  
> UAC                                   UAS
>  
>                  INV(offer)
>  ---------------------------------------------->
>                180(Answer)
> <---------------------------------------------
>                PRACK ( SDP/OFFER still required ???)
> ----------------------------------------------->

I assume that INV had Supported:100rel and 180 had Required:100rel.
If so, then the PRACK itself is required, but it need not have an offer.

>                200 OK (SDP/Answer still required ????)
> <---------------------------------------------

The 200 for the PRACK must have an answer if and only if the PRACK had
an offer.

Sounds like you haven't seen
https://datatracker.ietf.org/drafts/draft-ietf-sipping-sip-offeranswer

	Paul

>                200 OK(INV)
> <---------------------------------------------
>               ACK
> ----------------------------------------------->
>  
> Reagrds
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