[SIPForum-discussion] [Sip-implementors] Offer/Answer question

[Manpreet Singh]

Out of curiousity, why is 200OK to Invite not allowed to carry any SDP
once the reliable provisional response has completed the offer/answer?
Does that break something from a call flow standpoint? If the callee
wants to use a different codec right when call connects ( like switch
from g711 to g729 ), only way it would have to do this is via re-invites
or Update right after call actually connects. ( or delay 200OK and do
another offer/answer with UPDATE right before connecting it )

Thnx  

-----Original Message-----
From: Paul Kyzivat [mailto:pkyzivat at cisco.com] 
Sent: Monday, April 14, 2008 12:34 AM
To: Manpreet Singh
Cc: kaiduan xie; Bob Penfield; discussion at sipforum.org;
sip-implementors at lists.cs.columbia.edu
Subject: Re: [Sip-implementors] Offer/Answer question



Manpreet Singh wrote:
> Wasn't denying the use of update on confirmed dialog, just saying the 
> recommended use of UPDATE is for early dialog and not for confirmed 
> based on the spec.
> 
> ""Although UPDATE can be used on confirmed dialogs, it is RECOMMENDED 
> that a re-INVITE be used instead. This is because an UPDATE needs to 
> be answered immediately, ruling out the possibility of user approval. 
> Such approval will frequently be needed, and is possible with a 
> re-INVITE.""

IMO the "denial" is a bit overstated. It is only pointing out that its
inappropriate if the offer it carries will require an extended time for
approval before being answered. If that isn't to be the case then there
isn't any issue with using UPDATE.

Note that the issue with immediate response also applies to an UPDATE
used during an early dialog.

	Paul

> Thnx
> 
> -----Original Message-----
> From: Paul Kyzivat [mailto:pkyzivat at cisco.com]
> Sent: Saturday, April 12, 2008 11:49 PM
> To: Manpreet Singh
> Cc: kaiduan xie; Bob Penfield; discussion at sipforum.org; 
> sip-implementors at lists.cs.columbia.edu
> Subject: Re: [Sip-implementors] Offer/Answer question
> 
> It is permitted to use UPDATE after a dialog has been established. 
> AFAIK the flow shown is legal. In any case from the POV of the UAS, it

> is no different than if the ACK had been sent first and then the 
> UPDATE send, with the UPDATE arriving first, which can happen.
> 
> 	Paul
> 
> Manpreet Singh wrote:
>> I believe the recommended use of UPDATE for offer/answer is in early 
>> dialog state but after 200OK, its in confirmed dialog state. But if 
>> that limitation werent there, then it might just be valid to do it 
>> too. May be other folks can confirm?
>>
>> M
>>
>> -----Original Message-----
>> From: kaiduan xie [mailto:kaiduanx at yahoo.ca]
>> Sent: Friday, April 11, 2008 10:32 PM
>> To: Bob Penfield; Manpreet Singh; discussion at sipforum.org; 
>> sip-implementors at lists.cs.columbia.edu
>> Subject: Re: [Sip-implementors] Offer/Answer question
>>
>> Is the following case legal?
>>
>> UAC                              UAS
>> INVITE/SDP  ------------------->
>> <-------------------------------- 200/SDP, UPDATE/SDP
>> ---------------->
>> <------------ 200 for UPDATE/SDP
>> ACK(no SDP) ------------------>
>>
>> There is no PRACK in the call flow.
>>
>> Thanks,
>>
>> kaiduan
>> ----- Original Message ----
>> From: Bob Penfield <BPenfield at acmepacket.com>
>> To: Manpreet Singh <msingh at ibasis.net>; "discussion at sipforum.org"
>> <discussion at sipforum.org>; "sip-implementors at lists.cs.columbia.edu"
>> <sip-implementors at lists.cs.columbia.edu>
>> Sent: Friday, April 11, 2008 5:54:36 PM
>> Subject: Re: [Sip-implementors] Offer/Answer question
>>
>> Yes. The 200 OK (or the 180 if using 100rel) MUST have the answer.
>>
>> cheers,
>> (-:bob
>>
>> -----Original Message-----
>> From: sip-implementors-bounces at lists.cs.columbia.edu
>> [mailto:sip-implementors-bounces at lists.cs.columbia.edu] On Behalf Of 
>> Manpreet Singh
>> Sent: Friday, April 11, 2008 1:47 PM
>> To: discussion at sipforum.org; sip-implementors at lists.cs.columbia.edu
>> Subject: [Sip-implementors] Offer/Answer question
>>
>> For an INVITE carrying an offer, does the offer/answer has to 
>> complete
> 
>> within the INVITE transaction? Can it complete outside the 
>> transaction
> 
>> but within the same dialog? Call flow is:
>>
>> -------------->Invite ( offer )
>> <------------180 ( ringing )
>> <------------200OK ( empty..no offer )
>> ------------->ACK
>> <------------Re-Invite ( Answer to offer in first invite )
>> -------------->200OK
>> <--------------ACK
>>
>> M
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>>
>>
>>       
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