Subject: RE: [Sip] Doubt related to the contact header in the INVITE responses.

From: "Sanjay Sinha \(sanjsinh\)" <[email-masked]>
Date: Thu, 28 Sep 2006 10:02:32 -0400

Pl. see inline ..

________________________________

From: Gupta Vineet-A18467 [mailto:[email-masked]] 
Sent: Thursday, September 28, 2006 9:41 AM
To: [email-masked]
Subject: [Sip] Doubt related to the contact header in the INVITE
responses.

Hi, 

I had a doubt related to the setting of the contact header in responses
to INVITE request. 

 As per RFC-3261, it is clear that the remote-target (which is the URI
part of the contact header set by the remote party), can only be
modified through the INVITE request or any responses to INVITE request.
It cannot be modified through any other requests within the INVITE
dialog. 

It can be modified with UPDATE also. 

But what is not clear is that, "Whether some UAS can set a different
contact header, then the one it had set in a provisional response (like
183 session in progress), in subsequent provisional (like 180 ringing)
or final response to the INVITE transaction?" 

If the provisional response is sent reliably, then it does not make
sense for UAS to have different Contact header in provisional response
and the final response. Prack and ACK will be sent at different UAs
which may not even have knowledge of the dialog.

Sanjay

At present I am not able to think of the scenario, where such feature
might be required, but as I wanted to know whether an RFC-3261 compliant
SIP stack should allow/disallow this.

Regards, 
Vineet. 

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---

From: "Gupta Vineet-A18467" <[email-masked]>
Date: Thu, 28 Sep 2006 22:50:40 +0800

Hi Sanjay,
 
Thanks for the response. 
 
However, I think UPDATE request can also be sent before INVITE dialog is
established at the UAS through the receipt of ACK. So, I see that the
possibility of the ACK/PRACK being sent to the UAs which don't have  the
knowledge of the INVITE dialog, in case of the modification of the
target-URI through the UPDATE request too.
 
So, can we assume that even RFC-3261 does not restrict users from
setting the contact headers in different responses to the INVITE
request, even though such a feature may not serve any useful purpose (at
least, as per the use cases envisioned as of now).
 
Regards,
Vineet.

-----Original Message-----
From: Sanjay Sinha (sanjsinh) [mailto:[email-masked]]
Sent: Thursday, September 28, 2006 7:33 PM
To: Gupta Vineet-A18467; [email-masked]
Subject: RE: [Sip] Doubt related to the contact header in the INVITE
responses.

Pl. see inline ..

  _____  

Hi, 

Sanjay

Regards, 
Vineet.