Subject: [Sipping] SIP Status code for communicating about UA in minimal state- Post active dialog

From: "Rajeev Narang \(ranarang\)" <[email-masked]>
Date: Wed, 12 Apr 2006 12:13:36 +0530

Hi,
 
Say we have the following scenario:-
 
 phone1-----B2BUA1----dialog1 (active) ----B2BUA2----phone2
 
There is a session timers active on the dialog1. Say UA1 is the
refresher.
 
An event occurs which results in B2BUA2 loosing network with phone2. 
For our requirement we still want to allow dialog1 to be active with no
interupption to the periodic session refresh. The B2BUA2 must keep on
responding to the session refresh.
 
The requirement is that we want to communicate to B2BUA1 about this
recent situation with B2BUA2 in response to the session refresh. The
B2BUA1 must be allowed to take some specific action based on the state
of the B2BUA2. Also Proxy server between the UA's mustn't tear down the
call.
 
Basically the response code should be such that the session refresh
procedure must go "on" but remote (refresher) must come to know about
this situation.
 
>From the available SIP status codes the following are choices:-
1) 200 OK:- Using this status code would indicate a normal situation, so
doesn't seem appropriate.
2) 488 Not Acceptable Here:- Not sure if this will make sense for mid
call.
3) 480 Temporarily Unavailable:- Not sure if this will make sense for
mid call.
 
Any suggestions on the SIP Status code so that we can handle it in a
standard way.
 
How about creating a new SIP Status code.
Say:- "450 Call in Minimal/Preserved State"
 
Thanks much,
Rajeev
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From: "Dale R. Worley" <[email-masked]>
Date: Wed, 12 Apr 2006 09:52:18 -0400

On Wed, 2006-04-12 at 12:13 +0530, Rajeev Narang (ranarang) wrote:
> of the B2BUA2. Also Proxy server between the UA's mustn't tear down
> the call.
>  

The difficulty is that you want to communicate "this dialog is
continuing, but not really".  This seems to be sufficiently specialized
for your application that it is unlikely to be standardized.  I would
suggest designing an "out of band" communication channel between B2BUA1
and B2BUA2.  You could use INFO messages, or even your own method, to
implement this, or define some private headers you can piggyback on the
ordinary SIP transactions.

Dale