[asterisk-bugs] [Asterisk 0011536]: With "pedantic=yes" Asterisk shouldn't match To tag if the dialog is not established

[noreply at bugs.digium.com]

A NOTE has been added to this issue. 
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http://bugs.digium.com/view.php?id=11536 
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Reported By:                ibc
Assigned To:                
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Project:                    Asterisk
Issue ID:                   11536
Category:                   Channels/chan_sip/Interoperability
Reproducibility:            always
Severity:                   minor
Priority:                   normal
Status:                     acknowledged
Asterisk Version:           1.4.15  
SVN Branch (only for SVN checkouts, not tarball releases): N/A  
SVN Revision (number only!):  
Disclaimer on File?:        N/A 
Request Review:              
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Date Submitted:             12-13-2007 06:58 CST
Last Modified:              06-20-2008 11:43 CDT
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Summary:                    With "pedantic=yes" Asterisk shouldn't match To tag
if the dialog is not established
Description: 
Asterisk in SIP pedantic mode.

- Asterisk calls to an external SIP user in OpenSer proxy.
- After "Ringing" Asterisk sends CANCEL.
- OpenSer replies with "200 canceling" but Asterisk doesn't recognize it
so resends the CANCEL.

I've a theory of why it fails:

The "180 Ringing" contains a "To" tag:
  To: <sip:ibc at aliax.net>;tag=veuje

When Asterisk sends CANCEL OpenSer replies with:
  SIP/2.0 200 canceling
  To: <sip:ibc at aliax.net>;tag=373b8885156114ecb2c4bd665f9faf0b-f9aa

So Asterisk asumes wrong To tag (because it's different as the received
one) and discards it.

Of course, OpenSer proxy behaviour is correct: there could be many "180
Ringing" each one with different To tag in case of forking scenario, so the
To tag in the "200 canceling" from OpenSer *shouldn't* match any previous
"To" tag received in any provisional response.

About it I opened a thread in Sip-implementators mailist in which this
issue is explained:
 
https://lists.cs.columbia.edu/pipermail/sip-implementors/2007-October/017668.html


IMHO the solution would be:
Asterisk shouldn't try to match a To tag if the dialog is not yet
established. And Asterisk should assume that it can receive multiples To
tag in provisional responses in case of forking scenarios (there are more
SIP in the world than just single phones registered in Asterisk XD).
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---------------------------------------------------------------------- 
 Corydon76 - 06-20-08 11:43  
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I think the response you received on the SIP Implementors list was
incorrect.  The section that he cites says this:

<pre>
   While a CANCEL request is handled in a stateful proxy by its own
   server transaction, a new response context is not created for it.
   Instead, the proxy layer searches its existing response contexts for
   the server transaction handling the request associated with this
   CANCEL.  If a matching response context is found, the element MUST
   immediately return a 200 (OK) response to the CANCEL request.  In
   this case, the element is acting as a user agent server as defined in
   Section 8.2.  Furthermore, the element MUST generate CANCEL requests
   for all pending client transactions in the context as described in
   Section 16.7 step 10.
</pre>

Note the phrase "the element is acting as a user agent server".  That
means that the proxy is acting as a user agent server, and since the RFC
refers to an element, ANY element, including a proxy, must act the same
way.  In this case, I think that Asterisk is behaving correctly, and it is
the proxy which is misbehaving. 

Issue History 
Date Modified   Username       Field                    Change               
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06-20-08 11:43  Corydon76      Note Added: 0089021                          
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