[SIPForum-discussion] forwarding more than one 2xx in a proxy server

Robert Sparks rjsparks at nostrum.com
Fri Feb 2 15:39:23 UTC 2007

The text as written was intended to cause the proxy to forward the  
second and any subsequent 2xx responses statelessly
(search for the word statelessly in that section).

MANY proxy implementors have written code that does the correct thing  
here (if you are not sure what the correct thing
to do is, we can walk through it off-list).

Now, I have to point out that there is a known bug with moving that  
transition to terminated (see http://bugs.sipit.net/show_bug.cgi? 
 From that bug report:

> The current text in 3261 instructs a UAS to destroy an INVITE  
> transaction the
> instant it sends a 200.
> This has the unintended consequence that any retransmissions of the  
> request that arrive after that destruction will be treated as a new  
> request.
> This interacts both with endpoints and proxies (the deletion of the  
> server
> transaction combined with stateless forwarding of responses without  
> matching
> transactions provided forwarding of multiple 200s to forked INVITES).
> The fix will involve having the server transaction continue to  
> exist long
> enough to drain any retransmissions of the INVITE and related  
> changes to
> the UAS handling of retransmitting the 200s, and proxies handling  
> multiple
> 200s/stray responses.


On Feb 2, 2007, at 6:21 AM, Young-Geun Park wrote:

> Hi, all
> The following is described in 16.7.5, RFC3261(p110):
> After a final response has been sent on the server transaction,
> the following responses MUST be forwarded immediately:
> - Any 2xx response to an INVITE request
> (………….)
> This step, combined with the next, ensures that a stateful
> proxy will forward exactly one final response to a non-INVITE
> request, and either exactly one non-2xx response or *one or more*
> 2xx responses to an INVITE request.
> --
> The server tx’s state would transition to ‘terminated’ state  
> because of first 200 OK.
> So I think that it is impossible for second 200Ok to be forwarded  
> by the same server tx.
> I don’t know why it is possible.
> Best regards,
> Park
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