[reSIProcate] Call routed back to reSIProcate by SipX PBX after 302temp moved .

[Scott Godin]

The scenario you describe with the PSTN gateway boils down to the same
merge request detection issue.  The problem is possible either with
forking or with recursive redirecting proxies.

 

I'll try to reword Steven's original description - but I'll use a PSTN
gateway instead of a B2BUA for simplicity.

Steps:

1.        Call comes in from PSTN to gateway. 

2.       Gateway passes the call to a recursive redirecting proxy.

3.       Proxy recursively redirects to another endpoint on the same
gateway.

4.       The gateway receives a copy of the invite it sent out, but this
time with a different request uri and a loop is detected.

 

Scott

 

From: Robert Sparks [mailto:rjsparks at nostrum.com] 
Sent: Thursday, November 09, 2006 11:49 AM
To: Scott Godin
Cc: Steven Coule; resiprocate-devel at list.sipfoundry.org
Subject: Re: [reSIProcate] Call routed back to reSIProcate by SipX PBX
after 302temp moved .

 

Scott -

 

Could you re-sketch the problem for me (an example of the RURI and VIas
of both of the arriving requests would help).

 

I'm pretty sure you always want the RURI as part of that check (if
someone is running a pstn gateway using resip and a message 

forks to two different PSTN numbers through that gateway, the second one
mustn't get 482ed) , but before we dive into it, lets get 

a concrete example to work against.

 

RjS

 

On Nov 9, 2006, at 5:54 AM, Scott Godin wrote:





Hmm - that is an interesting problem.  Resip/dum is behaving to spec -
UA's are supposed to do merge request detection in this way.  But this
detection causes problems for B2BUA's in the scenario you described.
Maybe we should have an option for B2BUA's that allows including the
request URI in merge request detection.

 

I'd be interested to hear from others on what they think/know is correct
solution to this is.

 

BTW:  You mentioned that if you include the request uri in the merge
request matching, then you still get a loop detected - I don't quite
understand why that is happening.

 

Scott

 

From: resiprocate-devel-bounces at list.sipfoundry.org
[mailto:resiprocate-devel-bounces at list.sipfoundry.org] On Behalf Of
Steven Coule
Sent: Wednesday, November 08, 2006 9:22 AM
To: resiprocate-devel at list.sipfoundry.org
Subject: [reSIProcate] Call routed back to reSIProcate by SipX PBX after
302temp moved .

 

We have a problem with reSIProcate when operating as a B2BUA between
UACs and a proxy IP PBX such as SipX.

 

The scenario is: 

 

The standard INVITE call flow is from  (1) UAC1 -> (2) B2BUA -> (3) SipX
-> (4) B2BUA -> (5) UAC2 

 

Our B2BUA is registrar for UAC1 and UAC2, and the B2BUA also registers
to SipX with the ids of UAC1 and UAC2. SipX therefore believes both UAC1
and UAC2 are at the B2BUA ... There is only one B2BUA, (2) and (4)
represent flows through the B2BUA.

 

This works ok for a normal call. However if at step 4, the INVITE from
SIPX to B2BUA is rejected with a 302 to redirect the call to UAC3 (also
registered through our B2BUA) , SipX then sends another INVITE to the
B2BUA with an updated URI for UAC3 but with the To & From headers
unchanged. 

 

reSIProcate then returns an error 482 request merged to SipX  ... there
was some commented out code in MergedRequestKey which appeared to check
for a change in the request URI but adding this check again did not
resolve the issue, 482 was still returned.

 

We are wondering whether the problem is caused because we haven't
cancelled stage (5) before returning the 302 to SipX ... 

 

Any ideas as to why this happens?  I have an ethereal trace available if
that helps!

 

Steve Coule

 

Envox Worldwide

 

Envox Worldwide - A Global Leader in Voice Solutions

www.envox.com <http://www.envox.com/> 

 

 

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