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

Fri Nov 10 08:14:48 CST 2006

I found some older discussions on this same subject:

http://www1.ietf.org/mail-archive/web/sip/current/msg10443.html

http://www.atm.tut.fi/list-archive/sip/msg06721.html

It seems to me that a single UA phone device would want the merge
detection as specified in 3261 - ie. why ring for the same call on 2
different lines?  But UA's that handle multiple identities or route
calls differently based on request-uri (ie. B2BUA's, MediaServers,
Gateways, etc) would want to include the request uri in the merge
detection.  I can make this an option in the DUM master profile, if we
agree this is a good idea.

Scott

From: Robert Sparks [mailto:rjsparks at nostrum.com] 
Sent: Thursday, November 09, 2006 12:35 PM
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 .

I went back through 3261 and agree that it doesn't say to include RURI.
I have memories of filing this as a bug (and having this conversation

on the SIP list several years ago), but I don't find it in the bug
tracker now. I'll take it back through the SIP list again. But yeah - we
should be

including the RURI. 

RjS

On Nov 9, 2006, at 9:18 AM, Scott Godin wrote:

It seems that including the RequestUri in the merged request detection
would fix all of these and maintain "actual" merge detection.  Is there
any reason not to include this (other than it's not what 3261 says to
do)?

Scott

From: Robert Sparks [mailto:rjsparks at nostrum.com] 
Sent: Thursday, November 09, 2006 12:12 PM
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 .

And this is a problem - this is neither a loop nor a merge - it is two
real requests the TU should handle.

The redirection is a red-herring from a black-box functionality point of
view (if there are artifacts from having

sent the redirection to the first request causing the loop we can fix
the code so there's not). But this should

be handled no differently at the TU level than having the an invite
forked by a previous proxy to A and B

both of which land at me. If A arrives first and I reject it (with any
error response - think 404 instead of 3xx

for a moment), then B shows up, my TU needs to handle B as an
independent request, not treat it as a merge.

(To be complete in the description - if a proxy P1 forked to P2 and P3,
and each of those forwarded the request

to A at my TU, then the second one arriving I should reject with a 482 -
that's the actual merge case).

RjS

On Nov 9, 2006, at 8:55 AM, Scott Godin wrote:

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
<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
<mailto: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
<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
<mailto: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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