Subject: [SIP] Clarification on the proxy behaviour.

From: Sunitha Kumar <[email-masked]>
Date: Tue, 13 Jun 2000 17:59:31 -0700

Hi:

If a message goes through a proxy twice , ex:

client A----------> proxy1-------------> proxy 2
-------------------------->    proxy1.
                 sends  invite                forwards
this                           sends this back to proxy 1

proxy1----------------> client B.

In the above scenario, proxy 1 needs to distinguish between clientA-->
proxy1 INVITE, and proxy2--->proxy1 INVITE. This can be done in SIP by
putting a different branch in the Via.

My concern was that in the standard it is said that when a proxy sees
its own address in the Via, we need to
remove it , otherwise this may cause a loop. Now if we change the
branch, this will indeed not cause the loop.

However, I wanted to know if there was any other repurcussions if a
proxy does  this.  The SIP examples or the RFC as such does not mention
this scenario any where.

Thanks much !

--
Sunitha Kumar
http://www.vovida.com

---

From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 14 Jun 2000 00:15:02 -0400

This issue has been discussed numerous times on the list. It is referred
to as request "spiraling" and is not a loop. The mechanisms for
constructing the Via to support this are defined in the bis draft,
section 6.46. The text still needs some work though; a request is only a
loop if your IP address is there, AND, when you compute the hash over
the request URI, To, From, Call-ID, it matches the component in the
branch parameter.

-Jonathan R.

Sunitha Kumar wrote:
> proxy does  this.  The SIP examples or the RFC as such does not
> mention this scenario any where.
> 
> Thanks much !
> 
> --
> Sunitha Kumar
> http://www.vovida.com
> 
> 

-- 
Jonathan D. Rosenberg                       72 Eagle Rock Ave.
Chief Scientist                             First Floor
dynamicsoft                                 East Hanover, NJ 07936
[email-masked]                     FAX:   (973) 952-5050
http://www.cs.columbia.edu/~jdrosen         PHONE: (732) 741-7244
http://www.dynamicsoft.com

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---

From: Henning Schulzrinne <[email-masked]>
Date: Thu, 15 Jun 2000 14:50:52 -0400

Loop detection is described in 12.3.1 of the 2543bis draft. Suggestions
for improved wording are welcome. I added a reference to this section in
the Via description.
-- 
Henning Schulzrinne   http://www.cs.columbia.edu/~hgs