Subject: [Sipping] Multiple Third Party Registrations?

From: "Ali Cameron" <[email-masked]>
Date: Thu, 30 Jun 2005 15:09:59 +0100

I'm looking at the issue of third party registrations with SIP. My 
understanding is that it is supported in the standard, but is it widely 
implemented? Related to this, and in some ways the next step, is the issue 
of multiple third party registrations - could anyone please advise if they 
know of implementations that support this?

Thanks,
Ali

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From: "Dale Worley" <[email-masked]>
Date: Thu, 30 Jun 2005 10:17:24 -0400

> From: Ali Cameron

The only way to distinguish third-party registrations is by examining the
From: field, which is otherwise of no interest.  I expect that most SIP
registrars accept any third-party registration as long as it can be
authenticated.

Dale

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From: Arjun Roychowdhury <[email-masked]>
Date: Thu, 30 Jun 2005 12:12:47 -0400

Not sure what network you have in mind - 
I have not seen it used very often in the SIP implementations today
but it is being used in various IMS network/trials where the S-CSCF
acts as a 3rd party registrar
on behalf of the UE (user equipment) - you may want to refer to TS
24.229 for the procedures are guidelines.

regds
arjun

-- 
Arjun Roychowdhury

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From: Paul Kyzivat <[email-masked]>
Date: Thu, 30 Jun 2005 19:07:31 -0400

> 24.229 for the procedures are guidelines.

What IMS calls 3rd party registration bears only passing resemblance to 
what is usually called 3rd party registration in ietf.

The REGISTER message the S-CSCF generates has a Contact identifying 
itself, not the UE. So if it is anything, it is more like a 1st party 
registration. But the target is not in any real sense a registrar, so 
who knows what this is in reality.

In any case, I don't think that has any bearing on 3rd party 
registrations in SIP. Its unfortunate that the same name was used for both.

	Paul

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From: Arjun Roychowdhury <[email-masked]>
Date: Thu, 30 Jun 2005 23:48:01 -0400

Well, even though it provides a contact of the S-CSCF, the To header
is that of the public user identity of the UE and not itself. Per 3261
"The To header field contains the address of record whose 
registration is to be created, queried, or modified. " where as the
role of the Contact header is to create an address binding.

My interpretation of this text is that the To header idenfies whether
its a 3rd party registration or not and not whatever you put into
contact. therefore, this is more in line with the 'theoretical'
definition of 3261's third party registration, which is only
classified by the contents of the to header.

-- 
Arjun Roychowdhury