Subject: [Sip] Poll: expert review of draft-henrikson-sip-charging-information

From: "Dean Willis" <[email-masked]>
Date: Fri, 24 May 2002 14:27:32 -0500

You may recall that we're doing an Expert Review of
draft-henrikson-sip-charging-information.

If you have a strong opinion for, against, or supporting a need for
further work, or any further suggestions for enhancement, please post
them now.

--
Dean Willis

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---

From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 29 May 2002 16:03:31 -0400

First off, I have to apologize for the lateness of these comments. Given
the scope of my comments, I should have raised them earlier. 

I have some serious concerns about this draft.

Most notably, I disagree entirely with the assessment that the problem
isn't entirely solved by loose routing. When the S-CSCF sends a request
to an application server, it ought to be inserting two loose routes -
one that points to the AS, and another that points back to itself,
containing whatever context is needed for the S-CSCF to do what it needs
to do from that point forward. The draft makes the following statement:

>  One may consider using the Route header as a mechanism to get the 
>     request sent back to the S-CSCF.  However, Route headers don't 
>     automatically transit an AS acting as a B2BUA. This could be 
>     overcome by using loose-routing and application logic in the B2BUA.  
>     But that is not the full problem to be solved. A strong correlation 
>     of dialogs is also needed for accounting purposes to treat the 
>     sequence of dialogs as a concatenated single dialog. A common 
>     identification tag needs to be carried in each related dialog so 
>     that the charging functions can associate all the dialogs. 

A smart B2BUA will not discard loose routes, particularly not one thats
used in 3gpp for this reason exactly. Thus, the principal motivation
given, being able to corelate incoming INVITEs from outgoing ones in a
spiral - is not correct. We explicitly designed the loose routing stuff
to enable exactly this kind of function (remember the Bjorkner service
route draft?).

The other argument that is given here - correlation of dialogs for
accounting purposes - makes no sense to me. The route header provides
the ability for the S-CSCF to completely correlate the incoming INVITE
to the one it sent out. It therefore has all the information it needs to
account for the calls and to know which applications are invoked. 

The last thing I want to do is specify two ways of doing the same thing.
Given that this kind of correlation is square in the sights of loose
routing, I am concerned about the overlap.

-Jonathan R.

-- 
Jonathan D. Rosenberg, Ph.D.            72 Eagle Rock Avenue
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