Subject: [Sipping] To-header is possible solution to 3GPP Requ for originally dialle d user-ID?

From: Mayer Georg <[email-masked]>
Date: Wed, 6 Mar 2002 14:24:46 +0100

Hello,

as the dialog is now identified by Call-ID and only To- and From-Tags, there might be a chance to solve a 3GPP requirement very easily. Before dwelling in the 3G specific details I want to ask the general question:

Is a proxy allowed to change to content (besides the tags) of To and From headers?

Why would somebody (3GPP of course) need such an ill mechanism in a SIP network? 
In 3GPP IMS a (called) user may have several so-called public-user-identities (IMPU) of which only one needs to be registered explicitly with REGISTER and the others are implicitly registered. IMPUs are either sip:- or tel:-URLs. As user B may have more then one IMPU (one for work, one for friends, one for family...), she wants to get informed about the URL under which it was called. This is similar to the MSN (Multiple Subscriber Number) concept in ISDN.

So A calls B:
	INVITE	sip:[email-masked]
	To: "You owe me 10 Euro" <sip:my-best-friend@speed-dial>

The registrar of user B now replaces the request URI with the contact address of user B:
	INVITE	sip:a.b.c.d
	To: "You owe me 10 Euro" <sip:my-best-friend@speed-dial>

and after that, the originally dialled IMPU (sip:[email-masked]) is lost. 

So is there a chance that the registrar of user B or the outbound proxy of user A change the To-header in the INVITE in the following way:
	To: "You owe me 10 Euro" <sip:[email-masked]>

I'd be happy to get some comments from your side.

Thanks a lot
Georg

_______________________________________________________
Georg Mayer - Siemens AG
Information and Communication Mobile
ICM N PG SP ST N 1
Hofmannstr. 51, 81359 Munich, Germany
Fon: +49-89-722-33114
Fax: +49-89-722-62250
Mobile: +49-172-5371233
Email: [email-masked]

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