Subject: Re: [SIP] Second try : Questions about REGISTER

From: Sean Olson <[email-masked]>
Date: Tue, 2 May 2000 18:58:10 -0500 (CDT)

> This is exactly my point of confusion. The text in 4.2.6 is actually
> raising
> more questions than answering. I cannot think of a case when a mismatch
> in
> the domain of To header and Request-URI would be useful. If the proxy
> services
> more than 2 domains, the domain in To header and Request-URI would still
> be
> same or may be I am missing something.
> 

Virtual hosting. A single SIP proxy accepts (REGISTER) requests for multiple domains.
Depending on the domain, the proxy forwards the REGISTER request to a particular
provisioned registrar, in the process re-writing the domain of the request URI according
to that registrar's needs/whims. This could even involve forking of the REGISTER request.
The To: remains (of course) unchanged.

Or maybe load balancing. A single domain is split into logical sub-domains based on the
a combination of the user/To/From/whatever by a front-end proxy. The request-URI is
rewritten to reflect the particular sub-domain of the registrar to which the REGISTER 
request ultimately gets forwarded. The To: remains (of course) unchanged.

Or as indicated on page 28 under the Request-URI description, the registrar acting
as a VLR accepts registrations for domains other than the domain given in the 
Request-URI.

The To: header determines the registration that is affected. The request-URI 
determines the domain of the registrar. These are logically separate concepts and there
is no good reason to mandate that the domain in the To: is the same as the domain
in the Request-URI

Sean Olson <[email-masked]>

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