Subject: Request-URI and To header

From: Shail Bhatnagar <[email-masked]>
Date: Tue, 27 Jul 1999 15:17:22 -0400

If my target SIP URL is <sip:[email-masked]> and 
I resolve it to an IP address : 10.0.0.4, what should be my 
Request-URI and To header :

INVITE sip:[email-masked] SIP/2.0
To: <sip:[email-masked]>

or both should be same ??

-- 
Best regards,
Shail

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From: Jonathan Rosenberg <[email-masked]>
Date: Tue, 27 Jul 1999 16:35:18 -0400

> or both should be same ??

I'm guessing you're talking about a gateway? The process is as follows:

1. start with the called party address: sip:[email-masked]
2. place the called party address into the To field
3. place the called party address into the request URI
4. determine the server to send the request to; here its
10.0.0.4.
5. Send the message to the 10.0.0.4:

INVITE sip:[email-masked]
To: sip:[email-masked]

Now, lets say the server is a proxy at udp.com. The proxy receives this.
It determines that sip:[email-masked] is sip:[email-masked]. It
might know this from a registration, or from a database query, or any
location service. So, the proxy does the following:

1. places the translated address into the request URI
2. looks up the host portion to find the next hop server for it; say its
10.0.0.5.
3. sends the request to 10.0.0.5:

INVITE sip:[email-masked]
To: sip:[email-masked]

Lets consider a different case, where 10.0.0.4 is not the result of
looking up sip.udp.com in DNS, but rather a local proxy that the client
is configured to always send requests to. This proxy would receive the
request, and note that the request URI is for a user not in its own
domain. So, it looks up sip.udp.com in DNS, and finds a server for it.
Lets say the result is 1.2.3.4. So, it sends the request to 1.2.3.4:

INVITE sip:[email-masked]
To: sip:[email-masked]

Notice here the request URI has not changed. The local proxy has
effectively provided a remote DNS service. The gateway can send all its
requests there without having to have DNS support. The local proxy can
be used for other functions too, like call screening and others.

This is probably not clear from the spec. I think we need to clarify the
whole issue of setting the To and Request URI fields, and in particular
how this all interacts with registrations and record-routes.

Hope that answers your question,

Jonathan R.
-- 
Jonathan D. Rosenberg                       Lucent Technologies
Member of Technical Staff                   101 Crawfords Corner Rd.
High Speed Networks Research                Holmdel, NJ 07733
FAX: (732) 834-5379                         Rm. 4C-526
EMAIL: [email-masked]
URL: http://www.cs.columbia.edu/~jdrosen

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From: Shail Bhatnagar <[email-masked]>
Date: Tue, 27 Jul 1999 17:47:13 -0400

Jonathan, Thanks for the quick response. It really clears things up.

Regards,
Shail

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From: [email-masked]
Date: Wed, 28 Jul 1999 00:52:38 +0300

Hi,

> or both should be same ??

The 'To' header does not have to be changed when we resolve the host part of it.

The callee UAS/UAC will be probably configured for receiving calls addressed to
<sip:[email-masked]>, but not for a different SIP URL (with a different host
part)...

Regards,

Gonzalo