Subject: [SIP] Proxying user names to phone numbers

From: Eero Vaarnas <[email-masked]>
Date: Fri, 21 Jul 2000 14:52:35 +0300

I have a question about proxying invitations to a different user name
(or phone_number@host). At first, what fields should the Proxy Server
modify, and secondly by what field should the User Agent identify the
incoming INVITEs?
  I haven't found any call flow examples in the SIP WG pages or in this
list, and different SIP software and hardware show mixed results. If I
register address [email-masked] to be contacted at
[email-masked], most servers would send the INVITE
something like this:

INVITE sip:[email-masked] SIP/2.0
To: "user" <sip:[email-masked]>
From: "sender" <sip:[email-masked]>
Call-ID: [email-masked]
Via: SIP/2.0/UDP sip_proxy.domain.com:5060; branch=1
Via: SIP/2.0/UDP sender_machine.domain.com:5060
CSeq: 5 INVITE
Content-Type: application/sdp
Content-Length: 141
<!-- some sdp content -->

In other words, the request URI is changed, leaving the "To" field
unmodified. Most User Agents understand this INVITE, but some others
return "Not found 404". They work fine, if I create a user with the user
name "14471447" at the proxy also. Then the message looks like this:

INVITE sip:[email-masked] SIP/2.0
To: "14471447" <sip:[email-masked]>
From: "sender" <sip:[email-masked]>
Call-ID: [email-masked]
Via: SIP/2.0/UDP sip_proxy.domain.com:5060; branch=1
Via: SIP/2.0/UDP sender_machine.domain.com:5060
CSeq: 5 INVITE
Content-Type: application/sdp
Content-Length: 141
<!-- some sdp content -->

Somehow it seems that they check only that the user name in "To" field
matches. With phone numbers this makes sense, but with arbitrary user
names it seems weird. Shouldn't the idea be that any _address_ can be
mapped to any other, without the need to user names to be "global". 
  According to rfc2543, request URI is the field that identifies the
user in the final endpoint. Am I right that User Agents should answer to
INVITEs with their user name at the request URI, not in the "To" field?

-- 
Eero Vaarnas

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---

From: Jonathan Rosenberg <[email-masked]>
Date: Fri, 21 Jul 2000 11:58:41 -0400

Eero Vaarnas wrote:
> modify, 

as always, request URI.

and secondly by what field should the User Agent identify the
> incoming INVITEs?

request URI.

> <!-- some sdp content -->

Thats correct.

> <!-- some sdp content -->

This message would only get sent if the caller knew the called party as
sip:[email-masked], and explicitly addressed them as such.

> matches.

That is wrong. It is the request URI, for both phone numbers and names.

> With phone numbers this makes sense, but with arbitrary user

Absolutely correct.

We'll clarify and I'll add this to the FAQ.

-Jonathan R.

-- 
Jonathan D. Rosenberg                       72 Eagle Rock Ave.
Chief Scientist                             First Floor
dynamicsoft                                 East Hanover, NJ 07936
[email-masked]                     FAX:   (973) 952-5050
http://www.cs.columbia.edu/~jdrosen         PHONE: (732) 741-7244
http://www.dynamicsoft.com