[Iptel] Originating trunk group without calling number (Was [Re: Comments on Trunk Group ID])

Shan Lu wrote:

> Vijay,
[...]
> I am happy with the draft as far as destination TG is concerned. 
> But I don't think it should prescribe a formula for originating 
> TG whose validity is sometimes questionable.

I think you mean above that the validity of the calling party
number is questionable, not the trunk group's?

OK, so given the ensuing discussion on the appropriateness of
carrying a trunk group even if the calling party number is not
available, it would seem that there are three ways to move
forward.

I would like to reach consensus on one of them.  Let me list
them and provide some pros and cons.

(1) As suggested by Shan Lu, using a "tel:-;tgrp=foo" in
     the Contact URI.

(2) In the Contact, use a tel URI of the form:
     "tel:0000;tgrp=foo;phone-context=example.com"

(3) In the Contact, use a SIP URI of the form:
     "sip:anonymous;tgrp=foo;phone-context=example.com@example.com"

For (1), I wonder if the intent of the author of rfc2806-bis
was indeed to sanction such use.  While the ABNF may allow
it implicitly, should we endorse such a usage?  I am sure
with enough ingenuity, production rules of many ABNFs can
yield pretty interesting outcomes.

Maybe the WG can decide if the use of tel URI in this form
is okay.

In (2), the "0000" in the Contact URI serves as a filler.
The proxy receiving a request from its upstream gateway
with such a filler will know that an calling party number
was not provided.

Note that this case is distinct from a "0000" in the
R-URI of a request arriving from the PSTN, which could
signify a valid number in the domain of the proxy handling
the request.

(3) uses a SIP URI in the Contact header, avoiding the
ambiguities associated with (1) and (2).

My preference would be (3).

Any feedback and discussion most welcome.

Thanks,

- vijay
-- 
Vijay K. Gurbani  vkg@{lucent.com,research.bell-labs.com,acm.org}
Wireless Networks Group/Internet Software and Services
Lucent Technologies/Bell Labs Innovations, 2000 Lucent Lane, Rm 6G-440
Naperville, Illinois 60566     Voice: +1 630 224 0216

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