[Iptel] Is trunk group a new namespace?

Folks,

In order to close the last open issue with trunk-group, I had
a series of email exchanges with the WG chairs, the
results of which now need to go before the WG to decide how to
move forward.

The last open issue was how to resolve the case where an
incoming call request does not have a calling party's number
available.  How do we indicate the originating trunk group?

We had almost reached a solution in the form of the following
URI: Contact: <sip:telurifmt;tgrp=foo@example.com> (the
I-D exhorts originating trunk groups to go in the Contact
header).

In the email exchange with the WG chairs, Jonathan has
suggested a couple of issues: first, the fact that a trunk
group can exist without a phone number appears to imply that
it is cannot be associated with a tel URI and may, in fact,
indicate that this is a new resource complete with its
own scheme.  Something like:

    trgrp:trunk-group-id[:phone-number]@domain

Second, saving the originating trunk group in the Contact
header is not semantically correct; if the originating trunk
group is to be used for routing, then Contact is not the
semantically correct header to save this information in.

Here is my take on these issues.  The second one is easier
to tackle, so let me try that first.  Jonathan is accurate
in pointing out the semantic use of Contact header.  How-
ever, we reached a decision long time ago in the life of
the trunk-group I-D that we would like NOT to have parameters
like ;o-tgrp=xxx;t-tgrp=yyy in the R-URI.  Hence we
decided to put the originating trunk group in the Contact
header with the understanding that when it is used for
routing in the reverse side, it will appear in the R-URI
position.  But what if it is used in routing on the initiating
side?

The first issue -- trunk-group being a new resource --
is an interesting one.  It has ramificiations, if we decide
to go that route.  Where will it appear?  In a new header(s)?
as parameters to the R-URI or the Contact URI?  We will need
a short paragraph on how to convert trgrp URIs to sip URIs
or tell URIs, ...

So, we have some choices to make:

Regarding putting originating trunk group information: do we
want to leave it in the Contact header or find a new place
for it?

Regarding representing trunk group information itself: do we
want hash out more abstractly the relationship between the
trunk group and the phone number from a namespace prespective?

To make matters worse, I will point out that we already have
a few implementations that are following
http://www.ietf.org/internet-drafts/draft-ietf-iptel-trunk-group-02.txt.
So depending on what we decide, the implementations will be impacted.

Opinions and comments 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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