Subject: RE: [Sipping] How to indicate trunk groups in URI?

From: "Tom-PT Taylor" <[email-masked]>
Date: Tue, 27 Aug 2002 09:11:33 -0400

On the point of trunk groups split across gateways: it depends on whether
the gateway is analogous to a PSTN switch peripheral or to a PSTN switch.
"Gateway" in the Megaco sense corresponds to the former, hence it would be
quite reasonable according to typical PSTN practice to split trunk groups
across Megaco gateways.  In the present discussion, however, I think we are
using the term "gateway" for something which is analogous to the entire PSTN
switch.  Thus I agree with Mike's assertion that the term "trunk group" is
inappropriate for something supported by multiple gateways.  The closest
PSTN term I can come up with is "route".

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]
Sent: Monday, August 26, 2002 11:19 PM
To: [email-masked]; [email-masked]
Subject: Re: [Sipping] How to indicate trunk groups in URI?

In a message dated 8/26/02 12:15:20 PM Eastern Daylight Time,
[email-masked] writes: 

This comes from the Gateway Registration work in the IPTEL group. It 
represents resources in or beyond the gateway. Jon Peterson's just expired 
draft (draft-peterson-iptel-gwreg-arch-00.txt) describes an architecture for

using trunk groups in gateway registration. 

[MAP] I think the referenced Peterson draft contains the correct definition
of "trunk" and "trunk group". There was another definition floating around
that was causing trouble by relating it to what numbers were reachable
through it. 

The thing in the Peterson draft that might cause some difficulty is the
notion of a single "Trunk Group" spanning multiple gateways. It seems to
reflect the incorrect definition by referring to a Trunk Group spanning GW1
and GW2, maybe only because a common set of phone numbers (+1202 and
+1704...) are reachable through both parts. The question is whether or not
there is any requirement to support this case (spanning GWs). It would seem
that supporting this spanning would significantly complicate any use of the
registration function. 

There are already standardized schemes to refer to trunks and trunk groups
between PSTN switches (at least in the US). They generally begin with a
standardized identification for each entity (gateway in this case). It seems
that the task here is coding those identifiers into a URL-type format, not
defining a new scheme 

Mike Pierce 
Artel 
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---

From: "Bob Penfield" <[email-masked]>
Date: Tue, 27 Aug 2002 11:17:09 -0400

In this context, we are talking about a proxy which has determined that a
call needs to go to a given resource which exists behind multiple gateways.
That resource is a set of trunks. In this case, that set of trunks terminate
on a single PSTN switch, but they are connected to multiple gateways. On the
PSTN side it is a single trunk group, and that is the resource that needs to
be expressed. For the SIP routing, based on things like destination number
and preferred carrier, the desired target of the call is that single trunk
group. The information used to make the routing decision (carrier,
destination-prefix, trunk-group, circuit availability, etc) can be learned
from TRIP-GW, but that's a discussion for the IPTEL list. Once that target
trunk group has been determined, the SIP proxy must then select one of the
gateways connected to that trunk group to send the request to.

I think a URI parameter is the best way. The trunk group label itself can be
arbitrary since it is owned by the PSTN switch the gateways connect to. Only
the parameter name needs to be standardized. If a gateway registration
protocol (like TRIP-GW) is being used, the trunk group information only
needs to be provisioned in the gateways. All the SIP proxy needs to do is
take that label it learned and add it to the URI as a trunk group parameter.

cheers,
(-:bob

Robert F. Penfield
Chief Software Architect
Acme Packet, Inc.
130 New Boston Street
Woburn, MA 01801
[email-masked]

----- Original Message -----
From: "Tom-PT Taylor" <[email-masked]>
To: <[email-masked]>; "'Peterson, Jon'" <[email-masked]>;
<[email-masked]>
Sent: Tuesday, August 27, 2002 9:11 AM
Subject: RE: [Sipping] How to indicate trunk groups in URI?