Subject: [IPTEL] Definition of "trunk group"

From: [email-masked]
Date: Mon, 31 Dec 2001 14:12:27 EST

I have the following comments concerning the use of the term "trunk groups" 
based on the presentation in SLC and the discussion on the list:

I believe that a lot of the disagreement is related to the definition and 
concept of what a "trunk group" is. There was mention of a "trunk group" 
being those facilities through which one could get to a specific destination 
or reach a specific set of carriers. Also, the presentation showed a trunk 
group split across multiple Gateways.

For reference, the following 2 definitions come from American National 
Standard T1.523-2001:

trunk: 1. In a communications network, a single transmission channel between 
two points that are switching centers or nodes, or both. 2. [A] circuit 
between switchboards or other switching equipment, as distinguished from 
circuits which extend between central office switching equipment and 
information origination/termination equipment. [47 CFR Pt.36-A] Note: Trunks 
may be used to interconnect switches, such as major, minor, public and 
private switches, to form networks.

trunk group: Two or more trunks of the same type between two given points.

The definition of "trunk group" in telephony does not include where you can 
get to by going through it. As noted in SLC, in many cases, all destinations 
can be reached through a specific trunk group due to the routing which the 
next switch may do. Basic requirements in the US are that all carriers can be 
reached by the end user, so, in some cases, when talking about a trunk group 
from a Gateway which serves as the user's originating end office, that trunk 
group can reach every carrier and every destination. In others, if the trunk 
group in question connects to a specific carrier (the termination "point" of 
the trunk group), then it is likely that it can only reach that one carrier. 
When talking about a trunk group terminating at an end office (or a Gateway) 
then it can probably only reach destination connected to that end office.

It is not correct to depict a trunk group split between two Gateways unless 
the 2 Gateways are simply 2 physical devices which act as a single switching 
"point" controlled by a single MGC. In this case, the 2 physical devices are 
really 1 single Gateway for purposes of architecture and signaling with other 
MG/MGCs.

This issue in IPTEL can be simplified if the definition for "trunk group" in 
T1.523 (which is consistent with the usage in ITU-T) is accepted.

A further definition in T1.523 is:

route list: A specific list of trunk groups. [After T1.667-1999]

This is more similar to the term "trunk group" as being used in the IPTEL 
discussions. The function of "routing" a specific destination address in any 
switching element results in the determination of a "route list", which 
points to a list of trunk groups (alternate routes).

Mike Pierce
Artel
_______________________________________________
IPTEL mailing list
[email-masked]
http://lists.bell-labs.com/mailman/listinfo/iptel