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From: abvax!ncoast!fmsystm!macy@usenet.ins.cwru.edu
Newsgroups: comp.dcom.telecom
Subject: Re: Are DID Trunks Incoming Only?
Message-ID: <8909@accuvax.nwu.edu>
Date: 12 Jun 90 13:32:07 GMT
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X-Telecom-Digest: Volume 10, Issue 430, Message 7 of 13


In article <8726@accuvax.nwu.edu>:
>X-Telecom-Digest: Volume 10, Issue 417, Message 11 of 12

>>So are DID lines really only for incomming calls?  Is there a
>>technical reason or is the carrier trying to charge more?

>There probably is no technical reason why a two-way DID trunk couldn't
>be made but, to the best of my knowlege, it just hasn't been done yet.

Not really...

DID trunks are similar in operation to tie lines.  Two way tie lines
are a routine application, both in two wire and four wire operation,
using DX or E&M signalling.

Many CO's can accomodate two way tie line operation for Centrex
services.  1A and 5 ESS machines definitely can do this, I asked a
software engineer.

If the PBX to CO link is a T-1 span, then two way operation is also
easily supported.  AT&T has recently begun to offer Megacom WATS & 800
services in this fashion (in limited areas, and only if you ask).
Megacom 800 service is DID type service, only direct from the AT&T
switch, instead of the telco CO.

On non-Centrex equipped CO's, support for two way operation may not be
available, probably due to a lack of demand from the telco's.

>It would not be a simple change and there are some good reasons to
>keep things separate.

Call collision is possible, but careful software design prevents this.

Since the telco's are actively trying to compete against Centrex by
throwing as many obstacles in the PBX vendor's paths (and by foot
dragging) ... I do not see them making any effort to improve the
situation.


Macy M. Hallock, Jr.     macy@NCoast.ORG         uunet!aablue!fmsystm!macy
F M Systems, Inc. {uunet|backbone|usenet.ins.cwru.edu}ncoast!fmsystm!macy
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