Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!texbell!vector!telecom-gateway
From: bill@toto.UUCP (Bill Cerny)
Newsgroups: comp.dcom.telecom
Subject: Re: ISDN Subscriber Equipment
Message-ID: 
Date: 25 Sep 89 13:10:05 GMT
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In article , fff@mplex.UUCP
(Fred Fierling) writes:

> So, how would
> both telephones perform call set up and tear down on the one D channel?

On a basic rate interface (2B+D), the terminal equipment share the D
channel.  Call setup/teardown messages (Q.931) are message packets,
each containing a Terminal Equipment Identifier (TEI).  The TEI tells
the switch which terminal on the BRI is requesting a service, and
allows the switch to individually address each piece of terminal
equipment.  Not only is it possible to have both bearer (B) channels in
use simultaneously, you can also use the D channel for data
communication, all at the same time (e.g., a pc with an ISDN terminal
adapter that contains an X.25 PAD).

There's a clever mechanism for preventing signaling packet collisions
using the echo D channel, but that's beyond the scope of your query.


Bill Cerny		"The cost of living just went up another $1 a fifth."
bill@toto.cts.com					- W. C. Fields