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 Sender: news@vector.Dallas.TX.US Lines: 22 Approved: telecom-request@vector.dallas.tx.us X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@vector.dallas.tx.us X-TELECOM-Digest: volume 9, issue 408, message 9 of 9 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