fff@mplex.UUCP (Fred Fierling) (09/23/89)
>From what I've read I understand that the U interface would be provided
via an single pair coming from the CO to the subscriber's premises and
terminate on an NT1 box which would provide the S/T interface to all
digital telephones on the premises.
Assuming this is correct, I understand that it would be possible for two
independent calls to be handled on each of the B channels. So, how would
both telephones perform call set up and tear down on the one D channel?
Fred Fierling Tel: 604 875-1461 Microplex Systems Ltd, 265 East 1st Avenue
uunet!mplex!fff Fax: 604 875-9029 Vancouver, BC, V5T 1A7, Canadabill@toto.UUCP (Bill Cerny) (09/25/89)
In article <telecom-v09i0399m03@vector.dallas.tx.us>, 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
danny@uunet.uu.net (Danny Wilson) (09/26/89)
In article <telecom-v09i0399m03@vector.dallas.tx.us>, fff@mplex.UUCP (Fred Fierling) writes: > Assuming this is correct, I understand that it would be possible for two > independent calls to be handled on each of the B channels. So, how would > both telephones perform call set up and tear down on the one D channel? If you have two TE's on a single S/T bus (point to multipoint operation) there are two addressing schems that come into play. At the physical level, the S/T bus has a collision handling mechanism that restricts access to the bus to only one TE at a time. The NT (or switch) assigns a TEI (Terminal Endpoint Identifier) to each terminal device on the bus. TEI's can either be manually assigned by the service technician (dip switches etc) or can be assigned dynamically by management procedure software resident on the switch. Since the switch is aware of which TE is negotiating for a call it can assign one B-Channel to each TE device. In fact, in a multi-mode terminal, several calls can be active/suspended at one time, with each call having a distinct Layer 3 call reference value. Danny Wilson IDACOM Electronics danny@idacom.uucp Edmonton, Alberta {att, watmath, ubc-cs}!alberta!idacom!danny C A N A D A
goldstein@delni.enet.dec.com (09/26/89)
In article <telecom-v09i0399m03@vector.dallas.tx.us>, fff@mplex.UUCP (Fred Fierling) writes... >>From what I've read I understand that the U interface would be provided >via an single pair coming from the CO to the subscriber's premises and >terminate on an NT1 box which would provide the S/T interface to all >digital telephones on the premises. >Assuming this is correct, I understand that it would be possible for two >independent calls to be handled on each of the B channels. So, how would >both telephones perform call set up and tear down on the one D channel? The D channel has a contention-resolution protocol associated with it. Each terminal has a unique address (TEI) so the network knows which one is which; there's a procedure for auto-assigning TEIs, or they can be manually set. The TEI is part of the LAPD protocol, essentially a variant on LAPB with multiplexing. Fred
geek@media-lab.MEDIA.MIT.EDU (Chris Schmandt) (09/26/89)
In article <telecom-v09i0399m03@vector.dallas.tx.us> fff@mplex.UUCP (Fred Fierling) writes: >... I understand that it would be possible for two >independent calls to be handled on each of the B channels. So, how would >both telephones perform call set up and tear down on the one D channel? Not an issue. No different from setting up a voice call on the B1 channel and a data call on the B2 channel with today's sets. (my experience being limited to the AT&T 7506 set). During a "call", the D channel is in no way "dedicated" or tied to it. Q.931 provides bit fields to support connections to several entities simultaneously. In fact, while handling the above scenario I suspect you could also sustain an X.25 data link over the D channel, be reporting gas meter usage, etc. all at once. chris
deej@bellcore.bellcore.com (David Lewis) (09/28/89)
In article <telecom-v09i0399m03@vector.dallas.tx.us>, fff@mplex.UUCP (Fred Fierling) writes: > >From what I've read I understand that the U interface would be provided > via an single pair coming from the CO to the subscriber's premises and > terminate on an NT1 box which would provide the S/T interface to all > digital telephones on the premises. > Assuming this is correct, I understand that it would be possible for two > independent calls to be handled on each of the B channels. So, how would > both telephones perform call set up and tear down on the one D channel? First, the D-channel is a packet channel, so each message sent down the D-channel from the CPE to the switch is independent. The basic call control protocol for ISDN is Q.931. One required information element of each Q.931 message is the call reference value; this enables the machines on each side of the interface to agree on what call they're acting on. So when the CPE sends, for example, a Disconnect message, one information element is a call reference -- essentially, saying Disconnect Call #1. In addition, there is an optional information element in Setup and Connect Q.931 messages, called the Channel Identification information element. This enables the CPE to specify a specific channel, either at that user-network interface or at another user-network interface. In other words, CPE can send a message to the switch saying "setup a call on this UNI, B-channel 1." Or, "setup a call on UNI X, B-channel 2." It's not clear that all the wrinkles have been worked out of the latter case, tho... David G Lewis ...!bellcore!nvuxr!deej "If this is paradise, I wish I had a lawnmower."