Path: utzoo!attcan!uunet!decwrl!hayes.fai.alaska.edu!accuvax.nwu.edu!nucsrl!telecom-request From: cellar!martin@bellcore.bellcore.com (Martin Harriss (ACP)) Newsgroups: comp.dcom.telecom Subject: Re: TouchTone(tm) in the U.K. (was Re: Touchtone History) Message-ID: <9838@accuvax.nwu.edu> Date: 17 Jul 90 20:57:42 GMT Sender: news@accuvax.nwu.edu Reply-To: "Martin Harriss (ACP" Organization: Bellcore Lines: 107 Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 10, Issue 493, Message 6 of 9 In article <9673@accuvax.nwu.edu> iosg::robertsn@iosg.enet.dec.com (Nigel Roberts 0860 578600) writes: >This leads me to ask a few questions of the DIGEST. >What exactly is a TXE-2? (My guess is that it's a magnetic reed type >exchange). You are correct. The TXE2 is a crosspoint type switch using reed relay technology. I believe that the TXE2 design is too old to use integrated circuits; it uses discrete transistors. In particular, the control circuits are all hard wired logic (i.e. not program controlled.) >Is there any way it could support TouchTone? (A BT engineer once told >me that there might be some kind of black box which they can add). It could be done, but it would be a real hack. There are two problems with doing it the "right" way (the right way being to add TT receivers to the registers.) Firstly, (see above) the registers are hard-wired. It would be a real pain to modify them. Secondly, the fact that architechturally, the TXE2 is just an electronic step by step system. This is how a TXE2 works: When you pick up a phone you are connected through a series of reed relay crosspoint switches to a relay set. This relay set connects you to two things: the local register, and an outgoing junction to the group switching centre (GSC) - in your case Colchester. Dial tone is now returned to the caller from the local register. When you dial, your dial pulses go to two places. Firstly, they are counted by the TXE2 register. Secondly, they are passed along the junction to the GSC, where they step switches, get put into a register, or whatever, depending on what kind of equipment is at the GSC. In TXE2 parlance, this junction is known as the 'primary route'. After you have dialled the first two digits, the TXE2 register will decide one of three things: 1. The call is going to, or will be routed through, the GSC. In this case, the register releases itself from the circuit and the call proceeds by way of the already connected junction to Colchester. Any further digits that you dial are sent to Colchester without further ado. The register is, of course, now available for other calls. This means that a TXE2 need not store the dialled digits, nor does it have to translate them or pulse them out to another exchange. 2. The call is to your own exchange. In this case, the first two digits you dialled will have been 39. In this case, the register will signal the relay set to release the primary route and proceed to suck in the remaining four digits. After the last digit has been received, a completely new path is set up from your calling line circuit, through the crosspoint switches, through an "own exchange relay set", and back through the crosspoint switches to the called line circuit. The own exchange relay set is then responsible for ring current/tone or busy, as appropriate. 3. The call is to some other exchange to which the TXE2 has a direct route. In this case, after the initial digits are dialled, the route to the GSC will be cleared and a now route set up to the target exchange. Subsequent digits dialled will be sent directly to the target exchange. The 'dual destination' of your dial pulses is what makes it really difficult to add touch tone to TXE2's (Finally getting to the point, here.) Remember, the TXE2 does not suck in numbers and pulse them out again later. Adding TT receivers to the registers is conceptually simple, even if it is a nightmare from an engineering standpoint. The problem is that you have to have some way to convert the touchtones to dial pulses on the outgoing junctions - remember that TXE2's may be connected to GSC's that are still strowger, and cannot directly receive TT. About the best you could hope for would be to connect some kind of black box TT-to-pulse converter at some point along the switching train. But this does not help much, because it takes about as long for said black box to pulse out a number as it does for you to dial it. You might as well have a push button pulse phone. (N.B. The above description is for TXE2's which have linked numbering with their GSC. There are other situations; your milage may vary.) >Are there any more features available on the TXE-2 that we are not >being told about? As you might realise from the foregoing description, the TXE2 is quite a dumb beast, and adding nifty features does not really come within its scope. TXE2 ringback used to be 1267, sometimes 1267105. >And does anyone have a guess as to how long it will be before it is >updated to something modern? (I IMAGINE we've got another 19 years of >pulse dialling to put up with, but I hope I'm wrong ...) TXE2's are pretty reliable, I think. Seeing as how yours is only six or seven years old, it might be around for some time, unless either the requirement for lines goes up dramatically (TXE2's only handle about 3-4000 lines) or if it was second hand when it was put it - maybe as a stop gap measure. You never know with BT. Why not call your friend Sarah? Martin Harriss martin@cellar.bae.bellcore.com