edg@ames.arc.nasa.gov (Edward Greenberg) (07/27/89)
I enjoyed the discussion of running out of pairs in Chicago, and sent it to a friend of mine who isn't on the net. His response seems appropriate for the group, so I asked, and he gave permission to post it. Larry has been doing interconnect and telephone related engineering for about ten years now. I've listed his CompuServe ID for anyone who wants to correspond with him electronically, or you can write to him care of me. >Date: 25-Jul-89 04:31 PDT >From: Larry Rachman [74066,2004] >Subj: Reply to 'pairs' 25 July Greetings... Just (*finally*) was able to read the piece you sent me. The pair situation in NYC is similar, but for other reasons, namely the proliferation of CENTREX. When a 1000-phone office is equipped with a PBX, it needs only about 100 lines, and possibly a few dozen DID (direct inward dialing) trunks. When it switches over to CENTREX, the pair count goes up to 1000. And of course, fax machines, modems, and so forth make the problem even worse. The great saviour has been T1 carrier. Its a 1.544 megabit bidirectional link used to move digitized voice. Its implemented on two twisted pairs, and will typically handle 24 standard voice channels. What happens is these two pairs from the street go into a $15,000 'channel bank' on the customer's premises, and out come 24 dialtones! Pretty neat, eh? One of the stupidities of the whole thing, though, is that many customers are equipping with digital PABXs that can take T1 directly but, since there was no tariff for T1 service, the channel was broken up by a channel bank into 24 dialtones that entered the switch via 24 trunk ports. I heard a rumour (that *surely must be mistaken) about a customer who wanted a bunch of foreign exhange lines from Jersey and put up his own microwave link to hop the river (not unheard of), with a channel bank to funnel a bunch of dialtones into the link. Sure enough, right next to his channel bank was *ANOTHER* channel bank, this one provided by NYNEX, to make the NYNEX T1 into dialtones! One rather disturbing fact about T1 is that 1.544 megabaud dry (no battery) data sounds just like *nothing* if you listen with a butt set. Its not unheard of for installers to reassign one of these 'unused' pairs when hunting for a spare, and, of course, there go 24 voice (and sometimes 64kb data) circuits. A friend of mine who works for an ELFI in NYC has seen it happen several times. Hope all is well there; say hello, etc. for me, LR =================================== -edg -- Ed Greenberg uunet!apple!netcom!edg [Moderator's Note: My thanks for sharing your correspondence with the Digest readers. PT]
chip@vector.dallas.tx.us (Chip Rosenthal) (07/28/89)
Edward Greenberg <claris!apple!netcom!edg@ames.arc.nasa.gov> writes: >X-TELECOM-Digest: volume 9, issue 258, message 1 of 9 > One rather disturbing fact about T1 is that 1.544 megabaud >dry (no battery) data sounds just like *nothing* if you listen >with a butt set. What is a "butt set?" I would think an active line would be pretty noticable if the T1 pulse density requirements were met. -- Chip Rosenthal / chip@vector.Dallas.TX.US / Dallas Semiconductor / 214-450-5337 "I wish you'd put that starvation box down and go to bed" - Albert Collins' Mom [Moderator's Note: A 'butt set' is simply a telephone handset with a dial built in (and other nifty switches), ala Trimline. It has aligator clips on the wires running from it, which can be conveniently clipped on various wires in a terminal box. They are used by technicians to get an audible indication of what line(s) they are on at the time. PT]
jhh@ihlpl.att.com (John H Haller) (07/29/89)
In article <telecom-v09i0258m01@vector.dallas.tx.us>, claris!apple!netcom!edg@ ames.arc.nasa.gov (Edward Greenberg) writes: > >From: Larry Rachman [74066,2004] > The pair situation in NYC is similar, but for other reasons, > namely the proliferation of CENTREX. When a 1000-phone office is > equipped with a PBX, it needs only about 100 lines, and possibly > a few dozen DID (direct inward dialing) trunks. When it switches > over to CENTREX, the pair count goes up to 1000. And of course, > fax machines, modems, and so forth make the problem even worse. It is interesting how the marketing of Centrex has changed. Shortly before divestiture, it was very rare that a local operating company would want to sell Centrex service, probably because of the expense of all of those lines. They would rather sell a Dimension(r) plus a service contract. After divestiture, since they could not sell PBX's any more, suddenly Centrex marketing took a very large jump. Should the Bell companies get permission to start manufacturing, I wonder if Centrex services would become a pariah again. John Haller att!ihlpl!jhh