Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!zaphod.mps.ohio-state.edu!uwm.edu!linac!unixhub!ditka!zygot!john From: john@zygot.ati.com (John Higdon) Newsgroups: sci.electronics Subject: Re: Telephoe Equipment help! Message-ID: <32114@zygot.ati.com> Date: 19 May 91 05:44:33 GMT References: <7973@nst> Sender: news@ditka.Chicago.COM (Pulitzer at ditka) Reply-To: john@zygot.ati.com (John Higdon) Organization: Green Hills and Cows Lines: 35 In article <7973@nst> grayt@Software.Mitel.COM (Tom Gray) writes: >In article moonhawk@bluemoon.uucp (David Culberson) writes: > >: 4-W RPTR >: WITH DX >: SSP-1240 >: >You have a four wire repeater with DX loop signalling. The unit will >convert from E&M to DX type signalling. The 4W means that there are >separate transmission circuits for each direction of the voice path. > >Essentially E&M is a very simple signalling scheme which is useful >only for short distances. However it is very cheap and can be >used to interconnect central office switches which are within the >same building. Practically speaking, this unit is used by telcos to provide DX>E&M conversion for end users. A typical use would be for a customer to connect two PBX switches in separate locations (maybe even separate cities) together. He orders an "E&M tie line" from telco. This line has a separate pair for each direction of speech plus an "E" and an "M" lead that the PBXes use to signal to each other -- the "E" lead becoming the "M" lead at the other end and visaversa. This signaling can be off-hook, supervision, and even dialing. It is not practical to send these signaling leads over long distances, so the telco "phantoms" the information between the two voice pairs ("DX signaling") between the customer location and the CO. For an explanation of "phantom", see a telecom reference book. E&M signaling is not used much within telcos anymore, but rather by customers. -- John Higdon | P. O. Box 7648 | +1 408 723 1395 john@zygot.ati.com | San Jose, CA 95150 | M o o !