Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!zaphod.mps.ohio-state.edu!rpi!bu.edu!orc!decwrl!hayes!accuvax.nwu.edu!nucsrl!telecom-request From: john@bovine.ati.com (John Higdon) Newsgroups: comp.dcom.telecom Subject: Re: Are DID Trunks Incoming Only? Message-ID: <8907@accuvax.nwu.edu> Date: 13 Jun 90 01:18:15 GMT Sender: news@accuvax.nwu.edu Reply-To: John Higdon Organization: Green Hills and Cows Lines: 30 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 430, Message 5 of 13 Jim Dunn writes: > DID trunks are, in fact, for inward calls only, although that's > strictly a marketing decision on the part of the telephone company. > There is no "real" technical reason why DID trunks (which in fact are > four wire E&M wink start trunks or two wire loop/reverse battery > trunks) can't be used for two way traffic. Yes for E&M trunks, no for two wire loop/reverse battery. Back when I had my equipment vending operation, we had an office in San Jose and in San Francisco. The two PBXs were connected via an E&M trunk. Users in San Jose could call extensions in SF and make calls on the outside lines there as well as SF users doing the reverse. This is the nature of the E&M trunk: each end is the same in that there is no originating or terminating end. This is, as Mr. Dunn points out, the classic connection between telco central offices. But on two wire, there is an originating and terminating end. Normally the subscriber is the originating end, but in the case of DID the subscriber becomes the terminating end. The telco literally places a call on the subscriber's PBX. Since this is the circuit of choice for virtually all DID installations in this neck of the woods, it is accurate to say that it is not technically expedient to provide two way calling on DID. There is, of course, the final argument: that's the way it's specified in tariff. John Higdon | P. O. Box 7648 | +1 408 723 1395 john@bovine.ati.com | San Jose, CA 95150 | M o o !