Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uwm.edu!bionet!ames!ucsd!casbah.acns.nwu.edu!nucsrl!telecom-request From: Jim.Redelfs@iugate.unomaha.edu (Jim Redelfs) Newsgroups: comp.dcom.telecom Subject: Re: Two Questions From a Novice Message-ID: Date: 16 Feb 91 10:27:52 GMT Sender: news@casbah.acns.nwu.edu Reply-To: jim.redelfs@iugate.unomaha.edu Organization: TELECOM Digest Lines: 44 Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 11, Issue 123, Message 8 of 10 Christopher Wolf wrote: > What are the specified voltages that occur on the phone lines during > its normal operating phases? Speaking only of POTS (Plain Old Telephone Service) - my only area of "expertise", normal dialtone current varies between 48-52 VDC. Ringing current is around 100 VAC. > Also, how can so many people's conversations be transmitted over so > few wires, such as in the city, where there are only so many wires on > the poles? Cable, my friend ... cable. I suspect that the "wires" you see are either electrical (not telephone) or telephone cables. Most MAJOR cities have the bulk of their LARGE cables buried or in conduit underground. 900-pair cables (900 individual "lines") are common in my area (Omaha), but the lesser, "distribution" cables, usually 100-pairs or less, are commonly found hanging between rows of houses or along alleys. Multiplexing, or carrying multiple conversations on a single pair, is an aging, but widely used, technology - especially between Central Office switches. Telephone voice frequencys are very narrow (low fidelity) and, therefore, several can be allocated to the various frequencies available on a single, copper pair. As existing, copper-pair cable facilities reach their capacity, the solution is to either place more cable, or install "Pair Gain" systems. One used in my specific service area is called SLC96 (Slick-96) where, through the use of special equipment on BOTH ends of the cable, 96 "pairs" are achieved on the end by using FOUR, physical pairs of wire. Optical fiber cable is fast replacing large, copper-wire cable. This is a whole different ballgame -- transmitting thousands of conversations, digitally, on a beam of light! JR Copernicus V1.02 Elkhorn, NE [200:5010/666.14] (200:5010/2.14)