CMWOLF@mtus5.cts.mtu.edu (02/10/91)
Pardon a simple question from a college student ... What are the specified voltages that occur on the phone lines during its normal operating phases? 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? Christopher Wolf, Electrical Engineer MWOLF@MTUS5 Michigan Tech University
Jim.Redelfs@iugate.unomaha.edu (Jim Redelfs) (02/16/91)
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)
juliet@mhuxo.att.com (Juliet Sutherland) (02/19/91)
In article <telecom11.123.8@eecs.nwu.edu>, Jim.Redelfs@iugate. unomaha.edu (Jim Redelfs) writes: > 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. One minor quibble with the above. The SLC(R)-96 and SLC Series 5 carrier systems actually use 10 physical pairs. Each 96 line system uses four primary T1 lines and one protection T1 line (assuming it is supported by copper feeder rather than a co-located fiber mux). Each T1 line uses two pairs (one each for transmit and receive) for a total of 10 physical pairs. There may also be additional pairs associated with multiple systems for such things as test access, order wire, etc. The pair gain is still substantial, however. SLC is a registered trademark of AT&T Network Systems. Juliet Sutherland Digital Loop Carrier Systems AT&T Bell Laboratories juliet@mhuxo.att.com