ribers. By 1887, 146,000 miles of wire had been strung to connect 150,000 subscribers to nearly 750 main offices and 44 branch offices. As we described in Chapter 2, there were no switches initially, so tele- phones were sold in pairs, one for each end of the connection. Wires were strung in a haphazard fashion, attached to the outside of buildings, and strung across neighbors' rooftops; they threatened to fill the sky, as shown in Figure 3-3. Obviously, this one-to-one relationship was some- what limiting. A technique was needed that would allow one phone to connect to many. The answer came in the form of the central office. Connections were installed from all the phones in a local area to the central exchange, where operators could monitor the lines for service requests. The cus- tomer would then tell the operator whom they wanted to speak with, and the operator would set up the call using patch cords. When the parties had finished speaking, the operator would pull down the patch cord, free- Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Telephony Figure 3-3 Crossbars on pole being prepared to support an lawful lot of cable ing up the equipment for another call. This entire function was the first form of switching. The design soon became problematic, however, because an operator could typically monitor only about 100 positions effectively. The answer, of course, came with the development of the switch-first with Strowger's invention, and later from a series of switching innova- tions that led to the technology we have today. The first semiautomatic switch was installed in Newark, New Jersey, in 1914, and the first truly automatic switch went live in Omaha, Nebraska in 1921. For all this Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reser