ed- ing a dedicated circuit running from every customer to every other cus- tomer, each subscriber needed a single circuit that ran into the central exchange, where it appeared on the jack field in front of an operator (each operator managed approximately 100 positions, the optimum num- ber according to Bell System studies). When a customer wanted to make a call, he or she would crank the handle on the phone, generating current which would cause a flag to drop, a light to light or a bell to ring in front of the operator. Seeing the signal, the operator would plug a headset into the customer's jack appearance and announce that she was ready to receive the number to be dialed. The operator would then simply "cross- connect" the caller to the called party, then wait for the receiver to be picked up on the other end. The operator would periodically monitor the call and pull the patch cord down when the call was complete. Inciden- tally, note the roller skates on the feet of the supervisors. The cord boards were so long that the process of collecting tickets took far too long, so they added mobility! This model meant that instead of needing 3,997,999 circuits to provide universal connectivity for a town of 2,000 people, 2,000 were needed- rather significant reduction in capital outlay for the telephone company, wouldn't you say? Instead of looking like Figure 2-29, the network now looked like Figure 2-31. Figure 2-30 First women operators (Courtesy Lucent Technologies) 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. Protocols Chapter 2 Figure 2-31 Switched network; five users, five circuits Over time, manual switching slowly disappeared, replaced by mechanical switches initially followed by more modern all-electronic switches. The first true mechanical switches didn't arrive until 1892, when Almon Strowger's Step-by-Step switch was first installe