ated at the switching center. Mavis asks Gretchen who she wants to talk to, and Gretchen says "Carl." Mavis then physically moves wires at the switch- ing center in such a way that the wire from Gretchen's phone is directly connected to Carl's wire, and Gretchen and Carl are now ready to begin their conversation. Figure 2.1 A single wire between each phone Chapter Two The manual switching center, oper- ated by people like Mavis, was the only way to go until a little after 1889 when Almon B. Strowger, a mortician by trade, invented the first automatic switching center. It seems that Almon suddenly found that he Switching Center was no longer getting any business. Sur- prised, he investigated and discovered that the new telephone operator was also married to the competition and she was switching all funeral home calls to her husband. Determined to keep his mortician business alive (no pun intended), Almon created the first automatic switching center. Figure 2.2 These switching centers do not require Phones connected by a switching center anyone (and hence no competitor's wife) to transfer calls. Entering a 7-digit phone number automatically sets up the connection at the switching center. Today, all switching centers are automatic. Just briefly, how many wires are needed by a network using a switching center? Only N, where N is the number of users. That's far fewer than the many-wire system introduced first. 2.1.2 Connecting More People, Farther Apart Let's take this switching center idea a bit further. Consider Figure 2.3. A bunch of people are connected together in Fort Collins, Colorado, by a switching center in downtown Fort Collins. Then, in nearby Boulder, another group of people are con- nected together by a second switching center. How does someone in Boulder talk to a friend in Fort Collins? One easy way is to simply connect the switching centers, as shown in Figure 2.3. If we put several wires between the Fort Collins and Boulder switching centers, then several people in Fort Collins can talk to people in 