cost. It was very expensive to provision a cable pair for each customer. Figure 3-15 Along the street, terminal boxes (sometimes called B-Boxes) are installed. Each B-Box hosts an appearance of every pair of wires in the cable, which may contain as many as 500 pairs. With this design, every pair in the cable is potentially available to every home or business along the street, making installation extremely flexible. 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 Telephony With the arrival of time-division multiplexing, however, the "one dog, one bone" solution was no longer the only option. Instead, engineers were able to design a system under which customers could share access to the network as shown in Figure 3-16. This technique, known as a subscriber loop carrier (SLC), uses a collection of T1 carriers to combine the traffic from a cluster of subscribers and, thus, reduce the amount of wire required to interconnect them to the central office. The best known car- rier system is called the SLC-96 (pronounced SLICK), originally manu- factured by Western Electric/Lucent, which transports traffic from 96 subscribers over four, four-wire T-Carriers (plus a spare). A remote SLC terminal is shown in Figure 3-17. Thus 96 subscribers require only 20 wires between their neighborhood and the central office instead of the 192 wires that would otherwise be required. The only problem with this model is that customers are by and large restricted to the 64 Kbps of bandwidth that loop carrier systems assign to each subscriber. That means that subscribers wishing to buy more than 64 Kbps-such as those that want DSL-are out of luck. And since it is estimated that as many as 70 percent of all subscribers in the United States are served from loop carriers, this poses a problem that service providers are scram- bling to overcome. New versions of loop