hone, and most likely, their PC and modem, are connected via house wiring (sometimes called inside wire) to a device on the outside of the house or office building called a protector block (see Figure 3-12). It is nothing more than a high-voltage protection device (a fuse, if you will) designed to open the circuit in the event of a lightning strike or the pres- ence of some other high-voltage source. It protects both the subscriber and the switching equipment. The protector connects to the network via twisted pair wire. Twisted pair is literally that-a pair of wires that have been twisted around each other to reduce the amount of crosstalk and interference that occur between wire pairs packaged within the same cable. The number of twists per foot is carefully chosen. The twisted pair(s) that provides service to the customer arrives at the house on what is called the drop wire. It is either aerial, as shown in Figure 3-12 Protector block, shown at right 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 Figure 3-13, or buried underground. We note that there may be multiple pairs in each drop wire because today the average household typically orders a second line for a home office, computer, fax machine, or teenager. Once it reaches the edge of the subscriber's property, the drop wire typically terminates on a terminal box, such as that shown in Figure 3-14. There, all of the pairs from the neighborhood are cross-connected to the main cable that runs up the center of the street. This architecture is used primarily to simplify network management. When a new Figure 3-13 Aerial drop Figure 3-14 Terminal box, sometimes known as a "B- 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