bile customers were concerned with hav- ing their landline contacts have good sound even if their own sound had static from time to time. And third, a customer bringing an expensive car into a shop for cellular 1We have seen the SEND and END keys marked YES and NO on some portable user terminals. 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. Basic Wireless Telephony Basic Wireless Telephony telephone installation is annoyed enough at having one hole drilled in the roof without the extra indignity of having a second hole. The base station receives and demodulates the call as described in Chap. 4. The call is then routed onto a pipe connecting the base-station controller (BSC) to an MSC.3 These pipes are almost always digital links carried over wires, fiber optic cable, mi- crowave link, or whatever medium the wireless telephone carrier wants to use. The MSC routes calls and reroutes them during handoffs. The MSC is a telephone switch that can direct calls instant by instant, although some BSCs can switch hand- offs from sector to sector on the same cell. 4 The MSC has yet more trunks going to the PSTN, where the call is routed through a series of switches and transport to a local exchange office. The local exchange office routes the calls onto the local loop to the called party's telephone. 5 Depending wireless switch architecture, there also may be trunks from the MSC directly to long- distance carriers. If load requires, it is also possible to add trunks to other specific des- tinations, including nearby MSCs, 911 emergency call centers, and possibly Internet service providers. 5.1.2 Landline to wireless A call to a user terminal follows the same chain as a call from user terminal to land- line in reverse, but it has the extra burden of finding the user terminal. The user ter- minal can be found because, whenever it is turned on, it regis