modem technology. Dedicated private-line service, which would solve the problem, is far too expensive as an option, and because it is dedicated is not particularly efficient. Other solutions are required, and these have emerged in the form of access technologies that take advantage of either a conversion to end-to-end digital connectivity (ISDN) or expanded capa- bilities of the traditional analog local loop (DSL, 56K modems). In some cases, a whole new architectural approach is causing excitement in the industry (wireless local loop, or WLL). Finally, cable access has become a popular option as the cable infrastructure has evolved to a largely opti- cal, all-digital system with high-bandwidth, two-way capability. We will discuss each of these options in the pages that follow. 56 Kbps Modems With the accelerating proliferation of broadband access underway, it almost feels medieval to write about 56 Kbps modems. They are still out there, however, and a remarkably large number of them are still in use. In fact, I rely on the one in my laptop far more often than I care to, par- ticularly when I travel internationally. All too often I check into a hotel that doesn't have broadband of any flavor-wired or wireless. So, while this seems like a technology that is on its way out, it isn't-and I feel compelled to include it in the second edition of the book. One of the most important words in telecommunications is "virtual." It is used in a variety of ways, but in reality only has one meaning. If you see the word "virtual" associated with a technology or product, you should immediately say to yourself, "It's a lie." A 56 Kbps modem is a good example of a virtual technology. These devices have attracted a great deal of interest since they were introduced 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. Access Technologies Chapter 6 a few years ago. Unde