family that has achieved significant attention in the last couple of years. The attention is due to both successes and failings on the part of the 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 Access Technologies technology. When it works, it works extremely well. When it doesn't, it tends to fail loudly and publicly. The access technology that has enjoyed the greatest amount of attention in recent times is the digital subscriber line, or DSL. It provides a good solution for remote LAN access, Internet surfing, and access for telecom- muters to corporate databases. DSL came about largely as a direct result of the Internet's success. Prior to its arrival, the average telephone call lasted approximately four minutes, a number that central office personnel used while engineering switching systems to handle expected call volumes. This number was arrived at after nearly 125 years of experience designing networks for voice customers. They knew about Erlang theory, loading objectives, peak-calling days/weeks/seasons, and had decades of trended data to help them anticipate load problems. So in 1993, when the Internet-and with it, the World Wide Web-arrived, network performance became unpredictable as callers began to surf, often for hours on end. The aver- age four-minute call became a thing of the past as online service providers such as AOL began to offer flat rate plans that did not penal- ize customers for long connect times. Then, the unthinkable happened: Switches in major metropolitan areas, faced with unpredictably high call volumes and hold times, began to block during normal business hours, a phenomenon that had only occurred in the past during disasters or on Mothers Day. A number of solutions were considered including charging different rates for data calls than for voice calls, but none of these proved feasible unt