 industry, on the other hand, came about 50 years ago and didn't benefit from the rigorously administered, centralized management philosophy that characterized the telephone industry. Additionally, the typical 450 MHz cable system did not have adequate bandwidth to sup- port the bi-directional transport requirements of new services. Furthermore, the architecture of the legacy cable network, with its distributed power delivery and tree-like distribution design, does not lend itself to the same high degree of redundancy and survivability that the telephone network offers. Consequently, cable providers have been hard-pressed to convert customers who are vigorously protective of their telecommunications services. The Ever-Changing Cable Network Faced with these harsh realities and the realization that the existing cable plant could not compete with the telephone network in its original analog incarnation, cable engineers began a major rework of the network in the early 1990s. Beginning with the headend and working their way outward, they progressively redesigned the network to the extent that, in many areas of the country, their coaxial "local loop" is capable of compet- ing on equal footing with the telco's twisted pair-and in some cases beating it. The process they have used in their evolution consists of four phases. In the first phase, they converted the headend from analog to digital. 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 This allowed them to digitally compress the content, resulting in far more efficient utilization of available bandwidth. Second, they undertook an ambitious physical upgrade of the coaxial plant, replacing the one- inch trunk and half-inch distribution cable with optical fiber. This brought about several desirable results. First, by using a fiber feeder, net- work designers were able