ngle virtual 24 Mbps channel. As far as applications are concerned, Bellsouth plans to test VoIP and will include a trial of Microsoft's IPTV platform. High Bit Rate Digital Subscriber Line (HDSL) The greatest promise of HDSL is that it provides a mechanism for the deployment of four-wire T1 and E1 circuits without the need for span repeaters, which can add significantly to the cost of deploying data ser- vices. It also means that service can be deployed in a matter of days rather than weeks, something customers certainly applaud. DSL technologies in general allow for repeaterless facilities as far as 12,000 feet, while traditional four-wire data circuits-such as T1 and E1 -require repeaters every 6,000 feet. Consequently, many telephone com- panies are now using HDSL "behind the scenes" as a way to deploy these traditional services. Customers do not realize that the T1 facility they are plugging their equipment into is being delivered using HDSL tech- nology. The important thing is that they don't need to know. All the cus- tomer should have to care about is that there is now a SmartJack installed in the basement, and through that jack they have access to 1.544 Mbps or 2.048 Mbps of bandwidth-period. HDSL2 HDSL2 offers the same service that HDSL offers, with one added (and significant) advantage: It does so over a single pair of wire, rather than two. It also provides other advantages. First, it was designed to improve 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 vendor interoperability by requiring less equipment at either end of the span (transceivers, repeaters). Second, it was designed to work within the confines of standard telephone company Carrier Serving Area (CSA) guidelines by offering a 12,000-foot, wire-run capability that matches the requirements of CSA deployment strategies. (See the 