roperating with V.90 modems (for those who do not live close enough to a Telco CO-central office-to receive DSL service) and other existing technology. The absence of standards presented a challenge. AT&T Paradyne defended its proprietary Carrierless Amplitude and Phase Modulation (CAP) DSL. The American National Standards Institute (ANSI) advocated Discrete Multitone (DMT) technology-the ASNI Working Group T1E1.4 approved DMT in its T1.413ADSL standard. Discrete Multitone divides the 1 MHz spectrum offered by a phone line into 256 4 kHz channels and varies the bit densities on each channel to overcome noise and interference that may be present in sections of that spectrum. Proponents contend that DMT is better than CAP on noisy lines because it maximizes throughput on good channels and minimizes use of channels that have significant interference. In contrast, CAP uses Quadrature Amplitude Modulation (much like V.90 modems) and relies on a combination of amplitude modulation and phase shifts to increase line capacity over a single line. AT&T integrated a feature of DMT, Rate Adaptive Digital Subscriber Loop (RADSL) to reduce each customer's bandwidth relative to its distance from a central office (CO) and its wire quality-at the cost, of course, of bandwidth. To address the lack of interoperability between vendors, a consortium of organizations led by Intel, Microsoft, and Compaq announced the "Universal" Asymmetric Digital Subscriber Line (ADSL) Working Group. The group's stated purpose was to accelerate ADSL adoption and availability by proposing a simplified version that would deliver high-speed modem communications over existing phone lines to consumers, and would be based upon an open, interoperable ITU standard. By reducing the complexity of the on-site installation and eliminating the need for new wiring at the user's home, Universal ADSL promised to facilitate cost-effectively DSL deployment. Moreover, by leveraging existing rate adaptive ADSL (RAADSL or RADSL) technology, the standard promised to open th