to several megabits per second of data to be carried over the regular telephone twisted pair line. The xDSL family of technologies provides a wide variety of line driving schemes to accomplish and satisfy different market needs over today’s infrastructure. xDSL has application in both the corporate and residential environments as well as flexibility to meet the market challenges. Since xDSL operates at the physical layer of OSI seven layers standard, it can be used in conjunction with ATM and Frame Relay technology. The most promising of the xDSL technologies for integrated Internet access, intranet access, remote LAN access, video-on-demand, and lifeline POTS applications in the near term is ADSL or R-ADSL (a rate-adaptive version of ADSL). During the past year, ADSL has concluded trials by more than 40 network service providers throughout the world, primarily in North America and northern Europe. Service introduction began in 1997, but ADSL service is still being rolled out in many areas. In the meantime, xDSL technologies and standards will continue to evolve, as will user demand for these emerging services relative to other local access service alternatives. The ability to utilize the existing telephone copper wire infrastructure as well as interoperability with ATM and Frame Relay technology, position xDSL as the most promising of the broadband access technology options for both residential and business users.by: John Thomas ...
