municate with a category I (FDM) modem. ConclusionThe twisted pair wire between the telephone central office and end users of telecommunication services has a great deal more information capacity than used for the regular voice services. Several baseband and passband transmission systems collectively referred to as xDSL, have been developed over the last ten years that enable up 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 layer 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 usersReferences: 1.Marlis Humphrey and John Freeman, "How XDSL Supports Broadband Services to the Home", IEEE Network., vol. 11, no. 1, Jan-Feb 1997, ...
