HIGH BIT RATE DIGITAL SUBSCRIBER LINES - A REVIEW OF HDSL PROGRESS

This paper gives an overview of the progress that has been made in the evolution of technology to provide DS1 rate telephone access in a restricted segment of the loop plant without intermediate repeaters, loop conditioning, or pair selection in assignment. This technology has come to be called the high bit rate digital subscriber line (HDSL). Discussed are background information on electronics in the loop plant and characterization of the transmission environment in the relevant frequency band. The progress of the HDSL study project in the T1 subcommittee of the American National Standards Institute (ANSI), accredited Committee T1, Working Group T1E1.4 is outlined. Analytical and theoretical studies to determine the limits on the transmission capabilities of the loop plant, motivated by the need to determine the feasibility limits of HDSL's, are reviewed. Also reported on is progress in technical work on suitable transmission formats, including several innovative transmission architectures and work in the areas of timing, equalization, echo cancellation, and sundry other issues. Finally, the possibility of an asymmetrical digital subscriber line (ADSL), transmitting at the DS1 rate from the central office to a remote distribution point, through the entire nonloaded loop plant is discussed, as is duplex transmission at rates in excess of 10 Mb/s over shorter distances.