Embedded Tutorial ET2: Digital Subscriber Line

Abstract

Digital Subscriber Line (DSL) is a family of standards that allow existing twisted pair copper lines to carry modulated digital signals which uses telephone network and unused frequency Spectrum. In this tutorial we describe DSL (Digital Subscriber Line), comparing with POTS and ISDN. We explain the different DSL flavors available with the modulation techniques used and also discuss challenges in getting high performance and throughput, achieving xDSL rate and meeting the DSL standard. We begin by introducing DSL having a pair of modems CO (Central office) and CPE (Customer Premises Equipment) and talk about frequency spectrums. We explain the limitations of POTS (Plain Old Telephone System) with Dial-up Connection and ISDN (Integrated Services Digital Network), and advantages of DSL over POTS. Next we describe various flavors of DSL with their frequency spectrums, power enhancements, standardization, profiles, and band plans. We discuss different modulation techniques with their advantages and disadvantages, including Single carrier Modulation like CAP and QAM and Multi Carrier Modulation like DMT. We explain the interferers/noise: Line Attenuation, The channel attenuation, Bridged taps, Impulse noise, White noise, NEXT, FEXT, RE Interference. We conclude the tutorial with a description of full activation and initialization phases. The targeted audience for the tutorial is designers, developers, testers, people working in the area of VDSL, ADSL technology and People working on different platforms like DSLAM's, Central office, Customer premises equipment, Gateway products as well as products related to access network who are familiar with copper line and modems.