Introduction

Abstract

The second half of the 20th century has been a remarkable period for technological innovation, and particularly so for telecommunications. During the first half of the last century, telecommunications was almost entirely in the analog mode. Digital transmission of voice and low-speed data communications were the first ventures into digital transmission along a twisted pair telephone line. The invention of the transistor and the subsequent innovation of integrated circuits quickly led to a revolution in electronics and in communications in general. The rapid development of computer and consumer electronics, traditional telephone subscribers are ready for new services based on digital technologies. Driven by the deregulation in the telecommunications industry and the vast growth rate of internet users, world wide industry has made enormous efforts to deploy and standardize a multitude of various different access technologies ranging from media such as air, twisted-pair copper cables, coax cables and optical fibers. Applications such as video conferencing, fast internet downloads, digital television and tele-working have been made available to the public with wide coverage. With a powerful PC processing lots of information, the capability of a voice band modem becomes a limiting factor. The voice channel is limited by the 3.1 kHz band bottlenecking the achievable data-rate for integrating consumers to the evolving high-speed digital communication network. The drawback of a telephone modem can be overcome with the Digital Subscriber Line (DSL) technology. There were several key innovations such as Integrated Service Digital Network (ISDN) and High bit-rate Digital Subscriber Line (HDSL) that led to an application for a system that transmitted to the customer at a high data-rate for supporting entertainment features such as video on demand or simple download of any desired data. The emerging market ultimately led to the conception of the Asymmetric Digital Subscriber Line (ADSL). ADSL allows for simultaneous transmission of digital data and Plain-Old Telephone Service (POTS) signal on a twisted-pair wire. This fact turned out to be one of the success factors during the commercial launch of this product since it could be easily put on top of the already widely spreaded POTS system.