DSL: the physical medium and modulation techniques

With over 150 million lines deployed worldwide , the success of DSL technologies is well established. This worldwide success can be largely explained by the advent of the Internet in the late 90s, whose constant enrichment with multimedia content (audio, video) quickly highlighted the limitations of the analog modem and telephone network for data transport. Although the emergence of the Integrated Services Digital Network (ISDN) was an important step in addressing the strong residential demand for simultaneous telephone and data services, it was not until the arrival of asymmetrical digital subscriber line (ADSL) that subscribers' expectations in terms of high-speed access were fully met. ADSL gradually replaced the analog modem as the most widely deployed broadband technology to date.

In recent years, the emergence of IP telephony (VoIP) and IP television (IPTV) has prompted the development of new DSL technologies to provide increased capacity to support a multiservice offering, commonly known as triple play, combining high-speed Internet access, telephony and IP television. This development has led to the definition of two standards that are set to play a major role in the next decade: ADSL2plus and VDSL2. The latter enables bidirectional transmission of 100 Mbit/s over a single conventional telephone pair. The copper pair has not ceased to amaze, and engineers are constantly pushing back the arrival of optical fiber to the home.

This presentation covers the basic principles of DSL technologies, from the constraints of transmission over a twisted copper pair to the different modulations used, and also describes the typical architecture of a DSL access network.

This is the first in a series of two articles on DSL technologies:

DSL: the physical medium and modulation techniques ;

[TE 7 599] DSL technologies: past, present and future.