DSL

in full Digital Subscriber Line

Broadband digital communications connection that operates over standard copper telephone wires. It requires a DSL modem, which splits transmissions into two frequency bands: the lower frequencies for voice (ordinary telephone calls) and the upper band for digital data, especially for connection to the Internet. Data can be transferred via DSL at much higher rates than with ordinary dial-up modem service; the range of DSL signals, however, is very small. Connections can be made only within a few miles of the nearest transmitting station. DSL and “xDSL” are umbrella terms under which a variety of protocols and technologies fall. ADSL (Asymmetric DSL) is a popular type of DSL in which most of the bandwidth of the connection is devoted to downloading data from the network to the user, leaving only a small-scale connection for uploading data. In HDSL (High bit-rate DSL) and SDSL (Symmetric DSL) the data stream is symmetric; that is, the upstream and downstream rates are the same. UDSL (Unidirectional DSL), VDSL (Very high data rate DSL), and others still under development are intended to offer even greater rates of data transmission.

digital subscriber line

See DSL.

digital subscriber line [¦dij·əd·əl səb′skrīb·ər ‚līn]

(communications)

A system that provides subscribers with continuous, uninterrupted connections to the Internet over existing telephone lines, offering a choice of speeds ranging from 32 kilobits per second to more than 50 megabits per second. Abbreviated DSL.

(communications, protocol)

Digital Subscriber Line - (DSL, or Digital Subscriber Loop, xDSL - see below) A family of digital telecommunications protocols designed to allow high speed data communication over the existing copper telephone lines between end-users and telephone companies.

When two conventional modems are connected through the telephone system (PSTN), it treats the communication the same as voice conversations. This has the advantage that there is no investment required from the telephone company (telco) but the disadvantage is that the bandwidth available for the communication is the same as that available for voice conversations, usually 64 kb/s (DS0) at most. The twisted-pair copper cables into individual homes or offices can usually carry significantly more than 64 kb/s but the telco needs to handle the signal as digital rather than analog.

There are many implementation of the basic scheme, differing in the communication protocol used and providing varying service levels. The throughput of the communication can be anything from about 128 kb/s to over 8 Mb/s, the communication can be either symmetric or asymmetric (i.e. the available bandwidth may or may not be the same upstream and downstream). Equipment prices and service fees also vary considerably.

The first technology based on DSL was ISDN, although ISDN is not often recognised as such nowadays. Since then a large number of other protocols have been developed, collectively referred to as xDSL, including HDSL, SDSL, ADSL, and VDSL. As yet none of these have reached very wide deployment but wider deployment is expected for 1998-1999.

http://cyberventure.com/~cedpa/databus-issues/v38n1/xdsl.html.

2Wire DSL provider lookup.

["Data Cooks, But Will Vendors Get Burned?", "Supercomm Spotlight On ADSL" & "Lucent Sells Paradine", Wilson & Carol, Inter@ctive Week Vol. 3 #13, p1 & 6, June 24 1996].