DSL

Digital Subscriber Line: a technology that allows high-speed transmission of data, audio, and video, usually over standard telephone lines; a form of broadband transmission.

[1995-2000]

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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.

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▪ networking technology

in full  digital subscriber line 

      networking technology that provides broadband (high-speed) Internet connections over conventional telephone lines.

      DSL technology has its roots in work done by Bell Communications Research, Inc., in the late 1980s to explore the feasibility of sending broadband signals over the American telecommunications network. The first efforts in this area resulted in another high-speed Internet technology, called integrated services digital network ( ISDN). In the early 1990s the first variety of DSL, high-bitrate DSL (HDSL), was rolled out with the intent of being used for on-demand television. Initial efforts looked promising, but the rapidly growing number of channels provided by cable television companies made setting up an on-demand service financially less attractive. Soon after, DSL was repurposed for connecting devices to the Internet. Other varieties of DSL soon followed the creation of HDSL, including the most common type: asynchronous DSL (ADSL). Asynchronous refers to the way that more bandwidth is given to downstream traffic, which comes to the user from the Internet, than to upstream traffic, which goes from the user to the Internet. Traffic on DSL is transmitted over normal telephone lines through a DSL terminal adapter, also known as a DSL modem, which connects a computer or local computer network to the DSL line.

      Each DSL user has a dedicated telephone line, so unlike its closest competitor, cable Internet, signing up more neighbourhood customers does not degrade service. However, DSL is limited by distance. A user has to be within a few miles of a telephone switching office for DSL to work, and signal strength degrades even within that distance. In addition, DSL speeds have not improved much since being introduced—typically, they are 128 Kbps (128,000 bits per second) upstream and 512 Kbps downstream, though premium business services may be about 10 times faster—while cable, which is generally less expensive than DSL, offers speeds in excess of 1 Mbps (1 million bits per second) upstream and 16 Mbps downstream.

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