Digital Subscriber Line, or DSL, is a family of technologies that provide digital data transmission over the wires of a local telephone network.

Typically, the download speed of DSL ranges from 128 kilobits per second (kbit/s) to 24,000 kbit/s depending on DSL technology and service level implemented. Upload speed is lower than download speed for Asymmetric Digital Subscriber Line (ADSL) and equal to download speed for Symmetric Digital Subscriber Line (SDSL).

History

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The origin of DSL technology dates back to 1988, when engineers at Bellcore (now Telcordia Technologies) devised a way to carry a digital signal over the unused frequency spectrum available on the twisted pair cables running between the telephone company's central office and the customer premises. Implementation of DSL could permit an ordinary telephone line to provide digital communication without interfering with voice services. However, incumbent local exchange carriers (ILEC) were not enthusiastic about DSL, since it was not as profitable as installing a second phone line for consumers who preferred simultaneous dial-up internet and voice connections, and the broadband data connection would cannibalize existing ISDN customers. This changed in the late 1990s when cable television companies began marketing broadband Internet access. Realizing that most consumers would prefer broadband Internet to dial-up Internet, ILECs rushed out the DSL technology, which they had delayed implementing, as an attempt to win market share from the broadband Internet access offered by cable television operators.

DSL is the principal competition of cable modems for providing high speed Internet access to home consumers in Europe and North America. Older ADSL standards can deliver 8 Mbit/s over about 2 km (1.25 miles) of unshielded twisted pair copper wire. The latest standard, ADSL2+, can deliver up to 24 Mbit/s, depending on the distance from the DSLAM. ^* Some customers, however, are located farther than 2 km (1.25 miles) from the central office, which significantly reduces the amount of bandwidth available (thereby reducing the data rate) on the wires.

More on [ Digital Subscriber Line ]

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