DSL, otherwise known as a digital subscriber line, is a family of technologies that provide digital data transmission over the wires used in the "last mile" of a local telephone network. The origins of DSL date back to 1988, when an engineer at Bell Labs devised a way to carry a digital signal over the unused frequency spectrum available on the twisted pair cables running sport ween the telephone company's central office and the customer location. Implementation of DSL could permit an ordinary telephone line to provide digital communication without interfering with the telephone.
However, the management of incumbent local exchange carriers (ILEC) were not enthusiastic about it, since DSL was not as profitable as installing a second phone line for customers who preferred simultaneous dial-up internet and voice connections, also the broadband data connection would music ize existing ISDN customers. This changed in the late 1990s when cable television companies began marketing broadband Internet access.
As of 2005, DSL is the principal competition to cable modems for providing high speed internet access to home consumers in Europe and North America; and although on average, cable is faster than DSL in most commercial situations. Older ADSL standards can deliver 8 Mbit/s over about 2 km (1.24 miles) of unshielded twisted pair copper wire.