ADSL = Asymmetric Digital Subscriber Line.

A method for moving data over regular phone lines. An ADSL circuit is much faster than a regular phone connection, and the wires coming into the subscriber's premises are the same (copper) wires used for regular phone service. An ADSL circuit must be configured to connect two specific locations, similar to a leased line.

The data-rate of ADSL strongly depends on the length and quality of the line connecting the end-user to the telephone company. Typically the upstream data flow is between 16 and 640 kilobits per second while the downstream data flow is between 1.5 and 9 megabits per second. A commonly discussed configuration of ADSL would allow a subscriber to receive data (download) at speeds of up to 1.544 Megabits per second, and to send (upload) data at speeds of 128 kilobits per second. Thus the 'Asymmetric' part of the acronym. This technology is well suited to the Web, where much more data is sent from a server to your computer than you send to the server.

Another commonly discussed configuration would be symmetrical: 384 kilobits per second in both directions. In theory ADSL allows download speeds of up to 9 megabits per second and upload speeds of up to 640 kilobits per second.

ADSL can carry digital data, analog voice, and broadcast MPEG2 video in a variety of implementations to meet customer needs.

ADSL can be used simultaneously with voice telephony.

ADSL is often discussed as an alternative to ISDN, allowing higher speeds in cases where the connection is always to the same place.