A term related to all types of Digital Subscriber Lines, the two main types being ADSL and SDSL. Short for Assymetric Digital Subscriber Line, ADSL is a new technology that allows more data to be sent over existing copper telephone lines (POTS). ADSL supports data rates ranging from 1.5 to 9 Mbps when receiving data (known as the downstream rate) and from 16 to 640 Kbps when sending data (known as the upstream rate). Short for Symmetric Digital Subscriber Line, SDSL is a technology allowing more data to be sent over existing copper telephone lines (POTS); it supports data rates up to several Mbps. SDSL works by sending digital pulses in the high-frequency area of telephone wires, but it cannot operate simultaneously with voice connections over the same wires. Two other types of xDSL technologies are high-data-rate DSL, known as HDSL, and very high data-rate DSL, known as VDSL.

DSL technologies generally use sophisticated modulation schemes to pack data onto copper wires. They are sometimes referred to as “last-mile technologies” because they are used only for connections from a telephone switching station to a home or office and not between switching stations.

See Also: POTS.