Digital Subscriber Line (DSL) refers to a family of technologies that provide a digital connection to the telephone network. It is currently the principle competitor to Cable Modems to provide high speed Internet access to the home consumer. DSL is provided over the standard copper phone lines that provide the majority of traditionaltelephone service. Many DSL's can run in conjunction normal POTS service by utilising splitters and using non-voice-band frequencies.
Example DSL technologies (sometimes called xDSL) include:
- ISDN (pre-dates the use of the term DSL)
- IDSL (ISDN Digital Subscribe Line, a data-only ISDN variant)
- HDSL (High Bit Rate Digital Subscriber Line)
- ADSL (Asymmetric Digital Subscriber Line)
- SDSL (Symmetric Digital Subscriber Line, a standardised version of HDSL)
- VDSL (Very high speed Digitial Subscriber Line)
The reach restraints (line length from Central Office to Subscriber) reduce as the data rates increase, with technologies like VDSL being used for short range links (typically "Fibre to the Curb" network scenarios).
Many DSL technologies implement an ATM layer over the low-level bitstream layer to enable the adaptation of a number of different technologies over the same link.