Digital subscriber line

A digital subscriber line or digital subscriber loop (DSL) is a family of digital telecommunications protocols designed to allow high speed data communication over the existing copper telephone lines between end-users and telephone companies.

Background
When two conventional modems are connected through a (PSTN), it treats the communication the same as voice conversations. This has the advantage that there is no investment required from the (telco) but the disadvantage is that the  available for the communication is the same as that available for voice conversations, usually 64 kb/s  at most. The copper cables into individual homes or offices can usually carry significantly more than 64 kb/s but the telco needs to handle the signal as digital rather than analog signals.

History
Early throughput ranged from about 128 kb/s to over 8 Mb/s, the communication can be either symmetric or asymmetric, in which the available bandwidth may or may not be the same  and. Equipment prices and service fees also vary considerably.

There are many implementations of the basic scheme, differing in the communication protocol used and providing varying s. The first technology based on DSL was Integrated Services Digital Network (ISDN), although it is no longer recognized as such. Though initial deployment was limited in the 1990s, a number of other derivatives of DSL were developed, collectively referred to as xDSL, such as:
 * (ADSL)
 * (SDSL)
 * (HDSL)
 * Very high-speed digital subscriber line