DSL Service Providers
DSL, short for Digital Subscriber Line, refers to a family of technologies that provide a digital connection over the copper wires of the local telephone network. The local loop of analogue telephone connections usually limits communications to a low-frequency band of 0.3 - 4 kHz, but in practice the equipment can usually communicate using a much wider range of frequencies, ranging from these low frequencies up to 200 - 800 kHz, depending on the quality of the circuit and the sophistication of the equipment. DSL services often reserve the 0.3 - 4 kHz band for the "plain old telephone service" (POTS) over the same line.
A DSL connection takes place between equipment of the subscriber and the telephone exchange, with some other protocol used between the exchange and whoever the subscriber really wants to connect to, typically an Internet service provider. This differs from a normal telephone connection, where the public telephone network links subscribers to each other.
The subscriber end of the connection consists of a DSL modem, which has the job of converting the digital stream into analogue signals with various frequency bands, as required for the particular DSL variant in use. In addition the subscriber may need to install a passive electronic filter (known variously as a "splitter" or "filter" or "micro-filter") if using the POTS service on the same line (and possibly also to improve the DSL termination and prevent echoes). Subscribers can plug a filter into an existing telephone socket when using a "wires-only" service; or alternatively the DSL provider may install it.
At the exchange a digital subscriber line access multiplexer (DSLAM) terminates the DSL circuits and aggregates them, where they are handed off onto other networking transports. It also separates out the voice component.
DSL service providers provide the principal competition to cable Internet providers for providing high speed Internet access to home consumers.