Fast businessAsymmetric Digital Subscriber Line (ADSL) is one form of the Digital Subscriber Line technology, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. It does this by utilizing frequencies that are not used by a voice telephone call.
A splitter – or microfilter – allows a single telephone connection to be used for both ADSL service and voice calls at the same time. ADSL can generally only be distributed over short distances from the central office, typically less than 4 kilometres (2 mi), but has been known to exceed 8 kilometres (5 mi) if the originally laid wire gauge allows for farther distribution. In 2005, the ability to transmit copper ADSL/DSL services over a fiber optic cable became possible by utilizing the RLH ADSL/DSL fiber optic link, providing distances from one point to the opposite end of the system of more than 30 miles.

At the telephone exchange the line generally terminates at a DSLAM where another frequency splitter separates the voice band signal for the conventional phone network. Data carried by the ADSL is typically routed over the telephone company’s data network and eventually reaches a conventional Internet Protocol network.