Asymmetric Digital Subscriber Line (ADSL) is a form of DSL, 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. By using a splitter or micro filters this allows a single telephone connection to be used for both ADSL service and voice calls at the same time. As phone lines are so varied in quality and weren't initially provisioned with ADSL in mind it can generally only be used over short distances, typically less than 5 km.

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. The ATM stream carried by the ADSL physical layer is typically routed over the telephone company's data network to service center where the encapsulated IP packets are eventually routed onto a conventional internet network.