DSL Digital subscriber line D igital subscriber line ( DSL ; originally digital subscriber loop ) is a family of technologies that are used to transmit digital data over telephone lines . In telecommunications marketing, the term DSL is widely understood to mean asymmetric digital subscriber line (ADSL), the most commonly installed DSL technology, for Internet access . DSL service can be delivered simultaneously with wired telephone service on the same telephone line since DSL uses higher frequency bands for data. On the customer premises, a DSL filter on each non-DSL outlet blocks any high-frequency interference to enable simultaneous use of the voice and DSL services. The bit rate of consumer DSL services typically ranges from 256 kbit/s to over 100 Mbit/s in the direction to the customer ( downstream ), depending on DSL technology, line conditions, and ...