Phone networks were never intended to carry information at high speeds; by converting your voice into an electric signal, they were constructed to carry an analog voice. A modem converts digital signals into an analog audio signal that could readily be carried over a phone line. The technical limits of phone lines mean that the quickest is around 56Kbps.

DSL (digital subscriber line) technology gets around this issue by making use of the phone line to carry digital signals directly, without converting them to an analog signal first. This has three advantages: it enables much higher data rates when compared to a standard modem; the connection is constantly on, meaning you do not need to dial up each time you desire to use the Internet (and incur another price); and, because the copper cable is split at the exchange, you can use your home telephone while on the Internet. To put it differently, one phone line will suffice.

There are numerous kinds of DSL, but the one most easily accessible to little businesses and consumers is ADSL, or Asymmetric Digital Subscriber Line.