DSL (Digital Subscriber Line) is a family of technologies that provide broadband internet over the copper telephone lines already running to homes. It uses frequencies above those used for voice, so phone calls and data can share one line, separated by a filter at the socket.
Why it matters
DSL reaches many places where no cable or fiber exists. Its weakness is distance: signal attenuates along the copper, so speeds drop the farther you are from the exchange or street cabinet. ADSL gives much faster downloads than uploads; VDSL and VDSL2 reach higher speeds over shorter loops. Unlike shared cable, each customer has a dedicated line to the exchange, although the exchange's backhaul is shared.
Example
Two neighbours on the same ISP may see different speeds. One lives 500 m from the cabinet with VDSL2 and gets tens of Mbit/s; another lives 4 km from an ADSL exchange and gets only a few Mbit/s, a difference caused by line length and quality, not by the plan.
Common mistakes
- Skipping microfilters on phone sockets, which causes noise and disconnects.
- Using long, poor-quality extension wiring after the master socket.
- Expecting the advertised maximum speed regardless of line length.
Related
Get notified when this term updates
Plus occasional practical tips on uptime and monitoring, nothing else. Unsubscribe anytime.
This page is general information written by our editorial team and updated when documentation changes. Servers and providers differ, so test changes safely first. See our editorial policy and disclaimer.