Asymmetric Digital Subscriber Line

What Does Asymmetric Digital Subscriber Line Mean?

Asymmetric digital subscriber line (ADSL) is a type of DSL technology that provides greater bandwidth and provides higher-speed transmission over traditional copper telephone wires than conventional voice band modem. ADSL is characterized by “high speeds” and “always on” connectivity. This is achieved by using the frequencies not being used by voice calls.


ADSL was designed to support the typical home Internet user who downloads frequently rather than uploads data.

Techopedia Explains Asymmetric Digital Subscriber Line

ADSL is the most common type of DSL connectivity offered by Internet service providers as it uses wires that have already been laid for telephone service. This makes it a cheap and viable option for distributing Internet connectivity to homes.

For ADSL to work, only a microfilter and an ADSL modem need to be installed and so installation typically only takes a few hours, including the settings for the connection. With real-world speeds of about 2Mbps, it is well suited to home use.

A special filter called a microfilter is needed in order for the regular voice service and ADSL to be used at the same time. It is installed in the telephone line just before the modem and the telephone. Both modem and telephone connects to the microfilter.

Technically, ADSL can reach speeds of up to 6Mbps, but only receives 2Mbps downstream (download) and 512Kbps upstream (upload) speeds.

ADSL can only be distributed within short distances from the central office, usually less than 2.5 miles. It may exceed 5 miles if the gauge of the existing wires allow for further distribution.


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Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.