What Is ADSL?

Date First Published: 20th May 2022

Topic: Computer Networking

Subtopic: Data Transmission Technologies

Article Type: Computer Terms & Definitions

Difficulty Level: 6/10

Learn more about what ADSL is in this article.

ADSL stands for Asymmetric Digital Subscriber Line and it is a type of DSL broadband technology that transmits digital signals over telephone lines using copper wires. It is a simple and cheap connectivity that uses wires that have already been laid for telephone services. The word 'asymmetric' means that the upload speed is much slower than the download speed. This is due to it using most channels to send downstream to the user and only a small portion to upload data from the user. ADSL connections and other types of high-speed DSL were available in urban areas by 2000.

ADSL supports data transfer rates of up to 1.5 Mb/s – 9 Mb/s when receiving data (downloading) and data transfer rates of up to 16 – 640 Kb/s when sending data (uploading). Due to the copper wires, ADSL is a slower broadband option and is often used when fibre internet access, such as FTTC or FTTP cannot be afforded. Since most users receive much more data than they send, ADSL does not have a noticeable impact on the internet connection. However, for businesses that need to upload large files to a server on a daily basis or need a large speaking (upload) time for VoIP in video calls, ADSL is not suitable.

Requirements

All that is required for ADSL to work is an ADSL modem that connects to a telephone exchange and a microfilter which is installed on the subscriber’s telephone line and allows both ADSL and telephone services to be used at the same time. Both the modem and the telephone connect to the microfilter. It is more advanced than dial-up that had no microfilter, meaning that if someone answered the phone, the internet connection would go down, since it is not possible to have both services at the same time. Usually, ADSL is easy to set up and the installation only takes a few hours.

Note:

ADSL requires subscribers to be in close geographical locations to the telephone exchange. This distance is usually within 2 – 5 miles. Longer distances from the telephone exchange will result in a slower connection. However, loop extenders can be used to increase the strength of the signal when there is a longer distance between the subscriber and the telephone exchange.

History

In 1988, ADSL was originally patented. The expensive usage costs meant that it would be years before the technology was used. Signal processing was required in order for ADSL to reach higher speeds which made it an alternative to dial-up.

In the 1990s, ADSL was introduced. In the 2000s, it became more popular. Most telephone exchanges have upgraded to support ADSL as well as faster technologies, such as fibre.