ADSL (Asymmetric Digital Subscriber Line) is a form of DSL (Digital Subscriber Line) data communications technology that enables faster data transmission over copper telephone lines that that provided by a conventional dial-up or ISDN (voiceband) modem. A splitter (or microfilter) allows a single telephone connection to be used for both ADSL services and voice calls at the same time. All voice calls made on the line will be charged by the telecommunications provider at standard call rates.

ADSL can generally only be transmitted over short distances from the telecommunications exchange, typically less than 4 kms (or 8 kms in exceptional installations). ADSL services can be provided over a fibre optic link, provided distances from one point of the system to the opposite end of the same of more than 48 kilometers. Fibre connections are unfortunately not very common due to the high costs associated with installation and materials, resulting in it not being commonly available.

ADSL connections are always-on capable, high speed connections, established by configuring an ADSL modem or router to connect to the internet via the ISP's network. Three ADSL speed options are currently available in South Africa, being 384 kBits/s, 512 kBits/s and 4 096 kBits/s (4 MBytes/s). The telecommunication provider (Telkom) typically charges a fixed monthly line rental fee determined based on the speed of the line. The ISP will only charge for the actual amount of bandwidth used or minimum bandwidth bundle purchased, regardless of the duration of the connection. As a result an ADSL connection is ideally configured to remain permanently connected - providing you with internet and e-mail services immediately, rather than first having to establish a connection as is the case with a dial-up or ISDN connection.

For those users that require a large or unlimited amount of bandwidth every month, ISP's also offer uncapped ADSL accounts. These accounts are billed at a fixed monthly rate regardless of the internet bandwidth used, with the monthly rates once again calculated based on the line connection speed.