DSL, short for digital subscriber line, is a broad term for a digital high-speed data connection that uses the same wiring as a regular telephone line. Asymmetric DSL, or ADSL, is a specific type of DSL connection that divides the frequencies used to transmit data, which provides significantly improved download speeds at the cost of slower upload speeds.
DSL was developed and patented in 1988 by Bell Communications Research, Inc. The main advantages of DSL at the time were the speed it offered and the fact that, for the first time, it allowed people to use Internet and phone service at the same time. The main disadvantage was that the digital signal's strength decreased as distance from the provider's central office increased.
Although it uses the same wiring as previous technologies, DSL sends information digitally. This greatly increases the amount of information that can be sent at once. ADSL is the most common type of DSL connection. The opposite of ADSL is SDSL, which stands for symmetrical digital subscriber line. SDSL provides a high-speed data connection that gives equal priority to upload and download speed. Other types of DSL include Internet protocol subscriber line, rate-adaptive digital subscriber line, Uni-DSL and Etherloop.