Digital Subscriber Line (DSL)

DSL stands for digital subscriber line, which is a family of digital data transmission technology. Using DSL technology, both voice and data can be transmitted over the same telephone line simultaneously.

Telephone systems by themselves make inefficient use of the available network bandwidth because voice signals use low frequencies for transmission only. The higher frequencies are unused and can be used for the transmission of data. This is the concept on which DSL is based.

DSL works as follows. A DSL modem is installed at the user premises where the user's computer and telephone are connected to the modem. The modem acts as a frequency splitter, receiving various frequencies from the network, sending lower frequencies to the telephone and frequencies higher than 4 kHz to the computer. This way, both the data and voice signals are transmitted simultaneously without interfering with each other.

DSL comes in many different forms like SDSL (symmetric digital subscriber line), ADSL (asymmetric digital subscriber line), HDSL (high data rate digital subscriber line) and VDSL (very high rate digital subscriber line). The most popular among these is ADSL, which provides the user with higher download rates as compared to upload rates, justified by the fact that users download more data than they upload while surfing the Internet.

DSL download speed can vary from 512 to 24,000 kilobits per second (kbps). In the third quarter of 2007, the average DSL download speed in North America and Canada was approximately 3,000 kbps, whereas average speeds in the Asia Pacific area and Europe were respectively 15,000 and 5,500 kbps.