The Digital Subscriber Line, or DSL, is an advanced technology that can be used to carry digital data over the standard double twisted copper-wire PSTN network. DSL uses the unused frequency spectrum of the network to send digital data without extra cost or a separate network.
During the initial days the local exchanges did not show much interest in DSL as providing a new line for dial-up internet access was more profitable. However, as cable operators started providing broadband access through cable, the networks brought forward the DSL technology for providing broadband internet access to customers without the need of installing any new network infrastructure.
DSL can provide speeds between 128 kilobits per second and 24,000 kilobits per second. In Asymmetric DSL, the upload speed is usually lower than the download speeds, while in Symmetric DSL, they are equivalent. The fact that DSL utilized the available network and provides fast connectivity, and that the technology is frequently overhauled for new improvements means that DSL retains its popularity amidst other forms of connectivity.