DSL is a #Broadband technology that provides high-speed Internet via existing telephone cabling similar to Integrated Services Digital Network (ISDN). It is generally referred to as xDSL due to variety of existing flavours of DSL including Asymmetric DSL (ADSL) and Symmetric DSL (SDSL). The former offers faster download speeds than upload speeds and is usually subscribed by casual Internet users. The latter offers equal bandwidth in both directions, which is preferred in commercial settings.
Either way, DSL is distance sensitive due to its inability to amplify the signals and converted to other medium. It can reach a maximum distance of around 5.5 km.
Since human speech occupies frequencies of roughly 4kHz and the copper wires are capable of carrying 1 to 2MHz, it is possible to crave out a portion of it for the high-speed Internet connection provision. For upstream data, it will use up around 26 to 160kHz, whereas the downstream data will use up around 240 to 1500kHz. However, due to the nature of twisted-pair wires used by the telephone line, it is required by DSL to have specialised equipments such as low-pass filters (LPF) and DSL access multiplexers (DSLAM) to prevent interference between voice and data due to high frequencies. LPF is typically placed on all phone jacks that are not used by a computer in order to prevent interference. DSLAM functions as an aggregator for signals and acts as the access point to the Internet.