DSL   Prerequisite: A phone line (land line, not wireless) is required to qualify for service. ADSL: Asymmetric DSL. Download faster than upload. Shares both voice & Internet on the same line. SDSL: Symmetrical DSL. Download and upload speeds are same. Uses a separate dedicated Internet line and does not share voice. IDSL: ISDN DSL. DSL over an ISDN line DSL is telecommunications line that provides a fast, permanent connection to the Internet. DSL uses the copper wiring found in almost every home and office. Special hardware attached at both ends of the line allows data to transmit at a far greater speed than standard telephone wiring can. It also provides a constant connection to the Internet, 24/7, so there is no need to dial-in to an ISP each time you want to get online. A DSL line is also convenient because you only need one line to carry both voice and data signals (in other words, you don't have to get a second phone line with DSL). DSL is similar to ISDN in that they both operate over existing copper telephone lines and require short runs to a central office. (The reason why DSL is not yet available in many areas is because of the distance from a central office.) DSL provides higher speeds than ISDN, but with DSL, the connection speeds vary. Many people prefer the fixed speed of an ISDN (or a T1, for that matter). Connection speeds for DSL typically range from 512 Kbps to 8192 Kbps downstream and 128 to 2084 Kbps upstream.