xDSL - Computer Definition
Referring to any of a group of broadband digital access technologies operating over embedded unshielded twisted pair (UTP) telco local loops. xDSL technologies employ sophisticated compression algorithms and multiplexing techniques to derive performance that often exceeds 1 Mbps over a voice grade local loop. Most DSL technologies support simultaneous voice and high speed Internet access, and a number support video, as well. Most of the technologies involve centralized splitters, also called modems or filters, on the customer premises side of the loop. All DSL technologies support always-on data access, as the circuit is always available from the PC through the on-premises splitter to the centralized splitter and DSL access multiplexer (DSLAM) in the central office, or other centralized location, and to the Internet.Therefore, there are no dial-up delays such as those experienced when using a modem to establish a circuit-switched connection to the Internet over the public switched telephone network (PSTN).Table X-1 provides a comparative listing of a number of DSL technologies. Table X-1: DSL Technology Comparisons
|DSL Type||Max Reach||Applications|
|ADSL||18,000 ft||Consumer-class Internet|
|G.lite||18,000 ft||Consumer-class Internet|
|ADSL2||18,600 ft||Consumer-class Internet|
|ADSL2+||18,000 ft||Consumer-class, SME Internet|
|ADSL2-RE||20,700 ft||Consumer-class Internet|
|IDSL||18,000 ft||Consumer-class Internet|
|SHDSL||6,000 ft.||Business-class Internet|
|VDSL||1,000 ft||Voice, Data, Video|
|VDSL2: 12 MHz G.993.2 (2005)||1,000 ft||Voice, Data, Video|
|VDSL2: 30 MHz G.993.2 (2005)||500 ft||Voice, Data, Video|
A term related to all types of Digital Subscriber Lines, the two main types being ADSL and SDSL. Short for Assymetric Digital Subscriber Line, ADSL is a new technology that allows more data to be sent over existing copper telephone lines (POTS). ADSL supports data rates ranging from 1.5 to 9 Mbps when receiving data (known as the downstream rate) and from 16 to 640 Kbps when sending data (known as the upstream rate). Short for Symmetric Digital Subscriber Line, SDSL is a technology allowing more data to be sent over existing copper telephone lines (POTS); it supports data rates up to several Mbps. SDSL works by sending digital pulses in the high-frequency area of telephone wires, but it cannot operate simultaneously with voice connections over the same wires. Two other types of xDSL technologies are high-data-rate DSL, known as HDSL, and very high data-rate DSL, known as VDSL.
DSL technologies generally use sophisticated modulation schemes to pack data onto copper wires. They are sometimes referred to as “last-mile technologies” because they are used only for connections from a telephone switching station to a home or office and not between switching stations.
See Also: POTS.
Jupitermedia, Inc. xDSL. [Online, July 14, 2005.] Jupitermedia Website. http://www.webopedia.com/TERM/x/xDSL.html.