xDSL - technical 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

See also ADSL, ADSL2, ADSL2+, always on, broadband, compression, downstream, DSLAM, G.lite, HDSL, high speed, IDSL, ITU-T, local loop, multiplexer, SDSL, SHDSL, splitter, telco, upstream, UTP, VDSL, and x.