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Digital subscriber line (DSL) technology is a
modem technology that uses existing twisted-pair telephone lines to
transport high-bandwidth data, such as multimedia and video, to service
subscribers. The term xDSL covers numerous similar yet competing forms
of DSL, including asymmetric DSL (ADSL), single-line DSL (SDSL),
high-data-rate DSL (HDSL), RADSL (Rate-adaptive DSL), and very-high-data-rate DSL (VDSL).
xDSL is drawing significant attention from implementers and service
providers because it promises to deliver high-bandwidth data rates to
dispersed locations with relatively small changes to the existing telco
infrastructure. xDSL services constitute dedicated, point-to-point,
public network access over twisted-pair copper wire on the local loop
("last mile") between a network service provider's (NSP's)
central office and the customer site, or on local loops created either
intra-building or intra-campus. Currently the primary focus in xDSL is
the development and deployment of ADSL and VDSL technologies and
architectures. This section covers the characteristics and operations of
ADSL and VDSL.
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