from
The Free On-line Dictionary of Computing (8 July 2008)
Digital Subscriber Line
Digital Subscriber Loop
xDSL
<communications, protocol> (DSL, or Digital Subscriber Loop,
xDSL - see below) A family of {digital} {telecommunications}
{protocols} designed to allow high speed data communication
over the existing {copper} telephone lines between end-users
and telephone companies.
When two conventional {modems} are connected through the
telephone system ({PSTN}), it treats the communication the
same as voice conversations. This has the advantage that
there is no investment required from the telephone company
(telco) but the disadvantage is that the {bandwidth} available
for the communication is the same as that available for voice
conversations, usually 64 kb/s ({DS0}) at most. The
{twisted-pair} copper cables into individual homes or offices
can usually carry significantly more than 64 kb/s but the
telco needs to handle the signal as digital rather than
analog.
There are many implementation of the basic scheme, differing
in the communication {protocol} used and providing varying
{service levels}. The {throughput} of the communication can
be anything from about 128 kb/s to over 8 Mb/s, the
communication can be either symmetric or asymmetric (i.e. the
available bandwidth may or may not be the same {upstream} and
{downstream}). Equipment prices and service fees also vary
considerably.
The first technology based on DSL was {ISDN}, although ISDN is
not often recognised as such nowadays. Since then a large
number of other protocols have been developed, collectively
referred to as xDSL, including {HDSL}, {SDSL}, {ADSL}, and
{VDSL}. As yet none of these have reached very wide
deployment but wider deployment is expected for 1998-1999.
(http://cyberventure.com/~cedpa/databus-issues/v38n1/xdsl.html).
2Wire DSL provider lookup (http://2Wire.com/).
["Data Cooks, But Will Vendors Get Burned?", "Supercomm
Spotlight On ADSL" & "Lucent Sells Paradine", Wilson & Carol,
Inter@ctive Week Vol. 3 #13, p1 & 6, June 24 1996].
(2001-04-30)