XDSL
       x Digital Subscriber Line (ADSL, HDSL, SDSL, UDSL, VDSL), "xDSL"

	

	Digital Subscriber Line
Digital Subscriber Loop
xDSL

    (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)