digital subscriber line
     n : a generic name for digital lines that are provided by
         telephone companies to their local subscribers and that
         carry data at high speeds [syn: DSL]

	

	Digital Subscriber Line
     
         (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://www.cyberventure.com/~cedpa/databus-issues/v38n1/xdsl.html).
     
        2Wire DSL provider lookup (http://www.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)