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Digital Subscriber Line

The world is hungry for high speed Internet access. Telephone modem speeds have peaked. T1 and T3 services are now common offerings, but mostly for businesses. There is a massive rush to bring high bandwidth services to everyone. Enter DSL, the Digital Subscriber Line.

DSL can be an excellent alternative to cable modems, multiple telephone lines used for data access, DS1 (T1) and ISDN access services. For home Internet users, it includes the possibility of happier spouses, when they discover that Internet access and plain old telephone service (POTS) can simultaneously use a single twisted pair telephone line. Businesses will find that DSL, when it matures, will provide a simple high speed data connection that utilizes the existing telephone system. (Please review the DSL advantages and disadvantages).
Some DSL Facts

  • Many DSL modems will be offered as internal PCI cards (Cisco 605) or external devices (Cisco 675).
  • A splitter is required at the telephone entry point of the home or business to separate POTS (Plain Old Telephone Service) from DSL. This is for maintaining balanced DSL transmission lines.
  • DSL uses the same copper wires as your typical telephone.
  • DSL can use existing plant, or telephone network copper wires.
  • DSL will likely have maximum run lengths of 18,000 feet, or 5.5 km.  This is wire distance from the U.S. West central office.  It is not refering to line of site or driving distance.
  • DSL does not use the telephone company's switched circuit to pass along the high speed data. POTS and DSL signals are independent of each other.
  • POTS will occupy the band from 0 to approximately 4 kHz (see diagram below).
  • DSL can occupy from 0.1 MHZ (100 kHz) to over 5 Mhz. The most common DSL services will probably not exceed 1 MHz, since higher frequencies equate to higher signal loss (see diagram below).
  • Bibliography

    Author unknown, What Is...DSL and xDSL [WWW],
    http://www.whatis.com/dsl.htm, date unknown

    Author unknown, ADSL Forum Home Page [WWW],
    www.adsl.com, date unknown

    Westell, About DSL [WWW],
    www.westell.com/dslAbout.html, date unknown

    Paradyne Corp., The DSL Source Book (2d ed.) [WWW],
    www.paradyne.com/sourcebook_offer/index.html, 1997

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