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					        DSLs

Digital Subscriber Lines
 Digital Subscriber Lines (DSLs)
• Offered by Telephone Companies
  – Lines to customer premises are subscriber
    lines, which connect subscribers to the
    telephone system
  – These are digital
  – Hence “digital subscriber line”


         DSL       DSL        Telephone
                                                ISP
        Modem                  Network
Digital Subscriber Lines (DSLs)
• Offered by Telephone Companies
  – Several types of digital lines for subscribers
     • Some are for homes, others for businesses
  – For residential customers, usually multiplexes
    regular phone, high-speed data
     • Can use existing phone line coming into house
     • Can use Internet without tying up phone

        DSL                      Telephone
                                                       ISP
       Modem      Existing        Network
                 Phone Line
      Digital Subscriber Lines
• Most common for home is Asymmetric DSL
  (ADSL)
  – Upstream and downstream speeds are different
  – Upstream at 64 kbps or more
  – Downstream at 256 kbps to a few Mbps
  – Asymmetric speed is good for WWW
  – About $50 per month incl. ISP; more for faster service

      DSL       ADSL                Telephone
                                                        ISP
     Modem 64 or more kbps           Network

            256 kbps-a few Mbps
      Digital Subscriber Lines
• G.Lite (G.992.2) Standard
  – New ADSL standard from ITU-T
  – Up to 1.5 Mbps downstream speed
  – No carrier installation is necessary
  – Not being widely adopted by ADSL vendors
    yet
     DSL        ADSL         Telephone
                                           ISP
    Modem 64 or more kbps       Network

             Up to 1.5 Mbps
      Digital Subscriber Lines
• Digital Subscriber Line Access Multiplexer
  – Telco must install a DSLAM at end switching
    office
     DSL

                        Telephone
    DSL           DSLAM                     ISP
                         Network

     DSL
      Digital Subscriber Lines
• Splitting Voice and Data                 New

  – Voice and data are split at home by the DSL
    modem
  – Voice and data are also split at the telephone
    company’s first switching office

Computer
                                                 DSLAM

 Phone        DSL       DSL      DSL
             Modem              Splitter          Voice
                                                 Network
   DSLs Versus Cable Modem
           Service
• Both Expected to Sell Well
• Forecast for Worldwide Installations in 2004
   – Cable modem lines: 9 million
   – DSLs: 10 million
   – Source: Insight Research
• Cable is Available Mostly in Residential Areas
• Cable is only widespread in some countries,
  especially the United States

				
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posted:4/15/2013
language:English
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