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DSL Digital Subscriber Line. An Ngo. Agenda. The Need for Speed What is DSL? PROs & CONs DSL Compared Coverage & Providers. The Need for Speed. Explosive Growth of the Internet Increase Demand for High-Speed Access By Businesses & Individuals Increase Demand for New Applications

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Presentation Transcript
  • The Need for Speed
  • What is DSL?
  • PROs & CONs
  • DSL Compared
  • Coverage & Providers
the need for speed
The Need for Speed
  • Explosive Growth of the Internet
  • Increase Demand for High-Speed Access
    • By Businesses & Individuals
  • Increase Demand for New Applications
    • Real-time interactive multimedia
    • Video conferencing
    • Distance learning
what is dsl
What is DSL?
  • Digital Subscriber Line
    • A technology which uses the existing transmission medium (telephone wire) to provide high-speed transfer of information across the internet.
  • The Technology
    • DSL simply uses more of the bandwidth.
    • It utilizes the frequencies above the voice spectrum.
      • Greater than 4KHz
      • No interference to normal phone conversations (below 4KHz).
    • Thus, it can encode more data to achieve higher data rates than would otherwise be possible in the restricted frequency range of the old telephone network.
common types of dsl
Common Types of DSL
  • ADSL - Asymmetric transfer rates
    • ~6Mbps downstream / ~640Kbps upstream
  • SDSL - Symmetric
    • ~1Mbps up & down
  • HDSL - High Bit Rate Symmetric
    • ~2Mbps up & down
  • VDSL - Very High Bit Rate
    • Restricted to users less than a mile from Telco. (~50Mbps)
  • RADSL – Rate Adaptive
    • Automatically adjusts speed to the line condition.
    • Uplink rate depends on the downlink rate.
how it works
How It Works
  • A.Over the Wire: You are connected to another ADSL modem which also has a POTS splitter, which separates voice calls from data.
  • B.Telephone Calls: Voice calls are routed to the phone company's public switched telephone network (PSTN) and proceed on their way as usual.
  • C.Internet Requests: DSL Access Multiplexer links many ADSL lines to a single high-speed asynchronous transfer mode (ATM) line, which in turn connects to the Internet.
  • D.Back at You: The requested data is retrieved from the Internet and routed back to you.


pros cons


Up to 8 Mbps Downstream


Affordable (~$50/mo.)


Instant “always-on”


Uses existing copper infrastructure

Application Enhancements

Enables high quality real-time, interactive multimedia



Signal degradation with increasing distances

Load coils

Causes distortion at higher DSL frequencies


Cross-talk interference between adjacent pair of wires

Network Compatibility

DSL equipment must be compatible with Telco.

dsl compared
DSL Compared
  • ISDN
    • Pros: Widely available, permits fax, data, and voice on the same line.
    • Cons: Top speed of only 128Kbps, not available in all areas, often difficult to set up, expensive phone-company and ISP charges.
  • Satellite (DBS)
    • Pros: Available to anyone with an unobstructed view of the southern sky.
    • Cons: Top download speed of only 400Kbps is just a fraction of cable or DSL; requires an analog modem for uploads
  • Cable
    • Pros: Available wherever cable TV is; provides high-speed downloads and uploads; inexpensive.
    • Cons: Actual speeds reach only around 1.5Mbps downstream and 300Kbps upstream; you share bandwidth with others in your area; difficult to get in many older, urban buildings.
c urrent coverage area
Current Coverage Area
  • U.S.
  • Canada
  • Hong Kong
  • Singapore
  • Trial Basis: Most other industrialized countries.


dsl providers

Bell Atlantic

Dakota Services Limited

Intelecom Data Systems


Lotus/Bell Atlantic


Northland Communication

Pacific Bell

Southwestern Bell

DSL Providers