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Digital Subscriber Line (DSL)

Digital Subscriber Line (DSL). What is it? DSL is a technology for bringing high-bandwidth connections to homes and small business First Installations started in 1998 A DSL can carry both data and voice signals, and the data part is continuously connected Speed can go as high as 6.1 Mbps

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Digital Subscriber Line (DSL)

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  1. Digital Subscriber Line (DSL) • What is it? • DSL is a technology for bringing high-bandwidth connections to homes and small business • First Installations started in 1998 • A DSL can carry both data and voice signals, and the data part is continuously connected • Speed can go as high as 6.1 Mbps • Typical speeds are between 128 Kbps and 1.54 Mbps

  2. Digital Subscriber Line (DSL) • How it works • POTS and DSL • Two wire analog • Voice uses analog frequencies 0 to 3400 Hertz • DSL uses analog frequencies above 4000 Hertz • DSL Technology • Uses advanced modulation technologies on existing communications networks for high speed networking between a subscriber and a Telco • Assumes digital data does not require conversion to analog form and back

  3. Digital Subscriber Line (DSL) • How it works • DSL Access Multiplexer (DSLAM) and Splitter Technology • DSLAM combines the channels (bit streams) coming upstream from the users and splits data into cannels going down stream to the users (Multiplexing) • Splitter vs. Splitterless • Splitter uses four wires – two for voice, two for data • The splitter is at the customer site • Splitterless uses two wires • Splitter is at DSLAM • Uses filters for voice – Low-Pass Filter - filters everything above 4000 Hrtz

  4. Digital Subscriber Line (DSL) • Types of DSL • ADSL (Asymmetrical Digital Subscriber Line) • HDSL (High-Bit-Rate Digital Subscriber Line) • SDSL (Symmetrical Digital Subscriber Line) • RADSL (Rate Adaptive Digital Subscriber Line) • VDSL (Very High-Data-Rate Digital Subscriber Line)

  5. Digital Subscriber Line (DSL) • ADSL • Most common DSL • Distance from CO limited to 18,000 feet • Each line direct to DSLAM • Bandwidth • Upload – 64 Kbps to 640 Kbps (1.54 Mbps, If less than 12,000 feet) • Download – up to 9 Mbps • Two primary modulation implementations • CAP (Carrierless Amplitude Phase Modulation) • DMT (Discrete MultiTone)

  6. Digital Subscriber Line (DSL) • ADSL Modulation Technologies • CAP (Carrierless Amplitude Phase Modulation) • Separates Voice, Upload and Download into distinct bands • Bands Widely seperated • Default ANSI standard • Developed by AT&T • Uses a technique similar to QAM (Quadrature Amplitude Modulation)

  7. Digital Subscriber Line (DSL) • ADSL Modulation Technologies • DMT (Discrete MultiTone) • 256 channels @ 4.3125 KHz each • First channel (0 to 4.3125 KHz) voice • Each channel can be either upload or download • Each channel can carry 0 to 60 Kbps • Uses QAM (Quadrature Amplitude Modulation)

  8. Digital Subscriber Line (DSL) • HDSL (High-Bit-Rate Digital Subscriber Line) • The earliest variation of DSL to be widely used • Symmetrical • Data rate 2.048 • 13728 feet (4.2 km (2.6 mi)) without repeater • Separate phone line • Used to deliver t-1 circuit • Requires 2 independent twisted pairs

  9. Digital Subscriber Line (DSL) • SDSL (Symmetrical Digital Subscriber Line) • Single twisted pair • 10,000 feet (3 km (1.86 mi)) without repeater • 768 kbps maximum in both direction • RADSL (Rate Adaptive Digital Subscriber Line) • Adapts the transmission speed depending on the distance to the CO

  10. Digital Subscriber Line (DSL) • VDSL (Very High-Data-Rate Digital Subscriber Line) • Data rates • 12.9 Mbps to 52.8 Mbps download • 1.5 Mbps to 2.3 Mbps upload • Maximum distance 4,500 feet (1.35 km (0.83 mi) • Will require fiber to the neighborhood or fiber to the curb before it could be widely available

  11. Digital Subscriber Line (DSL) • Advantages • Operates over ordinary two-wire phone lines • Service is always connected • Enables high bandwidth and push technologies • Faster than analog, ISDN or wireless access • Cost effective to implement, requiring no expensive infrastructure build-outs (Except to alleviate distance restrictions) • Utilizes existing copper wire infrastructure • Service is the same for small and large companies alike • Utilizes standardized premise products such as splitters, DSL modems and PC cards • Access to other broadband services such as ATM • Allows rapid file transfer and faster downloads • Allows constant access to email and shared files

  12. Digital Subscriber Line (DSL) • Disadvantages • Distance sensitive • Not yet available everywhere • Splitters require in-house installation

  13. Cable Modem Technology • Cable Modem Termination System (CMTS) • Data Over Cable Service Interface Specifications (DOCSIS) • CMTS enables as many as 1,000 users to connect to the Internet through a single 6-MHz channel • Performance does not depend on distance

  14. Cable Modem Technology Disadvantages • Is not available everywhere • Subscriber density affects performance

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