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

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

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

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)

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)

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)

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)

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

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

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

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

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

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

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