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” Telephone Network Telephone Network ISP DSL Modem DSL Modem DSL

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 Telephone Network Telephone Network ISP DSL Modem DSL Modem Existing 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 Telephone Network Telephone Network ISP DSL Modem DSL Modem ADSL 64 or more kbps 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 Telephone Network Telephone Network ISP DSL Modem DSL Modem ADSL 64 or more kbps Up to 1.5 Mbps

Digital Subscriber Lines Digital Subscriber Line Access Multiplexer –Telco must install a DSLAM at end switching office Telephone Network Telephone Network ISP DSLAM DSL

Digital Subscriber Lines Splitting Voice and Data –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 DSL Modem DSL Splitter DSL DSLAM Voice Network Computer Phone New

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