DSLs Digital Subscriber Lines. Digital Subscriber Lines (DSLs) Offered by Telephone Companies...
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DSLs Digital Subscriber Lines
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Transcript of DSLs Digital Subscriber Lines. Digital Subscriber Lines (DSLs) Offered by Telephone Companies...
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”
TelephoneNetwork
TelephoneNetwork ISPISPDSL
Modem
DSLModem
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
TelephoneNetwork
TelephoneNetwork ISPISPDSL
Modem
DSLModem 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
TelephoneNetwork
TelephoneNetwork ISPISPDSL
Modem
DSLModem
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
TelephoneNetwork
TelephoneNetwork ISPISPDSL
Modem
DSLModem
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
TelephoneNetwork
TelephoneNetwork ISPISPDSLAMDSLAM
DSL
DSL
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
DSLModem
DSLSplitter
DSL
DSLAM
VoiceNetwork
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
