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URL: http://www.dslforum.org/
Asymmetric Digital Subscriber Line (ADSL) is the
formal name for what is being commonly called Digital Subscriber Line (DSL).
ADSL/DSL is the most commonly available DSL modem technology, and is currently
being implemented to connect residential customers to the Internet. ADSL converts
existing twisted-pair telephone lines into access paths for Plain Old Telephone
System (POTS) voice telephone circuits plus simultaneous high speed data
communications. ADSL transmit two separate data streams with much more
bandwidth devoted to the downstream than upstream leg. ADSL has a range of
downstream speeds depending on distance. For up to 9000, 12000, 16000, 18000
feet, the speed is 8.448, 6.312(DS2), 2.048(E1), and 1.544 (T1) Mbps
respectively. The upstream speeds range from 16 kbps to 640 kbps.
ADSL modems provide data rates consistent with North
American T-1 line 1.544 Mbps and European E1 2.048 Mbps digital hierarchies and
can be purchased with various speed ranges and capabilities. The minimum
configuration provides 1.5 or 2.0 Mbps downstream and a 16 kbps duplex channel;
higher speed configurations provide rates of 6.1 Mbps and 64 kbps duplex.
Products with downstream rates up to 8 Mbps and duplex rates up to 640 kbps are
available today. ADSL modems accommodate Asynchronous Transfer Mode (ATM)
transport with variable rates and compensation for ATM overhead, as well as IP
protocols. The modulation technique used is Quadrature Amplitude Modulation
(QAM). ADSL is officially ITU-T standard G-992.1.
Keywords:
Modem, serial, high speed, physical layer, Access Technology,
Asynchronous
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