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Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line (DSL) technology, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. ADSL differs from the less common symmetric digital subscriber line (SDSL).
A symmetric digital subscriber line (SDSL) is a digital subscriber line (DSL) that transmits digital data over the copper wires of the telephone network, where the bandwidth in the downstream direction, from the network to the subscriber, is identical to the bandwidth in the upstream direction, from the subscriber to the network.
Digital subscriber line (DSL; originally digital subscriber loop) is a family of technologies that are used to transmit digital data over telephone lines. [1] In telecommunications marketing, the term DSL is widely understood to mean asymmetric digital subscriber line (ADSL), the most commonly installed DSL technology, for Internet access .
The American National Standards Institute (ANSI) Telecommunications Committee created the first standardized ADSL specifications. They were published as ANSI T1.413-1995 and ANSI T1.413-1998 (sometimes called "issue 2") titled Network and Customer Installation Interfaces — Asymmetric Digital Subscriber Line (ADSL) Metallic Interface.
Specifically, it explored the feasibility of symmetric and asymmetric data rates exceeding 10 Mbit/s on short phone lines. VDSL2 standard is an enhancement to ITU T G.993.1 that supports asymmetric and symmetric transmission at a bidirectional net data rate up to 400 Mbit/s on twisted pairs using a bandwidth up to 35 MHz.
CAP was the original technology used for DSL deployments, but the most widely used method now is DMT. The graphs on the right summarise the speeds obtainable for each ADSL standard based on line length and attenuation .
Single-pair high-speed digital subscriber line (SHDSL) is a form of symmetric digital subscriber line (SDSL), a data communications technology for equal transmit and receive (i.e. symmetric) data rate over copper telephone lines, faster than a conventional voiceband modem can provide.
ITU G.992.3 is an ITU (International Telecommunication Union) standard, also referred to as ADSL2 or G.dmt.bis.It optionally extends the capability of basic ADSL in data rates to 12 Mbit/s downstream and, depending on Annex version, up to 3.5 Mbit/s upstream (with a mandatory capability of ADSL2 transceivers of 8 Mbit/s downstream and 800 kbit/s upstream). [1]