ANSI T1.413 defines the requirements for the single Asymmetric Digital Subscriber Line (ADSL) for the interface between the telecommunications network and the customer installation in terms of their interaction and electrical characteristics. ADSL allows the provision of voiceband services (including POTS and data services up to 56 kbit/s) and a variety of digital channels. In the direction from the network to the customer premises, the digital bearer channels may consist of full-duplex low-speed bearer channels and simpler high-speed bearer channels; in the other direction, only low-speed bearer channels are provided. Please wikify (format) this article or section as suggested in the Guide to layout and the Manual of Style. ... In telecommunications, ITU G.992. ... ADSL in Australia started off as ITU G.992. ... This is an ITU (International Telecommunication Union) standard, also referred to as, ADSL2. ... ITU G.992. ... This is an ITU (International Telecommunication Union) standard, also referred to as READSL2+. This extends the capability of basic ADSL by doubling the number of downstream bits. ... This is an ITU (International Telecommunication Union) standard, also referred to as ADSL2+M. This extends the capability of basic ADSL2 by doubling the number of downstream bits. ... Please wikify (format) this article or section as suggested in the Guide to layout and the Manual of Style. ... A telecommunications network is a network of telecommunications links arranged so that messages may be passed from one part of the network to another over multiple links. ... In electronics, voiceband means the typical human hearing frequency range that is from 20Hz to 20KHz. ... Plain old telephone service, or POTS, are the services available from analogue telephones prior to the introduction of electronic telephone exchanges into the public switched telephone network. ... In telecommunications and computing, bit rate (sometimes written bitrate) is the frequency at which bits are passing a given (physical or metaphorical) point. It is quantified using the bit per second (bit/s) unit. ... A digital system is one that uses discrete numbers, especially binary numbers, or non-numeric symbols such as letters or icons, for input, processing, transmission, storage, or display, rather than a continuous spectrum of values (an analog system). ... A duplex communication system is one where signal can flow in both directions between connected parties. ...

The American National Standards Institute (ANSI) Telecommunications Committee created the first standardized ADSL specification. It defines the minimum set of requirements for satisfactory performance of ADSL systems utilizing the Discrete Multi-Tone (DMT) line code. DMT divides the useful bandwidth of the standard two wire copper medium used in the PSTN, which is 0 to 1104 kHz, into 256 separate 4.3125 kHz wide bins called sub-carriers.

Up to 254 sub-carriers are used, each of these 254 sub-carriers can support the modulation of 0 to 15 bits. The data frame rate (baud rate) is 4000 frames per second, the maximum theoretical downstream data rate of an ADSL system is 15.24Mbit/s. However, because the data is split up into packets (actually Reed-Solomon encoded codewords) of 255 bytes, the maximum achievable downstream data rate is 8.128Mbit/s (including other overheads). It is possible to interleave two RS codewords and obtain one logical codeword of 510 bytes. If this is done, then the maximum theoretical download speed goes back up to around 15Mbit/s.

In the upstream direction, a maximum of 30 sub-carriers can be utilised, again each frame modulated with up to 15 bits. Taken with the frame rate of 4000/sec the maximum throughput is a shade over 1.5Mbit/s.

In order to combine the PSTN service with download and upload ADSL signals the bandwidth is split into discrete parts using frequency-division multiplexing (FDM). In this case: 0 - 4 kHz is POTS, 26 - 138 kHz is the upload band and 138 - 1100 kHz is the download band. The public switched telephone network (PSTN) is the concentration of the worlds public circuit-switched telephone networks, in much the same way that the Internet is the concentration of the worlds public IP-based packet-switched networks. ... Frequency-division multiplexing (FDM) is a form of signal multiplexing where multiple baseband signals are modulated on different frequency carrier waves and added together to create a composite signal. ...