ANSI T1.413 is a

technical standard A technical standard is an established norm or requirement for a repeatable technical task which is applied to a common and repeated use of rules, conditions, guidelines or characteristics for products or related processes and production methods, ...

that defines the requirements for the single

asymmetric digital subscriber line 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) for the interface between the

telecommunications network A telecommunications network is a group of nodes interconnected by telecommunications links that are used to exchange messages between the nodes. The links may use a variety of technologies based on the methodologies of circuit switching, mes ...

and the customer installation in terms of their interaction and electrical characteristics. ADSL allows the provision of

voiceband A voice frequency (VF) or voice band is the range of audio frequencies used for the transmission of speech. Frequency band In telephony, the usable voice frequency band ranges from approximately 300 to 3400 Hz. It is for this reason t ...

services including

plain old telephone service Plain old telephone service (POTS), or plain ordinary telephone system, is a retronym for voice-grade telephone service employing analog signal transmission over copper loops. POTS was the standard service offering from telephone companies from 1 ...

(POTS) and data services up to 56 kbit/s, and a variety of

digital Digital usually refers to something using discrete digits, often binary digits. Technology and computing Hardware *Digital electronics, electronic circuits which operate using digital signals ** Digital camera, which captures and stores digital ...

channels. In the direction from the network to the customer premises (

downstream Downstream may refer to: * Downstream (bioprocess) * Downstream (manufacturing) * Downstream (networking) * Downstream (software development) * Downstream (petroleum industry) * Upstream and downstream (DNA), determining relative positions on DNA ...

), the digital

bearer channel A bearer channel is a DS-0 that carries call content i.e. one that does not carry signaling. In the common-channel signaling scheme for telecommunications, signaling is sent out-of-band, while all other traffic rides bearer channels. When a call ...

s may consist of

full-duplex A duplex communication system is a point-to-point system composed of two or more connected parties or devices that can communicate with one another in both directions. Duplex systems are employed in many communications networks, either to allow ...

low-speed bearer channels and simpler high-speed bearer channels; in the other (

upstream Upstream may refer to: * Upstream (bioprocess) * ''Upstream'' (film), a 1927 film by John Ford * Upstream (networking) * ''Upstream'' (newspaper), a newspaper covering the oil and gas industry * Upstream (petroleum industry) * Upstream (software ...

) direction, only low-speed bearer channels are provided.

Description

The

American National Standards Institute The American National Standards Institute (ANSI ) is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The orga ...

(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.'' It defines the minimum requirements for satisfactory performance of ADSL systems using the

Discrete Multi-Tone Discrete may refer to: *Discrete particle or quantum in physics, for example in quantum theory *Discrete device, an electronic component with just one circuit element, either passive or active, other than an integrated circuit *Discrete group, a g ...

(DMT) line code. DMT divides the useful bandwidth of the standard two wire copper medium used in the

public switched telephone network The public switched telephone network (PSTN) provides infrastructure and services for public telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that are operated by national, regional, or local telep ...

(PSTN), which is 0 to 1104 kHz, into 256 separate 4.3125 kHz wide frequency bands called sub-carriers. Up to 254 sub-carriers are used downstream; each of these 254 sub-carriers can support the modulation of 0 to 15 bits per baud. The

baud In telecommunication and electronics, baud (; symbol: Bd) is a common unit of measurement of symbol rate, which is one of the components that determine the speed of communication over a data channel. It is the unit for symbol rate or modulat ...

is 4,000 symbols per second on each subcarrier. Thus the maximum theoretical downstream data rate of an ADSL system is 15.24 Mbit/s (254×15×4000). However, because the data is split up into packets (actually Reed–Solomon encoded

codewords In communication, a code word is an element of a standardized code or protocol. Each code word is assembled in accordance with the specific rules of the code and assigned a unique meaning. Code words are typically used for reasons of reliability ...

) of 255 bytes, the maximum achievable downstream data rate is 8.128 Mbit/s (including other overheads). It is possible to interleave two Reed-Solomon codewords and obtain one logical codeword of 510 bytes. If this is done, then the maximum theoretical downstream speed goes back up to around 15 Mbit/s. In the upstream direction, a maximum of 30 sub-carriers can be used, again each frame modulated with up to 15 bits. Taken with the baud rate of 4,000 per second per subcarrier, the maximum throughput is just over 1.5 Mbit/s. In order to combine voice telephone service with downstream and upstream ADSL signals the bandwidth is split into discrete parts using

frequency-division multiplexing In telecommunications, frequency-division multiplexing (FDM) is a technique by which the total bandwidth available in a communication medium is divided into a series of non-overlapping frequency bands, each of which is used to carry a separat ...

(FDM). In this case: 0–4kHz is for voice, 26–138 kHz is the upstream band and 138–1104 kHz is the downstream band. {{DEFAULTSORT:Ansi T1.413 Issue 2 Computer standards American National Standards Institute standards Digital subscriber line Telecommunications-related introductions in 1998