View source for ANSI T1.413 Issue 2

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'''ANSI T1.413''' is a [[technical standard]] that 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 [[plain old telephone service]] (POTS) and data services up to 56&nbsp;[[kbit/s]], and a variety of [[Digital data|digital]] channels. In the direction from the network to the customer premises ([[downstream (networking)|downstream]]), the digital [[bearer channel]]s may consist of [[duplex (telecommunications)|full-duplex]] low-speed bearer channels and simpler high-speed bearer channels; in the other ([[upstream (networking)|upstream]]) direction, only low-speed bearer channels are provided.

==Description==

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.''
It defines the minimum requirements for satisfactory performance of ADSL systems using the [[Discrete Multitone Modulation|Discrete Multi-Tone]] (DMT) line code. DMT divides the useful bandwidth of the standard two wire copper medium used in the [[public switched telephone network]] (PSTN), which is 0 to 1104&nbsp;kHz, into 256 separate 4.3125&nbsp;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]] is 4,000 symbols per second on each subcarrier. Thus the maximum theoretical downstream data rate of an ADSL system is 15.24&nbsp;Mbit/s (254×15×4000). However, because the data is split up into [[Packet (information technology)|packets]] (actually [[Reed–Solomon]] encoded [[Code word (communication)|codewords]]) of 255 bytes, the maximum achievable downstream data rate is 8.128&nbsp;Mbit/s (including other overheads). It is possible to [[forward error correction#Interleaving|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&nbsp;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&nbsp;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]] (FDM). In this case: 0–4&nbsp;kHz is for voice, 26–138&nbsp;kHz is the upstream band and 138–1104&nbsp;kHz is the downstream band.

{{DSL technologies}}

{{DEFAULTSORT:Ansi T1.413 Issue 2}}
[[Category:Computer standards]]
[[Category:American National Standards Institute standards]]
[[Category:Digital subscriber line]]
[[Category:Telecommunications-related introductions in 1998]]