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Encyclopedia > Asymmetric Digital Subscriber Line
DSL technologies
Technology ITU-standard
ADSL ANSI T1.413 Issue 2
ITU G.992.1 (G.DMT)
ITU G.992.2 (G.Lite)
ADSL2 ITU G.992.3/4
ITU G.992.3 Annex J
ITU G.992.3 Annex L
ADSL2+ ITU G.992.5
ITU G.992.5 Annex L
ITU G.992.5 Annex M
HDSL ITU G.991.1
HDSL2  
IDSL  
MSDSL  
PDSL  
RADSL  
SDSL  
SHDSL ITU G.991.2
UDSL  
VDSL ITU G.993.1
VDSL2 ITU G.993.2

Asymmetric Digital Subscriber Line (ADSL) is a form of DSL, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. It does this by utilizing frequencies that are not used by a voice telephone call. A splitter - or microfilter - allows a single telephone connection to be used for both ADSL service and voice calls at the same time. Because phone lines vary in quality and were not originally engineered with DSL in mind, it can generally only be used over short distances, typically less than 3mi (5 km).[citation needed] DSL redirects here. ... The International Telecommunication Union (ITU; French: Union internationale des télécommunications, Spanish: Unión Internacional de Telecomunicaciones) is an international organization established to standardize and regulate international radio and telecommunications. ... ANSI T1. ... In telecommunications, ITU G.992. ... ADSL in Australia started off as ITU G.992. ... ITU G.992. ... This is an ITU (International Telecommunication Union) standard, also referred to as, ADSL2. ... Annex J is an specification in ITU-T recommendations G.992. ... ITU G.992. ... 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 upstream bits. ... High bit rate Digital Subscriber Line (HDSL) was the first DSL technology that uses a higher frequency spectrum of copper, twisted pair cables. ... ITU G.991. ... HDSL2 is the 2nd generation of HDSL. Categories: | | ... ISDN Digital Subscriber Line (IDSL) transmits data digitally (rather than analog) on a regular twisted pair copper telephone line, across existing ISDN lines, at a rate of 144 kbit/s, slightly higher than a bonded dual channel ISDN connection at 128kbit/s. ... There are very few or no other articles that link to this one. ... Power line communication (PLC), also called Mains Communication or Power Line Telecoms (PLT) or Powerband, is a term describing several different systems for using power distribution wires for simultaneous distribution of data. ... Rate-adaptive DSL (RADSL) is a variation of ADSL technology. ... Symmetric Digital Subscriber Line (SDSL) is a Digital Subscriber Line (DSL) variant with E1-like data rates (72 to 2320 kbit/s). ... Symmetric high-speed digital subscriber line (SHDSL) is a telecommunications technology for Digital Subscriber Line (DSL) subscriber lines. ... Symmetric high-speed digital subscriber line (SHDSL) is a telecommunications technology for Digital Subscriber Line (DSL) subscriber lines. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... VDSL or VHDSL (Very High Speed DSL) is a DSL technology providing faster data transmission over a single twisted pair of copper wires. ... ITU G.993. ... VDSL2 (Very High Speed Digital Subscriber Line 2) is an access technology that exploits the existing infrastructure of copper wires that were originally deployed for POTS services. ... ITU G.993. ... DSL redirects here. ... For other uses, see Copper (disambiguation). ... A telephone line (or just line) is a single-user circuit on a telephone communications system. ... In electronics, voiceband means the typical human hearing frequency range that is from 20Hz to 20KHz. ... For other uses, see Modem (disambiguation). ... This article does not adequately cite its references or sources. ... A DSL filter is an analog low-pass filter installed on telephones and other analog devices to prevent interference between such devices and Digital Subscriber Line service operating on the same line. ...


At the telephone exchange the line generally terminates at a DSLAM where another frequency splitter separates the voice band signal for the conventional phone network. Data carried by the ADSL is typically routed over the telephone company's data network and eventually reaches a conventional internet network. In the UK under British Telecom the data network in question is its ATM network which in turn sends it to its IP network IP Colossus. A digital subscriber line access multiplexer, (DSLAM) is a multiplexer located in the telephone company exchange that provides consumers access to DSL services over twisted pair copper cabling. ... In the fields of communications, signal processing, and in electrical engineering more generally, a signal is any time-varying quantity. ... 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. ... The Internet Protocol (IP) is a data-oriented protocol used for communicating data across a packet-switched internetwork. ... BT Group plc (which trades as just BT, and is commonly known by its former name, British Telecom) is the privatised former British state telecommunications operator. ... Asynchronous Transfer Mode (ATM) is a cell relay, packet switching network and data link layer protocol which encodes data traffic into small (53 bytes; 48 bytes of data and 5 bytes of header information) fixed-sized cells. ... The Internet Protocol (IP) is a data-oriented protocol used for communicating data across a packet-switched internetwork. ...

Contents

Explanation

The distinguishing characteristic of ADSL over other forms of DSL is that the volume of data flow is greater in one direction than the other, i.e. it is asymmetric. Providers usually market ADSL as a service for consumers to connect to the Internet in a relatively passive mode: able to use the higher speed direction for the "download" from the Internet but not needing to run servers that would require high speed in the other direction. Symmetry is a characteristic of geometrical shapes, equations and other objects; we say that such an object is symmetric with respect to a given operation if this operation, when applied to the object, does not appear to change it. ... This article is about the computer terms. ...


There are both technical and marketing reasons why ADSL is in many places the most common type offered to home users. On the technical side, there is likely to be more crosstalk from other circuits at the DSLAM end (where the wires from many local loops are close to each other) than at the customer premises. Thus the upload signal is weakest at the noisiest part of the local loop, while the download signal is strongest at the noisiest part of the local loop. It therefore makes technical sense to have the DSLAM transmit at a higher bit rate than does the modem on the customer end. Since the typical home user in fact does prefer a higher download speed, the telephone companies chose to make a virtue out of necessity, hence ADSL. On the marketing side, limiting upload speeds limits the attractiveness of this service to business customers, often causing them to purchase higher cost Digital Signal 1 services instead. In this fashion, it segments the digital communications market between business and home users In telecommunication, the term crosstalk (XT) has the following meanings: 1. ... Siemens DSLAM SURPASS hiX 5625 A Digital Subscriber Line Access Multiplexer (DSLAM) allows telephone lines to make faster connections to the Internet. ... For the guitar distortion pedal, see BOSS DS-1. ...


How ADSL works

On the wire

Frequency plan for ADSL. The red area is the frequency range used by normal voice telephony (PSTN), the green (upstream) and blue (downstream) areas are used for ADSL.
Frequency plan for ADSL. The red area is the frequency range used by normal voice telephony (PSTN), the green (upstream) and blue (downstream) areas are used for ADSL.

Currently, most ADSL communication is full duplex. Full duplex ADSL communication is usually achieved on a wire pair by either frequency division multiplex (FDM), echo canceling duplex (ECD), or time division duplexing (TDD). FDM uses two separate frequency bands, referred to as the upstream and downstream bands. The upstream band is used for communication from the end user to the telephone central office. The downstream band is used for communicating from the central office to the end user. With standard ADSL (annex A), the band from 25.875 kHz to 138 kHz is used for upstream communication, while 138 kHz – 1104 kHz is used for downstream communication. Each of these is further divided into smaller frequency channels of 4.3125 kHz. During initial training, the ADSL modem tests which of the available channels have an acceptable signal-to-noise ratio. The distance from the telephone exchange, noise on the copper wire, or interference from AM radio stations may introduce errors on some frequencies. By keeping the channels small, a high error rate on one frequency thus need not render the line unusable: the channel will not be used, merely resulting in reduced throughput on an otherwise functional ADSL connection. Image File history File links ADSL_frequency_plan. ... A kilohertz (kHz) is a unit of frequency equal to 1,000 hertz (1,000 cycles per second). ... Westell Model 6100 ADSL modem An asymmetric digital subscriber line transceiver, also known as an ADSL modem or DSL modem, is a device used to connect a single computer to a DSL phone line, in order to use an ADSL service. ... Signal-to-noise ratio (often abbreviated SNR or S/N) is an electrical engineering concept defined as the ratio of a signal power to the noise power corrupting the signal. ... A telephone operator manually connecting calls with patch cables at a telephone switchboard. ... AM broadcasting is radio broadcasting using Amplitude Modulation. ...


Vendors may support usage of higher frequencies as a proprietary extension to the standard. However, this requires matching vendor-supplied equipment on both ends of the line, and will likely result in crosstalk issues that affect other lines in the same bundle.


There is a direct relationship between the number of channels available and the throughput capacity of the ADSL connection. The exact data capacity per channel depends on the modulation method used. In telecommunications, modulation is the process of varying a periodic waveform, i. ...


A common error is to attribute the A in ADSL to the word asynchronous. ADSL technologies use a synchronous framed protocol for data transmission on the wire. Asynchrony is the state of not being synchronized. ... Synchronization is coordination with respect to time. ...


Modulation

ADSL initially existed in two flavors (similar to VDSL), namely CAP and DMT. CAP was the de facto standard for ADSL deployments up until 1996, deployed in 90 percent of ADSL installs at the time. However, DMT was chosen for the first ITU-T ADSL standards, G.992.1 and G.992.2 (also called G.dmt and G.lite respectively). Therefore all modern installations of ADSL are based on the DMT modulation scheme. It has been suggested that VDSL2 be merged into this article or section. ... Carrierless Amplitude Phase Modulation is a non-standard variation of quadrature amplitude modulation (QAM). ... Orthogonal Frequency-Division Multiplexing (OFDM) — essentially identical to Coded OFDM (COFDM) — is a digital multi-carrier modulation scheme, which uses a large number of closely-spaced orthogonal sub-carriers. ... Year 1996 (MCMXCVI) was a leap year starting on Monday (link will display full 1996 Gregorian calendar). ...


ADSL standards

Standard name Common name  Downstream rate   Upstream rate 
ANSI T1.413-1998 Issue 2 ADSL 8 Mbit/s 1.0 Mbit/s
ITU G.992.1 ADSL (G.DMT) 12 Mbit/s 1.3 Mbit/s
ITU G.992.1 Annex A ADSL over POTS 12 Mbit/s 1.3 MBit/s
ITU G.992.1 Annex B ADSL over ISDN 12 Mbit/s 1.8 MBit/s
ITU G.992.2 ADSL Lite (G.Lite) 4.0 Mbit/s 0.5 Mbit/s
ITU G.992.3/4 ADSL2 12 Mbit/s 1.0 Mbit/s
ITU G.992.3/4 Annex J ADSL2 12 Mbit/s 3.5 Mbit/s
ITU G.992.3/4 Annex L[1] RE-ADSL2 5 Mbit/s 0.8 Mbit/s
ITU G.992.5 ADSL2+ 24 Mbit/s 1.0 Mbit/s
ITU G.992.5 Annex L[1] RE-ADSL2+ 24 Mbit/s 1.0 Mbit/s
ITU G.992.5 Annex M ADSL2+M 24 Mbit/s 3.5 Mbit/s
Frequencies spectrum of a Fritz modem on an ADSL belgian line.
Frequencies spectrum of a Fritz modem on an ADSL belgian line.

Annexes J and M shift the upstream/downstream frequency split up to 276 kHz (from 138 kHz used in the commonly deployed annex A) in order to boost upstream rates. Additionally, the "all-digital-loop" variants of ADSL2 and ADSL2+ (annexes I and J) support an extra 256 kbit/s of upstream if the bandwidth normally used for POTS voice calls is allocated for ADSL usage. ANSI T1. ... In telecommunications, ITU G.992. ... In telecommunications, G.DMT, or G.992. ... ADSL in Australia started off as ITU G.992. ... Asymmetric Digital Subscriber Line (ADSL) is a form of DSL, a data communications technology that enables faster data transmission over copper telephone lines than a conventional modem can provide. ... This is an ITU (International Telecommunication Union) standard, also referred to as, ADSL2. ... Annex J is an specification in ITU-T recommendations G.992. ... 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 upstream bits. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... 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. ...


While the ADSL access utilizes the 1.1 MHz band, ADSL2+ utilizes the 2.2 MHz band.


The downstream and upstream rates displayed are theoretical maxima. Note also that because Digital subscriber line access multiplexers and ADSL modems may have been implemented based on differing or incomplete standards some manufacturers may advertise different speeds. For example, Ericsson has several devices that support non-standard upstream speeds of up to 2 Mbit/s in ADSL2 and ADSL2+. Siemens DSLAM SURPASS hiX 5625 A Digital Subscriber Line Access Multiplexer (DSLAM) allows telephone lines to make faster connections to the Internet. ... Westell Model 6100 ADSL modem An asymmetric digital subscriber line transceiver, also known as an ADSL modem or DSL modem, is a device used to connect a single computer to a DSL phone line, in order to use an ADSL service. ... Ericsson () NASDAQ: ERIC. Founded in 1876, Ericsson is a leading provider of communications networks, related services and handset technology platforms. ...


Installation issues

ADSL Router by UTStarcom
ADSL Router by UTStarcom

Due to the way it uses the frequency spectrum, ADSL deployment presents some issues. It is necessary to install appropriate frequency filters at the customer's premises, to avoid interferences with the voice service, while at the same time taking care to keep a clean signal level for the ADSL connection. Image File history File linksMetadata Size of this preview: 562 × 599 pixelsFull resolution (1290 × 1375 pixel, file size: 349 KB, MIME type: image/jpeg) UTstarcom ADSL Router provided by Airtel in India for Broadband Access I, the creator of this work, hereby release it into the public domain. ... Image File history File linksMetadata Size of this preview: 562 × 599 pixelsFull resolution (1290 × 1375 pixel, file size: 349 KB, MIME type: image/jpeg) UTstarcom ADSL Router provided by Airtel in India for Broadband Access I, the creator of this work, hereby release it into the public domain. ...


In the early days of DSL, installation required a technician to visit the premises. A splitter was installed near the demarcation point, from which a dedicated data line was installed. This way, the DSL signal is separated earlier and is not attenuated inside the customer premises. However, this procedure is costly, and also caused problems with customers complaining about having to wait for the technician to perform the installation. As a result, many DSL vendors started offering a self-install option, in which they ship equipment and instructions to the customer. Instead of separating the DSL signal at the demarcation point, the opposite is done: the DSL signal is "filtered off" at each phone outlet by use of a low pass filter, also known as microfilter. This method does not require any rewiring inside the customer premises. A DSL filter is an analog low-pass filter installed on telephones and other analog devices to prevent interference between such devices and Digital Subscriber Line service operating on the same line. ... In telephone networks, the demarcation point is the point at which the telephone companys local loop network ends and connects with the telephone system or wiring at the customers premises. ... A DSL filter is an analog low-pass filter installed on telephones and other analog devices to prevent interference between such devices and Digital Subscriber Line service operating on the same line. ...


A side effect of the move to the self-install model is that the DSL signal can be degraded, especially if more than 5 voiceband devices are connected to the line. The DSL signal is now present on all telephone wiring in the building, causing attenuation and echo. A way to circumvent this is to go back to the original model, and install one filter upstream from all telephone jacks in the building, except for the jack to which the DSL modem will be connected. Since this requires wiring changes by the customer and may not work on some household telephone wiring, it is rarely done. It is usually much easier to install filters at each telephone jack that is in use. This article is about Physics. ...


Footnotes and references

  1. ^ a b ADSL2 Annex L is also known as RE-ADSL2, where 'RE' stands for 'Reach Extended.' With this ADSL standard, the power of the lower frequencies used for transmitting data is boosted up to increase the reach of this signal up to 7 kilometers (23,000 ft). The upper frequency limit for RE-ADSL2 is reduced to 552 kHz to keep the total power roughly the same as annex A. Since RE-ADSL2 is intended for use on long loops there isn't much (any) usable bandwidth above 552 kHz anyway. Although this standard has been ratified by the ITU, not all local loop network maintainers allow this protocol to be used on their network, simply because the extra power on the lower frequencies might cause problems for existing services due to crosstalk.

This article is about the location. ...

See also

DSL provides broadband Internet access to people around the world. ... DSL redirects here. ... Siemens DSLAM SURPASS hiX 5625 A Digital Subscriber Line Access Multiplexer (DSLAM) allows telephone lines to make faster connections to the Internet. ... ADSL speeds are limited by the distance from the central office or DSLAM. An ADSL loop extender (also known as an ADSL repeater) is a device that the telephone company can place midway between the subscriber and the central office to extend the distance and increase the channel capacity of... A low-pass filter is a filter that passes low frequencies but attenuates (or reduces) frequencies higher than the cutoff frequency. ... A DSL filter is an analog low-pass filter installed on telephones and other analog devices to prevent interference between such devices and Digital Subscriber Line service operating on the same line. ... Symmetric Digital Subscriber Line (SDSL) is a Digital Subscriber Line (DSL) variant with E1-like data rates (72 to 2320 kbit/s). ... Rate-adaptive DSL (RADSL) is a variation of ADSL technology. ... British Telecom introduced a plug and socket system to allow subscribers to connect telephones on the 19th November 1981. ... Broadband in telecommunications is a term that refers to a signaling method that includes or handles a relatively wide range of frequencies, which may be divided into channels or frequency bins. ... Categories: Wikipedia cleanup | Stub ... There are very few or no other articles that link to this one. ... This article or section does not adequately cite its references or sources. ... This is a list of device bandwidths: the channel capacity (or, more informally, bandwidth) of some computer devices employing methods of data transport is listed by bit/s, kilobit/s (kbit/s), megabit/s (Mbit/s), or gigabit/s (Gbit/s) as appropriate and also MB/s or megabytes per...

External links

  • The UNH-IOL DSL Knowledge Base (advanced tutorials)
  • ADSL, ADSL2 and ADSL2+ Speeds and Reach Compared
  • ADSL Research Report
  • ADSL Tutorial
  • Various ADSL Technical Information

  Results from FactBites:
 
Asymmetric Digital Subscriber Line - Wikipedia, the free encyclopedia (1342 words)
Asymmetric Digital Subscriber Line (ADSL) is a form of DSL, a data communications technology that enables faster data transmission over copper telephone lines than a conventional modem can provide.
With standard ADSL (annex A), the band from 25.875 kHz to 138 kHz is used for upstream communication, while 138 kHz – 1104 kHz is used for downstream communication.
ADSL technologies use a synchronous framed protocol for data transmission on the wire.
Digital Subscriber Line - Wikipedia, the free encyclopedia (1613 words)
Digital Subscriber Line technology was originally implemented as part of the ISDN specification.
ADSL technology dates back to 1988, when Joe Lechleider at Bellcore (now Telcordia Technologies) adapted DSL to carry a digital signal over the unused frequency spectrum available on the twisted pair cables running between the telephone company's central office and the customer premises.
This converts data from the digital signals used by computers into a voltage signal of a suitable frequency range which is then applied to the phone line.
  More results at FactBites »

 
 

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