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Related to ADSL: ADLS, HDSL


[a·dē·es ′el or ′ad·səl]
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


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(1) (Domain-Specific Language) See special-purpose language.

(2) (Digital Subscriber Line) A technology that increases the digital capacity of ordinary telephone lines (the local loops) into the home or office for Internet and TV service. Depending on the DSL version, speed is based on the distance between the customer and telco central office or telephone junction box.

DSL provides "always-on" operation. At the central office, DSL traffic is aggregated in a unit called the DSL Access Multiplexor (DSLAM) and forwarded to the appropriate ISP or data network. DSL arrived in the late 1990s with more version alphabet soup than most any other new transmission technology. See PPPoA and PPPoE.

Asymmetric - Fast Down, Slow Up

The following DSL versions provide a faster speed from the Internet to the user than the query to the Internet. For example, a request to view a website is a tiny amount of data, but the returning Web pages and graphics are a huge amount of data by comparison.

Asymmetric DSL
Asymmetric DSL (ADSL) shares ordinary telephone lines by using higher frequencies than human speech. To eliminate interference, the first DSL deployments required a technician from the phone company to install a splitter that divided the line into separate DSL and phone lines. Subsequent splitterless versions (known as G.Lite, Universal ADSL and ADSL Lite) eliminated the support visit but require the user to plug filters into every phone outlet.

ADSL is available in two modulation schemes: Discrete Multitone (DMT) or Carrierless Amplitude Phase (CAP). See CDSL, G.shdsl, ATU-C and ATU-R.

ADSL Transmission
The higher frequencies of DSL have to be filtered out for regular telephones, answering and fax machines.

The Filter
Low-pass DSL filters split the line between phone and DSL modem. When DSL is installed, every telephone and answering machine must plug into the filter.

RADSL (Rate Adaptive DSL)
RADSL is a version of ADSL that adjusts speeds based on signal quality. Many ADSL technologies are actually RADSL.

VDSL/VHDSL (Very High Bit Rate DSL)
VDSL is used as the final drop from a fiber optic junction point to nearby customers. VDSL lets an apartment or office complex obtain high-bandwidth services using their existing copper wires without having to replace them with optical fibers. Like ADSL, VDSL can share the line with the telephone.

Whereas VDSL achieves 50 Mbps transmission speed at 1,000 feet, VDSL2 extended the length of the path to 3,300 feet and delivers 100 Mbps at 1,600 feet. See Gfast.

Symmetric - Same Speed Both Ways

The following DSL versions provide the same speed both up and down.

HDSL (High Bit Rate DSL)
HDSL provides T1 transmission over copper wires without the additional provisioning required for setting up T1 circuits, such as bridged tap removal and repeater installation. HDSL requires two cable pairs up to 12,000 feet, while HDSL-2 requires only one cable pair and spans 18,000 feet. HDSL does not allow line sharing with analog phones.

SDSL (Symmetric DSL)
SDSL is an HDSL variation that is rate adaptive, uses one cable pair and is offered in speeds from 144 Kbps to 1.5 Mbps. Like HDSL, SDSL does not share lines with analog phones.

IDSL is a slightly faster basic BRI ISDN service. It uses the 16 Kbps "D" channel for data rather than call setup to achieve 144 Kbps instead of 128 Kbps. It also offers the longest distance of 26,000 feet. Unlike standard ISDN, IDSL does not support analog phones, and signals are not switched through the telephone network. Since IDSL uses the same 2B1Q line coding as ISDN, ISDN customers can use existing BRI terminal adapters and routers. See ISDN.

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References in periodicals archive ?
On the other hand, ADSL internet users grew by 0.57%, increasing from 4.92 million in August to 4.95 million in September.
The company's ADSL Protocol Analyzer Software works to analyze both the upstream and downstream connection through the Handshake, Channel Discovery, Channel Analysis and Exchange phases of the initialization process.
The Arab Advisors Group has analysed the ADSL service provision and rates in Algeria, Bahrain, Egypt, Iraq, Jordan, Kuwait, Lebanon, Libya, Mauritania, Morocco, Oman, Palestine, Qatar, Saudi Arabia, Sudan, Syria, Tunisia, UAE and Yemen.
Chunghwa boasts 2.1 million ADSL clients, for a market share of over 90%.
The AR-7211A/B ADSL router features an RJ-11 WAN port for the ADSL connection and an RJ-45 Ethernet LAN port for a wired connection with other network devices.
ADSL remains the prevailing Internet broadband technology in the Arab World.
The new offer as well has something for the existing ADSL customers if they decide to upgrade to the higher package.
SMEs should make it a priority to protect their ADSL connection with an additional Firewall.
The Telecommunications Ministry and state-owned OGERO Company have installed ADSL in 32 centers in Beirut, Tripoli, Sidon, Zahle and some parts of Mount Lebanon.
Lightspeed Communications chief executive Shaikh Abdulla bin Khalid Al Khalifa said: "We are aware of the fact that a large segment of the Bahraini society would like to acquire ADSL service at homes but refrain from subscribing to this service as the fees may be unsuitable for some.
According to the report, the number of ADSL users in Japan will reach 14.8 million by year-end, up 11.1% year-on-year though slower than the previous year, while the number of FTTH users will leap 89.1% to 4.6 million.