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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

ADSL - (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

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 ?
Two months later, WHOI scientists Dan Lizarralde and Adam Soule used a camera system on the end of a sea cable equipped with the SDSL data-link to explore the Guaymas Basin, about 2,000 meters (1.24 miles) deep in the Gulf of California.
No pricing details for the PureStream SDSL service were disclosed.
Leading players in the sector believe SDSL will signify an increase in internet and e-commerce opportunities for more than 10,000 businesses across the region.
SDSL (Symmetric Digital Subscriber Line) caters for customers who need to send out very large files, such as publishers, architects, advertisers, designers and those in the financial services industry.
To qualify for the SDSL broadband pilot scheme, companies must be based in Coventry and Warwickshire and must employ fewer than 250 staff and have an annual turnover of less than pounds 26 million.
IPCentrex(TM) is also a key enabler of new SDSL offerings, as it typically targets the same market segment.
The system has multi-service capabilities that supports both voice applications, plain old telephone service (POTS) and integrated services digital network (ISDN), as well as broadband applications, such as asynchronous digital subscriber line (ADSL), G.lite, symmetrical digital subscriber line (SDSL) and g.shdsl.
SDSL, on the other hand, is more of a business class DSL offering the user equal upload and download speeds that can service more users than ADSL.
Symmetric DSL (sDSL), which usually costs a premium, is two-way: It can send and receive simultaneously, and both upload and download speeds are the same.
The SiriusT SuD2000 MicroDSLAM provides either six or 12 ports of SDSL at speeds up to 2.3 Mbps.
A major conference organised by DIALnet, entitled 'Broadband - The Education Ravolution' saw the company announce it's strategy for ADSL (Asymmetrical Digital Subscriber Line) provision to the education sector, and gave a 150 strong audience of education professionals alive demonstration of SDSL (Symmetrical Digital Subscriber Line) technology.
(Nasdaq:CNXT), a provider of semiconductor system solutions for communications applications, has expanded its ZipWire family of multi-mode broadband modem solutions to support the full range of business-class symmetric digital subscriber line (SDSL) standards including the recently ratified G.991.2 symmetric high-bit-data-rate DSL (G.shdsl) specification.