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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

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 ?
In an IDSL arrangement, mutually agreed upon, system-wide best practice guidelines for managing infectious or suspected infectious disease would be in place.
-- The recent confirmation by the Dell'Oro Group (November 1999) that Copper Mountain ranked first overall in business DSL (SDSL and IDSL) revenues in 1998, and continued to lead the business DSL market in 1999 with the number one ranking by revenue and ports deployed through the first three quarters of 1999.
yesterday in Super Market F-6 a mobile fast food Dhaba ' Abey Khao' run by all DEAF, celebrated IDSL by holding play cards and people from civil society including women and children joined them in celebrations.
"With one platform we can use SDSL, ISDN DSL (IDSL), and G.lite to provide flexible, customer-oriented solutions.
(NE Voice & Data) IDSL, DS3, OC3 Salem, Concord,
Any employers interested can contact IDSL on 0121 522 6969.
Israeli-based RAD Data Communications has launched the ASMi-31 CQ Quad IDSL modem card, its new high-density solution for extending the local loop over twisted pair, two-wire unconditioned lines.
There is a plethora of DSL flavors either available or on the horizon (ADSL, G.lite, HDSL, IDSL, SDSL, VDSL, etc.).
Covad expects to begin offering the Netopia R7200-T SDSL Router and the Netopia R3100-T IDSL Router to its DSL customers by early December.
Xpeed Inc., a supplier of Digital Subscriber Line Customer Premise Equipment modems, has signed a reseller agreement for its Xpeed 300 SDSL PCI Adapter and Xpeed 200 IDSL PCI Adapter with Ascend Communications.
Some ISPs have rolled out IDSL (ISDN, Digital Subscriber Line) service.