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(organic chemistry)
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


(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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The DMT App was awarded the First Prize at the iN.LAB InnovJAM Mobile Learning Innovation Day, held on the 27 July 2018 - an initiative by SkillsFutureSG and the Institute for Adult Learning Singapore.
DMT gives PS Logistics inroads to the 53-foot trailer market and the ability to enhance its over-length service to existing and future customers.
The disposition of DMT, resulting from PBI's strategic review announced in November 2017, further enhances the company's focus on higher growth markets.
The first scientific studies on the psychotropic effects of N,N-Dimethyltryptamine (DMT) began to be carried out in the mid-1950s.
Following Amendment No.18 of the Motor Traffic Act 2017, the Department of Motor Traffic (DMT) had decided to add two new classes of vehicles, for the issuance of driving licenses.
Together with Oxxynova, we are fully backward-integrated into the two key raw materials: Oxea is the largest European producer of 2-EH, and Oxxynova is the leading European producer of DMT."
As for production, nickel DSO went down by 6 percent from 24.9 million dry metric tons (DMT) to 23.35 million DMT, while MNCS improved by 5 percent from 83,339 DMT to 87,612