Telephone in London cockney rhyming slag is dog 'n' bone, bone obviously rhyming with phone, In cockney the rhyming word is often dropped leaving just dog. In cockney, the wife is called your trouble and strife.

Dog food

Interim software used internally for testing purposes. Developers who use their own software will learn what is needed and what needs to be fixed. Eat your own dog food is the suggestion to software developers to actually use the products they develop.


  1. The closure containing the cellular PCS equipment. Some have heaters and airconditioning units for environmental control. The doghouse is located in a hut near the antenna.

  2. Doghouse is where your customers will put you if they have problems with their cellular or fixed phone service.


A system of noise/hiss reduction invented by Ray Dolby, widely used in consumer, professional and broadcast audio applications. This technology is now also used to provide High Definition Television's clear sound. See HDTV.


  1. In the broadest sense, a "domain" is a sphere of influence or activity. In the vernacular, domain equals turf. In the MIS world, a domain is "the part of a computer network in which the data processing resources are under common control." In the Internet, a domain is a place you can visit with your browser ” i.e., a World Wide Web site. In reality, "a place you can visit" might be a single computer. It might be a group of computers masquerading as a single computer. Or it might even be a logical/physical partition of a computer or group of computers. On the Internet, the domain is the address that gets you there, and consists of a hierarchical sequence of names (labels) separated by periods (dots). Examples of the 100 million plus Internet domain addresses include and

    A Top Level Domain (TLD) is defined as the alphabetical address suffix, which identifies the nature of the organization, e.g. com, edu, net, org. Currently, the central naming registry on the Internet is administered by the Internet Assigned Numbers Authority, (IANA), which includes the National Science Foundation (NSF), InterNIC, Network Solutions Inc., and the International Ad Hoc Committee (IAHC)..IANA, in turn , assigned responsibility to ICANN (Internet Corporation for Assigned Names and Numbers) for coordination of the following globally unique identifiers required for the Internet to function: Internet domain names, Internet Protocol (IP) address numbers, and protocol parameters and port numbers .

    Only a select few Top Level Domains currently can be registered. The original TLDs include .com (commercial), .edu (educational institution), .gov (government), .org (non- profit organization), .net (network provider) and .mil (military). There was a proposal that beginning in March 1998, new TLDs would be created in order to expand the available address options. After much wrangling, the decision was made on November 16, 2000 to create the following new TLDs: .aero (aviation industry), .biz (business), .coop (business cooperatives), . info (general use), .museum (museums), . name (individual, personal use), and .pro (professionals).

    Example domain names include "" and "" They are different sub-domains, also known as secondary domains under the Top Level Domain. The secondary domain name can be up to 67 characters in length. Allowable characters include English letters , numbers, dots (i.e., "."), and underscores (i.e., "_"). Proposals are being considered to include certain non-English alphabets, such as Arabic, Chinese, and Japanese.

    What you put in front of your domain name is entirely up to you, as long as the name is globally unique, and as long as it does not violate the naming convention in terms of total length and allowable characters. For example, everything addressed to or will be routed to the domain "" for resolution (further routing, processing, etc.). Under the supervision of ICANN, the Council of Registrars ( CORE ) has authorized over 100 independent, for-profit companies around the world to assign TLDs. The authorized registrars assign those TLDs through the SRS (Shared Registry System), which is a neutral, shared repository of URLs (Uniform Resource Locators), i.e., domain names or Web addresses.

    Preceding both the secondary and Top Level Domain, increasingly can be found tertiary domains. For instance, a large organization might have hosts "" and "" The tertiary domain might be called "", with hosts "" and "" The domain may also include a geographical suffix in the form of a country code, indicating that the target organization is physically located outside the U.S. For example, .au is for Australia, .nz for New Zealand, and .po for Poland, and .za for South Africa (from the Boer "zud," meaning "south"). Without a geographical suffix, it is assumed that the address identifies a device physically located in the U.S., where the Internet originated. Note that if a country code is used, it becomes the TLD and the alphabetical address suffix such as .com becomes the secondary domain name.

    In order to route the user or the user 's mail to the correct location (correct domain) a "dip" is made into a database housed on a Domain Name Server (DNS). The DNS translates the alphabetical address into an IP (Internet Protocol) address, which corresponds to a logical address which is tied to a physical device in the form of a server, which is located at physical address, which is connected to the Internet. ICANN is responsible for the stable operation of the Internet's root server system. That master DNS database is downloaded to local DNS servers on a periodic basis in order that all DNS server databases are synchronized. See also Domain Controller, Domain Defined Attribute, Domain Name, Domain Name Server, Domain Naming System, Federated States of Micronesia, gTLD, Tuvalu, and URL.

  2. Electronic mail vendors define domain in various ways. PC Magazine's networking editor, Frank Derfler defines a domain as referring to a set of hosts on a single LAN that needs only one intermediary post office to move mail from one host to another. A domain may consist of only one host, depending on its design and implementation.

  3. In IBM's SNA, a domain is a host-based systems services control point (SSCP), the physical units (PUs), logical units (LUs), links, link stations and all the affiliated resources that the host (SSCP) can control. In Microsoft networking, a domain is a collection of computers that share a common domain database and security policy that is stored on a Windows NT/2000 Server domain controller. Each domain has a unique name.

Domain Controller

For a Windows NT Server domain, the primary or backup domain controller that authenticates domain logons and maintains the security policy and the master database for a domain.

Domain Defined Attribute

DDA. In X.400 addressing, the DDA is a special field that may be required to assist a receiving E-mail system in delivering a message to the intended recipient. Up to four DDAs are allowed per address, with each DDA address entry made up of two parts , a type and a value. For example, if I were a subscriber to MCI Mail and I wanted to send a message to Harry Newton, this is how I would address it:

TO: Harry Newton

EMS: CompuServe / 592-7515


MBX: DDA=ID=70600,2451

If I were a subscriber to CompuServe, the only addressing information I would need would be the number 70600,2451.

Domain Forwarding

See Domain Pointing.

Domain Name

In the broadest sense, a "domain" is a sphere of influence or activity. In the vernacular, domain equals turf. In the MIS world, a domain is "the part of a computer network in which the data processing resources are under common control." In the Internet, a domain is a place you can visit with your browser ” i.e. a World Wide Web site. In reality, "a place you can visit" might be a single computer. It might be a group of computers masquerading as a single computer. Or it might even be a logical/physical partition of a computer or group of computers. On the Internet, the domain name is the address that gets you there, and consists of a hierarchical sequence of names (labels) separated by periods (dots). Examples of the 100 million plus Internet domain addresses include (Computer Telephony magazine),,, (Teleconnect magazine), or (CT Expo). All domain names have extensions. The common Top Level Domain extensions include the following:

Domain Name Extension

See Domain name.

Domain Name Server

Domain Name Server (DNS) is a computer on the Internet which contains the programs and files which make up a domain's name database. Using a name server is much like placing a call to a 800/888 voice telephone number. The 800/888 number requires a "dip" into a database (on the DNS) in order to translate the name (e.g., into a telephone number (IP address), which you then use to establish connection with the person (host computer). In other words, the DNS translates the logical alphanumeric address into a logical IP address associated with an applications server (or perhaps, a logical partition of a server), which is connected to the Internet. The telephone network (Internet) addresses by telephone number (IP address), not really by the person's (domain's) name. See Domain and Domain Naming System.

Domain Name Server

DNS. Flood attacks send a high volume of Internet traffic to the name servers that are responsible for a particular Web domain, rendering those servers unresponsive . During the 2003 Iraqi War, Al-Jazeera's English and Arabic language Web sites were subject to DNS Flood Attacks. These attacks came shortly after Al-Jazeera published photos of U.S. soldiers who had been taken prisoner by Iraqi forces inside Iraq.

Domain Name

Country Codes

.arpa (Old style Arpanet)

Country Codes are included where nation-

.de (Germany)

.lu (Luxembourg)

.biz Businesses

al boundaries are crossed, and succeed

.dk (Denmark)

.lv (Latvia)

.com (Commercial)

the organizational extension. Where

.do (Dominican Republic)

.mt (Malta)

.edu (Educational)

used, these ccTLDs (country code Top

.ec (Ecuador)

.mx (Mexico)

.gov (Government)

Level Domains) become the Top Level

.ee (Estonia)

.my (Malaysia)

.org (Non-Profit Organization)

Domain, and the gTLD becomes the

.es (Spain)

.nl (Netherlands)

.mil (Military)

Second Level Domain. Examples of

.fi (Finland)

.no (Norway)

.net (Network Provider, e.g., an ISP)

ccTLDs include the following:

.fr (France)

.nz (New Zealand)

New ones now include

.ae (United Arab Emirates)

.gr (Greece)

.pe (Peru)

.biz for businesses and corporations

.ag (Antigua and Barbuda)

.gt (Guatemala)

.ph (Philippines)

.info for information-based services such as newspapers, libraries, etc.

.ar (Argentina)

.hk (Hong Kong)

.pl (Poland)

.name for individuals' and personal websites

.at (Austria)

.hr (Croatia)

.pt (Portugal)

.pro for professions such as law, medicine, accounting, etc.

.au (Australia)

.hu (Hungary)

.ro (Romania)

.aero for services and companies dealing with air travel

.be (Belgium)

.id (Indonesia)

.ru (Russian Federation)

.coop for cooperative organizations

.bm (Bermuda)

.ie (Ireland)

.se (Sweden)

.museum for museums, archival institutions, and exhibitions

.bn (Brunei Darussalam)

.il (Israel)

.sg (Singapore)


.bo (Bolivia)

.int (International)

.si (Slovenia)


.br (Brazil)

.in (India)

.su (Former USSR)


.ca (Canada)

.is (Iceland)

.th (Thailand)


.cc (Cocos Islands)

.it (Italy)

.tw (Taiwan)


.ch (Switzerland)

.jm (Jamaica)

.ug (Uganda)


.cl (Chile)

.jp (Japan)

.uk (United Kingdom)


.cn (China)

.kr (South Korea)

.us (United States)


.co (Colombia)

.kw (Kuwait)

.uy (Uruguay)


.cr (Costa Rica)

.kz (Kazakhstan)

.ve (Venezuela)


.cy (Cyprus)

.lk (Sri Lanka)

.za (South Africa)


.cz (Czech Republic)

.lt (Lithuania)


Domain Name Squatter

A person who registers many URLs ” e.g.,, ” in his own name and then sits on them until someone expresses an interest in buying them. He then sells them for whatever he can get ” from $100 to $100,000, to who knows .

Domain Naming System

DNS. in Unix-based networks, of which the Internet is the largest, a domain naming system is the commonly accepted way of naming computers on the network. Domain naming system is sometimes referred to as the BIND (Berkeley Internet Name Domain) service in BSD Unix, a static, hierarchical naming service for tcp/ip hosts. A DNS server computer maintains a database for resolving host names and IP addresses, allowing users of computers configured to query the DNS to specify remote computers by host names (in words) rather than IP addresses (which are only numbers). DNS domains should not be confused with Windows NT networking domains, although Windows NT does support and can use the Internet's DNS scheme. See Domain.

Domain Parking

Same as Domain Pointing.

Domain Pointing

I have one domain site. It's called I have another called when you punch up the second one in your Internet Browser, you'll end up at the first one. That's called Domain Pointing, Forwarding or Parking.

Domestic Arc

The portion of the geostationary orbit allowing a satellite to return a footprint that almost covers the continental United States.

Dominant Carrier

The long distance service provider which dominates a particular market and is subject to tougher regulation than its competitors . An FCC term . Essentially it means AT&T.

Domino Server

The Internet and Intranet server packaged with Lotus Notes. Domino is the server, Lotus Notes is the client.


Domestic Communications Satellite.

Don't Answer Recall

Allows an extension user on a PBX to automatically retry a call by dialing a special digit code.

Donald Elliptical Projection

Named after Jay K. Donald of AT&T, who invented in 1956 the basis for the V&H system used to rate calls in North America and many other countries . The concept is one of flattening the Earth, as it is much easier to calculate the distance between two points using a flat plane. The more difficult process would be that of performing a trigonometric function using degrees, minutes and seconds of latitude and longitude. See also V&H.

Done Deal

A term used in the secondary telecom equipment business. Term used between seller and buyer to signify that a sale has been agreed to and an oral contract is now in effect, binding both parties to the agreed-to-sale as if a written contract has been signed. A written contract submitted later that does not conform to the original oral agreement is not justification for dissolving the original agreement unless both parties agree to the new written contract.


  1. A device to prevent copies made of software programs. A dongle is a small device supplied with software that plugs into a computer port. The software interrogates the device's serial number during execution to verify its presence. If it's not there, the software won't work. A dongle is also called a hardware key.

  2. A small pigtail cable with a connector at one end that attaches to a PCMCIA card (also called a PC card) inside your laptop and has an RJ-11, RJ-45, coax, or other connector at the other end. A dongle is used to connect the laptop to a network, a telephone line, or directly to another computer. See also Xjack ” which is another alternative to a PC Card modem dongle.

  3. An issue of SunExpert Magazine defines dongle as a 15-pin to 13-pin adapter. It is primarily used for large color monitors that require the 13W3 13-pin adapter.


Donkeypower is a unit of power equal to 250 watts. It is computed that one donkeypower is 1/3 of a horsepower.


A software program that allows access to files and programs not built into an electronic bulletin board system, thus letting users run them on-line.


See Dedicated Outside Plant.


To add impurities. See Doped Fiber and Semiconductor.

Doped Fiber

Fiber optical cable treated with erbium. Such cable can carry signals three times farther than untreated fiber. Doped fiber is now the fiber of choice in long distance networks.

Doped Fiber Amplifier

DFA. An amplifier used in fiber optic systems to amplify light pulses. Such amplifiers typically are known as EDFAs (Erbium-Doped Fiber Amplifiers ) as they are doped with erbium, a rare-earth element. DFAs are more effective than regenerative repeaters in many applications, as they simply amplify the light pulses through a chemo-optical process. Regenerative repeaters, on the other hand, require that the light signal be converted to an electrical signal, amplified, and then re-converted to an optical signal. Additionally, DFAs can simultaneously amplify multiple wavelengths of light in a Wavelength Division Multiplex (WDM) fiber system. See also EDFA, SONET and WDM.

Dopeler Effect

The Washington Post's Style Invitational asked readers to take any word from the dictionary, alter it by adding, subtracting or changing one letter, and supply a new definition. This one is one of the winners. The Dopeler Effect is the tendency of stupid ideas to seem smarter when they come at you rapidly .


See Semiconductor and Doped Fiber.

Doppler Aiding

A signal processing strategy that uses a measured doppler shift to help the GPS Global Positioning System) receiver smoothly track the GPS signal. It allows more precise velocity and position measurement.

Doppler Effect

The apparent change in wavelength of sound or light caused by the motion of the source, observer or both. Waves emitted by a moving object as received by an observer will be blueshifted (compressed) if approaching, redshifted (elongated) if receding. It occurs both in sound and light. How much the frequency changes depends on how fast the object is moving toward or away from the receiver.

Doppler Shift

Doppler shift In radio communications is the apparent change of received frequency due to the relative motion of a transmitter, such as one on board a satellite and/or the motion of a mobile receiver; named after Christian J. Doppler (1803-53), Austrian physicist .


  1. Disk Operating System, as in MS-DOS, which stands for MicroSoft Disk Operating System. A disk operating system is software that organizes how a computer reads, writes and reacts with its disks ” floppy or hard ” and talks to its various input/output devices, including keyboards, screens, serial and parallel ports, printers, modems, etc. Until the introduction of Windows, the most popular operating system for PCs was MS-DOS from Microsoft, Bellevue, WA.

  2. DoS is Denial of Service. See Denial of Service.


Distributed Open Signaling Architecture. AT&T's preferred IP telephony architecture. It is incompatible with MGCP. See MGCP.


A dot is an integral part of an email address or a web site. You say "dot," not "period," since for most people a period means the end of a sentence . The English say "full stop," which is even more specific. My email address is "harry underscore newton (my mailbox) at msn (the site domain) dot com (commercial domain)." Keyboard translation: "" Dots are now replacing dashes in phone numbers. My phone number used to be 212-206-7140. Now many people believe it's 212.206.7140. Artists prefer the dots in phone numbers since dots save space. Some people claim it's the Swiss minimalist influence. See also Dot Address.

Dot Address

Also known as "Dotted Quad" and "Dotted Decimal Notation." A set of four numbers connected with periods that make up an Internet address; for example,

Dot Addressable Graphics

Refers to the mode of operation on a dot matrix printer which allows you to control each element in the dot matrix printhead. With this feature, you may produce complex graphics drawings.

Dot Com Company

A company which operates its business mainly on the Internet, using ".com" URLs. is the best example for the dot com company. As known as a Web retailer.

Dot Pitch

A measure of the clarity of a color monitor. Dot pitch measures the vertical distance between the centers of like-colored phosphors on your screen measured in millimeters. The smaller the distance, the sharper the monitor. Dot pitch is the major determinant in the clarity of an image on screen. You can't do anything about it. When you buy a monitor, you buy it with a certain dot pitch and you're stuck with that dot pitch. You may be able, however, to do something about improving convergence and focus ” the other measures of the clarity of a color monitor.

Dot Zero

When new software is issued, it often bears the number .0 (i.e. dot zero) as in MS-DOS 5.0. The theory among software gurus is that you should always avoid a "Dot Zero" revision, since it will likely contain bugs and that one should wait for 4.01 or 5.01 etc. This theory has some validity, although MS-DOS 5.0 came out very clean and was not revised until 6.0.

Dot-com Company

A company which operates its business mainly on the Internet, using ".com" URLs. is the best example for the dot com company. As known as a Web retailer.

Dotted Decimal Notation

Also known as "Dotted Quad" and "Dot Address." A set of four numbers connected with periods that make up an Internet address; for example,

Dotted Quad

Also known as "Dot Address" and "Dotted Decimal Notation." A set of four numbers connected with periods that make up an Internet address; for example,

Dotting Sequence

A cellular radio term. An alternating series of 38 bits used for the purpose of symbol (bit) timing recovery at the CDPD Mobile Data BAse Station (MDBS) for reverse channel transmissions by the CDPD Mobile End System.

Double Buffering

The use of two buffers rather than one to temporarily hold data being moved to and from an I/O device. Double buffering increases data transfer speed because one buffer can be filled while the other is being emptied.

Double Camp-On Indication

A PBX feature. A phone attempting to camp on to another phone which is already being "camped on" shall receive a distinctive audible signal and may be denied the ability to camp-on.

Double Click

With a Mac and an IBM-compatible PC running Windows, double-clicking carries out an action, such as beginning a new program. Press and release the mouse button twice in rapid succession to double-click. If you don't double click fast enough, it won't work. Some mouse software allow you to assign the left hand button on the mouse to a single click and the right hand button to a double click. This is very useful.

Double Crucible Method

A method of fabricating optical fiber by melting core and clad glasses into two suitably joined concentric crucibles and then drawing a fiber from the combined melted glass.

Double Density

Refers to a diskette which can contain twice the amount of data in the same amount of space as a single-density diskette. For example, a double-density 360k diskette has a 720k storage capacity. These days double density is an obsolete term, since there are now disks that are "double double" density. Most 3 1/2 inch disks will now hold twice 720K ” or 1,440,000 bytes. These are called high density disks. Toshiba has introduced a "double double double" floppy, which will hold 2,880,000 bytes. But it hasn't caught on, yet.

Double Ended Synchronization

A synchronization control system between two exchanges, in which the phase error signals used to control the clock at one exchange are derived from comparison with the phase of the internal clock at both exchanges.

Double Gang Receptable

See Back Box.

Double Interrupted Ring

Two quick rings followed by a period of silence indicating the arrival of an outside call in some systems.

Double Modulation

Modulation of a carrier wave of one frequency by a signal wave, this carrier then being used to modulate another carrier wave of different frequency.

Double Pole

A double pole switch is one which opens and closes both sides of the same circuit simultaneously. Most electrical circuits open and close with only one side being broken.

Double Pull

A method for pulling cable into conduit or duct liner that is similar to backfeed pulling except that it eliminates the need to lay the backfeed cable on the ground.

Double- Shielded Twisted Pair


Double Sideband Carrier Transmission

DSBTC. That method of transmission in which frequencies produced by the process of Amplitude Modulation (AM) are symmetrically spaced above and below the carrier. The carrier level is reduced for transmission at a fixed level below that which is provided to the modulator . Carrier is usually transmitted at a level suitable for use as a reference by the receiver except in those cases where it is reduced to the minimum practical level (suppressed carrier). See also Amplitude Modulation, DSBSC, SSB and VSB.


Two trailer homes stapled together with a modest gabled roof.


A device which doubles the distance of certain types of circuits. HDSL (High bit-rate Digital Subscriber Line) is a repeaterless means of provisioning a T-1 access circuit over a standard UTP (Unshielded Twisted Pair) local loop. Signal attenuation issues limit the range, however, to 12,000 feet on 24 gauge wire, and 9,000 feet on 26 gauge wire. A doubler can be added at that point in the outside plant to double the distance range, and a second doubler can be added to triple the range. As the doublers are line- powered , no local power supply is required. See also Attenuation, HDSL, Outside Plant, Repeater, T-1 and UTP.

Doubly Clad Fiber

An optical fiber, usually single mode, that has a core surrounded by an inner cladding of lower refractive index, which is in turn surrounded by an outer cladding, which has a higher refractive index than the inner cladding. This type of construction is often employed in single-mode fibers to reduce bending losses.


Data Over Voice. A technology that allows data to be transmitted along with voice over a single voice-grade local loop. As the circuit typically is analog, a modem is required. There are several approaches to DOV. One approach uses FDM (Frequency Division Multiplexing), with voice traveling at 4 KHz and below, and data at higher frequencies. This approach is used in most DSL (Digital Subscriber Line) technologies, including ADSL and G.lite. Other approaches send data during periods of silence in a voice conversation. See also ADSL, DSL, FDM, and G.lite.

Down Converter

A device for lowering the frequency of a modulated radio frequency carrier ” typically one from a satellite or a distant microwave antenna. See Downconverter.

Down Sampling

A sampling technique used in conjunction with certain compression algorithms, such as Wavelet Transform. Down-sampling computation involves disregarding certain samples; for instance, "down-sampling by two" considers only every other sample. This approach is an operation fundamental to the Fast Pyramid Algorithm used in wavelet transform, which is commonly applied to compression of image information. Up- sampling effectively is the reverse process of decompression on the receiving end of the data transfer. See Wavelet Transform, Fast Pyramid Algorithm and Up-Sampling.

Down Tilt

A modification of an antenna radiation pattern which focuses energy along a line tilted below the horizontal radiation line. Down tilt uses energy which would otherwise be radiated toward the sky or into the ground.


A circuit that lowers the high-frequency signal to a lower, intermediate range. The three types of downconversion are signal, dual and block downcon- version. Downconversion is accomplished by an integrated assembly of components which convert microwave signals (e.g. those from a satellite) to an intermediate frequency range for further processing. A downcoverter generally consists of an input filter, local oscillator filter, IF filter, mixer and frequently an LO frequency multiplier and one or more stages of IF amplification. May also incorporate the local oscillator, AGC/gain compensation components and RF preamplifier.

Downline Loading

A system in which programs are loaded into the memory of a computer system, such as a LAN bridge, router or server, via the same communication line(s) the system normally uses to communicate with the rest of a network. As opposed to systems in which all programs are loaded into the computer from a disk or tape associated with the computer. A PC connected to a LAN may use this type of loading when it is first turned on in the morning to get the information it needs from a file server. Diskless PCs always work this way.


  1. The part of a transmission link reaching from a satellite to the ground. Some satellite transmission circuits, especially international ones, are priced and billed separately for the uplink and the downlink. This is because their transmissions are provided by different carriers .

  2. In packet data communications, a downlink is a link from an NC or PAD to another NC or PAD on a different level. The defining of downlinks and uplinks depends on the network configuration of PADs, their relationships to each other and the direction of data transmission.


  1. To receive data from another computer (often called a host computer or host system or just plain host) into your computer. It's also called to RECEIVE. The opposite is UPLOAD or TRANSMIT. You have to be very careful distinguishing between the two. Choosing the "Download" option in some communications programs automatically erases a file of the same name that was meant for transmission. If that happens, stop everything. Grab your file unerase program and use it. Don't wait. If you wait, you may write over your erased file and never get it back. See Download Fonts.

  2. The Vermonter's Guide to Computer Lingo defines download as to take the firewood off the pickup.

Downloaded Fonts

Fonts that you send to a printer either before or during the printing of a document. When you send a font to a printer, it is stored in printer memory until it is needed. Downloaded fonts are one reason for loading lots of RAM memory into your printer.


See Down Sampling.


Downsizing is what happens when companies move from large computer systems to smaller systems. There are four major reasons companies downsize from mainframe-based computer to local area network-based computing:

  1. They save money. There are several reasons:

    1. Mainframe computers cost lots each month in maintenance. They require costly maintenance agreements with the supplier, e.g. IBM. Servers are usually bought without maintenance agreements. When they break, the managers or the workers simply replace the broken parts themselves .

    2. Mainframe computers cost lots to program. There are comparatively few programs available for mainframes, compared to the plethora of off-the-shelf programs available for workstations.

    3. Servers require a far less costly home to live. You don't need air-conditioning, special buildings with raised floors, etc.

  2. Servers today have the power of mainframes 10 years ago. In fact, servers are now beginning to acquire more power than mainframes of ten years ago. And as servers increasingly acquire several processors, they will leap in power beyond what mainframes have.

  3. Servers are typically manufactured from off-the-shelf, standard components that are usually available from several manufacturers. As a result, there is constant competition and constant improvement in quality and features.

  4. Servers are much more flexible tools to design networks. You can start with one baby network containing one server and several workstations (a.k.a. clients ) and confined to one floor of one small building and grow to a huge, complex network containing thousands of workstations, dozens of servers and spanning the globe.

To most people, downsizing is not only swapping out the "big iron" (the mainframe) and bringing in servers and local area networks. It's also a new way of thinking about the way corporations are organized. Downsizing is often accompanied by re-engineering, which is basically re-organizing for a greater focus on the customer ” a focus which means responding faster to customer needs. See Servers.


  1. Refers to the relative position of two stations in a local area network ring topology. A station is downstream if it receives a token after the previous station. See also Downstream Channel.

  2. In a communications circuit, there are directions of transmission ” coming to you and going away from you. Downstream is another term for the transmission coming towards you. Downstream is used in cable TV ” for the signal flowing to you from the cable head end. Downstream is used in modem connection for information coming at you. See Upstream Channel.

Downstream Channel

The frequency multiplexed band in a CATV channel which distributes signals from the headend to the users. Compare with Upstream Channel, the band of frequencies on a CATV channel reserved for transmission from the user to the CATV company's headend.

Downstream Physical Unit



The total time a telephone system is not working due to some software or hardware failure. Downtime is also defined as a time interval when a system is not in use either because of equipment failure ( unplanned downtime) or scheduled maintenance (planned downtime).


  1. Dial Pulse (as in dialing a phone) or Data Processing. Also called EDP for Electronic Data Processing. Now more commonly called Management Information Systems ” or MIS. See Dial Pulse.

  2. Demarcation Point. The point of a demarcation and/or interconnection between telephone company communications facilities and terminal equipment, protective apparatus, or wiring at a subscriber's premises. Carrier-installed facilities at or constituting the demarcation point consist of a wire or a jack conforming to Subpart F of Part 68 of the FCC Rules.


  1. Digital Port Adapter. A Northern Telecom word.

  2. Demand Protocol Architecture. A technique for loading protocol stacks dynamically as they are required. It is associated with adapter cards in workstations and servers. Only the protocol stacks that are required for a particular communications sessions are loaded. Examples of such stacks include TCP/IP, XNS, SPX/IPX and NetBios.


Double Pole Back Connected.


Double Pole Front Connected.


Digital passage service. DPS allows overseas carriers to interconnect with other overseas carriers between cable heads, earth stations, or border crossing points. The DPS is based on DS3s, which are diversely routed and continuously monitored .


Digital PBX. Not a common term. Most PBXs these days are digital. And they are simply called PBXs.


Differential Pulse Code Modulation, or Delta Pulse Code Modulation. DPCM is a variant of PCM, the technique generally used for converting analog voice signals into digital signals for transmission over a digital transmission system and through a digital switch. PCM samples the amplitude (i.e., signal strength, or volume level) of the native analog voice information stream at a rate of 8,000 times per second at precise intervals of 125 microseconds, i.e., 1/8000th of a second. PCM encodes each voice sample into an 8-bit byte, which yields a bandwidth requirement of 64 Kbps (64,000 bits per second). DPCM expresses each sample as the difference, or delta, between one sample and the previous sample, thereby requiring only four bits, rather than eight. As a result, DPCM voice requires bandwidth of only 32 Kbps, rather than 64 Kbps. Unfortunately DPCM sacrifices some voice quality in the process. DPCM also is used in some video compression applications, but also suffers from loss of quality. See also ADPCM and PCM.


Digital Personal Communications Services. See PCS.


Dots Per Inch. A measure of a scanner's ability to scan. The higher the number, the sharper the image and the greater the potential size of the image. See Scanner Accuracy.


Digital Private Line Billing.


An acronym for DOS Protected Mode Interface. DPMI is an industry standard that allows MS-DOS applications to execute code in the protected operating mode of the 80286 or 80386 processor. The DPMI specification is available from Intel Corporation. It is a superset of the VCPI (Virtual Control Program Interface) specification for controlling multiple programs inside a PC, as well as programs that use protected mode.


Display Power Manager Signaling is a power reduction feature that places a computer monitor in reduced power when the monitor is still on but has been idle for some time.


Digital Private Network Signaling System. A standard in Britain which enables PBXs from different manufacturers to be tied together with E-1 lines and pass calls transparently between each ” as easily as if the phones were extensions off the same PBX and were simply making intercom calls. The international version of DPNSS is called Q.SIG, which is now becoming Q.931, which is Euro-ISDN.


Dedicated Pair Out (DPO) and Dedicated Pair In (DPI). If you move out of a residential apartment, the pair that you were using is dedicated to that Apt. so when the next occupant moves in, it is a flick of a switch to get phone service turned on. That's called Dedicated Pair Out. The DPI pair is the OE (Office Equipment) or the Switch pair. Now the pair in the C.O. (Central Office), when it's joined to the DPO pair, is often called a MATED PAIR. The DPI pair is mated to the DPO pair.


Distributed Processing Peripheral.


Dual port RAM.


Elimination of an existing subscriber account; deprovisioning of a subscriber account includes subscriber account deregistration and device de-activation.


Differential Phase Shift Keying, also called dibit phase shift keying. A 4-level phase shift technique. See Differential Phase Shift Keying.


Double-pole single throw.


Dial pulse terminate.


  1. Digital Processing Unit.

  2. Dynamic Path Update. Allows IBM networks to add new network nodes or change backup routing paths while the front-end is still operating.

  3. Director of Public Utilities, a title often found at a state regulatory commission.


DataPath loop eXtension.


Distributed Queue Dual Bus. The Metropolitan Area Network (MAN) access technique defined by the IEEE 802.6 standard for Switched Multimegabit Data Service (SMDS). Based on QPSX (Queued Packet Synchronous Exchange), developed at the University of Western Australia (of which fact Harry Newton is ever so proud), DQDB operates by maintaining a queue at each station to determine when the station may access its dual buses. The dual buses provide bidirectional transmission between originating and terminating stations with excellent congestion control ensured through the network, from endto-end. DQDB consists of two uni-directional buses connected as an open ring (i.e., each bus is not directly interconnected ). It provides for full duplex operation between any two nodes. Each SMDS cell consists of 5 bytes of control information, involving a header and trailer, plus 48 bytes of payload. See also SMDS and ATM.


Differential Quadrature Phase Shift Keying. An improvement on QPSK, this compression technique transmits only the differences between the values of the phase of the sine wave, rather than the full absolute value. QPSK makes use of two carrier signals, separated by 90 degrees. See also PSK and QPSK.


Digital Radio.


Draco was an Athenian lawgiver. Around 621 B.C., the Greeks became tired of the privileged few making all the decisions. So, Draco was appointed to draft a set of laws, which turned out to be especially harsh . Those in debt could be enslaved, but only if they were members of the lower class. (He was tough, but not stupid.) Draco introduced the concept of "intent" to murder. He also introduced the distinctions between justifiable, accidental and intentional homicide. When asked about the harshness of his punishments, he supposedly said that the death penalty was appropriate for even so slight a crime as stealing a cabbage. Excessively severe rules or laws have come to be known as draconian in nature. See also Trivia.

Draft Proposal

An ISO standards document that has been registered and numbered but not yet approved.


Dragging is a way of moving an item on the screen using your mouse. To drag a window in Windows, for example, move the mouse pointer onto a window's title bar, then hold down the mouse button while moving the mouse across your desktop. When you release the mouse button, the window will remain in its new location. Apply this technique to drag any data object, such as icons or list box items.

Drag And Drop

The "drag and drop" definition defines how objects from one desktop application can be "dragged" out of that application, through clicking on the object with a mouse, across the desktop and "dropped" on another application. Most of the graphics operating systems, like Windows, Apple's Macintosh and Sun Sparc use Drag and Drop.

Drag Line

A length of rope or string used to pull wire and cable through conduit or inaccessible spaces. Drag lines are often inserted in wall and ceilings during construction to ease future wire installation.

Drag Queen

A drag queen is a man who likes to dress as a woman . In the 1940s, California law made it illegal to dress as a member of the opposite sex. Drag queens avoided this restriction by pinning pieces of paper to their dresses which read "I'm a boy!" The courts accepted the argument that anyone wearing such a notice was technically dressed as a man, not a woman. Some people claim that DSL lines are really T-1 lines in drag, but at a much lower price.

Drain Wire

In a cable, an uninsulated wire laid over the component or components and used as a ground connection.


  1. Dynamic Random Access Memory. Pronounced "dee-ram." The readable/writable memory used to store data in older PCs. DRAM stores each bit of information in a "cell" composed of a capacitor and a transistor . Because the capacitor in a DRAM cell can hold a charge for only a few milliseconds , DRAM must be continually refreshed to retain its data. In contrast, Static RAM, or SRAM, requires no refresh and delivers better performance, but it is more expensive to manufacture. See also DDR-SDRAM, EDO RAM, Flash RAM, FRAM, Microprocessor, RAM, RDRAM, SDRAM, SRAM, and VRAM.

  2. Digital Recorder Announcer Module.


In the manufacture of wire, pulling the metal through a die or series of dies in order to reduce the diameter to a specified size.

Drawing Tools

A computer imaging term. The means of creating freehand lines or basic geometric shapes . Paint packages often provide an ellipse-drawing function as a variation of the circle (or vice versa) and a square drawing function as a variation of the rectangle. Virtually all packages offer filled geometric figures, the fill item being either a solid color or a pattern.


Digital Radio Broadcasting.


Digital Radio Concentrator System.

Dress down day

A workday when employees are allowed to dress casually. When things were better economically, there were more dress down days.

Dressing Cable

You "dress" cable by taking multiple cables and joining them together neatly with cable ties. A nicely -dressed, clean installation is a sign of telephony professionalism . It still exists.


  1. When a carrier frequency changes due to a transmitter problem. It can be caused by bad connections or defective components, temperature changes or diffraction . Crystal oscillators are the most drift-reliable circuits.

  2. When customers leave and go to another carrier. See also Churn.

  3. A long-term and usually steadily increasing change in a parameter, such as frequency, from its nominal value.

  4. The tendency of a geosynchronous satellite in orbit to move towards one of the two satellite stable points, at 75 E and 105 W.

Drill Down

Microsoft jargon which means to learn more about a subject.

Drip Irrigation

One thing not to do is mess your company's entire relationship with a customer in the beginning of that relationship by unveiling a massive, complicated profile or questionnaire. Instead, gather the information that is useful for the current transaction, remember it, and build your relationship's context over time, little by little. Think of the task as a kind of "drip irrigation" for the relationship. This definition from

Drip Loop

Several inches of slack in a cable that prevents water from collecting on the cable or running along the surface of the cable. A drip loop between the LNB of a satellite dish and the entry point into the building also allows some free movement of the dish while adjusting it.


Shortened word for hard drive.

Drive By Spamming

You have an "office" in your truck. You find a local WiFi hotspot ” an area you can receive and transmit 8021.11(b) or (a) wireless transmissions. You park your truck in the area. You send out three million spam emails. Then you disappear. No one can trace who sent them (and thus stop future transmissions) because you're long gone. Next time, one hopes, the owner of the WiFi hotspot you used will improve his security and you won't be able to get on. Many WiFi hotspots don't have security and can easily be found with a sniffer. See Sniffer.

Drive Icon

A Windows NT term. An icon in a directory window in File Manager that represents a disk drive on your system. Different icons depict floppy disk drives, CD-ROM drives, network drives , etc.

Drive Mappings

A Novell NetWare term. Drive mappings provide direct access to particular locations in the directory structure. They are a "shorthand" method for accessing directories on a disk. Instead of typing in the complete path name of a directory that you want to access, you can simply enter a drive letter that has been assigned to that directory. NetWare recognizes two types of drives (physical drives and logical drives) and three types of drive mappings (local, network, and search drive mappings).

Drive Test

Hang a cell phone antenna from a crane in its proposed spot before construction of the permanent tower. Then technicians drive around with phones to see the range of the proposed spot. This way they see if it is worth having a tower in that proposed location.

Drive Type

A number representing a standard configuration of physical parameters ( cylinders , heads and sectors) of a particular type of hard disk drive. You need to know your drive's drive type; otherwise the BIOS of your machine will not recognize your drive on boot up and your PC will not work. Normally this information of your drive's type resides in memory kept alive by a small lithium battery. However, should the lithium battery die, your PC will "forget" which drive it has and it will ask you. If you don't know, you're in big trouble. Your PC simply won't work. My recommendation: write the drive type on two labels ” one to stick on the drive and the other to stick on the bottom of your machine. This way you'll be able to find it easily. You will usually find the drive type's number on paperwork sent originally with your machine.


A Windows NT term. Allows you to change drives by selecting one of the drive icons.


A driver (which is always software) provides instructions for reformatting or interpreting software commands for transfer to and from peripheral devices and the central processor unit (CPU). Many printed circuit boards which you drop into a PC require a software driver in order for the other parts of the computer and the software you're running to work correctly. In other words, the driver is a software module that "drives" the data out of a specific hardware port. The port in question will usually have another device connected, such as a printer or modem, and the driver will be organized in software (i.e. configured) to communicate with the device.


The McDonald's in Ft. Huachuca was the first restaurant to have a drive through window. The drive through allowed soldiers from Ft. Huachuca to get food since uniforms were not permitted in business establishments.

Driveway effect

A special quality exhibited by a radio program that causes listeners to stay in their cars after they have arrived home so they can hear the end of the program.


  1. A wire or cable from a pole or cable terminal to a building.

  2. That portion of a device that looks toward the internal station facilities, e.g., toward an AUTOVON 4-wire switch, toward a switchboard, or toward a switching center.

  3. Single channel attachment to the horizontal wiring grid (wall plate, coupling, MODMOD adapter).

  4. The central office side of test jacks .

  5. To delete, intentionally or unintentionally, part of a signal for some reason, e.g., dropping bits.

Drop And Insert

That process wherein a part of the information carried in a transmission system is demodulated (dropped) at an intermediate point and different information is entered (inserted) for subsequent transmission.

Drop Cable

  1. The outside wire pair which connects your house or office to the transmission line coming from the phone company's central office. See also DROP WIRE, which is different.

  2. In local area networks, a cable that connects a network device such as a computer to a physical medium such as an Ethernet network. Drop cable is also called transceiver cable because it runs from a network node to a transceiver (a transmit / receiver) attached to the trunk cable.

Drop Channel Operation

A type of operation where one or more channels of a multichannel system are terminated (dropped) at any intermediate point between the end terminals of the system.

Drop Clamp

A piece of equipment used to attach aerial wire to a J hook or Ram's Horn on a building or pole.

Drop Loop

The segment of wire from the nearest telephone pole to your home or business.

Drop Outs

Drop outs are one major cause of errors in data communications circuits. The technical definition is that the signal level drops more than 12 dB (decibels) for more than 4 milliseconds. It means some of your data will not arrive . A four millisecond drop out in a transmission at 2,400 bits per second will lose about ten bits. A "drop out" is similar to a person's voice fades away in a telephone conversation. To correct the problem of drop out,we will ask the person (or computer) at the other end to repeat what they just said. "Huh?" This is called retransmission of data. In telephony, drop outs are defined as incidents when signal level unexpectedly drops at least 12 dB for more than 4 milliseconds. (Bell standard allows no more than two drop outs per 15 minute period.)

Drop Reel

A reel used to transport and distribute drop wire.

Drop Repeater

A repeater that is provided with the necessary equipment for local termination (dropping) of one or more channels of a multichannel system.

Drop Set

All parts needed to complete connection from the drop (wall plate, coupling, MOD-MOD) to the terminal equipment. This would typically include a modular line cord and interface adapter.

Drop Shipment

Equipment shipped to a buyer from a location separate from the seller's premise . If this third location is a different company, then this third-party supplier bills the seller and the seller bills the buyer. This saves time, but the seller loses control over the equipment's condition.

Drop Side

Defines all cabling and connectors from the terminal equipment to the patch panel or punch down block designated for terminal equipment at the distribution frame.

Drop Wire

Wires going from your phone company to the 66 Block or protector in your building. See also Distribution Cable.


A short period of time during which a transmission service looses the ability to transmit data. Bell System specifications define a dropout as any such loss which lasts for more than four milliseconds. See DROP OUTS for a longer explanation.


The system will be dropped. Typically it means that a set of changes has been made operational in the telephone or computer system. This is interesting because the meaning is the opposite of what you would think.

Dropped Call

A call in which the radio link between the cellular customer and the cell site is broken. Dropped calls can happen often, and for many reasons, including terrain, equipment problems, atmospheric interference, and traveling out of range. In short, a dropped call is a call terminated by other than the calling or called party.


  1. Distribution and Replication Protocol. A proposal for an alleged improvement to HTTP. DRP is intended to improve on HTTP in two ways: by enabling multiple files to be downloaded over a single connection and by limiting the amount of data that needs to be downloaded each time a user returns to a Web site or downloads an update of an application. Currently HTTP requires a separate connection for each item being downloaded, which can slow the download process if many connections need to be opened. HTTP is also stateless, meaning that no information about a Web site is maintained on the client machine once the user moves on to another site, with the exception of a temporary cache and cookies. See HTTP. DRP is currently being studied by The World Wide Web Consortium (W3C).

  2. Disaster Recovery Plan. The procedures that are to be executed to restore telecom, data, phone and network operations if catastrophe were to occur (e.g. a fire, a floor, a terrorist act, etc.).


  1. Digital Reference Signal.

  2. Digital Reconfiguration Service. DRS is intended for those private line customers who reconfigure their networks regularly or from disaster recovery to accommodate their applications such as video conferencing, high speed backups , etc.


DS3 Redundancy and Termination.


  1. Dial repeating tie line.

  2. Dial repeating trunk line.


Dial repeating tie trunk.


  1. DACS Remote Unit.

  2. Digital Remote Unit. An NEC term. It's a multiplexer used to distribute NEC Dterm digital telephones and analog sets throughout the user's communications network, whether that network is local or geographically dispersed. The multiplexing technology used is North American Standard T-1 and European Standard E-1.

Drug Runs

Bus trips to Mexico and Canada chartered by US senior citizens looking to "score" cheaper prescription drugs.

Drum Factor

In facsimile systems, the ratio of drum length to drum diameter. Where drums are not used, it is the ratio of the equivalent dimensions.

Drum Speed

The angular speed of the facsimile transmitter or recorder drum, measured in revolutions per minute.

Drunken Swede

A way of describing the sound of a computer doing text-to-speech conversion. "Why, he sounds like a drunken Swede." This great definition from Stuart Segal of Phone Base Systems, Inc. in Vienna, VA. Says Stuart, "Our people think that a drunken Swede has recorded this message." It is possible to have a computer generate speech that doesn't sound like a drunken Swede if you throw sufficient horsepower (MIPS and memory) at it. Throwing sufficient horsepower, however, has been expensive, until recently. Drunken Swedes are going to get less and less common as horsepower gets cheaper and cheaper.


Cable with no electronics and with no telecommunications transmission on it. In short, raw copper pair. You rent raw copper pair when you want to put your own electronics on it.

Dry Cell

A type of primary cell in which the electrolyte is in the form of a paste rather than that of a liquid.

Dry Contact

A dry contact refers to a circuit with an energy level such that a spark is not created in a mechanical relay or switch contracts when the circuit is opened. As a result, no cleaning of the contacts takes place (sparking vaporizes contact materials thereby continually exposing fresh contact material). Sometimes general purpose contacts are gold-flashed so the relay or switch can be used on dry circuits; when used on higher energy circuits the gold coating is destroyed , but no damage is done except that the contact should not be used to carry dry circuit signal levels again. A dry contact might operate a relay which might turn something of higher power on or off. For example, a low voltage signal in a key system might cause a dry contact to close, thus causing much higher voltage to flow to a bell, a klaxon, a strobe light. And, yes, there is a "wet" contact. The term "mercury-wetted relay" refers to a relay or switch in which the movable contact of the device makes contact with a pool of mercury . In fact, before solid-state devices, this was a common technology for switching dry circuits.

Dry Copper Pair

A dry copper pair or circuit is one which is has no electronics (e.g., load coils, repeaters or subscriber carrier systems) between the wire center and the customer premises. Such electronics interfere with the provisioning and support of high- speed data lines, such as DSL (Digital Subscriber Line) services, which many CLECs are interested in selling. See also CLEC, Dedicated Inside Plant, Dry Copper, DSL, ILEC and See Dry Twisted Pair.

Dry Electrolytic Condenser

An electrolytic condenser in which the electrolyte is in the form of a paste or jelly rather than that of a liquid.

Dry Loop Powering

Refers to local (not span) powering, and a transmission medium other than copper wire (microwave/fiber optic).

Dry Pair

A "dry pair" is a simple pair of wires with no voltage, signals or protocols, just two wires. These are sometimes used for alarm systems but can conceivably be used for other communications if the pair is "loop qualified" before implementation.

Dry T-1

A T-1 line with an unpowered interface. A T-1 line with a power is called "Wet."

Dry Twisted Pair

Also known as "dry copper," a dedicated twisted-pair circuit without loading coils or any sort of electronics, whatsoever. Dry twisted pair circuits are commonly leased from the LEC for burglar alarm circuits, with one end terminating at the customer's premise in an alarm box and with the other end terminating at the premise of the alarm company. Recently, a number of CAPs (Competitive Access Providers), CLECs (Competitive Local Exchange Carriers) and ISPs (Internet Service Providers) have been leasing dry copper circuits from telephone companies for purposes of provisioning high- speed xDSL services. Since such xDSL services compete with LEC services and since xDSL can cause crosstalk problems with adjacent pairs in the same cable system and since it deprives them of revenue, several of the LECs recently have refused to lease dry copper. See Coppertone.


  1. Digital Signal. See DS-, DS-0, DS-1.

  2. Danske Standardiseringsrad (Danish Standards Institution).

  3. An ATM term. Distributed Single Layer Test Method: An abstract test method in which the upper tester is located within the system under test and the point of control and observation (PCO) is located at the upper service boundary of the Implementation Under Test (IUT) - for testing one protocol layer. Test events are specified in terms of the abstract service primitives (ASP) at the upper tester above the IUT and ASPs and/or protocol data units (PDU) at the lower tester PCO.

See also DS-.


Digital Signal (level). A hierarchy of digital signal speeds used to classify capacities of digital lines and trunks. The fundamental speed level is DS-0 (64 Kbps, i.e., 64 Kilobits per second, or 64,000 bits per second), which is a voice grade channel. That is the bandwidth you need when you use traditional PCM (Pulse Code Modulation) to sample a voice call 8,000 times a second and encode it in an 8-bit code, yielding 8 x 8,000 = 64,000 bits per second. The highest speed in the digital signal (DS) hierarchy is DS-4, at about 274 Mbps. The full DS hierarchy is as follows : DS-1, DS-1C, DS-2, DS-3, DS-4. The DS hierarchy takes different forms in different parts of the world, where different standards generally apply. In North America, it takes the form of T-carrier; in Europe, E-carrier (generally known as the international standard); and in Japan, J-carrier. In North America, therefore, DS-1 becomes T-1, DS-2 becomes T-2, and so on. The only exception is DS-0, which is known as DS-0 across all of the various standards. The full T-carrier hierarchy, for example, comprises T-1 at 1.544 Mbps, T-1C at 3.152 Mbps, T-2 at 6.312 Mbps, T-3 at 44.736 Mbps and T-4 at 274.176 Mbps. Technically speaking, the originating data stream is in the form of a DS-1, at the speed specified by the prevailing standard. When the data stream arrives at the channel bank, which is the point of demarcation, it is framed according to the prevailing standard, signaling and control bits are added, and the signal is encoded into the proper electrical format. For example, a data stream of 1.536 Mbps arrives at the channel bank, 0.008 Mbps of framing bits are added, and the signal exits the channel bank at a T-1 signaling rate of 1.544 Mbps. See the following DS-x definitions. Also, see channel bank, and T-.


Digital Signal, level 0. A DS-0 is a voice-grade channel of 64 Kbps (i.e., 64,000 bits per second. This channel width is the worldwide standard speed for digitizing one voice conversation using PCM (Pulse Code Modulation. The analog signal is sampled 8,000 times a second, with each sample encoded into an 8-bit byte (thus 8 x 8,000 = 64,000). There are 24 DS-0 channels in a T-1, the North American version of DS-1. See also DS-, and PCM.


Digital Signal, level 1. It is 1.544 Mbps (i.e., 1.544 million bits per second) in North America (T-1) and Japan (J-1), and 2.048 Mbps in Europe (E-1). Why there's no consistency is one of those wonderful, unanswered, questions. T-1 is the original standard, having been developed by Bell Telephone Laboratories in the 1950s. Subsequently, the ITU-T developed the European E-1 standard, variant, which runs at 2.048 Mbps. The Japanese developed the J-1 standard, which also runs at 1.544 Mbps, but is incompatible with T-1. The T-1 standard, at 1.544 Mbps, for example, supports 24 voice conversations, each encoded at 64 Kbps. The E-1 standard, at 2.048 Mbps, supports 30 conversations, plus two signaling and control channels, for a total of 32 channels, each of 64 Kbps. See also DS-.


Digital Signal, level 1 Combined. The total signaling rate is 3.152 Mbps in North America and comprises two T-1s (two J-1s in Japan), at 1.544 Mbps each, which are interleaved to support 48 DS-0s. The additional 64 Kbps is overhead used to support additional signaling and control requirements. DS-1C is seldom used, outside of limited telco applications. There is no European equivalent. See DS- and DS-1.


Digital Signal, level 2. DS-2 effectively translates to T-2 in North America, and J-2 in Japan. (There is no European equivalent.) DS-2 supports a total signaling rate of 6.312 Mbps. It is the equivalent of 4 T-1s, and supports 96 DS-0 channels of 64 Kbps, plus overhead in support of additional requirements for signaling and control functions. DS-2 is used in carrier (telco) applications, and only rarely. See DS-, DS-0, DS-1, T-1 and T-2.


Digital Signal, level 3. In North America and Japan, DS-3 translates into T-3, which is the equivalent of 28 T-1 channels, each operating at total signaling rate of 1.544 Mbps. The 28 T-1s are multiplexed through a M13 (Multiplex 1 to 3) Multiplexer), and 188 additional signaling and control bits are added to each T-3 frame. As each frame is transmitted 8,000 times a second, the total T-3 signaling rate is 44.736 Mbps. In a channelized application, T-3 supports 672 channels, each of 64 Kbps. In the European hierarchy, a DS-3 is in the form of an E-3, which runs at a total signaling rate of 34.368 Mbps, supports 480 channels, and is the equivalent of 16 E-1s. A J-3 runs at 32.064 Mbps, supports 480 channels, and is the equivalent of 20 J-1s. If you're moving a DS-3 (or any other DS signal) across continents, the standards of the target country rule. Channels get muxed and demuxed, with signaling conventions translated, as well. Here is a question from a reader: On the US side T-1s are in multiples of 24x64 Kbps circuits and in the UK we have two-megabit circuits with 30x64 Kbps. If we were to want to interconnect to the US at DS-3 level, would we receive 28 T-1's with 6 spare channels, or do they get muxed and demuxed into multiples of 30 when they arrive over this side of the world? Answer: They get muxed and demuxed, along with signaling conventions translated into multiples of 30 when they arrive in the U.K. DS-3 is also called T-3. See DS-, DS-0, DS-1, T-1, T-2 and T-3.


Digital Signal, level 4. T-4 runs at a total signaling rate of 274.176 Mbps in North America in support of 168 T-1s, yielding 4032 standard voice-grade channels. E-4 runs at 139.264 Mbps in Europe in support of 64 E-1s, yielding 1920 voice-grade channels. J-4 runs at 397.200 Mbps in Japan in support of 240 J-1s, yielding 5760 channels. See DS- 0, DS-1, T-1, T-2 and T-3.


Usually written DS-0 (and pronounced D S zero). Digital Signal, level Zero. DS0 is 64 Kbps. As the basic building block of the DS hierarchy, it is equal to one voice conversation digitized under PCM. Twenty-four DS-0s (24x64 Kbps) equal one DS-1, which is T- 1, or 1.544 Mbps. See DS-0.


Refers to a process where a subrate signal (2.4, 4.8, or 9.6 Kbps) is repeated 20, 10 or 5 times, respectively to make a 64 Kbps DS-0 channel.


Refers to a process performed by a subrate multiplexer where twenty 2.4 Kbps, ten 4.8 Kbps, or five 9.6 Kbps signals are bundled into one 64 Kbps DS-0 channel.


See DS-1.


See DS-2.


See DS-3.


An ATM term. Physical Layer Convergence Protocol: An alternate method used by older T carrier equipment to locate ATM cell boundaries. This method has recently been moved to an informative appendix of the ATM DS3 specification and has been replaced by the HEC method.


See DS-4.


  1. Distributed Systems Architecture, the network architecture developed by Honeywell.

  2. Directory System Agent. The software that provides the X.500 Directory Service for a portion of the directory information base. Generally, each DSA is responsible for the directory information for a single organization or organizational unit.

  3. Data Service Adapter.


Destination Service Access Point. The logical address of the specific service entity to which data must be delivered when it arrives at its destination. This information may be built into the data field of an IEEE 802.3 transmission frame.


Digital Supervisory Audio Tones. A supervisory signaling scheme used in NAMPS ” a new form of digital cellular radial called Narrow-band Advanced Mobile Phone service. See also NAMP.


Digital Sound Broadcasting.


Double SideBand Suppressed Carrier. A variation on the theme of DSBTC (Double SideBand Transmitted Carrier), DSBSC uses less power since the carrier is not sent. The same amount of bandwidth is used, and carrier synchronization is lost. See also Amplitude Modulation, DSBTC, SSB and VSB.


Double SideBand Transmitted Carrier. A form of Amplitude Modulation (AM) used to encode analog signals for transmission over a digital facility. DSBTC multiplies the carrier signal by modulating the amplitude (volume) of the carrier signal, plus adding a dc (direct current) component. The resulting output has some level of redundancy as the output is the sum of the carrier signal plus symmetric components in sidebands, which are some frequency separation from the carrier frequency. See also Amplitude Modulation, DSBSC, SSB and VSB.


Digital Selecting Calling. A synchronous system developed by the International Radio Consultative Committee (CCIR), used to establish contact with a station or group of stations automatically by radio. The operational and technical characteristics of this system are contained in CCIR Recommendation 493.


Dispersion Shifted Fiber (DSF) improves on Non Dispersion Shifted Fiber (NDSF) by shifting the interface between the fiber core and cladding. DSF suffers from the noise phenomena of chromatic dispersion and waveguide dispersion. Those two types of dispersion seriously impact the integrity of the optical signals at windows (i.e., wavelength ranges) other than 1310nm (nanometers). However, other wavelengths in higher windows are much better suited for long haul transmission. DSF solves the dilemma through several types of fiber: Zero Dispersion Shifted Fiber (ZDSF) and Non Zero Dispersion Shifted Fiber (NZDF). ZDSF shifts that interface to the point that chromatic dispersion and waveguide dispersion cancel each other out at 1550nm (nanometers), rather than the 1310nm window used in NDSF. DWDM (Dense Wavelength Division Multiplexing) and EDFAs (Erbium- Doped Fiber Amplifiers) work in this window. In this window, however, another noise problem surfaces in the form of four-wave mixing, in which the signal wavelengths interact to create additional wavelengths, which serve to confuse the signal. Non Zero Dispersion Shifted Fiber (NZDF) shifts the point of optimal dispersion just a bit higher than the range in which EDFAs operate, thereby essentially eliminating the problem of four-wave mixing. See also Chromatic Dispersion, Dispersion, DWDM, EDFA, Four-Wave Mixing, NDSF, Waveguide Dispersion, Wavelength and Window.


DiffServ Code Point. See also Differentiated Services.


Call Waiting Display with Disposition.


Direct Service Dialing Capability. Network services provided by local switches interacting with remote data bases via CCIS.


  1. Data Switching Equipment.

  2. An ATM term. Distributed Single-Layer Embedded (Test Method): An abstract test method in which the upper tester is located within the system under test and there is a point of control and observation at the upper service boundary of the Implementation Under Test (IUT) for testing a protocol layer, or sublayer, which is part of a multi-protocol IUT.


Digital Speech Interpolation. A compression technique for squeezing more voice conversations onto a line. DSI digitizes speech so it can be cut into slices, such that no bits are transmitted when no one is speaking. As soon as speech begins, bits flow again. See Digital Speech Interpolation.


Defense Systems Information Agency. A U.S. government agency under the DOD (Department of Defense). DSIA's mission is "to plan, engineer, develop, test, manage programs, acquire, implement, operate, and maintain information systems for C4I (Command, Control, Communications and Computers and Intelligence) and mission support under all conditions of peace and war." DSIA was established on May 12, 1960, and assumed all responsibilities of the DCA (Defense Communications Agency) on June 25, 1991. DSIA is responsible for all aspects of systems and networks, including the DDN (Defense Data Network) and the DSN (Defense Switch Network). See also DDN and DSN.


See ADSL, CLEC and Digital Subscriber Line.

DSL Bonding

Take two DSL 1.5 megabit per second lines. Join them together. Get double the speed. When I wrote this, DSL bonding was available to join two DSL lines together. But I've heard they're working on bonding eight 1.5 megabit per second lines together, enabling service to 12 megabits per second.

DSL Filter

Digital Subscriber Line filter. Let's say you have one phone line. On that phone line you run a high-speed DSL broadband circuit to the Internet and several normal household analog phones. Without a DSL filter, you are likely to hear excessive hum on your phone conversations. Also your caller ID probably won't work. A DSL filter is a low- pass filter that removes the high-end frequencies that could cause interference between the analog voice signals and the high-speed packet data signals over an ADSL line. ADSL (Asymmetric Digital Subscriber Line) supports both telephone service over an analog channel operating at frequencies of 4 kHz and below, and high-speed digital packet data at frequencies of 25 kHz and above. The DSL filter is physically a small box, one end of which protrudes a male RJ-11 plug. That's for inserting into a phone jack. On the other side of the box are two female RJ-11 connectors ” one for your phone and/or your phone-based alarm system and one for your ADSL modem. The DSL filter essentially provides a fourth- order low-pass filter circuit that allows voice and low-speed data to pass through unfiltered , while blocking the high frequencies of DSL and other potential sources of disturbance. The filter also provides a way for alarm companies to install equipment at a place where DSL service has been previously installed. You have to install DSL filters at every outlet in your home. Or ... there is an alternatives. It's called installing a splitter. Splittered ADSL involves a centralized splitter, into which the DSL filter is embedded. ADSL Lite, or G.Lite, the new version of DSL, is a splitterless version involving microfilters that sit between the individual analog telephone sets and jacks. The DSL filters do the same thing, in either case. See also ADSL and Filter.

DSL Forum

The DSL Forum is an industry association formed to promote the DSL concept and to facilitate the development of DSL system architectures and protocols for major DSL applications. As the forum comprises competing companies, it does not publish material that discusses line codes or basic modulation systems, or any other material that addresses individual company or product attributes. See also ADSL and VDSL.


Digital Subscriber Line Access Multiplexer. A device used in a variety of DSL technologies, which are lumped under the category of xDSL, with "x" being the generic "what- ever." A DSLAM serves as the point of interface between a number of subscriber premises and the carrier network. At each subscriber premises is a splitter or a standalone modem, depending on the specific form of xDSL involved. The DSLAM generally is positioned in the ILEC's (Incumbent Local Exchange Carrier's) Central Office (CO). Alternatively, a Mini- DSLAM may be enclosed in a ngDLC (next generation Digital Loop Carrier), essentially servicing as a remote DSLAM. The DSLAM is a packet multiplexer, serving to multiplex the data (and perhaps voice) packets from multiple customers in order to transmit them over one or more high-speed circuits. In an integrated voice/data DSL application, the voice packets are forwarded to the PSTN (Public Switched Telephone Network), or perhaps an IP voice network, and the data packets are forwarded to the Internet, often over an ATM-based data network. See also ADSL, Digital Subscriber Line, DLC, ngDLC, and xDSL.


Digital Storage Media Command And Control. Network protocols specified in Part 6 of MPEG-2 (ISO 13818) standards dealing with user-to-network and user-to-user signaling and communications.


Directory Services Markup Language, or the most promising way to generate directory services in XML, the standard language used in e-commerce. DSML makes directory services easily able to use XML, allowing a simpler way for customers and partners to link with companies regardless of their current directories at their own sites.


  1. Distributed Systems Network, the network architecture developed by Hewlett- Packard.

  2. Double Shelf Network.

  3. Defense Switch Network. The private, long haul, switched network used by the U.S. military in support of voice communications. DSN replaced AUTOVON, which was developed during the "Cold War." DISA (Defense Information Systems Agency) is responsible for the DSN. See also AUTOVON and DISA.


  1. See DS-0.

  2. Days Sales Outstanding. Another way of saying accounts receivable, usually measured in days.


An AT&T Digital Data Service standard that specifies a means of multiplexing several subrate data channels within one DSO. Five 9.6, ten 4.8 or 20 2.4 Kbps subrate channels may be multiplexed within one DSO.


  1. Display System Protocol.

  2. Digital Signal Processor. A Digital Signal Processor is a specialized computer chip designed to perform speedy and complex operations on digitized waveforms. Useful in processing sound (like voice phone calls) and video. See Digital Signal Processor for a much better explanation.

DSP Modem

Digital Signaling Processor chip set used for analog modem emulation. The software is programmable for easy upgrades.


Downstream Physical Unit. A Physical Unit that is located downstream from the host.


Data Set Ready. This signal is on pin 6 of the RS-232-C connector. It means the modem (which some telephone companies call a "data set") is ready to send data from the terminal. Some modems use Data Set Ready. Some don't. Modems that are snooty enough to give you the DSR signal, are obnoxious enough to not work until they receive the DTR (Data Terminal Ready) signal from the terminal on pin 20. By bridging pins 6 and 20 on the connector at the modem, you can usually get it to work. If it doesn't, bridge in pin 8 (carrier detect) as well.


Digital Short Range Radio.


  1. Direct Station Select. A piece of key telephone equipment usually attached to an operator's phone set. When the operator needs to call a particular extension he/she simply touches the corresponding button on the Direct Station Select equipment. Typically DSS equipment/feature is part of a Busy Lamp Field (BLF), which shows with lights what's happening at each extension. Is it busy? Is it on hold? Is it ringing?

  2. Decision Support Systems. Computerized systems for transforming data into useful information, such as statistical models or predictions of trends, usually in a graphical format, which is used by management in the decision-making process. See Decision Support Systems.

DSS2 Setup

Digital Subscriber Signaling System 2 is a signaling protocol that specifies the procedures for the establishment, maintenance and clearing of point-to-multipoint VCCs (Virtual Channel Connections) at the B-ISDN (Broadband ISDN) UNI (User Network Interface). Such a connection is a collection of associated ATM VCC unidirectional links connecting two or more endpoints. See also ATM, B-ISDN, UNI and VCC.


Direct Sequence Spread Spectrum. A technique used in spread spectrum radio transmission systems, such as Wireless LANs and some PCS cellular systems. DSSS involves the conversion of a data stream into a stream of packets, each of which is pre-pended by an ID contained in the packet header. The stream of packets then is transmitted over a wide range of frequencies, using an approach known as "scattering." A large number of other transmissions also may share the same range of frequencies at the same time, with the potential for overlapping of packets. The receiving device is able to distinguish each packet in the packet stream by reading the various IDs, treating competing signals as noise. In a wireless LAN environment, DSSS typically operates in the 2.4 GHz frequency band, which is one of the ISM (Industrial Scientific Medical) bands defined by the FCC for unlicensed use. Although some manufacturers continue to use DSSS, Frequency Hopping Spread Spectrum (FHSS) is the preferred approach. See also 802.11b, CDMA, FHSS, ISM and Spread Spectrum.


Daylight Savings Time.


See DTM.


Dual-scan Super Twisted Nematic). A laptop-display technology that uses two display layers to overcome color shifting that occurs with supertwist displays. It's a less expensive alternative to thin film transistor and active matrix displays and has a faster video scan rate than the lower-cost STN design. The screen pointer is less apt to temporarily disappear when moved rapidly, plus the screen will scroll more smoothly. Although the displays are brighter, the screens tend to look blurry when viewed at an angle.


Digital Service Unit, also called Data Service Unit. Converts RS-232-C or other terminal interface to DSX-1 interface. See Data Service Unit.


The devices used to access digital data channels are called DSU/CSUs (Data Service Unit/Channel Service Units). At the customer's end of the telephone connection, these devices perform much the same function for digital circuits that modems provide for analog connections. For example, DSU/CSUs take data from terminals and computers, encode it, and transmit it down the link. At the receive end, another DSU/CSU equalizes the received signal, filters it, and decodes it for interpretation by the end-user.


Digital Simultaneous Voice and Data. Technology in a modem that allows you to send and receive voice and data (fax, images, files, etc.) on the same "conversation" on one analog phone line. DSVD allows the simultaneous transmission of data and digitally- encoded voice signals over a single dial-up analog phone line. DSVD modems use V.34 modulation (up to 33.6 kilobits per second), but may also use V.32 bis modulation (14,400 kilobits per second). DSVD modems reserve eight kilobits per second for voice transmissions. The remaining bandwidth is available for data transmission. The DSVD voice coder is a modified version of an existing specification and is defined as G.729 Annex A. The DSVD voice/data multiplexing scheme is an extension of the V.42 error correction protocol widely used in modems today. DSVD also specifies fallbacks that enable DSVD modems to communicated with standard data modems (i.e. V.34, V.32 bis, V.32 and V.22).

What Can You Do With DSVD? (Below is good manufacturer promotion on DSVD. The words came from Rockwell.)

Have you ever promised someone on the telephone that you'd fax a document to them, then forget to send it? Have you ever traveled cross-country or halfway around the world to make a presentation? Have you considered expensive video conferencing hardware and applications as a way to communicate? Ever been frustrated waiting online, hoping to get some technical support?

When you need to work on a project, spreadsheet or presentation with someone from another location, a DSVD modem lets you do it without leaving your office or requiring costly video conferencing equipment. Both parties can simultaneously collaborate on a shared document, each viewing and discussing the additions and modifications made. This can slash time and money previously wasted exchanging faxes and relying on overnight express mail deliveries. Computer and software demonstrations can be easily conducted through a DSVD modem. This is a great way to highlight or test market new features and get immediate customer feedback. For the computer company, DSVD means fewer support follow-up calls and lower telephone bills. With a DSVD modem, you will be able to dial your favorite online catalog showrooms, browse the aisles , ask a salesperson a question or two, then place an order. Unlike other online "malls", with DSVD the human interface is still intact. While you're interactively shopping you can talk with salespeople or even other shoppers, just like the real mall. See V.70.


DSX. Also known variously as a DACS (Digital Access Cross-Connect System) and a DCC (Digital Cross-Connect), a DSX is a manual bay, panel or some other device that is used to interconnect digital circuits. A DSX-1 interconnects DS-1 (T-1 or E-1) circuits, as DSX-2 interconnects DS-2 (T-2 or E-2) circuits, and a DSX-3 connects DS-3 circuits (T-3 or E-3).


Direct termination. DT allows long distance carriers to bypass the LEC and terminate the switched traffic over dedicated (non-LEC) facilities to the customer premises. Direct termination calls are routed using six or ten-digit screening in the terminating long distance switch.


  1. Digital Trunk Controller. See also STC.

  2. Digital Transmit Command.

  3. Digital Traffic Channel. A digital cellular term. Defined in IS-136, the DTC is the portion of the air interface which carries the actual data transmitted. The DTC operates over frequencies separate from the DCCH (Digital Control CHannel), which is used for signaling and control purposes. See also DCCH and IS-136.


Document Type Definition often used in relationship with the Extensible Markup Language (XML). See cXML, SGML, XML, and XML Schema.


Data Terminal Equipment. A terminal device in the data world. DTE is part of a broader grouping of equipment known as CPE (Customer Premises Equipment), which includes voice, as well as data, terminals. At the terminal end of a data transmission, DTE comprises the transmit and receive equipment. DTE can be in the form of a dumb terminal (i.e., a terminal without embedded intelligence in the form of programmed logic), a semi-intelli- gent terminal, or an intelligent host computer (i.e., a PC, mid-range or mainframe computer). DTE interfaces to a circuit through DCE (Data Communications Equipment). See DCE and DTE.


Data terminal equipment/data communications equipment rate. A designation for the maximum rate at which a modem and a PC can exchange information, expressed in kilobits per second (kbps). For maximum performance, a modem must support a DTE-DCE rate in excess of its maximum theoretical throughput.


A line of proprietary electronic phones made by NEC for use with its PBXs. The Dterm terminal derives its intelligence from its own microprocessor, which detects events and accepts direction from the PBX.


Direct To Home. Intended as a replacement for C-band satellite systems, DTH was proposed to operate on medium-powered FSS (Fixed Satellite Systems) in the Ku-band. DTH was superseded by DBS (Direct Broadcast Satellite), which allows the use of even smaller receive antennas than possible with DTH. See also Direct Broadcast Satellite and KU Band.


Digital Trunk Interface.


An ATM term. Designated Transit List: A list of nodes and optional link IDs that completely specify a path across a single PNNI peer group.

DTL Originator

An ATM term. The first switching system within the entire PNNI routing domain to build the initial DTL stack for a given connection.

DTL Terminator

An ATM term. The last switching system within the entire PNNI routing domain to process the connection and thus the connection's DTL.


Dial Tone Line.


Digital Trunk and Line Unit. Provides system access for T1-carrier lines used for inter office trunks or remote switching module umbilicals.


According to, DTM (Dynamic synchronous Transfer Mode)is a network protocol for high speed networking developed for dynamic transport of integrated traffic. It is a transport network architecture based on circuit-switching augmented with dynamic reallocation of bandwidth. The protocol is designed to be used in integrated services networks. It supports point-to-point, multicast and broadcast communication, i.e. a DTM network will be used for both distribution and unicast communication. DTM includes switching and a signaling protocol and can thus, in contrast to say SDH/SONET, set up multi-rate channels (circuits) on demand, and the capacity of a channel can be changed according to traffic characteristics during operation. Additionally, resources can be reallocated between nodes according to the current demands. In this way, free bandwidth is allocated to nodes with highest demands, providing an autonomous and efficient dynamic infrastructure.


Dual Tone Multi-Frequency. A fancy term describing push button or Touchtone dialing. (Touchtone is a not registered trademark of AT&T, though until 1984 it was.) In DTMF, when you touch a button on a push button pad, it makes a tone, actually a combination of two tones, one high frequency and one low frequency. Thus the name Dual Tone Multi Frequency. In U.S. telephony, there are actually two types of "tone" signaling, one used on normal business or home pushbutton/touchtone phones, and one used for signaling within the telephone network itself. When you go into a central office, look for the test board. There you'll see what looks like a standard touchtone pad. Next to the pad there'll be a small toggle switch that allows you to choose the sounds the touchtone pad will make ” either normal touchtone dialing (DTMF) or the network version (MF).

The eight possible tones that comprise the DTMF signaling system were specially selected to easily pass through the telephone network without attenuation and with minimum interaction with each other. Since these tones fall within the frequency range of the human voice, additional considerations were added to prevent the human voice from inadvertently imitating or "falsing" DTMF signaling digits. One way this was done was to break the tones into two groups, a high frequency group and a low frequency group. A valid DTMF tone has one tone from each group. In other words, each DTMF tone has two tones. Here is a table of the DTMF digits with their respective frequencies. One Hertz (abbreviated Hz.) is one cycle per second of frequency.

When you touchtone, each button makes two tones. Here's how to figure out what they are. They were deliberately designed so people couldn't whistle them.

How each touchtone button makes two tones

Low tones
























High Tones






Normal telephones (yours and mine) have 12 buttons , thus 12 combinations. Government Autovon (Automatic Voice Network) telephones have 16 combinations, the extra four (those above) being used for "precedence," which in Federal government parlance is a designation assigned to a phone call by the caller to indicate to communications personnel the relative urgency (therefore the order of handling) of the call and to the called person the order in which the message is to be noted. See also LONG TONES and the four following definitions.

DTMF Automatic Routing

This is a term relating to a fax server operating on a Novell file server. In this system, the fax software assigns a four-digit number to each user. A fax sender dials the fax line, and after the fax server answers, it sends a special auto routing request signal. The sender dials the four-digit number for the correct user, and the fax is automatically sent to the user's workstation on the LAN.

DTMF Cut-Through

The capability of a voice response system to receive DTMF tones while the voice synthesizer is delivering information, i.e. during speech playback. This capability of DTMF cut-through saves the user waiting until the machine has played the whole message (which typically is a menu with options). The user can simply touchtone his response anytime during the message ” when he first hears his selection number, when the message first starts, etc. When the voice processor hears the touchtoned selection (i.e. the DTMF cut-through), it stops speaking and jumps to the chosen selection. For example, the machine starts to say, "If you know the person you're calling, touchtone his extension in now." But before you hear the "If you know" you push button in 230, which you know is Joe's extension. Bingo, the message stops and Joe's extension starts ringing. DTMF Cut-Through is also known as touchtone type-ahead.

DTMF Register

A printed circuit card in a switch that converts the DTMF signals coming from the phone into signals which can be used by the switch's stored program control, central computer to do its switching, etc.

DTMF To Dial Pulse Conversion

A PBX feature. DTMF (push button) phones are very popular. But sometimes you install a PBX with push button phones in an area which doesn't have a central office which will respond to push button tones. It's old. In this case, anyone dialing on a push button phone will find that the PBX converts that dialing to rotary pulsing when the PBX accesses a trunk which can't handle push button dialing. All this doesn't speed up the time the call takes to get through. It just speeds up the user's dialing and makes him or her feel she is dealing with a more modern phone system.


Dial Tone Office.


DeskTop Publishing.


Data Terminal Ready. A control signal sent from the DTE to the DCE that indicates that the DTE is powered on and ready to communicate. DTR can also be used for hardware flow control.


  1. Digital Termination Systems. DTS is a digital microwave transmission technology designed for facilities bypass applications in short-hop, line-of-sight situations. DTS useful in high-volume, pure-data applications in urban settings where line costs are high. DTS requires FCC license and is referred to formally by the FCC as Digital Electronic Message Service, or DEMS.

  2. Distributed Time Service. DTS is a feature of DCE (Distributed Computing Environment), a developing open standard championed by The Open Group. DTS is a mechanism that would allow distributed computing systems to synchronize their system clocks. See also DCE and The Open Group.


Dial Tone Speed Recording.


Digital Trunk Testing.


Digital Test Unit. A generic term for a device used to test the performance of digital circuits. While a DTU can be in the form of a standalone device, it also can be in the form of a set of programmed logic on a chipset contained under the skin of another device. For example, and in a telecommunications network context, a DTU might be termed as the capability of a DSU/CSU (Digital Service Unit/Channel Service Unit) to respond to the request of a carrier for a loopback test, which is used to test the integrity of a four-wire digital circuit such as a T-1. Similarly, it might be the capability of a NIU (Network Interface Unit) to respond to an ALTS (Automated Line Testing System) for a line test on an ISDN line. A DTU might test across a wide range of circuit integrity parameters including physical integrity (e.g., electrical opens and shorts), electrical ground, signal strength, electrical noise levels, and bit error rate (ber). See also CSU, DSU, Loopback Test and NIU.


Digital TV. The generic term for television systems employing digital, rather than analog, technology. All HDTV (high definition TV) is digital. Not all digital TV is high definition. An HDTV picture is made up of 1,080 interlaced scan lines (1080i) or 720 progressive (780p) scan lines. Standard-definition digital television and other digital-TV formats aren't as sharp but still look better than standard analog TV. This is easily confused with digital cable, which does not necessarily deliver an enhanced picture, but typically delivers additional channels. Since most TV content originally starts out as analog, rather than digital, it has to be digitized through a codec (coder/decoder). Once digitized, it can be compressed for efficiency of storage, and can be more easily edited and otherwise manipulated, and reproduced. DTV transmission offers the advantages of compression for efficiency of bandwidth utilization (in other words, it uses less bandwidth), improved error performance for improved picture and sound quality, and more effective network management and control. The full benefits of DTV are best realized if the terminal device (i.e. your TV set) is digital. A digital TV set sometimes allows the program to be compressed and archived (i.e., stored) for replay, and certainly offers better quality of picture and sound. See also ATV, HDTV and SDTV.


Battery-saving feature on a cellular phone that cuts back the output power when you stop speaking.


Fiber Optic Connector developed by Nippon Electric Group.


Directory User Agent. The software that accesses the X.500 Directory Service on behalf of the directory user. The directory user may be a person or another software element.


Distributed Update Algorithm. A routing algorithm that provides fast rerouting (convergence) with minimal consumption of resources.

Dual Attachment Concentrator

DAC. A concentrator that offers two S ports for connections to the FDDI network and multiple M ports for attachment of devices such as workstations and other concentrators . A DAC takes maximum advantage of the resiliency of the FDDI dual counter-rotating ring architecture through connection to both rings, unlike a SAC (Single Attachment Concentrator). Connection of devices through the concentrator obviates the need for each device to attach directly, thereby reducing the number of optoelectric conversions and resulting in reduced cost of attachment. The concentrator also serves as a point of contention for network access. See also Single Attachment Concentrator, Single Attachment Station, Dual Attachment Station and FDDI.

A concentrator that offers two connections to the FDDI network capable of accommodating the FDDI dual ring, and additional ports for connection of other FDDI devices.

Dual Attachment Station

DAS. A device such as a workstation which connects directly to both FDDI dual counter-rotating rings, rather than gaining ring access through a Dual Attachment Concentrator (DAC). A DAS allows access to two separate cable systems at the same time, providing protection against cable failure or damage. See also Single Attachment Concentrator, Single Attachment Station, Dual Attachment Concentrator and FDDI.

Dual Band

  1. Dual band describes a cellular phone handset which works on dual frequency bands. For example, both the 800 MHz (analog AMPS) and 1900 MHz (digital) bands for North America. This allows the phone to switch between the two bands. The reason you'd want this is simple: Digital service is often cheaper and better in areas you can get it. But you can't get it everywhere. If you travel you need a cell phone you can use everywhere. Thus the idea of carrying a dual band cell phone and subscribing to a service that gets you access to both. In Europe and many other countries, a dual band cell phone will work on both the 900 MHz and 1800 MHz GSM bands, supporting seamless hand-off between the two frequency bands for carriers using both. See also AMPS, Dual Band GSM Phone, GSM and Tri-Mode.

  2. A Satellite that can operate on C-band and Ku-band signals.

Dual Band GSM Phone

Dual Band wireless phones are capable of operating on GSM 900 and 1900 networks simultaneously. If your local U.S. service is GSM 1900, a dual-band phone would allow roaming almost anywhere in the world. Dual band phones are also available for operation on European GSM 900 and 1800 networks.

Dual Cable

A two-cable system in broadband LANs in which coaxial cable provides two physical paths for transmission, one for transmit and one for receive, as against dividing the capacity of a single cable.

Dual Coat

An optical fiber coating structure consisting of a soft inner coating and a hard outer coating.

Dual Duplex

A term sometimes used to describe HDSL (High bit rate Digital Subscriber Line), a relatively new technology which commonly is used to provide T-1 and E-1 local loops. HDSL makes use of 2 twisted pair loops , with each operating in full duplex. The traditional approach to T-1 provisioning involves 2 twisted pairs, each operating in simplex. See also HDSL.

Dual Feedhorn

A Satellite Term. A feedhorn that can simultaneously receive both horizontally and vertically polarized signals.

Dual Fiber Cable

A type of optical fiber cable that has two single-fiber cables enclosed in an extruded overjacket of polyvinyl chloride with a rip cord for peeling back the overjacket to access the fibers.

Dual Headset

Also known as an integrated headset. A special type of headset for the blind. One jack plugs into a telephone and another jack plugs into a telephone and another jack plugs into a specially configured PC. This PC provides voice synthesized output. The dual headset allows a visually impaired TSR (Telephone Sales Representative) hands-free capability. Example: The Social Security Administration has numerous blind TSRs handling incoming public calls. Dual headsets allow these blind TSRs to perform their duties with no deterioration in public service. This definition provided by Matt Gottlieb, telecommunications specialist for the Social Security Administration.

Dual- homed Firewall

A firewall that connects simultaneously to two different networks (e.g. the public Internet and a private intranet); as such it acts as a security gate- keeper that determines which traffic is allowed to pass and which traffic is blocked.

Dual Homed Gateway

A dual homed gateway is a computer that runs firewall software and has two network interface boards: One board is attached to an untrusted network, and the other board is attached to a trusted network. A dual-homed gateway relays information between the two networks and prevents any direct contact between them. Both circuit-level gateways and application-level gateways are dual homed gateways.

Dual Homing

  1. The process of using two geographically diverse frame relay port connections, each with its own set of virtual circuits, to support a network location running critical business applications which cannot afford network down time.

  2. A method of cabling FDDI concentrators and stations that permits a alternative path to the dual ring. Can be used in a tree or dual ring of trees topology.

  3. Where a device is connected to the network via two independent access points (points of attachment). One access point is the primary connection; the other is a standby connection that is activated in the event the primary connection fails.

Dual Line Registration

The ability to have two cellular telephone numbers in a single cellular telephone. This allows the user to have service on two cellular systems without "roaming" in a second city (and paying higher toll charges) or to have one number on the wireline and one number on the non-wireline system. This assures the cellular user of backup. I know a salesman who lives in Los Angeles, but spends much of his week serving customers in Phoenix. He has a cellular phone with Los Angeles number and a Phoenix number.

Dual Line Service

Telephone service where two pairs of wires are connected to the premises. One or both could be in service.

Dual LNB

A LNB is a line noise block downconverter. It is used in a TVRO (TV Receive Only) system to allow you to receive satellite signals. A dual LNB allows you to simultaneously receive two satellite channels. You can, for example, watch live TV on one channel, while recording another channel on your recording device, e.g. VCR or TiVO.

Dual Mode

Dual mode is the cellular industry's term for a cellular phone which will work for both analog and digital cellular phone systems. The cellular phone industry is going digital. Today's analog phones won't work on tomorrow's digital systems. But some phones ” dual mode ” will work on both. You may need to buy them over today's analog phones. You also need to be careful that the digital mode which you get in your dual mode cellular phone will work with the digital technology of your local carrier. That's not as standard, as yet, as today's analog technology, which works universally in North America. In short, there are many variations of digital cell phones service in North America, many of which are incompatible.

Dual NAM

Allows a cellular phone user to have two phone numbers with the same or separate carriers. Very useful for someone who spends half his life in one place and half in another. For example, a friend of mine lives in LA, but works weekdays in Phoenix. His handheld cellular has phone numbers from LA and Phoenix carriers.

Dual Processing

An SFT II configuration under Novell's NetWare that assigns parts of the operating system to separate processors. Because SFT II is split into two engines (the IOEngine and the MSEngine), it is possible to install each engine on a separate CPU, creating dual processing system. However, unless such a system is extremely busy, the extra CPU will not help network performance. Dual processing improves performance only when the servers are being used at near-maximum capacity.

Dual Rate Speech Coder for Multimedia Communication

A voice compression algorithm specified as ITU-T G.723.1 (1991) and falling under the H.324 umbrella, Dual Rate compresses voice from 64 Kbps down to 6.3 and 5.3 Kbps. High-rate compression at 6.3 Kbps uses the MP-MLQ (MultiPulse-Maximum Likelihood Quantization) algorithm, and low-rate uses ACELP (Algebraic Code Excited Linear Prediction). These compression levels yield highly efficient use of bandwidth, but impact voice quality to a considerable extent. Dual rate also imposes compression delay of 30.0 ms (milliseconds, or thousandths of a second). H.324 is the ITU-T recommendation for low bit-rate multimedia communications over the analog PSTN (Public Switched Telephone Network) through V.34 modems, which are limited to 28.8 Kbps. (Nobody in his right mind would buy a V.34 modem today.) Such a high level of compression is necessary in support of multimedia, as video and other visual information streams require a lot of bandwidth to yield even poor quality. Crummy video and crummy voice quality, both in a single standard. Who could ask for anything more? See also ACELP, H.324, and MP-MLQ.

Dual Ring Of Trees Topology

An FDDI network topology of concentrators and nodes that cascades from concentrators on a dual ring.

Dual Scan Display

An LCD display used in laptop computers. The screen is refreshed much quicker than in standard displays and use less power.

Dual Tone Multi-Frequency

DTMF. A way of signaling consisting of a push button or touchtone dial that sends out a sound which consists of two discrete tones, picked up and interpreted by telephone switches ” either PBXs or central offices. See DTMF for a bigger explanation.

Dual Universal Asynchronous Receiver Transmitter

Dual Universal Asynchronous Receiver Transmitter. A DUART provides hardware support for two serial communications ports.


Dual Universal Asynchronous Receiver Transmitter. A DUART provides hardware support for two serial communications ports.

Dub Dub Dub

The weird shortening of www for the World Wide Web, as in: "My web site is dub dub dub"

Duck Test

If it walks, talks and quacks like a duck, it's a duck.


A pipe, tube or conduit through which cables or wires are passed. Duct space is always at a premium. If you ever install a duct, make sure it's twice the diameter you think you need. If you're lucky, it will last a couple of years. The cost of putting in thicker or extra ducts is peanuts compared to the cost of having to install additional ones later.

Digging up places is getting very expensive, despite Ditch Witch, a company that makes the greatest backhoe trenching equipment. And also has the greatest name.

Duct Cycle

The relationship between the time a device or facility is used and the time it is idle.

Duct Liner

A small diameter pipe or tubing placed inside conventional underground conduit so you can install fiber optic or cables. Its main purpose is to provide a clean, continuous path with known frictional characteristics.


An arrangement of ducts, for wires or cables, arranged in tiers.


Capable of being drawn out, hammered thin or being flexed or bent without failure.


See Pathway.


The word "dude" was coined by Oscar Wilde and his friends . It is a combination of the words "duds" and "attitude." He meant it in the use of a man excessively concerned with his clothes, grooming and manners. These days dude just means a switched-on (i.e. knowledgeable) person.


Dumb User Error. A term that lacks in cleverness what it makes up for usefulness . Used by Help Desks.

Due Date

The date an event is to occur, i.e., an installation, a move, a change or a disconnect. Some vendors quote accurate due dates. Penalty clauses work most effectively in ensuring due dates are met. See also PISD.

Due Diligence

An in-depth examination of a proposed private placement or IPO that the potential investors (you and me), investment bankers and lawyers for the underwriters conduct as part of the process of raising money or taking a company public. They speak with management about the company's prospects, strategy, competitors, and financial statements. Information that is material to the company's prospects must be disclosed in the private placement memorandum (PPM) or IPO prospectus .


Something, or someone, lacking in intelligence, i.e., stupid. In our context, there are dumb terminals, dumb networks, dumb switches, and so on. Dumb things work, but at a very simple level and very inexpensively. Any intelligence involved in an associated process is provided by something else.

Dumb Network

A communications network that, in contrast to the public switched telephone network (PSTN), relies on information provided by the sender to route the transmission. A network in which the intelligence is located on the periphery, e.g. Ethernet.

Dumb Remote

A dumb remote is a remote physical partition of an intelligent switch, which usually is in the form of a CO (Central Office), although it also can be a PBX. The CO, for example, contains all, or most of, the intelligence and memory required to perform the call processing functions and to provide special services. The dumb remote, which may be in the form of either a dumb switch or a line shelf (i.e., line concentrator) is connected to the centralized CO by a signaling and control link over which the call processing queries and instructions are transmitted between the two devices. See also Remote Line Concentrator.

Dumb Switch

A slang word for a telecommunications switch that contains only basic switching software and relies on instructions sent it by an outside computer. Those instructions are typically fed the "dumb" switch through a cable from the computer to one or more RS-232 serial ports which the dumb switch sports. The switch makes no demands on what type of computer it talks to, but simply insists that it be able to feed the computer questions and promptly receive responses in a form that it (the switch) can understand. Plain ASCII is OK. For example, the dumb switch might signal the computer, "A call is coming in on port 23, what do I do now?" The computer might reply "Answer it and transfer it to extension 23." Or it might say "answer it and put it on hold," or "answer it, put it on hold and play it recording number three." In essence, a dumb switch is anything but. It is in reality an empty cage containing whatever network interface cards the user has chosen. Each of these network interface cards is designed to "talk" to one type of telephone line. That line might be a T-1 line. It might be a normal tip and ring loop start line. It might be a tie trunk with E&M signaling. The card may handle one or many lines, but always of the same type. The card knows how to answer a call or pulse out a call on that particular type of line. It has all the telephony smarts. What it lacks is the intelligence of what to do with the calls. That is provided by the outside computer. Well, almost. Most "dumb" switches do contain rudimentary intelligence ” a small computer and some memory. That computer is usually programmed to handle "default" calls ” and to handle calls should the link to the outside computer fail, or the outside computer itself fail. Dumb switches come in flavors all the way from residing in their own cabinet to being printed circuit cards which reside in one or more of the personal computer's slots. Dumb switches are programmed to do "specialized" telecom applications, for example emergency 911, added value 800 services, cellular switching, automatic call distributors , predictive dialers, etc. They can, of course, be programmed to be "normal" PBXs. The question increasingly being asked is "If I want to program a specialized telecom application should I use a dumb switch or should I use an open PBX?" And the answer is "It depends." Depends on what you want to do. Depends on what software is available, etc. See also OAI.

Dumb Terminal

A computer terminal with no processing or no programming capabilities. Hence, it derives all its power from the computer it is attached to ” typically over a local hardwire or a phone line. A dumb terminal does not employ a data transmission protocol and only sends or receives data one character at a time, sequentially. There are many reasons for "dumb" terminals. They're cheap. They're foolproof. Operators don't have to mess with floppy disks, etc. The require minimal training. Dumb terminals are typically used for simple data entry and data retrieval tasks . Their disadvantage is that everything must come from the central computer ” not only the information (data record) but also the form in which to put it. This has led to the creation of "intelligent" terminals, which have a modicum of capabilities ” such as an inbuilt (with software) form, some smart function keys and perhaps, a modicum of processing power, etc.

Dumb Terminal Access

An Internet Access Term. Telnet shell command that allows remote terminals to connect to a LAN host. Basic terminal server support over the same modems and phone lines used for remote access.


One who asks if the kids would care to order dessert.

Dummy Load

A dissipative impedance-matched network, used at the end of a transmission line to absorb all incident power, usually converted to heat.


To copy the entire contents of something ” memory, a file on a disk, a complete disk ” to a printer or another magnetic storage medium. A dump is often called a "core dump," which is a bigger dump than dump.

Dumpster Dipping

Same meaning as Dumpster Diving.

Dumpster Diving

Also known as Dumpster Dipping, Dumpster Diving is searching for access codes or other sensitive information in the trash. In North America, large trash receptacles ” those found outside buildings ” are often known as dumpsters. One pieced of folk lore is that Bill Gates of Microsoft fame started off as a dumpster diver . It's now against the law.


Microsoft's acronym for Dial-Up Networking. Files on PCs with the extension DUN mean that they contain instructions to dial up an ISP ” Internet Service Provider ” and get access to the Internet. Such DUN file includes the phone number to dial, the account name and the password. It should dial your PC's modem, handshake with the ISP's modem at the other end, handshake with the ISP's server as regards your user name and password and get you on the Internet.

Duobinary Signal

A pseudobinary-coded signal in which a "O" ("zero") bit is represented by a zero-level electric current or voltage; a "1" ("one") bit is represented by a positive-level current or voltage if the quality of "O" bits since the last "1" bit is even. and by a negative-level current or voltage if the quantity of "O" bits since the last "1" bit is odd. Duobinary signals require less bandwidth than NRZ. Duobinary signaling also permits addition of error-checking bits.


Similar to monopoly except there are two licensed competitors per market instead of one. The cellular business in the United States is a duopoly. Each major city in the United States has two licensed cellular providers ” a feat accomplished by the FCC. As a result, prices in most cities as between the carriers are identical.


Data User Part. Higher-layer application protocol in SS7 for the exchange of circuit switched data; not supported by ISDNs.


  1. Simultaneous two-way transmission in both directions. A data communications term.

  2. Two-sided printing.

  3. Two hard disks that have separate disk controllers and are mirror copies of each other. Data is written simultaneously to both. See Mirroring.

Duplex Cable

A two-fiber cable suitable for duplex transmission. One fiber is used for communicating one-way. The other fiber is used for communicating the other way.

Duplex Circuit

A telephone line or circuit used to transmit in both directions at the same time. Also referred to as full duplex as opposed to half duplex which allows transmission in only one direction at one time.

Duplex Operation

The simultaneous transmission and reception of signals in both directions.

Duplex Signaling

DX. A direct current signaling system that transmits signals directly on the cable pair. Duplex signaling is a facility signaling system and range extension technique that used bridge type detection of small dc changes. Duplex signaling is typically used on long metallic trunks.

Duplex Transmission

The simultaneous transmission of two series of signals by a single operating communicating device. A data communications term.


  1. A device which splits a higher speed source data stream into two separate streams for transmission over two data channels. Another duplexer at the other end puts the two slower speed streams back together into one higher-spread stream.

  2. A waveguide device designed to allow an antenna to be used both transmission and reception simultaneously.


Depressed urban professionals; former white- collar workers who are now unemployed or working for minimum wage.


The elapsed time between answer and disconnect for any given call.


A phone call or e-mail message you send to someone after a long silence ” just to "shake off the dust" and see if the connection still works.

Duty Cycle

The ratio of operating time to total elapsed time for a device that operates intermittently. Usually expressed as a percentage.


Digital Video.

DVAC line

Dedicated Voltage AC ” dedicated phone line installed by the phone company, usually for high end alarm monitoring systems and also used by some merchants for their POS systems. With an alarm system, it enables the central station to transmit a signal to the alarm panel about every 30 seconds to make sure the line has not been cut. Typically very expensive and used in high risk sites such as banks, jewelry stores, apartment building fire systems etc.


Digital Video Broadcast and Digital Audio Video Council (DAVIC) technology is the incumbent European standard for digital set-tops and is now starting to gain momentum for cable modems. The standard describes the out-of-band and in-band transmission options applicable to interactive set-top boxes and cable modems. respectively, enabling the deployment of interactive TV, data, and voice services over a common platform. DVB/DAVIC is challenging DOCSIS for dominance in Europe. DVB started in Europe in 1993 in liaison with the European Broadcasting Union (EBU), the European Telecommunications Standards Institute (ETSI) and the European Committee for Electrotechnical Standardization (CENELEC). The DVB Project is a consortium of more than 300 organizations in 57 countries round the world. In contrast to traditional government-driven regulatory activities, the DVB Project is market-driven and works to commercial terms with the aim of promoting DVB technologies through attaining economies of scale and through making its specifications and standards open and available to all. DVB uses MPEG-2 video and audio compression and though video in name, is capable of delivering any information that can be digitized, whether it is standard-definition TV (NTSC, PAL or SECAM), high-definition TV (HDTV) or broadband data and interactive services, which are supported by return channels (RC). DVB specifications and standards now are available for conventional broadcast, microwave, cable, satellite, satellite master antenna and satellite TV, as well as for satellite news gathering. Return channel specifications and standards are available for cable, Digital Enhanced Cordless Telecommunications (DECT), Local Multipoint Distribution System (LMDS), Public Switched Telephone Network (PSTN), Global System for Mobile (GSM) and satellite return paths. In 15 countries in Europe and in Australia and New Zealand, terrestrial (conventional broadcast) digital TV is based on DVB. The satellite version, DVB-S, is almost universally adopted round the world, and several international satcom systems are implementing DVB with various configurations of the return channel.


Digital Video Compression. Process by which multiple videoservices, or channels, are broadcast on one satellite transponder . Performed by turning analog audio and video into digital (computer) information for broadcasting.


Digital Video Disc. Also called Digital Versatile Disc. A DVD is a 5" diameter optical disc ” the exact same size as the common compact disc (CD) which is used for distributing software or music. The big difference is that a DVD holds 4.7 gigabytes, which is seven times as much as a CD, which holds 650 or 700 gigabytes. DVDs are standard animals these days and can played in all manner of players, including PCs. They are often called DVD-video and come with a movie on it. DVDs are following the path of CDs. First the playback variety came out. Then the record variety came out. In DVDs, the record variety takes all manner ” DVD-R, DVD-RAM, DVD-RW, DVD+RW and DVD+R. The distinctions are actually based on how the data is written to and read from the disk. In my readings I came across a excellent explanation by Honda Shing, Chief Technology Officer for InterVideo, the company that makes WinDVD, the popular software DVD player. Honda writes, "Imagine if the entire world agreed on a single language for all written documents, say English. In the United States we would continue to create English documents and books in which one reads left to right. But another country might prefer to write and read English right to left. And yet another, top to bottom, and so on until the effect became that although all documents were created in a single language, it would be very difficult for a person from one country to read a document from another country. DVD recording is in a similar state of confusion. DVD is such a new technology that these issues have yet to work themselves out, so you have no choice other than understanding them all. One easy way to think about the formats is as five completely different kinds of DVD disks.

"First, let's divide the formats up. The first thing to note is that DVD-R and DVD+R disks can only be recorded once. You only get one chance to record your DVD movie (or whatever) to this kind of disk It's like pouring cement , once it is done you'll need to destroy it to change it. Further, DVD-R discs come in two types: DVD-R(A), for "authoring," and DVDR(G), for "general." Both DVD-R and DVD+R discs will play in most DVD players, even older ones. So if you put your movie on this kind of disk there is a high probability that it will play in your living room. However, DVD-R(A) drives can not record to DVD-R(G) disks, and vice versa.

"There are also DVD formats that can be recorded more than once. DVD+RW, DVD-RW and DVD-RAM disks can all be recorded thousands of times. If you don't like how your DVD movie turns out, you can record a new version right on the same disk. These disks are more like painting a wall ” if you don't like the color you just put on a new coat. Each of these rewritable formats are a little different. DVD-RAM, for instance, was created for storage of computer data ” like backing up your hard drive. If you want to get a DVD writer to back up computer data, DVD-RAM is a solid option. However, if you plan to make your own DVD movies, one of the other formats may be better suited for that activity. Most DVD players can't play DVD-RAM disks.

"The DVD-RW and DVD+RW formats are both good for making DVD movies but are essentially engaged in a Beta versus VHS-type battle. The consumer market will ultimately determine which format wins or if they end up combining into a single standard, but it is important to understand that neither is yet a universal standard. Another thing to note is that many DVD players won't play any kind of rewritable disk. Most of the newer players will play these kinds of disks, but if you have an older DVD player it may not. In general, the newer your DVD player, the more likely it is to play all the recordable formats. There are web sites like, and that list compatible players and formats, but these are not unabridged resources either. Use them as a general guide.

"That covers the basic DVD writable formats. The last point of concern is the DVD drive itself. This is the part of your computer that will actually record your data or movie onto the DVD disc. Thankfully, if you have made it this far you are almost home. The different types of DVD drives basically break down into the same formats as the DVD writable formats. Therefore, there are DVD-RAM drives, DVD-R drives, etc. on down the line. It is also increasingly likely that DVD burners will come with the ability to record to more than one format, for example a manufacturer may offer a DVD+R/RW drive, meaning that it can record both DVD+R and DVD+RW discs. When considering DVD media (the actual silver discs) and DVD burners, make sure that both the discs and drive are the same format. Step one: Decide what you want to use your DVD burner for. If you want to back up computer data, a DVD-RAM burner is a good choice. If you want to record movies and music choose another kind of burner. Step 2: Decide where you will be watching your DVDs. If you plan to send your homemade DVD movies to friends and relatives with older DVD players, you will want to make sure you get a DVD-R or DVD+R burner . If you plan to watch your DVD movies on a computer or a newer DVD player, any format will likely do. Step 3: Match 'em up. Remember the children's clothing brand Garanimals? If a shirt had a lion on it, you had to find a pair of shorts with a lion on it. If you got a Garanimal shirt with a lion on it and shorts with a fox then they would be different sizes and would not match. DVD is the same way. You need to make sure that your DVD media and DVD drive are the same."


See DVD.


See DVD.


See DVD.


See DVD.


See DVD.


A generic term for DVD that has a movie recorded on it. The good news is that all DVD players and DVD drives can play DVD-Video. See DVD for a much fuller explanation.


Digital Video Interactive. A name for including still and moving video pictures in material shown on a PC's screen. DVI is part of multimedia. DVI is also Intel's old name for its scheme for digitizing and compressing video and audio for storage, editing, playback and integration into PC applications. The name has been replaced on the software side with Indeo video technology, on the retail side with Smart Video Recorder and on the hardware side with i750 Processors. See DIGITAL VIDEO INTERACTIVE for a much bigger explanation.


The Distance Vector Multicast Routing Protocol is used for the communication and distribution of multicast routing table information. It is based on the RIP protocol used in unicast routing.

Dvorak Keyboard

A keyboard, invented mainly by August Dvorak, on which letters and characters are arranged for faster and easier typing than on the standard QWERTY keyboard. The QWERTY keyboard was actually designed to be difficult to use, to slow down typists so they wouldn't jam the old typewriters' mechanisms! In that respect the QWERTY keyboard resembles the present touchtone in that it also was designed to be slow and difficult to use so that it wouldn't confuse the early and slow telephone central offices of the time.


Digital Video Recorder. Another name for a Personal Video Recorder. See PVR.


Digital Video Services.


Pronounced "Divitz." Stands for Desktop Video conferencing Telecommunications System.


Dense Wavelength Division Multiplexing. DWDM is the higher-capacity version of WDM (Wavelength Division Multiplexing), which is a means of increasing the capacity of fiber-optic data transmission systems through sending many wavelengths of light down a single strand of fiber. WDM systems support as many as four wavelengths. Commercially available DWDM systems support from 8 to 40 wavelengths. The capacity is steadily increasing, both by ever-expanding channel counts and faster signal rates supported by the individual wavelengths. Each wavelength operates as though it were a separate light pipe, with each currently supporting signal rates as high as OC-192 transmission (9.953 Gbps ” thousand million bits per second). Generally, existing systems make a trade-off between channel count and maximum supported rate: the current maximum channel count of 40 is limited to OC-48 rates of 2.488 Gbps, thereby yielding an aggregate signal rate on one strand of fiber of almost 100 Gbps. Systems which support higher signal rates (i.e., OC-192), support fewer than half as many channels. At OC-192, a 40-channel system would yield an incredible 400 Gbps, rounded up. While such a system is not currently available, it may not be far away. Within the next 2-3 years it is reasonable to expect to see systems supporting on the order of 100 wavelengths of OC-192 each, providing almost one terabit per second transport! In fact, the next generation of DWDM, dubbed UDWDM ( Ultra -Dense Wavelength Division Multiplexing), is planned to support as many as 400 wavelengths. The highest rate as of December, 2001 is 80 Gbps x 80 wavelengths (also called Lambdas) = 6.4 Tbps (Terra bits per sec) per a SINGLE fiber hair strand!

DWDM lately has challenged SONET/SDH as the broadband optical technique of choice in the carrier domain. SONET offers considerable advantages, including strong standards development, and very powerful network management capabilities. The criticisms of SONET include its TDM (Time Division Multiplexing) nature, which is considered inappropriate for IP (Internet Protocol) traffic; its bandwidth limitations, even at OC-768 rates of 40 Gbps; and its high level of overhead, which directly reduces user data payload, although it yields considerable network management capabilities advantages. Perhaps the greatest criticism is SONET's high cost, especially considering that an increase in bandwidth (e.g., OC-48 to OC-192) requires that the transmitting laser diode, the receiving light detector, and all intermediate optical repeaters be upgraded. DWDM, as we have discussed, is an optical transmission technique that allows multiple light signals operating at different wavelengths (i.e., frequencies of light) to share a single fiber. The aggregate bandwidth yielded can be much greater than that supported by SONET. DWDM also is far less expensive. On the downside, DWDM does not offer the same inherent network management capabilities and does not offer the same level of standards development, which translates into lack of interconnectivity and interoperability between network elements of disparate origin. Further, and as we mentioned above, each wavelength in a DWDM system is, in essence, a separate circuit. Therefore, all traffic riding over that wavelength is transported and switched as a single entity, from point of origin to point of termination. As a result, a wavelength must carry traffic of the same type (e.g., circuit-switched voice, packet voice, IP packet data, ATM, or Frame Relay), with the same QoS (Quality of Service) requirements, originating at the same place, and destined for the same place. All of that means that each wavelength must be filled to capacity, or that there must be enough available wavelengths that capacity can afford to be underutilized . The arguments over SONET vs. DWDM rage, and will continue to do so for many years. Either approach is correct, and even optimal, depending on the applications focus of a given carrier. In fact, SONET and DWDM can, and often will, coexist, with SONET-framed data riding over DWDM wavelengths. That's my view, at least. See WDM (Wavelength Division Multiplexing) for much more detailed explanation. See also SONET and WWDM.


Dots-in-a-well. A manufacturing technique used to improve performance of diode lasers, which are lasers that input information into optical networks. The simplest diode laser is a sandwich of n-type and p-type semiconductors. The areas where the n-type and p-type materials meet contain tiny wells known as "quantum wells", which are layers of semiconductor so thin that they are essentially two-dimensional. The performance of diode lasers is improved when tiny islands ("dots") of a different semiconductor are embedded into these wells. This is achieved by depositing a semiconductor on top of another semiconductor of different atomic spacing. The atoms in the two materials attempt to line up, however the top layer deforms under the strain and breaks into billions of islands, the quantum dots. The dots reduce the lasers operating current because they trap charge very effectively and make the lasers resistant to changes in temperature. Another advantage is that the dots can be tuned so that they only emit light at certain wavelengths, which can be used where optical fibers are used to carry many different channels of data at different wavelengths. See also Semiconductor, Injection Laser Diode.

Dwell Time

The period of time that a satellite is over the desired area of coverage. The term has commercial significance in LEO (Low Earth Orbiting) and MEO (Middle Earth Orbiting) satellite systems. In such systems, the individual satellites in a constellation travel in elliptical orbits, rather than in traditional geosynchronous orbits. See LEO and MEO.


Data Warehousing Institute. A Special Interest Group dedicated to "helping organizations increase their understanding and use of business intelligence by educating decision makers and I/S professionals on the proper deployment of data warehousing strategies and technologies." DWI has over 3,000 members.


See Discrete Wavelet Multi-Tone.


Dialable Wideband Service.

DX Signaling

A form of DC (direct current) signaling in which the differences in voltage on two pairs of a four-wire trunk indicates the supervision information, i.e. the call's beginning, its end, etc. See Duplex Signaling.


Digital Cross Connect. See DCS.


Data eXchange Interface. A specification developed by the SMDS (Switched Megabit (or Multi-megabit) Data Services) Interest Group to define the interaction between internetworking devices and CSUs/DSUs that are transmitting over an SMDS access line. SMDS is a way for a corporate network to dial up switched data services as fast as 45 megabits per second. The ATM Forum defines DXI as "a variable length frame-based ATM interface between a DTE and a special ATM CSU/DSU. The ATM CSU/DSU converts between the variable-length DXI frames and the fixed-length ATM cells ."

Dye Sublimation

a spectacular printing process where exactly measured temperatures control the amount of ink transferred from colored ribbons to paper. Under high temperature and pressures, the ink is not melted, but is transformed directly to gas, which hardens on the paper after passing through a porous coating. Dye sub printers create very nearly continuous tones, making them great for natural images. Because the gas makes "fuzzy" dots, dye sub is not recommended for sharp-edged "computer-y" graphics or type. But it does turn out gorgeous photo-like images.


In English, dynamic means that things are changing. In telecomese, it tends to mean that our equipment ” hardware and/or software ” can respond instantly to changes as they occur. For example, dynamic routing in the call center world means that we can switch incoming calls from moment to moment. We may want to do this because we want calls from the east to go to our call center in the east when our eastern call center is busy. So we may want to flip the calls over to our northern call center when both our eastern and western call centers are busy. You get the idea.

Dynamic Adaptive Routing

See Dynamic Routing.

Dynamic Address Mapping Service

A service which provides a lookup function between text-based strings and IP addresses and/or telephone numbers, in which the result of the lookup can change relatively quickly over time (hence the use of the word "dynamic.")

Dynamic Answer

This a term typically used in Automatic Call Distributors. The ability to dynamically assign the number of ring cycles (interrupt, more or less) to the queue period when agents are unavailable. The implication of being able to assign this number allows return supervision to the calling in person to be delayed and thus not allow billing on 800 INWATS lines to begin. This is a money saving feature. But it can cost you some customers if they get bored waiting for your phones to pick up.

Dynamic Backup

A backup made while the database is active.

Dynamic Bandwidth Allocation

The capability of subdividing large, high- capacity network transmission resources among multiple applications almost instantaneously, and providing each application with only that share of the bandwidth that the application needs at that moment. Dynamic bandwidth allocation is a feature available on certain high-end T-1 multiplexers that allows the total bit rate of the multiplexer's circuits to exceed the bandwidth of the network trunk. This works because the multiplexer only assigns channels on the network trunk to circuits that are transmitting.

Dynamic Beam Focusing

When you have a curved cathode ray tube, the distance between the gun which shoots the electrons and all the parts of the screen are equal. When you have a flat screen, the distance varies slightly. Some beams have to travel further. When some have to travel not so far, Dynamic beam focusing, a term I first heard used by NEC, focuses each electron to the precise distance it must travel, thus ensuring edge-to-edge clarity on the screen.

Dynamic Binding

Binding is converting symbolic addresses in the program to storage- related addresses. Dynamic binding occurs during program execution. The term often refers to object-oriented applications that determine, during run time, which software routines to call for particular data objects. Also called Late Binding.

Dynamic Capacity Allocation

The process of determining and changing the amount of shared communications capacity assigned to nodes in the network based on current need.

Dynamic Configuration Registry

A part of Chicago (Windows 4.0) which contains a list of all the various hardware bits and pieces that make up your computer. The dynamic configuration registry is a vital element of what Microsoft calls "Plug and Play," which is the ability to remove and add bits and pieces of hardware while the machine is running and have the machine automatically recognize those hardwares and alert applications accordingly .

Dynamic Data Exchange

DDE. A form of InterProcess Communication (IPC) in Microsoft Windows and OS/2. When two or more programs that support DDE are running simultaneously, they can exchange information, data and commands. In Windows 3.xx this capability is enhanced with Object Linking and Embedding (OLE). See OLE.

Dynamic Frequency Selection.

DFS. See 801.11a.

Dynamic Gain Equalizer

Erbium doped fiber amplifiers (EDFAs) are one of the critical enablers of dense wavelength division multiplexing (DWDM). However, EDFAs have a gain that varies across the wavelength spectrum, creating a problem in cascaded amplifier systems. If the gain varies by 1 dB between the best and worst DWDM channels and there are 10 amplifiers in a link, then the signals will vary by 10 dB by the end of the transmission line. Since the signal-to-noise performance depends on the received power, the worst channel will have much poorer transmission quality than the best channel. To avoid this problem, it is important to make the gain constant across the wavelength spectrum of the EDFA, i.e. to flatten the gain. Static approaches, such as pre-emphasis and gain flattening filters, exist to flatten the output of an EDFA. However, static approaches cannot respond to variations in the EDFA gain due to changes in channel usage, changing traffic patterns, amplifier aging or to the power transfer due to stimulated Raman scattering. These varying power differences again limit the signal-to-noise ratio that can be achieved at the receiver. Dynamic gain equalizers (DGEs), also called dynamic gain flattening filters (DGFFs), are use to control the EDFA gain even when faced with varying amplifier gain effects. By dynamically adjusting the amplifier gain, the total gain error function can be reduced, enabling new extended-reach and ultra-long-haul DWDM systems.

Commercial dynamic gain equalizer products are available based on planar lightwave circuits, MEMS, liquid crystal, and acousto-optic technology. Key parameters on the filtering performance of the device include the insertion loss, polarization dependent loss, dynamic range, residual gain ripple and spectral response function. The control algorithm is also critical for a dynamic device, and can affect the overall response time and iterations required to achieve the desired gain flattening.

While there are multiple technologies of dynamic gain equalizers, there are two main approached used for DGEs. The first approach creates a dynamic spectral response by controlling the amplitude of multiple sinusoidal filters with differing periods. The number of Fourier elements or stages used in the device determines the resolution of the DGE and the residual gain ripple. The acousto-optic effect, either in a bulk crystal or directly in the fiber, liquid crystals and lattice-filter planar lightwave circuits all employ this approach to create the controllable response filter. With the Fourier filter approach, the control algorithm often uses a convergence method, iterating the response multiple times to arrive at the minimum error function.

The second approach with a much more predictive control algorithm is based on slicing the spectrum and controlling individual elements. These approaches employ a demultiplexing element to provide the spectral slices with the control provided by micro-electro-mechanical systems (MEMS) or thermo-optic planar circuits. To obtain a continuous response function, the filtering element can be placed inside an interferometer, where the phase of the signal rather than the amplitude in controlled. The phase control creates attenuation when combined with the unaltered path in the interferometer.

Dynamic Gain Flattening Filters

DGFFs. See Dynamic Gain Equalizer.

Dynamic Host Configuration Protocol

DHCP. A protocol for automatic TCP/IP configuration that provides static and dynamic address allocation and management. See DHCP for a much longer explanation.

Dynamic HTML

Dynamic HTML combines HTML, scripts and style sheets to bring animation to the Web. With Dynamic HTML, you can program your Web site such that a visitor surfing it alights on a button or some object and instantly a "help" or "explanation" balloon pops up. This balloon explains in greater detail what will happen if the visitor clicks on the button. Or the type may change and suddenly become bigger. Dynamic HTML is being incorporated into both Netscape and Microsoft Internet Explorer. The World Wide Web Consortium is considering the various flavors of dynamic HTML as part of its DOM (Document Object Model) specification. See also

Dynamic IP Addressing

The Internet has an address for every "thing" attached to it at that very moment. That 'thing" might be your browser-equipped tiny PC, or it might be a gigantic web site server with thousands of people grabbing files off it. That address is in a standard form and is called an IP (Internet Protocol) address. It is in the following form: You need an IP address so the Internet can route files, emails and messages back and forth to your PC. There are two types of IP addresses ” static and dynamic. Static is an address you have all the time. If you're on a corporate network, you'll have a static address. If you are behind a hardware firewall, you'll have a static address. A dynamic address is one that changes every time you connect to the Internet. For example, you might connect to the Internet, you might be assigned this address: Next time you connect that might be changed to Those numbers are real. They're actually numbers I was assigned when I connected on two occasions one after another. The reason for dynamic addresses is that it things easier for users and for ISPs ” Internet Service Providers. ISPs, for example have a limited number of addresses they can assign to their users. So they assign them on the fly ” the essence of dynamic IP addressing. Virtually all the 500 or so million people who regularly surf the Internet do so through dynamic IP addressing. See Dynamic IP Addressing Allocation.

Dynamic IP Address Allocation

Allows a user to be assigned an IP address which is selected on the fly from a list of available addresses. See Dynamic Host Configuration Protocol (DHCP) and IP Network Control Protocol (IPCP). See also Dynamic IP Addressing.

Dynamic Link Library

DLL. An executable code module for Microsoft Windows that can be loaded on demand and linked at run time, and then unloaded when the code is no longer needed.

Dynamic Load & Stress Testing

An advanced and accurate form of load testing, dynamic load and stress testing more accurately presents the variety of stimulus of external callers , systems and networks to a computer telephony system. It will test your system using real-world user actions and a realistic call mix and busy hour usage profile. Most modern computer telephony network and systems provide a number of services to their users. Each of those services may stress the system in a different fashion. As the usage patterns of those users is varied and what each user will do can vary significantly, it is critical to load test systems with traffic patterns as dynamically and as close as possible to the way the system will be used in the real world. This definition courtesy of Steve Gladstone, author of the book Testing Computer Telephony Systems, available from 212-691-8215.

Dynamic Load Balancing

A technique where a switching system, particularly multiple connected ACDs, apportion incoming calls (the load) to balance the workload. This is done dynamically in real time.

Dynamic Loud Speaker

A loud speaker in which the diaphragm is driven by means of a small "voice coil" suspended in a powerful magnetic field.

Dynamic Memory

The most common form of memory, used for RAM, with an access speed ranging from about 60 to 150 nanoseconds. (A nanosecond is a billionth of a second.) Dynamic memory is an inexpensive but relatively complicated form of semiconductor memory with two states: presence and absence of electrical charge. Dynamic memory requires a continuous electrical current. All data is lost when the power is cut. Frequent saving files to disk helps preserve your data.

Dynamic Microphone

A microphone, the coil of which is moved in a strong magnetic field by vibrations striking the diaphragm to which it is attached. Electrical currents are thus generated in the moving coil.

Dynamic Node Access

A high-speed bus invented by Dialogic to join together multiple voice processing PEB-based systems. PEB stands for PCM Expansion Bus. See PEB.

Dynamic Overload Control

DOC. The feature of a switch which uses its translation tables and intelligence to allow the switch to adapt to changes in traffic loads by rerouting and blocking call attempts.

Dynamic Page Assembly

You visit a web site. It knows who you are because of your cookie. It makes a web page just for you ”knowing your likes and dislikes. Also known as User Personalization.

Dynamic Path

Fibre Channel term. A communication path in which any node can communicate with any other node ( assuming no third node is already communicating with the target). See Permanent Path.

Dynamic Port Allocation

In a voice processing system running multiple applications, dynamic port allocation is automatic allocation of ports based on the traffic being used by each application.

Dynamic RAM

RAM memory that requires data to be refreshed periodically to prevent its loss in memory.

Dynamic Random Access Memory

RAM which requires electronic refresh cycles every few milliseconds to preserve its data. See also Random Access Memory.

Dynamic Range

In a transmission system, the ratio of the overload level to the noise level of the system, usually expressed in decibels. The ratio of the specified maximum level of a parameter (e.g., power, voltage, frequency, or floating point number representation) to its minimum detectable or positive value, usually expressed in decibels.

Dynamic Resource Allocation

The assignment of network capacity to specific users and specific services as required on a moment-to-moment basis.

Dynamic Routing

Routing that adjusts automatically to changes in network topology or traffic. Dynamic routing automatically accomplishes load balancing, therefore optimizing the performance of the network "on the fly." Static routing, on the other hand, involves the selection of a route for data traffic on the basis of predetermined routing options preset by the network administrator. Dynamic routing is more effective, but the routers are more costly and the more complex decision-making process imposes additional delays on the subject packet traffic. See also Router.

Dynamic Storage Allocation

The allocation of memory space while a program is running. The memory is released when the program is complete.

Dynamic Synchronous Transfer Mode

See DTM.

Dynamic Variation

A short time variation outside of steady-state conditions in the characteristics of power delivered to communication equipment.

Dynamically Adaptive Routing

An algorithm, used for route determination in packet-switched networks that automatically routes traffic around congested , damaged, or destroyed switches and trunks and allows the system to continue to function over the remaining portions of the network.

Dynamically Assigned IP Address

See IP Addressing.


An electrical machine which generates a direct current.


A direct current machine having two windings on its armature: one acting as a motor, the other as a generator.

Newton[ap]s Telecom Dictionary
Newton[ap]s Telecom Dictionary
ISBN: 979387345
Year: 2004
Pages: 133 © 2008-2017.
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