digital subscriber line (DSL)In Integrated Services Digital Networks (ISDN), equipment that provides full-duplex service on a single twisted metallic pair at a rate sufficient to…
digital switchA switch that performs time-division-multiplexed switching of digitized signals.
digital switchingSwitching in which digitized signals are switched without converting them to or from analog signals.
digital synchronizationSynchronization based on the start of a transmitted digital data unit, such as a bit, character, block, or frame.
Digital Television (DTV)Any technology, using any of several digital encoding schemes, used in connection with the transmission and reception of television signals.
digital test access unit (DTAU)A generic term for the functions associated with accessing one or more channels within a digital signal for the purpose of testing.
digital transmission groupA group of digitized voice or data channels or both with bit streams that are combined into a single digital bit stream for transmission over…
digital transmission systemA transmission system in which (a) all circuits carry digital signals and (b) the signals are combined into one or more serial bit streams that include…
digital videoA video (television) signal represented by computer-readable binary numbers that describe luminance levels as well as a finite set of colors.
digital voice transmissionTransmission of analog voice signals that have been converted into digital signals.
digital watermarkAn identification code or bit pattern integrated into multimedia data that aids copyright owners in identifying illegally distributed audio, video, or…
digital-to-analog (D-A) converterA device that converts a digital input signal to an analog output signal carrying equivalent information.
digitizeThe process of converting an analog value into a digital (numeric) representation.
digitizerDevice that converts analog information into a digital format; for flat graphic material, such as maps, a digitizer can either be flatbed or scanning.
digitizer tabletA graphics drawing tablet used with a puck or stylus.
digroupAbbreviation for digital group. In telephony, a basic digital multiplexing group.
DINAbbreviation for Deutsches Institut für Normung.
DipThe angle that a planar geologic surface, for example, a fault, is inclined from the horizontal.
DIP switchA group of subminiature switches mounted in a package compatible with standard integrated-circuit sockets.
diplex operationThe sharing of one common element, such as a single antenna or channel, for transmission or reception of two simultaneous, independent signals on two…
diplexerA three-port frequency-dependent device that may be used as a separator or a combiner of signals.
dipole antennaUsually a straight, center-fed, one-half wavelength antenna.
dipulse codingThe coding of "1's" and "0's" in a message in which one full cycle of a square wave, i.e.
direct accessThe ability of an electric power consumer to purchase electricity from a supplier of their choice without being physically inhibited by the owner of the…
direct addressIn computing, an address that designates the storage location of an item of data to be treated as an operand.
direct bondAn electrical connection using continuous metal-to-metal contact between the members being joined.
Direct Broadcast Satellite (DBS/DISH)A high-powered satellite that transmits or retransmits signals which are intended for direct reception by the public.
direct callA facility-handled call in which the network interprets the call request signal as an instruction to establish a connection based on previously designated…
direct connect1. In computer systems, a permanent communications link that connects directly to a mainframe computer through a terminal controller, usually at binary…
direct current signaling (DX signaling)In telephony, a method whereby the signaling circuit E & M leads use the same cable pair(s) as the voice circuit and no filter is required to separate the…
direct dialing serviceA service feature that permits a user to place information concerning credit card calls, collect calls, and special billing calls into the public…
direct distance dialing (DDD)A network-provided service feature in which a call originator may, without operator assistance, call any other user outside the local calling area.
direct inward dialing (DID)A service feature that allows inward-directed calls to a PBX to reach a specific PBX extension without human intervention. Synonym network inward dialing.
direct orbitFor a satellite orbiting the Earth, an orbit in which the projection of the satellite on the equatorial plane revolves about the Earth in the same…
direct outward dialing (DOD)An automated PBX service feature that provides for outgoing calls to be dialed directly from the user terminal. Synonym network outward dialing.
direct rayA ray of electromagnetic radiation that follows the path of least possible propagation time between transmitting and receiving antennas.
direct recordingIn facsimile systems, recording in which a visible record is produced, without subsequent processing, in response to received signals.
direct-buried cableA communication cable manufactured or produced for the purpose of burial in direct contact with the earth.
direct-sequence modulationIn spread-spectrum systems, modulation in which a sequence of binary pulses is used directly to modulate a carrier, usually by phase-shift keying.
direct-sequence spread spectrum1. A system (a) for generating spread-spectrum transmissions by phase-modulating a sine wave pseudorandomly with a continuous string of pseudonoise code…
directed broadcast addressAn Internet Protocol address that specifies "all hosts" on a specified network.
directed netA radio net in which no station other than the net control station may communicate with any other station without first obtaining permission from the net…
direction findingA procedure for obtaining bearings of radio frequency emitters by using a highly directional antenna and a display unit on an intercept receiver or…
direction of scanningIn a facsimile transmitting apparatus, the scanning of the plane (developed in the case of a drum transmitter) of the message surface along lines running…
directional antennaAn antenna in which the radiation pattern is not omnidirectional, i.e., a nonisotropic antenna.
directional couplerA transmission coupling device for separately sampling (through a known coupling loss) either the forward (incident) or the backward (reflected) wave in a…
directionalizationThe temporary conversion of a portion or all of a two-way trunk group to one-way trunks favoring traffic flowing away from a congested switch.
directive gainOf an antenna, the ratio of (a) 4 times the radiance, i.e., power radiated per unit solid angle (watts per steradian), in a given direction to (b) the…
directory access protocol (DAP)A directory protocol that defines the exchange of requests and outcomes between user and system. [T1.667-1999]
Directory Assistance (DA)A service providing the requested telephone number for a given name and address.
Directory Assistance Call Completion (DACC)After the telephone number has been received, DACC is a service that permits a call to be completed to the requested number, typically at the calling…
directory numberA network (sub)address (from a telephone user perspective) such as the telephone number in the telecommunication network.
directory server (DS)A unit consisting of a DSA (directory system agent) and possibly other application processes (such as registration management) to provide the directory…
directory system agent (DSA)The software that provides the X.500 directory service for a portion of the directory information base.
directory user agent (DUA)The software that accesses the X.500 directory service on behalf of the directory user.
DisabledWhen applied to privilege: a privilege that is inactive, i.e., has its effective flag cleared [POSIX.6].
disabling toneA tone, transmitted over a communications path, used to control equipment. Note: An example of a disabling tone is a tone that places an echo suppressor…
disaster recovery planA written and approved course of action to take after a disaster strikes that details how an organization will restore critical business functions and…
disciplined developmentDevelopment of a system or part of a system where the documentation and evidence of testing against the documentation is to normal industry standards.
disclosureA disclosure document explains how a financial product or offering works. It also details the terms to which you must agree in order to buy it or use it…
disconnectIn telephony, the disassociation or release of a switched circuit between two stations.
disconnect command (DISC)In Link-Layer protocols, such as high-level data link control (HDLC), synchronous data link control (SDLC), and advanced data communication control…
disconnect signalIn a switched telephone network, a supervisory signal transmitted from one end of a user line or trunk to indicate at the other end that the established…
disconnect switchIn a power system, a switch used for closing, opening, or changing the connections in a circuit or system or for purposes of isolation.
disconnect timingThe timing of the period during which a hang-up signal is being received from the called end office and an off-hook signal is being received from the…
disconnect-control officeThe switching entity that performs disconnect timing and that decides when the connection is to be cleared.
discretionary access control (DAC)1. [A] means of restricting access to objects based on the identity and need-to-know of users and/or groups to which the object belongs.
discriminatorThe part of an FM receiver that extracts the desired signal from an incoming FM wave by changing frequency variations into amplitude variations.
discussion threadIn a discussion board or Web discussions, a series of messages or comments in which replies to a message or comment are nested directly under it, instead…
disengagement attemptAn attempt to terminate a telecommunications system access. Note: Disengagement attempts may be initiated by a user or the telecommunications system.
disengagement denialAfter a disengagement attempt, a failure to terminate the telecommunications system access.
disengagement failureFailure of a disengagement attempt to return a communication system to the idle state, for a given user, within a specified maximum disengagement time.
disengagement originatorThe user or functional unit that initiates a disengagement attempt. Note 1: A disengagement originator may be the originating user, the destination user…
disengagement phaseIn an information transfer transaction, the phase during which successful disengagement occurs.
disengagement requestA control or overhead signal issued by a disengagement originator for the purpose of initiating a disengagement attempt.
disengagement timeThe average value of elapsed time between the start of a disengagement attempt for a particular source or destination user and the successful…
disengagement-denial probabilityThe ratio of disengagement attempts that result in disengagement denial to the total disengagement attempts counted during a measurement period.
disk packAn assembly of magnetic disks that can be removed as a whole from a disk drive together with a container from which the assembly must be separated when…
disketteAn inexpensive, low-capacity storage medium, usually measuring 3.5 inches in diameter, often referred to as a floppy disk.
disparityIn pulse-code modulation (PCM), the digital sum, i.e., the algebraic sum, of a set of signal elements.
DispersionDistortion of the shape of a seismic-wave train because of variation of velocity with frequency.
dispersion-limited operationOperation of a communications link in which signal waveform degradation attributable to the dispersive effects of the communications medium is the…
dispersion-shifted fiberA single-mode optical fiber that has its minimum-dispersion wavelength shifted, by the addition of dopants, toward its minimum-loss wavelength.