distributorIn data transmission, a device that accepts a data stream from one line and places a sequence of signals, one or more at a time, on several lines, thus…
disturbance voltageAn unwanted voltage induced in a system by natural or man-made sources. Note: In telecommunications systems, the disturbance voltage creates currents that…
DitheringIn printing, dithering is usually called halftoning, and shades of gray are called halftones.
diurnal phase shiftThe phase shift of electromagnetic signals associated with daily changes in the ionosphere.
divergenceThe expansion or spreading out of a vector field; usually said of horizontal winds. It is the opposite of convergence.
DiversityThe distribution and abundance of different plants and animals within an area.
diversity combinerA circuit or device for combining two or more signals carrying the same information received via separate paths or channels with the objective of…
Diversity FactorThe ratio of the sum of the noncoincidental maximum demands of two or more loads to their coincidental maximum demands for the same period.
diversity gainIn radio communications, the ratio of the signal field strength obtained by diversity combining to the signal strength obtained by a single path.
diversity receptionRadio reception in which a resultant signal is obtained by combining or selecting signals, from two or more independent sources, that have been modulated…
diversity transmissionRadio communication using a reception technique in which a resultant signal is obtained by combining signals (a) that originate from two or more…
divestitureThe court-ordered separation of the Bell Operating Telephone Companies from AT&T.
DODesignated Office the national Office or intergovernmental organization of or acting for the Contracting State designated by the applicant under Chapter I…
DOD master clockThe master clock to which time and frequency measurements for the U.S. Department of Defense are referenced, i.e., are traceable. Note 1: The U.S.
DomainA sub-network of servers and computers within a LAN. Domain information is useful when restoring backup tapes, particularly of email.
domain nameThe conventional Internet name for a network or computer system, which name consists of a sequence of two or more groups of characters separated by…
Domain Name Server (DNS)A Domain Name Server is a computer designated to holding a list of domain names and their corresponding IP addresses.
domain name service (DNS)A service to map fully qualified domain names to IP addresses and vice versa. [2382-pt.35]
Domain Name System (DNS)(DNS)Hierarchical distributed database used for name/address translation and client-server rendezvous.
domestic fixed public serviceA fixed service, the stations of which are open to public correspondence, for radiocommunications originating and terminating solely at points all of…
domestic public radio servicesThe land mobile and domestic fixed public services, the stations of which are open to public correspondence. [47CFR]
dominant modeIn a waveguide that can support more than one propagation mode, the mode that propagates with the minimum degradation, i.e.
Dominate1. An implementation-defined relation between the values of MAC labels or Information Labels which satisfies partial order algebraic property [POSIX.6]. 2.
DonorIn a solar photovoltaic device, an n-type dopant, such as phosphorus, that puts an additional electron into an energy level very near the conduction band…
DopantA chemical element (impurity) added in small amounts to an otherwise pure semiconductor material to modify the electrical properties of the material.
Doppler Effectapparent change in frequency of a wave due to the relative motion of the source and observer.
doppler shiftThe degree of observed change in frequency (or wavelength) of a wave due to the doppler effect.
Dot PitchDistance of one pixel in a CRT to the next pixel on the vertical plane. The smaller the number, the higher quality display.
dotted decimal notationThe notation used to represent the four byte values of an IP address. Each byte is represented as a value between 0 and 255, for instance 129.12.0.1.
double length keyA cryptographic key having a length of 112 bits plus 16 parity bits. [After X9.24]
double modulationModulation in which (a) a subcarrier is modulated with an information-bearing signal and (b) the resulting modulated subcarrier is then used to modulate…
double resolution still imageA still image transmitted in the standardized video stream encoded to twice the horizontal and twice the vertical resolution as the previous motion video…
double-ended queue (dequeue)A queue in which the contents may be changed by adding or removing items at either end.
double-ended synchronizationFor two connected exchanges in a communications network, a synchronization control scheme in which the phase error signals used to control the clock at…
double-frequency shift keying (DFSK)Frequency-shift keying in which two telegraph signals are multiplexed and transmitted simultaneously by frequency shifting among four frequencies.
doubly clad fiberA single-mode fiber that has two claddings. Note 1: Each cladding has a refractive index that is lower than that of the core.
down-converterA device for performing frequency translation in such a manner that the output frequencies are lower in the spectrum than the input frequencies.
Downgrade1. Change the security class of an object to one which does not dominate the original [CESG]. 2.
downlink1. A data link from a satellite or other spacecraft to a terrestrial terminal. 2. A data link from an airborne platform to a ground-based terminal.
downloadTo transfer a copy of a file residing on a remote computer to a user's computer.
downstreamThe region extending in a 3' direction from a gene.
downtimeThe interval during which a functional unit is inoperable.
DPCMAbbreviation for differential pulse-code modulation.
DPSKAbbreviation for differential phase-shift keying.
draggingThe act of modifying all or part of the display on a monitor by selecting some object and moving the pointing device such that the displayed object moves…
drop and insertIn a multichannel transmission system, a process that diverts (drops) a portion of the multiplexed aggregate signal at an intermediate point, and…
drop channel operationOperation in which one or more channels of a multichannel system are terminated, i.e.
drop repeaterIn a multichannel communications system, a repeater that has the necessary equipment for the local termination, i.e.
DropoutBrief signal loss caused by a tape head clog, defect in the tape, debris, or other feature that causes an increase in the head-to-tape spacing.
drum factorIn facsimile systems in which drums are used, the ratio of drum length to drum diameter. 2.
drum speedIn facsimile systems, the rotation rate of the facsimile transmitter or recorder drum. Note: Drum speed is usually expressed in revolutions per minute.
DTE clear signalA call control signal sent by data terminal equipment (DTE) to initiate clearing.
DTE waiting signalA call control signal, sent by the data-circuit-terminating-equipment/data-terminal-equipment (DCE/DTE) interface, that indicates that the DTE is waiting…
DTMFData Tone Multiple Frequency ( TelComm /Computer term).
dual accessThe connection of a user to two switching centers by separate access lines using a single message routing indicator or telephone number. 2.
dual busA pair of parallel buses arranged such that the direction of data flow in one bus is opposite to the direction of data flow in the other bus.
dual controlIn security systems, a process of using two or more separate individuals (or entities), operating together (but with split knowledge) to protect sensitive…
dual diversityThe simultaneous combining of (or selection from) two independently fading signals, so that the resultant signal can be detected through the use of space…
dual homingThe connection of a terminal so that it is served by either of two switching centers.
dual in-line package (DIP)An electronic package with a rectangular housing and a row of pins along each of two opposite sides.
dual seizureThe condition that occurs when, in both-way operation, two exchanges attempt to seize the same circuit at approximately the same time. [T1.