daisy-chaining - A physical topology for wiring devices in sequence.

dark fiber - An optical fiber strand that is not in use and may or may not be terminated.

data - Electronically encoded information. (TIA)

data center - A building or portion of a building whose primary function is to house a computer room and its support areas.

data communication - The transmission and reception of electronically coded information.

data compression - Enables devices to transmit or store the same amount of data in fewer bits.

Data Encryption Standard (DES) - Uses 40 and 56 bit keys to encrypt text into 64 bit blocks. (ANSI)

datafill - Contents of the fields and tables in the system software load that determine the operational configuration.

datagram - A piece of message sent over a packet switching network containing the address.

datagram service - A network on which the delivery of messages is not guaranteed; rather, messages are delivered on a best-effort basis.

data integrity - 1. The assurance that a given data retains its original meaning and value and has not been corrupted. 2. The degree in which a collection of data is complete, consistent, and accurate. (IEEE)

Data Link layer - The Open Systems Interconnection Reference Model layer responsible for providing reliable data transfer in the form of frames on a LAN. Also called Layer 2.

Data Link layer address - See medium access control (MAC) address.

data network - An interconnected system of computers, peripherals, and software over which commands, files, and messages are sent and received.

data protection - Techniques used to guard the confidentiality, integrity, and availability of data.

data rate - The number of bits of information transmitted per second.

data service unit (DSU) - A customer premises device that frames and channelizes the user's data for transmission on the digital network.

data terminal equipment (DTE) - 1. The term used in the IEEE 802.3 standard to refer to a station (computer) or port that serves as the data transmission source, data transmission destination, or both, for the purpose of sending or receiving data over the network. 2. A device producing data to be transmitted across an intemetwork.

data transfer rate - The rate at which information is transferred between network devices over a communications channel. Also called throughput or operating speed.

data vaulting - The process of storing a backup of organizational data at a different geographic location than the original. This location should be where it can be protected from hardware failure, theft, fire, and other similar threats.

DB## connector - A connector widely used for connections between data equipment, available in a variety of configurations (e.g., DB15, DB25). Also called a D-subminiature connector.

dB(A) - Decibels (dB) above reference noise, adjusted for frequency (with F1A weighting). Adjusted reference noise is equivalent to a 1004 hertz (Hz) test tone at --85 dBm.

dBi - Decibel levels referenced to a theoretical isotropic antenna. Used to express antenna gain.

dBm - 1. Decibel referenced to 1 milliwatt (mW); 0 dBm is equal to 1 mW; -10 dBm corresponds to 0.1 mW; -20 dBm corresponds to 0.01 mW; -30 dBm corresponds to 0.001 mW. 2. Psophometrically weighted noise power in decibels, with respect to a power level equivalent to an 800 Hz test tone at 0 dBm.

DBmOp - Psophometrically weighted noise power in decibels, with respect to a power level equivalent to an 800 Hz test tone at 0 dBm.

dBmV - Decibel referenced to 1 millivolt often used in cable antenna television installations across 75 ohms.

dBrnc - Decibels above reference noise (with C-message weighting). Reference noise is equivalent to a 1004 Hz test tone at-90 dBm.

dBu - Decibel referenced to 0.775 volt (V); 0 dBu is equal to 0.775 V (rms).

dBV - Decibel referenced to 1 volt (V); 0 dBV is equal to 1 V (rms).

deadbolt - A bolt operated manually and nonactuated by springs. When locked, the bolt cannot be forced back. A deadbolt is operated (projected and retracted) by a key cylinder or lever handle.

deadend - Guying placed at the end of a pole line run or at corners.

dead latch - A latch in which the latch bolt is positively held in the projected position by an auxiliary mechanism.

dead zone - The distance on a length of optical fiber following a Fresnel reflection (event) in which an optical time domain reflectometer cannot detect additional events.

decibel (dB) - A logarithmic unit for measuring the relative voltage, power (in watts) or strength (in voltage or current) of a signal. A decibel is one tenth of a bel. See also bel.

dedicated in-floor service fitting - See insert.

dedicated LAN - A network on which a separate communications channel is assigned exclusively to each device by using switching technologies.

de facto standard - An informal standard resulting from popular acceptance of a product or practice.

degradation - The decline in operational performance.

de jure standard - A standard formally documented by a committee responsible for establishing its specifications.

delay on break - A term used to describe a mode of operation relative to timing devices. The delay begins when the initiate switch is opened (delay break of initiate switch).

delay on energization - A term used to describe when the initiate switch is closed for application of power to the input.

delay skew - The difference,in propagation delay between the pair with the highest and the pair with the lowest propagation delay value within the same cable sheath.

delay spread - The standard deviation of the delay of reflections of a radio frequency wave that is weighted proportional to the energy in the reflected waves.

delayed egress - A delayed egress device allows a 15 second delay in opening a door required by building code to be equipped with panic or fire exit hardware.

delta (delta-connected) power system - A power system having none of the normal current-carrying conductors connected to ground.

delta power supply - A three-phase system with no grounded conductor connection.

demand priority - An arbitration scheme that provides network access on the basis of the priority level of the message or sending device.

demarcation point (DP) - 1. A point where the operational control or ownership changes. (TIA) 2. The point of interface between service providers and customer facilities.

demilitarized zone (DMZ) - network lobby network.

demodulation - The recovery of information from a modulated carrier of a signal having substantially the same characteristics as the original information.

demodulator - An electronic device that information from a modulated removes signal.

demultiplexer (DP) - A device that separates two or more signals that have been combined into a multiplexed signal.

demultiplexing - The process of reconstituting the individual channels from the composite signal.

depressed-clad - An optical fiber, usually singlemode, that has double cladding, with the outer cladding having a refractive index ratio between that of the inner cladding and the core. This reduces macrobending losses and provides lower dispersion over a wider wavelength range. Also called a dual clad.

design development (DD) - A design phase that follows a schematic design and is prior to construction documents.

design drawing - Graphical and textual information organized on a two-dimensional surface for the purpose of conveying data about a specific portion of a project. (Construction Specifications Institute, Uniform Drawing System, 1997)

design manual - A collection of guidelines, requirements, and accepted practices intended to cover design, installation, and administration of systems that fall within a defined scope.

design specification - Documentation that defines a goal or set of goals including specific performance and design parameters.

designation strip - Label that may be color coded, placed on terminal blocks, and used for identification (e.g., circuits).

design-build construction - A method of construction when a contractor is employed to both design and build a project.

despread - The process of filtering out or shrinking a digitally coded signal to its original form in the direct sequence (pseudo-noise) technology.

detail drawing - A detailed graphical representation of a specific area or element of construction, often not drawn to scale.

detector (optical) - An optoelectronic transducer that converts light to an electrical signal.

Deutsche Industries Norm (DIN) - The German Institute for Standardization is a registered association recognized by the German government as the national standards body and represents German interests at international and European level standards forums.

device (protection) - A protector, protector mount, protector unit, or protector module.

device (work area) - A telephone, personal computer, graphic or video terminal, or building automatic control.

device address - An address to uniquely identify each device on a network. The address is coded in the physical hardware. See also network address and medium access control (MAC) address.

device box - See outlet box (telecommunications).

dialer - 1. Software used by remote stations to connect to the network over telecommunications circuits. Also called remote client software. 2. A standalone device used with alarm systems to dial-out to a central monitoring station.

dibit (data transmission) - Two bits; two binary digits. (IEEE)

digital - See digital signal.

die - A steel block or plate with small conical holes through which wire is drawn.

dielectric - A material that is nonmetallic and noncenductive used to insulate a conductor.

dielectric cable - A nonconducting cable (e.g., optical fiber cable with no metallic members).

dielectric constant - A unit of relative electric permittivity of an insulator.

differential-mode (DM) circuit - The closed circuit for the intended signal current.

differential-mode (DM) voltage - The symmetrical noise voltage that appears equally and in opposite phase in each active signal-carrying conductor. Contrast with common-mode voltage.

diffraction - The bending of radio, sound, or lightwaves around an object, barrier, or aperture edge.

digital alarm communicator system (DACS) (dialer) - A system in which signals are transmitted from a digital alarm communicator transmitter (DACT) located at the protected premises through the public switched telephone network to a digital alarm communicator receiver so that it may seize the line to which it is connected. The seizure disconnects any private telephone equipment beyond the DACT's point of connection.

digital certificate - A security tool used to authenticate a message. It ensures the recipient that the message originated from a source whose identity has been verified by the issuer of the certificate.

digital color code (DCC) - A specific code used to identify analog cell sites. (Nortel)

digital enhanced cordless telecommunications (DECT) - A standard developed by the European Telecommunication Standards Institute. DECT defines the radio connection between two points and can be used for remote access to public and private networks.

digital input (DI) - The input to a device that receives a digital signal from an output device.

digital key - A bit sequence used by a security tool to encrypt a message prior to transmission to keep its contents confidential and used by the recipient to restore the encrypted message. See also key.

digital output (DO) - The output of a device that sends a digital signal to an input device.

digital signal - A signal that encodes information in the form of a sequence of discrete states. For example, a binary signal uses two states to encode the two states (0,1). Contrast with analog signal.

digital signature - A bit sequence used by a security tool to authenticate a message. It ensures the recipient that the message was not modified after being transmitted by the sender.

digital subscriber line (xDSL) - A family of digital technologies designed to provide a variety of data transfer rates using different encoding and delivery methods. See also asymmetric digital subscriber line.

diplexer - A three-port frequency-dependent device that may be used as a separator or a combiner of signals. Duplex transmission through a diplexer is not possible. (ATIS)

diplexing - Diplexing is combining the output of two or more transmitters into a single antenna system or the reception of two or more signals of different frequencies.

dipole array - See antenna array.

dipole - An antenna formed by splitting two wires of a two-wire transmission line, and bending them back to form a single straight line. The antenna feed is in the middle of the dipole antenna, where the split occurs. A dipole antenna is a resonant antenna. The optimal length of a dipole antenna is one half of the wavelength of the signal being received or transmitted by the antenna. A dipole antenna is a narrowband antenna, operating efficiently in only a narrow band of frequencies.

direct attached storage (DAS) - The combination of a high-speed interface and shared disk drives, where the disk drives are connected directly to the serversinternally or externally.

direct broadcast satellite (DBS) - A service that uses satellites to broadcast multiple channels of television programming directly to a small-dish antenna.

direct connection - The act of connecting a cable to customer equipment without the use of a patch panel or terminal block.

direct current (dc) - A constant-value electric current that flows in one direction in an electric circuit.

direct current (dc) loop resistance - Cable conductor resistance with the far end of the cabling shorted. This is the resistance for two conductors of a metallic cable.

direct digital control (DDC) - A control loop used in building automation systems in which a microprocessor-based controller controls equipment (e.g., air handlers, chillers, boilers) based on sensor inputs and set-point parameters according to a sequence of operations.

direct hold magnetic lock - An electric magnet is mounted to a doorframe opposite a metal plate. When energized, the lock bands to the armature and locks the door.

direct sequence spread spectrum (DSSS) - 1. A technique used to structure signal process utilizing a digital code sequence having a chip rate much higher than the information signal bit rate. Each information bit within a digital signal is transmitted as a pseudorandom sequence of chips. 2. Using a spreading code, the transmitted signal is spread over a wide frequency band. The spreading code is reapplied to the transmitted signal at the receiver.

direct sound - Sound that travels directly from a speaker to a listener without having undergone any reflection.

direct wave - Direct wave is the portion of the wave that travels from transmitting to receiving antenna. It is limited to the distance from the transmitter to the horizon, plus a small distance added by the wave's attempt to bend with the surface of the Earth.

direct-buried cable - A telecommunications cable designed to be installed under the surface of the earth, in direct contact with the soil. (TIA) Contrast with underground cable.

directional antenna - An antenna characterized by a broad coverage zone that preferentially sends or receives signals in a specific direction. See also omnidirectional antenna and unidirectional antenna.

directional coupler - A device with one input port and two or more output ports that splits a single signal to multiple outputs while providing a high attenuation for reverse signals.

directivity - The ratio of the maximum sensitivity of an antenna to its average sensitivity. It varies directly as the effective aperture of the antenna and inversely as the square of the wavelength.

directory - A database of the resources available on a network. Typically, it contains records far devices, software applications, data files, users, and groups.

disaster recovery - The procedures and actions taken to restore network operations after an event that destroys or disables some or all of the network. See also backup storage.

discone antenna - A development of the ground-plane antenna in which a circular disc is substituted for the monopole so that the antenna has a broadband response.

discrimination - The process of selecting the desired signal of the proper input level.

disk cache - An area of computer memory where data is temporarily stored on its way to or from a disk drive. See also caching.

disk duplexing - The simultaneous writing of all data to be stored onto two hard disks, where each hard disk is connected to a separate controller card.

disk mirroring - The simultaneous writing of all data to be stored onto two hard disks, where both hard disks are connected to the same controller card. If one of the hard disks fails, the other continues to provide storage services.

diskless workstation - A personal computer that depends upon a network server for loading data and applications. Diskless workstations are configured without a floppy or hard disk drive, thereby providing additional security.

dispersion - 1. The loss of signal resulting from the scattering of light pulses as they are transmitted through a medium. 2. The widening or spreading out of the modes in a light pulse as it progresses along an optical fiber. 3. The characteristics of the sound coverage field of a speaker.

dispersion shifted - A singlemode optical fiber that has a nominal zero-dispersion point at a wavelength of 1550 nanometer. Contrast with dispersion unshifted.

dispersion unshifted - A singlemode optical fiber that has a nominal zero-dispersion point at a wavelength of 1300 nanometer. Also called conventional or unshifted optical fiber.

distance vector algorithm - A network routing protocol that uses the number of hops (links between routers) to determine efficient routing, based on the Bellman-Ford algorithm.

distortion - A change in the shape of a signal's waveform.

distributed access control - An access control system in which all control decisions are made at the local controllers, independent from a host computer. Local controller events are uploaded to a host computer periodically for review and storage.

distributed antenna system (DAS) - Systems that transmit or relay radio frequency signals (e.g., signals from cellular/ personal communications system telephones, text pagers, wireless LANs) within buildings, structures, tunnels, or other areas where wireless services cannot be otherwise provided.

distributed queue dual bus (DQDB) - The DQDB IEEE 802.6 standard used in metropolitan area networks.

distribution cable - See horizontal cable.

distribution cell - The cellular floor sections from which cables emerge into work areas.

distribution device (DD) - A facility located within the dwelling unit for interconnection or cross-connection. (TIA)

distribution device cord - A telecommunications cord that extends between the distribution device and the auxiliary disconnect outlet. (TIA)

distribution duct - A raceway of rectangular cross-section placed within or just below the finished floor and used to extend the wires or cables to a specific work area. (TIA)

distribution frame - A structure with terminations for connecting the cabling of a facility in such a manner that interconnection or cross-connections may be readily made. (TIA)

distribution panel - A wiring board that provides a patch panel function and mounts either in a rack or on a wall.

distribution ring (D-ring) - Wire management ring shaped like the letter D for routing and supporting distribution cables and jumpers/patch cables on a backboard.

distribution system (DS) - A bridging engine in access points that is used to connect access points together. The connection can be wired or wireless.

diverse route - An alternative routing for cables and/or services to provide a different pathway for resilience or security. See also alternate route.

diversity reception - A technique used to improve the reception ability of a wireless network device (e.g., access point). A second antenna is built into the wireless device, which uses the antenna with the best reception.

divestiture - Transferring of title or loss of ownership as a result of government order, usually as a result of misdeed or in the interest of avoiding a monopolistic business environment.

Division 1 - A division in the Construction Specifications Institute MasterFormatT"" that standardizes the way information about a nonresidential construction project is organized. Division 1 is subordinate to the general conditions and supersedes part 1 of each section. (CSI)

door contact - A recessed or surfacemounted peripheral device that provides the electronic access control with an input that reports the status of a door or passageway that is being monitored.

door-forced alarm - An alarm generated when a door is forced open.

door held open alarm - An alarm generated when a door is held open beyond the designated period of time as programmed in the controller.

door position switch - A switch that is used to monitor whether a door is in an opened or closed position.

door switch - A switch that reflects the status of the door: open or closed.

dopant - An impurity added usually in minute amounts to a pure basic substance to alter its properties. In the manufacturing of optical fibers, dopant is used to increase the optical fiber core's refractive index to that of the cladding.

double-gang box - A device used to house telecommunications or electrical cabling for the purpose of attaching outlets and faceplate or cover that houses connectors for the interconnection of equipment. Its size is roughly twice that of a single-gang box.

down conductor - A conductor that connects air terminals to ground on the outside of a structure. Used with lightning protection systems.

down guy - A steel messenger (strand) that connects the suspension strand, span guy, or other items of aerial plant to an anchor and rod.

downlink - 1. Signals transmitted from satellites to ground stations. 2. In demand priority access method, the communications channel between a repeater and a connected end node or between a repeater and a lower-level repeater.

download - To send information from a host computer to a controller.

downtilt - A deliberate rotation of the antennas E-plane pattern (a common method used when co-channel interference is an issue). (Nortel)

downtime - The interval during which a functional system is inoperable.

draft international standard (DIS) - A draft version of a standard in which all member comments have been incorporated.

draft proposal - An International Organization for Standardization standard document that has been registered and numbered but not yet given final approval.

drag line - Pull cord or line installed in a cable pathway. The line may be used for pulling in a stronger strength rope to pull cable(s) of greater mass and weight into the finished conduits.

drain wire - A noninsulated conductor placed in electrical contact with a shield, acting as a coupled bonding conductor, and intended to optimize shielding effectiveness.

draw - Payment method for a project in which the contractor receives an initial payment on commencement of the contract and makes periodic draws during the term of the project.

drawing set - A set of drawings that shows the dimensions and the relationship between components of a building project.

dressing - Placing cables into a neat and symmetrical pattern for proper alignment and positioning for termination.

dressing block - A plastic receptacle used to form and hold connectors to allow wire termination.

drip loop - The length of cable, usually on the exterior of a building, placed above the entry point of the building, extended to below the entry point, and looped back up to the entry point of the structure. The use of such cable installation will impede moisture infiltration.

drop and insert - A process where a part of the information carried in a transmission signal passing through the repeater site is demodulated (dropped) to serve local consumers from the repeater site or information is inserted for further transmission.

drop cable - 1. A branch cable. 2. The cable allowing connection and access to and from the trunk cable of a network.

drop ceiling - See suspended ceiling.

drop wire - An aerial cable that connects a serving outdoor terminal to a building or structure.

dry contact - A switch or relay contact that is not connected to other voltage sources.

drywall - An interior wall construction consisting of gypsum or plasterboard.

D-subminiature connector - See DB## connector.

dual clad - See depressed clad.

dual foil - A secondary foil placed around foiled twisted-pair cable.

dual simplex link - A communications channel consisting of two signal paths, one in each direction.

dual-attachment concentrator (DAC) - A fiber distributed data interface concentrator that has four-fiber, dual link connections to both the primary and backup ring paths. Contrast with single-attachment concentrator.

dual-attachment station (DAS) - A fiber distributed data interface Class A station with four-fiber, dual link connections to both the primary and backup ring paths. If the primary ring breaks, the station will use the secondary .ring. Contrast with single-attachment station.

dual-duplex signaling - A form of bidirectional signaling in which data transfer can flow in both directions at the same time over a single communications channel. See full-duplex signaling, half-duplex signaling, and simplex signaling.

dual-ring topology - A ring topology that allows each device or network to have two connections to each adjacent device or network (e.g., SONET, fiber distributed data interface).

duct - 1. A single enclosed raceway for conductors, wires, or cables. See also raceway. 2. An enclosure in which air is moved. Generally part of the heating, ventilating, and air-conditioning system of a building.

ductbank (DB) - An arrangement of ducts, for wires or cables, in tiers. (TIA)

ducted skirting - A cable raceway with a removable cover made of either wood, plastic, or metal found on the perimeter of walls of a building. May have separate channels for power in telecommunications. See also raceway.

ductpic - Plastic insulated conductor cables designed for placement underground.

duct plug - A fitting capping the end of a duct, or fittings to surround cables within the duct, designed to provide a gas- and liquid-tight seal.

duplex - A simultaneous two-way independent transmission in both directions. See also half-duplex and full-duplex signaling.

duplex connector - See connector, duplex; optical fiber.

duplexer - A device that isolates the receiver from the transmitter while permitting them to share a common antenna.

duty cycle - The percentage of "on" time or operating time a device experiences.

dynamic power control (DPC) - The capability of raising and lowering a mobile's transmitting power in real time to help reduce interference.

dynamic range - A combination of the total pulse power of an OTDR laser source and the sensitivity of the associated sensor. Measurements are listed as a value reported in dB where larger values mean longer distance capability.