F connector - A 75-ohm radio frequency connector typically used in cable television and on entertainment devices for coaxial cable.

fabric - An interconnection scheme that enables communications between any two connected devices or networks through a series of interlinked switches.

fabrication tolerances - Establishes a statistical range of acceptability for properties of products before they are incorporated into the project. (CSI)

faceplate - A protective and/or decorative plate for an outlet.

facility code - The coded data in access control cards that identifies the location of the access control system.

fade bandwidth - The narrow bandwidth where fading is witnessed.

fade margin - A design allowance that provides for sufficient system gain or sensitivity to accommodate expected fading for the purpose of ensuring that the required quality of service is maintained.

fading - The variation in path loss between the transmitter at one station and its normal receiver at the following station.

failback - Restoration of normal operation from a failover.

fail latched - Provides a locking device that on loss of power will latch or remain latched but does not necessarily restrict movement from the secured side.

fail locked - An electric lock that requires power to unlock. Also called fail secure.

failover - The automatic transfer of control from a primary to a backup system as a strategy for fault tolerance.

fail-safe door - When the power fails at a door, the door automatically unlocks, allowing exit and entrance.

fail-safe lock - A lock that automatically unlocks a door upon loss of power. It takes power to lock a device of this type. A fail-safe lock is used for life safety applications. Also called power lock.

fail-secure door - When the power fails at a door, the door automatically locks and will not allow entrance but will continue to allow exit.

fail-secure lock - A device that automatically locks a door upon loss of power. It takes power to unlock this type of device. Also called power unlock.

fail unlocked - An electric lock that automatically unlocks with any power interruption. Also called fail-safe.

fallback - The ability of an access point to lower the transfer rate as the signal level from the mobile station drops below the level required to maintain a reliable connection.

false ceiling - See suspended ceiling. (TIA)

false event - A reading on an optical time domain reflectometer that is caused by the improper use of the test set or the test setup presents a false reading in the test results.

fanned - Separated cable conductors, strands, or pairs.

fan out - 1. Used to describe the physical preparation of wire pairs exiting the jacketed cable to facilitate placement and termination in a splice or connecting block. 2. A device used to enable termination of optical fiber strands.

Faraday's law - The physical law that a changing magnetic field produces an associated electric field.

far-end crosstalk (FEXT) loss - A measure of the unwanted signal coupling from a transmitter at the near end into another pair measured at the far end, and relative to the transmitted signal level. Also called input/output far-end crosstalk loss. (TIA)

fault management - The detection, isolation, and correction of hardware or software conditions that disrupt network operations.

fault tolerance - The ability of a system to continue operations after the failure of one or more components or communications paths.

fault voltage (current) - See foreign voltage (current).

FC connector - See fiber connector.

feedback - An unwanted oscillation or tone that quickly increases in audible level.

feeder duct - See header duct and trench duct.

feed horn - A device that concentrates radio frequency energy into a waveguide, antenna radiator, or antenna reflector.

ferroresonance - The resonance of iron molecules due to the application of a magnetic field that produces a magnetic flux on the iron structure. This is the principle of operation of transformers.

ferroresonant transformer - A device that gives regulated alternating current (ac) voltages, capable of acting as a stepup or step-down voltage transformer and as an ac voltage regulator.

ferrule (optical fiber) - The alignment sleeve portion of an optical connector used to protect and align the stripped optical fiber.

fiber - See optical fiber.

fiber connector (FC) - A type of optical fiber connector identifiable by its round, threaded connector body. The threaded design provides for a secure optical fiber connection. May be of metal or composite material.

fiber distributed data interface (FDDI) - A fault-tolerant token-passing network protocol based on single or dual optical fiber rings.

fiber distribution hub (FDH) - Network equipment required to house passive components and to terminate in-building optical fiber distribution cables.

fiber distribution terminal (FDT) - Network equipment (passive) required to terminate fiber jumpers to each line unit.

fiber distribution unit - An administrative housing used to terminate fiber cables and connectors for the purpose of interconnections and cross-connection.

fiber optic - See optical fiber.

fiber optic cable - See optical fiber cable.

fiber optic flashlight - See optical fiber flashlight.

fiber optics - A communications system that uses optical fiber as its media.

fiber span - A length of optical fiber cable between poles or maintenance holes.

fiber strand identifier - A clamp-on testing unit for optical fiber that places a microbend into the cable to detect light escaping from the fiber.

fiber to the curb (FTTC) - In an FTTC outside plant residential cabling system, singlemode optical fiber is extended to the pedestal, which is at the curb near the home. Depending on the termination point, the system can be referred to as an FTTx system, where "x" represents the home, business, premises, or curb. The drop from the curb to the home is typically balanced twisted-pair, although if FTTC is used to provide video, a dual drop cable containing both balanced twisted-pair and coax may be cost effective in comparison with the cost of the electronics needed to multiplex and demultiplex telephony and video bandwidth signals over a balanced twisted-pair drop alone.

fiber to the home (FTTH) - A technology that provides voice, data, and video services from the telephone company's branch office to local customers over an all optical fiber link.

fiber to the premises (FTTP) - See fiber to the curb (FTTC).

Fibre Channel - A high-speed, point-to-point network protocol commonly associated with storage area network technologies.

field engineering - Consists of taking the measurements, facility placement, and layout from the field observations. Field engineering includes site surveying and layout.

field observation reports - Site visits are documented in the form of a field observation report, with any observed deficiencies clearly noted, to keep the owner informed of construction progress and events taking place on the construction site. (CSI)

field order (FO) - Allows the engineer to authorize or order minor variations in the work when such changes do not involve a change in contract price or contract time. These orders must be in writing, but do not require an executed change order or the owner's signature. (CSI)

fill - 1. A sequence of added bits used to meet timing, sizing, or spacing requirements in and between messages. 2. Use of material (or material used) to equalize or raise earth topography to a certain elevation.

filled cable - A cable that contains waterblocking gel material inside the sheath to prevent the penetration of moisture into the cable.

fill ratio - The ratio of actual space occupied to potential total space by any material that fills a container. Typically expressed as a percentage of the total cross-sectional space. In the case of round telecommunications cables, a conduit, for example, may become completely full of cable with a 60 percent fill ratio because round cables filling a round space (e.g., conduit) does not allow for 100 percent full. Water, for instance, may completely fill a conduit with a 100 percent fill ratio.

filter - 1. A process or device that examines all incoming traffic for specific characteristics (e.g., source address, destination address, protocol, virus) and determines whether to accept, forward, or discard that traffic based on the established criteria. 2. A device that selectively sorts and passes through a desired range of signals (e.g., noise suppression).

filtering - A process that examines all incoming data for specific characteristics (e.g., source address, destination address, protocol) and determines whether to accept, forward, or discard that traffic based on the established criteria. See also filter.

filter mask - Protective breathing apparatus worn whenever harmful dust, gas, smoke, chemical vapor, or some other pollutant is present at the work site.

final acceptance - Final acceptance of the work is indicated by issuance of final payment. Final payment is recommended by the architect or engineer only after all project closeout procedures have been completed. (CSI)

fingerprint reader - A biometric reader that identifies a person based on the person's fingerprint pattern.

finish grade - The top surface of lawns, walks, or other improved surfaces after the completion of grading operations.

fire alarm (FA) - A system that provides a reasonable level of safety by reducing the probability of injury and loss of life from fire, smoke, and heat in buildings by providing detection, suppression, and notification functions.

fire alarm code - A code that specifies when a fire alarm system is required.

fire alarm control panel (FACP) - A system-level controller that initiates sequences of operation for fire detection, suppression, and notification functions.

fire alarm standard - A standard that prescribes such requirements as the spacing and placing requirements of fire detection and alarm equipment. This addresses how a fire alarm system is to be installed, tested, inspected, maintained, and monitored.

fire break - A fire-rated material, device, or assembly of parts installed along a cable, other than at a cable penetration of a firerated barrier, to prevent the spread of fire along a cable. (TIA)

fireproof - A property of a material (e.g., masonry, block, brick, concrete, gypsum board) that does not support combustion even under accelerated conditions. No material is entirely fireproof.

fire-rated door - A door assembled of various materials and types of construction used in wall openings to retard the passage of fire. These doors are rated in hours or fractions of hours.

fire rating system - See fire resistance rating.

fire resistance - A property of a material or assembly of materials that can withstand combustion and delay the passage of flame for some known period of time.

fire resistance rating - The time in hours, or fraction thereof, that a material or assembly of materials will withstand the passage of flame and the transmission of heat when exposed to fire under specified conditions of test and performance criteria. (TIA)

fire retardant (FR) - Any substance added to delay the start of fire ignition or to slow the spread of flame by the burning material.

fire shield - A fire-rated material, device, or assembly of parts between pathways (e.g., between two parallel cable trays or between layers in vertically stacked trays) to prevent propagation of flames from one pathway to an adjacent pathway. (TIA)

firestop - A fire-rated material, device, or assembly of parts installed in a penetration of a fire-rated barrier. (TIA)

firestop seal - See firestop system. (TIA)

firestop system - A specific construction consisting of the material(s) (firestop penetration seals) that fill the opening in the wall or floor assembly, and around and between any items that penetrate the wall or floor (e.g., cables, cable trays, conduit, ducts, pipes), and any termination devices (e.g., electrical outlet boxes) along with their means of support.

firewall - 1. A continuous barrier used to prevent fire spreading from one fire zone or area to another. 2. One or more security mechanisms (hardware and/or software) designed to prevent, detect, suppress, and/or contain unauthorized access to a network.

Firewire - IEEE 1394 serial bus protocol for high-speed communications.

fire zone - A contained area completely enclosed by fire-resistant rated walls, floors, and ceilings

first generation (1G) mobile telephony - Based on analog technology. 1G systems have been phased out and replaced with faster, more reliable digital cellular systems.

fish tape - A tool or device made of steel or fiberglass that can be pushed into a conduit to assist in installing a pull line or to pull cable(s).

fixed device - Any low-voltage device permanently affixed to a surface for purposes of security, fire detection or other control, data, or entertainment applications. (TIA)

flash cut - A process of migrating from an existing system to another where all circuits are cutover at once. See also cutover and hot cut.

flashing - Pieces of sheet metal or the like used to cover and protect certain joints and angles.

flat network - A network that consists of a single broadcast domain. See also broadcast domain.

FLEXT - Synchronous, one-way, time-slot, paging protocol.

flexible conduit - A raceway of circular cross-section that is bendable without the use of tools.

flex life - A qualification of the number of times a cable may be bent before breaking.

float current - The current that is drawn by a battery when it is being kept in a fully charged state. This current will be determined by the float voltage. See also float voltage.

float voltage - The voltage at which a battery is maintained (floated) in order to keep it in a fully charged state. See also float current.

flooding - The process used by switches/ bridges and routers to direct a message to all outgoing ports, with the exception of the port or interface on which the traffic was received.

floor distributor (FD) - The distributor used to connect horizontal cable and cabling subsystems or equipment. International equivalent term for horizontal cross-connect.

floor plan - 1. A scaled diagram or plan of a building floor or other structure. 2. Plan showing the layout of a building floor.

floor-serving terminal - The space where backbone and auxiliary disconnect coaxial cables terminate to support a single level of living units.

floor slab - 1. That part of a reinforced concrete floor, which is carried on beams below. (TIA) 2. A concrete mat poured on subgrade serving as a floor rather than as a structural member.

flow control - A mechanism used to manage the frame exchange rate between source and destination devices that prevents the source from overwhelming the destination.

foil shield - A thin plastic and metal laminated tape wrapped around the cable conductors and acting as a shield against electromagnetic interference and preventing emission of electromagnetic energy.

foil twisted-pair (FTP) cable - See screened twisted-pair cable.

foiled twisted quad (FTQ) cable - A cable with two individual groups of four twisted conductors surrounded by an overall foil shield.

foldback splicing - Process of folding back conductors in a splice for future maintenance or rearrangements.

footprint - The area where a piece of equipment or furniture rests on the floor with its moving parts in a closed position.

foreign voltage (current) - Any unwanted voltage (current) imposed on a system that is not supplied from the central office or from telephone equipment or from within the system itself. Also called fault voltage (current).

form and dress cable - Line up cables side-by-side, shape into sweeping arcs, and join cable into bundles with tie wrap, or other means, to hold bundles together.

form factor - In computers, the size, configuration, or physical arrangement of a device, in physical terms rather than capability.

forwarding - The transferring of a message to another network by an internetworking device. See also filtering.

forwarding logic - The set of rules used by a switch to process the messages received from LAN devices.

forward packet data channel (F-PDCH) - The cdma2000 1xEV-DV data channel on the forward link. forward proxy See Internet acceleration.

forward voice channel (FVC) - Works in pair with the reverse voice channel for a subscriber call. (Nortel)

fragment-free switching - See modified cut-through.

frame A - data unit created at Layer 2 of the Open Systems Interconnection Reference Model. It contains the data and control information necessary to transfer a message from one device to another on the same network.

frame check sequence (FCS) - The product of an error-detecting code normally inserted as the final field in a block of transmitted data.

Frame Relay (FR) - A network protocol designed to transport messages rapidly overextended distances via a mesh network, using virtual circuits and switches. A high-performance derivative of X.25.

frame synchronization (FS) - A 32-bit post office code standardization advisory group paging code used to identify the beginning of each message batch.

franchise - A right-of-way granted for placement of outside plant facilities within the domain of public or private property.

free space loss - The signal loss that occurs between two isotropic antennas in free space, unaffected by blocking, refraction, diffraction, or absorption.

free space optics (FSO) - Low power laser beam used for outdoor point-to-point high rate, protocol independent, transmission.

frequency (freq) - The number of cycles that a periodic signal completes in a given time; if the unit of time is one second, the frequency is stated in hertz (Hz). One Hz is equal to one cycle per second.

frequency band - A range of communications frequencies.

frequency converter - Integrated component assemblies used for converting signals into various frequency ranges for further processing.

frequency deviation - The change of a carrier frequency as the result of modulation measured in percent of deviation.

frequency-division multiplexing (FDM) - A system that allows the transmission of more than one signal over a common path, by assigning each signal a different frequency band.

frequency-hopping spread spectrum (FHSS) - A modulation technique that employs rapid changing of the transmission frequency in a predetermined, pseudorandom pattern. Communication is accomplished by synchronizing the transmitter and receiver.

frequency modulation (FM) - Modulation in which the instantaneous frequency of a sine wave carrier is caused to depart from the center frequency by an amount proportional to the instantaneous value of the modulating signal. In FM, the center frequency is called the carrier frequency.

Fresnel reflection - Reflection of a portion of incident light at a discrete interface between two media having different refractive indices or media discontinuity.

Fresnel zone - The circular zone about the direct path between an electromagnetic wave transmitter and receiver in an unbounded transmission medium free of radiation sources.

frost line - The deepest level below grade to which frost penetrates in a particular geographic area. Usually specified in 50year increments.

full-duplex signaling - The transmission of data in two directions simultaneously. See also dual-duplex signaling, half-duplex signaling, and simplex signaling,

functional design process - A network design process where the designer begins by examining the types of applications and services that are to be supported by the network. Also called top-down design. Contrast with physical design process.

furcating harness - An assembly used to increase the effective outer diameter of strands within an optical fiber cable to enable connector termination, typically provided in either 6- or 12-strand configurations. Also called a fan out.

furcation - The process of covering a 250 micron coated optical fiber with a 900 micron buffer tube to facilitate field connectorization.

furcation tubing - Flexible tubes used to increase the effective outer diameter of coated optical fiber strands (typically from 250 micron to 900 micron) to enable connector termination and provide physical protection of the coated strands.

fuse - An overcurrent protective device with a circuit-opening fusible element that is severed (open) when heated by the passage of an overcurrent.

fuse cable link - A length of cable that is two gauges smaller than the conductors of the cable being protected and at least 0.6 m (2 ft) long. Fuse cable is inserted in the plant and intended to open on excessive foreign power currents.

fuse link - See fuse cable link.

fusing - 1. The process of joining optical fibers together by fusion. 2. The process of joining materials through a chemical or heating process.

fusion splice - A permanent joint accomplished by applying localized heat sufficient to fuse the ends of two optical fibers together, forming a continuous single optical fiber.