See F region.

That portion of the ionosphere existing between approximately 160 and 400 km above the surface of the Earth, consisting of layers of increased free-electron density caused by the ionizing effect of solar radiation.

Note 1: The F region reflects normal-incident frequencies at or below the critical frequency (approximately 10 MHz) and partially absorbs waves of higher frequency.

Note 2: The… (Read More →)

In laser diodes, a phenomenon in which a high field intensity of stimulated optical radiation causes degradation of the facets, i.e., those forming the cavity mirrors, decreasing reflectivity and resulting in a decrease of the internal quantum efficiency and an increase in the threshold current.

1. A fixed, mobile, or transportable structure, including (a) all installed electrical and electronic wiring, cabling, and equipment and (b) all supporting structures, such as utility, ground network, and electrical supporting structures.
2. A network-provided service to users or the network operating administration.
3. A transmission pathway and associated equipment.
4. In a protocol applicable to a data unit, such… (Read More →)

A group of interconnected equipment and transmission media uniquely identified and dedicated to a specific type of service. [T1.238-1994/97]

A two-digit code (FC) used in the exchange-carrier-to-interexchange carrier (EC-to-IC) facility/service selective signaling protocol and the IC-to-EC facility/service selective signaling protocol that identifies the type of facility requested. [T1.104-1991]

The electrically interconnected system of conductors and conductive elements that (a) provides multiple current paths to the earth electrode subsystem, and (b) consists of the earth electrode subsystem, the lightning protection subsystem, and the fault protection subsystem.

The particular group of facilities to route the call. [T1.667-1999]

The specific member of a trunk group or a multi-line hunt group. [T1.667]

1. A form of telegraphy for the transmission of fixed images, with or without half-tones, with a view to their reproduction in a permanent form. [47CFR] In this definition the term telegraphy has the same general meaning as defined in the Convention. [NTIA] [RR]
2. The process by which fixed graphic images, such as printed text and pictures, are scanned,… (Read More →)

1. In a facsimile receiver, a device that changes the signal modulation from frequency-shift keying (FSK) to amplitude modulation (AM).
2. In a facsimile transmitter, a device that changes the signal modulation from amplitude modulation (AM) to frequency-shift keying (FSK).

At any point in a frequency-shift facsimile system, the numerical difference between the frequency that corresponds to a white signal and the frequency that corresponds to a black signal.
Note: Facsimile frequency shift is usually expressed in hertz. [From Weik '89]

In facsimile systems, the baseband signal that results from the scanning process.

In a facsimile system, the equipment that converts the facsimile picture signal into a recorded copy.

In a facsimile receiver, the device that performs the final conversion of the facsimile picture signal to an image of the object, i.e., makes the recorded copy.

In a facsimile system, the signal level at any point in the system.
Note 1: The facsimile signal level is used to establish the operating levels.
Note 2: The facsimile signal level is usually expressed in dB with respect to some standard value, such as 1 mW (milliwatt), i.e., 0 dBm.

In a facsimile system, the equipment that sends and receives facsimile signals.
Note: Full-duplex facsimile transceivers can send and receive at the same time; half-duplex facsimile transceivers cannot.

In a facsimile system, the equipment that converts the baseband picture signals, i.e., the baseband signals resulting from scanning the object, into signals suitable for transmission by a communications system.

1. In signal propagation, see fading.
2. In video, the act of dissolving a video picture to either a color, pattern, or titles.
Note: Fading a video image is often used as an artistic tool in video productions, usually seen as a fade to black.
3. In audio, a decrease in the sound level until it is no longer audible.

1. 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.
2. The amount by which a received signal level may be reduced without causing system performance to fall below a specified threshold value. Synonym fading margin.

In a received signal, the variation (with time) of the amplitude or relative phase, or both, of one or more of the frequency components of the signal.
Note: Fading is caused by changes in the characteristics of the propagation path with time.

The probability distribution that signal fading will exceed a given value relative to a specified reference level.
Note 1: In the case of phase interference fading, the time distribution of the instantaneous field strength usually approximates a Rayleigh distribution when several signal components of equal amplitude are present.
Note 2: The field strength is usually measured in volts per meter.… (Read More →)

Synonym fade margin.

See failure, graceful degradation.

1. Of a device, the capability to fail without detriment to other devices or danger to personnel.
2. Pertaining to the automatic protection of programs and/or processing systems to maintain safety when a hardware or software failure is detected in a system. [NIS]
3. [The] automatic protection of programs and/or processing systems when hardware or software failure is detected. [INFOSEC-99]… (Read More →)

[The] selective termination of affected nonessential processing, when hardware or software failure is determined to be imminent. [INFOSEC-99]

1. Operation that ensures that a failure of equipment, process, or system does not propagate beyond the immediate environs of the failing entity.
2. A control operation or function that prevents improper system functioning or catastrophic degradation in the event of circuit malfunction or operator error.

The temporary or permanent termination of the ability of an entity to perform its required function.

[An] Unauthorized access to data resulting from a hardware or software failure. [INFOSEC-99]

[The methods] used to detect imminent hardware or software failure and provide fail safe or fail soft recovery. [INFOSEC-99]

The controlling of congestion in gateways by restricting every host to an equal share of gateway bandwidth.
Note: Fair queuing does not distinguish between small and large hosts or between hosts with few active connections and those with many.

In information assurance, a sector consisting of a header but no data, used in large numbers on a diskette to cause an unauthorized copying program to fail to copy the diskette. [2382-pt.8]

The time required for the amplitude of a pulse to decrease (fall) from a specified value (usually 90 percent of the peak value exclusive of overshoot or undershoot) to another specified value (usually 10 percent of the peak value exclusive of overshoot or undershoot).
Note: Limits on undershoot and oscillation, i.e., hunting, may need to be specified when specifying fall… (Read More →)

See illegal character.

A condition where a phase-locked loop controlling a clock locks on a frequency other than the correct frequency.
Note 1: False clock can occur when there is excessive phase shift, as a function of frequency, in the loop.
Note 2: False clock often occurs where the false frequency is a harmonic of the correct frequency.

A condition where a phase-locked loop locks to a frequency other than the correct one, or to an improper phase.

Synonym break out.

A directional antenna producing a main beam having a large ratio of major to minor dimension at any transverse cross section.

Synonym breakout cable.

Abbreviation for Frequently Asked Questions file. An online file that contains frequently asked questions with answers provided to assist new users and avoid repetitive offline inquiries.
Note: An FAQ file is usually created for Internet news groups, but is also used in other applications.

Synonym far-field region.

Synonym far-field region.

An indication returned to a transmitting node (source) that an errored block has been detected at the receiving node (sink). [T1.105-1988]

Crosstalk that is propagated in a disturbed channel in the same direction as the propagation of a signal in the disturbing channel.
Note: The terminals of the disturbed channel, at which the far-end crosstalk is present, and the energized terminals of the disturbing channel, are usually remote from each other.

An associated, loop signaling, customer installation located at the far end of the network transmission path from the network interface (NI) described in the designated document. [T1.407-1990]

An indication returned to a transmitting link terminating equipment (LTE) upon receipt of a line AIS (alarm indication signal) code or detection of an incoming line failure at the receiving LTE. [T1.105-1988]

The diffraction pattern of a source (such as an LED, ILD, or the output end of an optical fiber) observed at an infinite distance from the source.
Note 1: A far-field pattern exists at distances that are large compared with s2/, where s is a characteristic dimension of the source and is the wavelength. For example, if the source is… (Read More →)

A radiation pattern measured at the far field of an antenna or other emitter.

The region where the angular field distribution is essentially independent of distance from the source.
Note 1: If the source has a maximum overall dimension D that is large compared to the wavelength, the far-field region is commonly taken to exist at distances greater than 2D2/ from the source, being the wavelength.
Note 2: For a beam focused at infinity,… (Read More →)

A magneto-optic effect in which the polarization plane of an electromagnetic wave is rotated under the influence of a magnetic field parallel to the direction of propagation.
Note: The Faraday effect may be used to modulate a lightwave.

A packet switching technique that increases the throughput by eliminating overhead.
Note 1: Overhead reduction is accomplished by allocating flow control and error correction functions to either the user applications or the network nodes that interface with the user.
Note 2: Cell relay and frame relay are two implementations of fast packet switching.

An optional user facility in the virtual call service of CCITT X.25 protocol (now, ITU-T X.25 protocol) that allows the inclusion of user data in the call request/connected and clear indication packets.
Note: Fast select is an essential feature of the CCITT X.25 (1984) protocol.

Fiber Access Terminal

A client-centric computing model where software must be installed on each client in a network. This often requires that each client computer be upgraded to the same level.

1. An accidental condition that causes a functional unit to fail to perform its required function.
2. A defect that causes a reproducible or catastrophic malfunction.
Note: A malfunction is considered reproducible if it occurs consistently under the same circumstances.
3. In power systems, an unintentional short-circuit, or partial short-circuit, between energized conductors or between an energized conductor and ground.

Powering system that monitors for emulated human contact faults and controls power delivered to ensure fault energy is limited.

The National Electrical Code defines FMPS as a power distribution system consisting of a class 4 circuit where the system monitors for faults and controls power delivery to prevent a shock or fire hazard.

In network management, the set of functions that (a) detect, isolate, and correct malfunctions in a telecommunications network, (b) compensate for environmental changes, and (c) include maintaining and examining error logs, accepting and acting on error detection notifications, tracing and identifying faults, carrying out sequences of diagnostics tests, correcting faults, reporting error conditions, and localizing and tracing faults by examining… (Read More →)

In a facility power distribution system, the subsystem that provides a direct path from each power sink to the earth electrode subsystem.
Note: The fault protection subsystem is usually referred to as a "green wire. "

The extent to which a functional unit will continue to operate at a defined performance level even though one or more of its components are malfunctioning.

Acronym for facsimile.

Abbreviation for functional component.

Fault, Configuration, Accounting, Performance, and Security

Abbreviation for Federal Communications Commission. The U. S. Government board of five presidential appointees that has the authority to regulate all non-Federal Government interstate telecommunications (including radio and television broadcasting) as well as all international communications that originate or terminate in the United States.
Note: Similar authority for regulation of Federal Government telecommunications is vested in the National Telecommunications and… (Read More →)

The Federal Communications Commission program and associated directives intended to assure that all connected terminal equipment and protective circuitry will not harm the public switched telephone network or certain private line services.
Note 1: The FCC registration program requires the registering of terminal equipment and protective circuitry in accordance with Subpart C of part 68, Title 47 of the Code… (Read More →)

Abbreviation for frame check sequence. See cyclic redundancy check.

Frequency Division Duplex

Abbreviation for fiber distributed data interface.

See fiber distributed data interface.

See full width at half maximum.

Abbreviation for frequency-division multiplexing.

Abbreviation for frequency-division multiple access.

Fiber Distribution Terminal

Abbreviation for full duplex. See full-duplex (FDX) circuit, full-duplex (FDX) operation.

Functional Entity

A code (or codes) used to select/activate a service feature (e.g., forwarding, using two- or three-digit codes preceded by * or 1 1 or ,, and which may precede subsequent digit selection). [T1.667-1999]

Forward Error Correction

Future Entitlement Control Message

See FCC.

A two-digit location code which indicates the U. S. geographic area (States, Territory, Offshore areas) affected by the EAS alert. The location codes are derived from the Federal Information Processing Standard (FIPS) numbers as described by the U. S. Department of Commerce in the National Institute of Standards and Technology publication FIPS PUB 6-4.

The body responsible for coordinating networking needs among U. S. Federal agencies.

A switched long-distance telecommunications service formerly provided for official Federal Government use.
Note: FTS has been replaced by Federal Telecommunications Service 2000 (FTS2000).

See FTS2000.

1. To supply a signal to the input of a system, subsystem, equipment, or component, such as a transmission line or antenna.
2. A coupling device between an antenna and its transmission line.
Note: A feed may consist of a distribution network or a primary radiator.
3. A transmission facility between (a) the point of origin of a signal, such… (Read More →)

In the encoder, the signal path from the input of the PCM-to-uniform-PCM converter to the output of the adaptive quantizer. In the decoder, the feed-forward path is the signal path from the input of the feed-forward inverse adaptive quantizer to the output of the synchronous coding adjustment block. [T1.310-1991]

1. The return of a portion of the output, or processed portion of the output, of a (usually active) device to the input.
Note 1: The feedback signal will have a certain magnitude and phase relationship relative to the output signal or the input signal. This relationship can be used to influence the behavior, such as the gain and stability,… (Read More →)

The signal path from the input of the bit-masking block to the output of the adaptive predictor. [T1.310-1991]

Signal distortion resulting from reflected waves in a transmission line that is many wavelengths long and mismatched at both the generator and the load ends.

A radio link from an Earth station at a given location to a space station, or vice versa, conveying information for a space radiocommunication service other than for the fixed-satellite service. The given location may be at a specified fixed point, or at any fixed point within specified areas. [NTIA] [RR]

The boundary of a trusted region [CESG].

The ability of features outside a trusted region to penetrate a fence - thus leading to a potential or actual breach of the System Security Policy [CESG].

Abbreviation for front-end processor.

A principle stating that a ray of light follows the path that requires the least time to travel from one point to another, including reflections and refractions that may occur. Synonym least-time principle. [From Weik '89]

A photodetector using photogeneration of carriers in the channel region of a field-effect transistor structure to provide photodetection with current gain.

1. [An] AIS-provided restriction to prevent a program from accessing data in another user's segment of storage. [NIS]
2. [An] information-system (IS) hardware-provided restriction to prevent a program from accessing data in another user's segment of storage. [INFOSEC-99]

See optical fiber.

A device that amplifies an optical signal directly, without the need to convert it to an electrical signal, amplify it electrically, and reconvert it to an optical signal.
Note 1: One type of fiber amplifier uses a doped fiber (e.g., a fiber doped with erbium), which bears the communication signal, and which is optically pumped with a laser having a… (Read More →)

The longitudinal center of symmetry of an optical fiber, i.e., the locus of points that are determined by the centers of mechanical symmetry of the outside diameters of fiber cross sections sampled continuously along the length of the fiber.

See bandwidth (of an optical fiber).

See buffer.

See fiber optic cable.

See cutoff wavelength.

See dispersion.

A concept, defined in ANSI standards, for an optical-fiber-based token-ring network, featuring (a) dual counter-rotating logical rings, each with a data transmission capacity of 100 Mb/s, (b) reliable data transfer, (c) active link monitoring, (d) station management, and (e) survivability features.
Note 1: The four standards are (a) ANSI X3T
9. 5, containing Physical Media Dependent (PMD) specifications, (b) ANSI… (Read More →)

See bus.

A telecommunications cable in which one or more optical fibers are used as the propagation medium. [After 2196]
Note 1: The optical fibers are surrounded by buffers, strength members, and jackets for protection, stiffness, and strength.
Note 2: A fiber-optic cable may be an all-fiber cable, or contain both optical fibers and metallic conductors. One possible use for the metallic… (Read More →)

See optical isolator.

A communications link that transmits signals by means of modulated light propagated in an optical fiber.

The branch of optical technology concerned with the transmission of light through fibers made of transparent materials such as glasses and plastics. [2196]
Note 1: Telecommunications applications of fiber optics use flexible low-loss fibers, using a single fiber per optical path. Present-day plastic fibers have losses that are too high for telecommunications applications.
Note 2: Various industrial and medical applications… (Read More →)

See pigtail.

Typically either a VDSLx or Hybrid Fiber Coax type architecture. Fiber is run to within a few hundred feet of the homes and then either the existing twisted pair or coax is used to pump the signal into the house.

Typically either a VDSLx or ADSLx architecture where fiber is run deeply into a neighborhood to increase the bit-rate; however, the last few thousand feet are still over the existing copper.

Fiber goes directly all the way to the home, apartment complex, or small business. This is a more generic term than FTTH (Home), since typically these architectures are used for more than just homes.

The degree to which a system, or a portion of a system, accurately reproduces, at its output, the essential characteristics of the signal impressed upon its input or the result of a prescribed operation on the signal impressed upon its input.

A network designed for e-mail distribution through individual bulletin board systems rather than through Internet servers.

1. The volume of influence of a physical phenomenon, expressed vectorially.
2. On a data medium or in storage, a specified area used for a particular class of data, e.g., a group of character positions used to enter or display wage rates on a screen.
3. Defined logical data that are part of a record.
4. The elementary unit of… (Read More →)

The irradiance of an electromagnetic wave under specified conditions.
Note: Field intensity is usually expressed in watts per square meter.

1. The magnitude of an electric, magnetic, or electromagnetic field at a given point.
Note: The field strength of an electromagnetic wave is usually expressed as the rms value of the electric field, in volts per meter. The field strength of a magnetic field is usually expressed in amperes per meter Synonym radio field intensity.
2. The electric field strength… (Read More →)

Synonym flag.

A flexible insulated wire used in field telephone and telegraph systems.
Note 1: WD-1 and WF-16 are types of field wire.
Note 2: Field wire usually contains conductors and high-tensile-strength strands serving as strength members.

A restricted radiation device which establishes a radio frequency field in its vicinity and detects changes in that field resulting from the movement of persons or objects within the radio frequency field. Examples: microwave intrusion sensors; devices that use rf energy for production line counting and sensing. [NTIA]

Abbreviation for first-in first-out.

1. The largest unit of storage structure that consists of a named collection of all occurrences in a database of records of a particular record type.
2. A set of related records treated as a unit, for example, in stock control, a file could consist of a set of invoices.

The property of a file indicating access permissions for a process related to the process' user or group identification. A process is in the file ACL class of a file if the process is not in the file owner class and the effective user ID of the process matches the user ID of a user entry in the ACL associated… (Read More →)

Synonym FTP archive.

1. A suffix that is preceded by a decimal (". ") and that is appended to a computer file name.
Note: Common filename extensions with their meanings are: . wpd = a type of word-processing document . doc = a type of word-processing document. exe = executable code or a self-extracting archive file. . gif = a graphical interchange format… (Read More →)

The property of a file indicating access permissions for a process related to the process' user and group identification. A process is in the file other class of a file if the process is not in the file owner class, file group class, or file acl class [POSIX.6].

A per-file privilege value that specifies global behavior for all privileges defined in the implementation [POSIX.6].

A per-privilege attribute of a file that is used during exec() processing in computing the privileges of any process executing that file [POSIX.6].

A state variable that identifies a value for all defined file privilege flags for all privileges defined in an implementation and a value for all file privilege attributes defined in an implementation [POSIX.6].

1. The execution of appropriate administrative, technical, or physical means to guard against the unauthorized access to, modification of, or deletion of a file. [After 2382-8]
2. [The] aggregate of processes and procedures designed to inhibit unauthorized access, contamination, elimination, modification, or destruction of a file or any of its contents. [INFOSEC-99]

[A] means by which access to computer files is limited to authorized users only. [INFOSEC-99]

1. A high-capacity disk storage device or a computer that each computer on a network can use or access and retrieve files that can be shared among attached computers.
2. A program, running on a computer, that allows different programs, running on other computers, to access the files of that computer.

Synonym FTP archive.

In networking, a service to move a part or the whole of a file's content over a computer network. [2382-pt.35]

The Transmission Control Protocol/Internet Protocol (TCP/IP) protocol that is (a) a standard high-level protocol for transferring files from one computer to another, (b) usually implemented as an application level program, and (c) uses the Telnet and TCP protocols.
Note: In conjunction with the proper local software, FTP allows computers connected to the Internet to exchange files, regardless of the computer… (Read More →)

An application's service and protocol based on the concept of virtual file store.
Note: FTAM allows remote access to various levels in a file structure and provides a comprehensive set of file management capabilities.

Applications concerned with the storage, manipulation, and exchange of information between application processes in the form of files. [T1.210-1993]

See bit stuffing.

See bit stuffing.

[A] COMSEC item used to transfer or store key in electronic form or to insert key into a crypto-equipment. [INFOSEC-99]

The area where the coverage contour of an FM translator or booster station is within the protected contour of the associated primary station (i.e., predicted
0. 5 mV/m contour for commercial Class B stations, predicted
0. 7 mV/m contour for commercial Class B1 stations, and predicted 1 mV/m contour for all other classes of stations). [47 CFR
7
4. 1201]

A signal unit that is transmitted when there are no message signal units or link status signal units to be transmitted. It contains only error control and delimitation information. [T1.226-1992]

A cable that has a nonhygroscopic material, usually a gel, inside the jacket or sheath.
Note 1: The nonhygroscopic material fills the spaces between the interior parts of the cable, preventing moisture from entering minor leaks in the sheath and migrating inside the cable.
Note 2: A metallic cable, such as a coaxial cable or a metal waveguide, filled with… (Read More →)

Abbreviation for first-in last-out.

In electronics, a device which transmits only part of the incident energy and may thereby change the spectral distribution of energy:
(a) high pass filters transmit energy above a certain frequency;
(b) low pass filters transmit energy below a certain frequency;
(c) band pass filters transmit energy of a certain bandwidth;
(d) band stop filters transmit energy outside a specific… (Read More →)

A method of encoding information for digital transmission in which (a) a binary 0 is encoded as a +90° change in the carrier phase and a binary 1 is encoded as a -90° change in the carrier phase, and (b) abrupt phase transitions are smoothed by filtering or other functionally equivalent pulse shaping techniques.

A last-choice trunk group that receives overflow traffic, may receive first-route traffic and for which there is no alternate route. There are various types of final trunk groups, differentiated by the type of traffic that they carry. [T
1. Rpt 11-1991]

A computer-operating-system command for accessing limited network-user-account information.
Note: Finger is limited to providing information such as the full name of the account holder and address information, intentionally made public by the account holder. Finger is also used to establish the existence of an address and to discover whether or not the account is currently logged on.

1. In an information transaction, a call in which the call originator or call receiver terminates the communication and goes on hook, i.e., hangs up.
2. In an information transfer transaction, the termination of the information transfer phase.

Acronym for Federal Information Processing.

In the Federal government, any equipment or interconnected system or subsystems of equipment (as defined in 41CFR) used in the automatic acquisition, storage, manipulation, management, movement, control, display, switching, interchange, transmission, or reception of data or information.

In the Federal government, any organized combination of FIP equipment, software, services, support services, or related supplies.

Federal Information Processing Standard

[A] key management protocol based on public key cryptography. [INFOSEC-99]

1. A computer that (a) acts as an interface between two networks (e.g., the Internet and an private network, respectively), and (b) regulates traffic between those networks for the purpose of protecting the internal network from electronic attacks originating from the external network. The firewall is capable of handling the following tasks: (a) isolating internal and external traffic (a bridge… (Read More →)

1. Software that is embedded in a hardware device that allows reading and executing the software, but does not allow modification, e.g., writing or deleting data by an end user.
Note 1: An example of firmware is a computer program in a read-only memory (ROM) integrated circuit chip. A hardware configuration is usually used to represent the software.
Note 2:… (Read More →)

Of silica-based optical fibers, the transmission window at approximately 830 to 850 nm. [FAA]

A queuing discipline in which entities in a queue leave the queue in the same order in which they arrive.
Note 1: Service, when available, is offered to the entity that has been in the FIFO queue the longest.
Note 2: FIFO techniques are used in message switching.

A queuing discipline in which entities in a queue leave the queue in the reverse order from that in which they arrived.
Note: An understanding of FILO techniques is important in the understanding of store-and-forward capabilities in packing switching.

Traffic that has not been route-advanced at any switching system. [T
1. Rpt 11-1991]

Acronym for foreign instrumentation signals intelligence.

A telephone service that allows individuals to receive, via a single number, telephone calls in various locations (e.g., home, office, or car phone) from call originators not necessarily using the same common carrier.

In personal communications service (PCS), terminal access to a network in which there is a set relationship between a terminal and the access interface.
Note: A single "identifier" serves for both the access interface and the terminal. If the terminal moves to another access interface, that terminal assumes the identity of the new interface.

See pad.

A service feature that permits an attendant on an assisted call to retain connection through the attendant position for the duration of the call.
Note: The attendant will usually receive a disconnect signal when the call is terminated.

A fixed station used in connection with (a) the alignment of microwave transmitting and receiving antenna systems and equipment, (b) coordination of microwave radio survey operations, and (c) cue and contact control of television pickup station operations. [47CFR]

A radiocommunication service between specified fixed points. [NTIA] [RR] [47CFR]

1. A station in the fixed service. [NTIA] [RR] [47CFR]
2. The term "fixed station" in the fixed public or fixed public press service includes all apparatus used in rendering the authorized service at a particular location under a single instrument of authorization. [47CFR]

Synonym read-only storage.

Modulation in which the significant condition for any signal element is based on a fixed reference.

1. A radiocommunication service between Earth stations at given positions when one or more satellites are used; the given position may be a specified fixed point or any fixed point within specified areas; in some cases this service includes satellite-to-satellite links, which may also be effected in the inter-satellite service, the fixed-satellite service may also include feeder links for other… (Read More →)

Data compaction accomplished by storing or transmitting data only when the data fall outside prescribed limits.
Note: An example of fixed-tolerance-band compaction in a telemetering system is the transmission of the temperature only when the temperature is above or below preestablished threshold limits. Thus, the recipient of the transmission is to assume that the value is in the prescribed range… (Read More →)

In data transmission or processing, an indicator, such as a signal, symbol, character, or digit, used for identification.
Note: A flag may be a byte, word, mark, group mark, or letter that signals the occurrence of some condition or event, such as the end of a word, block, or message. Synonym field tag.

In data transmission or processing, a sequence of bits used to delimit, i. e. mark, the beginning and end of a frame.
Note 1: An 8-bit sequence is usually used as the flag sequence; for example, the 8-bit flag sequence
0111111
0.
Note 2: Flag sequences are used in bit-oriented protocols, such as Advanced Data Communication Control Procedures (ADCCP), Synchronous… (Read More →)

To send nasty or insulting messages, usually in response to someone's having broken the rules of Internet etiquette (called netiquette).

1. A signal generated by the momentary depression of the telephone switchhook or other device.
Note: A flash may be used to request additional services.
2. An on-hook signal of a defined duration, used to activate network features. [T1.401-1988]

In computer-based equipment (such as MP3 players, digital cameras, and palm-held computers), a type of memory storage device approximately the size of a matchbook, capable of recording several megabytes of (usually compressed) digitized audio files or data files. Synonym flash memory card.

A supplementary calling feature provided by the near-end customer interface (CI) that is activated or controlled through the use of one or more flash signals. [T1.407-1997]

Synonym flash card.

A category of precedence reserved for initial enemy contact messages or operational combat messages of extreme urgency. Brevity is mandatory. [JP 1-02]

A loop-open signal of 300 to 1000 ms at the network interface (NI) that is generated by the network, typically under the control of the far-end customer interface (CI), to control supplementary calling features when such features are provided by the near-end CI. [T1.407-1997]

Fading in which all frequency components of a received radio signal vary in the same proportion simultaneously.

Telephone service in which a single payment permits an unlimited number of local calls to be made without further charge for a specified period of time.

In a noise-measuring set, a noise weighting based on an amplitude-frequency characteristic that is flat over a frequency range that must be stated.
Note 1: Flat noise power is expressed in dBrn (f1 - f2) or in dBm (f1 - f2).
Note 2: "3-kHz flat weighting" and "15-kHz flat weighting" are based on amplitude-frequency characteristics that are flat between 30… (Read More →)

1. In computer security, an error of commission, an omission, or an oversight that allows protection mechanisms to be bypassed or disabled.
2. [An] error of commission, omission, or oversight in an information system (IS) that may allow protection mechanisms to be bypassed. [INFOSEC-99] Synonym loophole. [2382-pt.8]
3. An error of commission, omission, or oversight in a system that allows… (Read More →)

1. System analysis and penetration technique in which the specification and documentation for an information system (IS) are analyzed to produce a list of hypothetical flaws. This list is prioritized on the basis of the estimated probability that a flaw exists, on the ease of exploiting it, and on the extent of control or compromise it would provide. The prioritized… (Read More →)

A rule stating that if the thumb of the right hand points in the direction of an electric current, then the curled fingers point in the direction of the magnetic field that encircles the current; and further, if the curled fingers of the right hand describe the electric current in a solenoid, then the thumb points in the direction of… (Read More →)

Synonym diskette.

In video, any of several visual artifacts similar to (i.e., manifested as) a stroboscopic effect (jerkiness), sometimes caused by or related to vertical synchronization characteristics or video field display rates. [JSB]

A device that may assume either one of two reversible, stable states.
Note 1: The flip-flop is used as a basic control element in computer and communications systems.
Note 2: In a flip-flop, the transition from one stable state to the other is unstable, i.e., for the very short period during which the transition takes place, both outputs may assume… (Read More →)

Operation of a dc system with the battery, rectifier, and load all connected in parallel. The battery charger supplies the normal dc load plus any battery self-discharge current or recharge current required after a discharge. [T1.330-1997]

See conference floating.

A magnetic head floating on a layer of air away from the recording surface. Synonyms air-floating head, flying head. [ANSDIT]

Data compaction accomplished by using coefficients, a base, and exponents to specify the scale, range, or magnitude of numbers.
Note: An example of floating-point coding compaction is using
11
9. 8 × 106,
11
9. 8(6), or
11
9. 86 to represent 119,800,00
0. If the number is rounded to 120,000,000, it might be written as 1206 or 127 in… (Read More →)

In facsimile, the optical method of scanning in which the object is floodlighted and the scanning spot is defined by a masked portion of the illuminated area.

In a telephone network, nondeterministic routing in which a dialed number received at a switch is transmitted to all switches, i.e., flooded, in the area code directly connected to that switch; if the dialed number is not an affiliated subscriber at that switch, the number is then retransmitted to all directly connected switches, and then routed through the switch that… (Read More →)

Insertion of a large volume of data resulting in denial of service. [INFOSEC-99] Synonyms [in e-mail and forum postings] mail bombing, spamming; [in radio and wireline communications] flood-search routing, pilot-make-busy.

A substance surrounding the buffer tubes of a fiber-optic cable, to prevent water intrusion into the interstices in the event of a breach of the jacket. [FAA]

Synonym diskette.

Acronym for floating-point operations per second.
Note: For example, 15 Mflops equals 15 million floating-point arithmetic operations per second. [From Weik '89]

See transmit flow control.

A procedure for controlling the rate of transfer of data among elements of a network, e.g., between a DTE (data terminal equipment) and a data switching exchange network, to prevent overload.

Synonym flowchart.

A graphical representation in which symbols are used to represent such things as operations, data, flow direction, and equipment, for the definition, analysis, or solution of a problem. Synonym flow diagram.

On a flowchart, a line that (a) has an indicated direction, (b) represents a connection between other symbols, and (c) indicates the sequence of operations or the transfer of control.

File Delivery over Unidirectional Transport

Rapid variation of signal parameters, such as amplitude, phase, and frequency.
Note: Examples of flutter are (a) rapid variations in received signal levels, such as variations that may be caused by atmospheric disturbances, antenna movements in a high wind, or interaction with other signals, (b) in radio propagation, a phenomenon in which nearly all radio signals that are usually reflected… (Read More →)

1. The lines of force of a magnetic field.
2. Obsolete synonym for radiant power.

Synonym floating head.

In an oscillator, the continuation of oscillations after removal of the control stimulus.
Note 1: The flywheel effect is usually caused by interacting inductive and capacitive circuits in the oscillator.
Note 2: The flywheel effect may be desirable, such as in phase-locked loops used in synchronous systems, or undesirable, such as in voltage-controlled oscillators. Synonym flywheeling.

Synonym flywheel effect.

Abbreviation for frequency modulation.

That form of interference to the reception of other broadcast stations, which is caused by the presence of an FM broadcast signal of 115 dB (562 mV/m) or greater signal strength in the area adjacent to the antenna of the transmitting station. The 115-dB contour is referred to as the "blanketing area. " [47CFR]

See translator.

Synonym capture effect.

See capture effect.

The quotient obtained by dividing the signal-to-noise ratio (SNR) at the output of an FM receiver by the carrier-to-noise ratio (CNR) at the input of the receiver.
Note: When the FM improvement factor is greater than unity, the improvement in the SNR is always obtained at the expense of an increased bandwidth in the receiver and the transmission path.

The point in an FM receiver at which the peaks in the rf signal equal the peaks of the thermal noise generated in the receiver.
Note: A baseband signal-to-noise ratio of about 30 dB is typical at the improvement threshold, and this ratio improves 1 dB for each decibel of increase in the signal above the threshold.

In an FM receiver, the effect produced when the desired-signal gain begins to limit the desired signal, and thus noise limiting (suppression).
Note: FM threshold effect occurs at (and above) the point at which the FM signal-to-noise improvement is measured.

A change in the value of the FM threshold of a receiver.
Note: FM threshold extension may be obtained by decreasing the operational bandwidth, thus decreasing the received noise power and allowing the threshold of the desired signal to occur at a lower signal input level.

Fixed/Mobile Convergence

Abbreviation for fiber optics.

Synonym thread.

In satellite communications, that portion of the Earth's surface over which a satellite antenna delivers a specified amount of signal power under specified conditions.
Note: The limiting case of footprint area is somewhat less than one-half the Earth's surface, and depends on the altitude of the satellite. ,ifootryc,

Synonym illegal character.

A procedure of transferring signaling traffic from one signaling route to another, when the signaling route in use fails or is required to be cleared of traffic. [T1.110-1987]

A network-provided service in which a telephone in a given local exchange area is connected, via a private line, to a central office in another, i.e., "foreign", exchange, rather than the local exchange area's central office.
Note: To call originators, it appears that the subscriber having the FX service is located in the foreign exchange area.

1. Intelligence information derived from electromagnetic emissions associated with the testing and operational deployment of foreign aerospace, surface, and subsurface systems.
2. Technical information and intelligence information derived from the intercept of foreign instrumentation signals by other than the intended recipients. Foreign instrumentation signals intelligence is a category of signals intelligence.
Note: Foreign instrumentation signals include but are not limited… (Read More →)

The study of digital evidence resulting from a security incident. It involves collection, detection, and analysis pf digital data within an investigative process. The goal of forensics is to do a structured investigation and find out exactly what happened on a digital system, and who was responsible for it. Often, the results of a forensic investigation are used in criminal… (Read More →)

A special instance of a LoST server. It is part of the Location to Service Translation (LoST) protocol query process and allows client functional elements to discover call routing information outside of its domain (typically their ESInet or state level ECRF/LVF).

A special instance of a LoST server. It is part of the Location to Service Translation (LoST) protocol query process and allows client functional elements to discover call routing information outside of its domain (typically their ESInet or state level ECRF/LVF).

An HTML-based, interactive, ease-of-use Web site feature, containing checkboxes, option lists, text boxes, and buttons that allow users to submit pre-formatted requests or queries or to respond to pre-formatted questions.

A complete and convincing mathematical argument, presenting the full logical justification for each proof step, for the truth of a theorem or set of theorems. The formal verification process uses formal proofs to show the truth of certain properties of formal specification and for showing that computer programs satisfy their specifications [TCSEC].

1. A mathematically precise statement of a system security policy. Some formal modeling techniques include: state transition models, temporal logic models, denotational semantics models, and algebraic specification models [POSIX.6].
2. A mathematically precise statement of a security policy. To be adequately precise, such a model must represent the initial state of a system, the way in which the system progresses… (Read More →)

A Top-Level Specification that is written in a formal mathematical language to allow theorems showing correspondence of the system specification to its formal requirements to be hypothesized and formally proven [TCSEC].

The process of using formal proofs to demonstrate the consistency (design verification) between a formal specification of a system and a formal security policy model or (implementation verification) between the formal specification and its program implementation [TCSEC].

1. The arrangement of bits or characters within a group, such as a word, message, or language.
2. The shape, size, and general makeup of a document.

1. In video and television technology, a device that allows the reformatting of a digital data stream originating from one sampling structure (lines per frame, pixels per line) into a digital data stream of another sampling structure for the purposes of recording or passing the original data stream through distribution devices designed to accommodate the latter structure.
Note: Since, in… (Read More →)

A combination of data units grouped in a prescribed sequence.

See language processor.

Any conductor that may provide an unintended path for signals.
Note: Examples of fortuitous conductors are water pipes, wires, cables, and metal building and equipment structural members.

Distortion resulting from causes generally subject to laws concerning random occurrences.

A computer conference devoted to a specific subject, having an initiator, members, readers, and possibly moderators. [2382-pt.35] Synonyms chat group, discussion group, discussion list, discussion thread, followup, interest group, library, newsgroup, yythread.

In a telecommunications system, a feature in which supervisory signals are forwarded in advance of address signals in order to seize assets of the system before attempting to establish a connection.

The channel of a data circuit that transmits data from the originating user to the destination user.
Note: The forward channel carries message traffic and some control information.

In a transmission line, an echo propagating in the same direction as the original wave and consisting of energy reflected back by one discontinuity and then forward again by another discontinuity.
Note: Forward echoes can be supported by reflections caused by splices or other discontinuities in the transmission medium (e.g., optical fiber, twisted pair, or coaxial tube). In metallic lines,… (Read More →)

A system of error control for data transmission wherein the receiving device has the capability to detect and correct any character or code block that contains fewer than a predetermined number of symbols in error.
Note: FEC is accomplished by adding bits to each transmitted character or code block, using a predetermined algorithm.

A bit in a signal unit which indicates the start of a retransmission cycle. [T1.226-1992]

Synonym ionospheric scatter.

The data reconstitution of a later version of data by using an earlier version and data recorded in a journal. [2382-pt.8]

The deflection--by diffraction, nonhomogeneous refraction, or nonspecular reflection by particulate matter of dimensions that are large with respect to the wavelength in question but small with respect to the beam diameter--of a portion of an incident electromagnetic wave, in such a manner that the energy so deflected propagates in a direction that is within 90° of the direction of propagation… (Read More →)

The confidence that the compromise of a long-term private key does not compromise any earlier session keys. [After X9.42]

A field in a signal unit used to identify the transmitted message signal units. [T1.226-1992]

A signal sent in the direction from the calling to the called station, i.e., from the original data source to the original data sink.
Note: The forward signal is transmitted in the forward channel.

1. Frequency of Optimum Transmission,
2. Frequency of Optimum Traffic,
3. Fiber Optic Terminals.

A two-way circuit using two paths so arranged that the respective signals are transmitted in one direction only by one path and in the other direction by the other path.
Note: The four-wire circuit gets its name from the fact that, historically, two conductors were used in each of two directions for full-duplex operation. The name may still be applied,… (Read More →)

A repeater, consisting of two amplifiers, one associated with each direction, used in a four-wire circuit.

A balanced transformer used to perform a conversion between 4-wire and 2-wire operation.
Note 1: For example, a 4-wire circuit may, by means of a 4-wire terminating set, be connected to a 2-wire telephone set. Also, a pair of 4-wire terminating sets may be used to introduce an intermediate 4-wire loop into a 2-wire circuit, in which loop repeaters may… (Read More →)

The definition of a periodic waveform of arbitrary shape as a summation of sine waves having specific amplitudes and phases, and having frequencies corresponding to the harmonics of the waveform being defined.
Note: A Fourier analysis is particularly well suited for communications equipment design and for predicting the performance of a given design. [From Weik '89]

A standard test message that includes all the alphanumerics on a teletypewriter and also function characteristics (yyspace, figures shift, letters shift).
Note: An example of a fox message is "THE QUICK BROWN FOX JUMPED OVER THE LAZY DOG'S BACK
123456789
0. "

Field Programmable Gate Array

Abbreviation for forward propagation ionospheric scatter. See ionospheric scatter.

Abbreviation for frames per second. In video and television, the number of images contained in a single second of a moving picture.
Note: Thirty fps is considered full-motion video in NTSC systems, while 25 fps is considered full-motion in PAL and SECAM systems. Many proprietary video technologies produce 15 fps video; 24 fps is considered full-motion in motion-picture technology.

Frame Relay

A mathematical formula or algorithm that constitutes or defines an efficient way of formulating computer graphics. Fractal graphics translate the natural curves of an object into mathematical formulas, from which the entire image can later be constructed. Fractals are self-similar in that any piece of the fractal design contains a miniature of the entire design. A fractal is completely described… (Read More →)

Synonym fractional frequency offset.

The deviation of the frequency of an oscillator from its nominal constant frequency, normalized to the nominal frequency.

A measure of the deviation of the frequency of a signal from a reference, expressed as a ratio. The ratio is dimensionless but typically expressed as parts per million, ppm. For example,
4. 6 ppm =
4. 6/10
6. Fractional frequency offset = [(f-fr) / fr] where: f = the actual frequency output of the signal in question, and fr… (Read More →)

In telecommunications, a portion of the
1. 544 Mb/s (T1-aggregate) bit stream; the available fractions being determined by the type of multiplexer used to achieve the T1 aggregate bit stream.

1. The process in which an IP (Internet protocol) datagram is broken into smaller pieces to fit the requirements of a given physical network; the reverse process of reassembly.
2. The physical separation of portions of a file on a computer disk.

1. In data transmission, the sequence of contiguous bits delimited by, and including, beginning and ending flag sequences.
Note 1: A frame usually consists of a specified number of bits between flag sequences and usually includes an address field, a control field, and a frame check sequence.
Note 2: Frames usually consist of a representation of the original data to… (Read More →)

1. In the reception of framed digital data, the extent to which a received frame is correctly aligned with respect to the clock at the receiver.
2. The state in which the frame of the receiving equipment is synchronized with that of the received signal. [T1.107-1988]

See cyclic redundancy check.

The time between the beginning of a frame and the end of that frame.
Note: For fixed-length frames, at a fixed data rate, frame duration is constant.

Synonym frame rate.

A device that can seize and record a single frame of video information out of a sequence of many frames.

The process of comparing one sequence of frames with another sequence of frames in order to determine the correspondence between frames in each sequence and the correspondence of individual frames.
Note: One means to test the correspondence between two video frames is to compare their digital representations on a pixel by pixel basis, and summarizing over all pixels as the… (Read More →)

Bits (binary digits) that are added at regular intervals to a digital signal at the sending end of a digital link and used to provide network functions such as framing, operations, administration, and maintenance. [T1.107-1988]

The distance, time, or number of bits between corresponding points, i.e., significant instants, in two consecutive frames. [From Weik '89]

The number of frames transmitted or received per unit time.
Note 1: The frame rate is usually expressed in frames per second.
Note 2: In television transmission, the frame rate must be distinguished from the field rate, which in the NTSC and other systems, is twice the frame rate. Synonym frame frequency.

An interface protocol for statistically multiplexed packet-switched data communications in which (a) variable-sized packets (frames) are used that completely enclose the user packets they transport, and (b) transmission rates are usually between 56 kb/s and
1. 544 Mb/s (the T-1 rate).
Note 1: In frame relay, (a) there is neither flow-control nor an error-correction capability, (b) there is information-content independence,… (Read More →)

A data unit exchanged at the user-network interface and having a format based on that defined in CCITT Recommendation Q.921 (1988) (ANSI T1.602). [T1.606-1990]

The data unit exchanged at the functional boundary between the core function of Q.921 and the end-to-end protocol implemented above the core functions of Q.92
1. [T1.606-1990]

The number of octets after the address field and before the frame check sequence (FCS) field in a frame. The octet count is done either before zero-bit insertion or after zero-bit extraction. [T1.615-1992]

In the reception of framed data, the loss of synchronization between a received frame and the receiver clock, causing a frame misalignment event, and resulting in the loss of the data contained in the received frame.
Note: A frame slip should not be confused with a dropped frame where synchronization is not lost, e.g., in the case of buffer overflow.

Of a received stream of framed data, the process by which incoming frame alignment signals, i.e., distinctive bit sequences, are identified, i.e., distinguished from data bits, permitting the data bits within the frame to be extracted for decoding or retransmission.
Note: The usual practice is to insert, in a dedicated time slot within the frame, a noninformation bit that is… (Read More →)

In digital communications, a prescribed recurring pattern of bits transmitted to enable the receiver to achieve frame synchronization.

Synonym reframing time.

In the transmission of data frames, a distinctive sequence of bits used to accomplish frame alignment.
Note: A frame-alignment signal may also contain additional bits for status, control, and error detection.

A time slot occupying the same relative position in every frame and used to transmit the frame alignment signal. [T1.107-1988]

With respect to television or other video display technologies, the process of transforming from one standard frame rate to another, using an algorithm.
Note: Standard display rates of 24, 25,
2
9. 97, 30, and 60 fps (frames per second) presently exist.

An interface through which information flow is partitioned into physical, periodic frames consisting of overhead information and an information payload.

1. In time-division multiplexing reception, synonym frame synchronization.
2. In video reception, the process of adjusting the timing of the receiver to coincide with the received video synchronization pulse.
3. In facsimile, the adjustment of the facsimile picture to a desired position in the direction of line progression.

1. A bit used for frame synchronization.
2. In a bit stream, a bit used in determining the beginning or end of a frame.
Note 1: The framing bit occurs at a specific position in the frame.
Note 2: In a bit stream, framing bits are noninformation bits.
Note 3: Framing in a digital signal is usually repetitive.

See frame-alignment signal, framing bit.

Synonym far-field diffraction pattern.

Synonym far-field region.

A radio net in which any station may communicate with any other station in the net without first obtaining the permission of the net-control station.
Note: Permission to operate as a free net is granted by the net-control station until such time as a directed net is established by the net-control station. [From Weik '89] See [for Internet systems] freenet.

The routing of messages in such a manner that they are forwarded toward their destination or addressee over any available channel without dependence upon predetermined routing. [From Weik '89]

A theoretical concept of space devoid of all matter.
Note: Free space also implies remoteness from material objects that could influence the propagation of electromagnetic waves.

In a synchronized oscillator, the capability to operate in the absence of a synchronizing signal.

Coupling of magnetic, electric, or electromagnetic fields that are not confined to a conductor.
Note: Coupling by the deliberate introduction of capacitors and inductors is not considered free-space coupling.

The signal attenuation that would result if all absorbing, diffracting, obstructing, refracting, scattering, and reflecting influences were sufficiently removed so as to have no effect on propagation.
Note: Free-space loss is primarily caused by beam divergence, i.e., signal energy spreading over larger areas at increased distances from the source.

A system of computer networks (usually funded by individuals or organizations) consisting of community-based bulletin board systems with, e.g., e-mail, information services, interactive communications, and conferencing, and that are available to the user free of charge, or for a small membership fee. See [for radio communications] free net.

Software that is developed usually by individuals or small companies and distributed, usually via FTP, at essentially no cost to the recipient.
Note: Often the developer or another party retains the copyright to the software product; therefore, freeware is not necessarily in the public domain, and its distribution may be controlled by the copyright owner.

A frame of visual information that is selected from a set of motion video frames, and is held in a buffer.

Television in which fixed ("still") images are transmitted sequentially at a rate far too slow to be perceived as continuous motion by human vision.
Note: Transmission of an image is usually performed periodically by a processing unit that contains memory in which data representing the image are stored. For an image of specified quality, e.g., resolution and color fidelity, freeze-frame… (Read More →)

The condition that occurs when an earlier nonactive speaker on an input transmission trunk channel becomes active and cannot immediately be assigned to a bearer channel, due to lack of free instantaneous transmission capacity. [T1.309-1990]

The ratio of the total time that the individual channels experience the freeze-out condition to the total time of the active intervals, and their corresponding hangover times and front end delays, for all transmission trunks over a fixed interval of time, e.g., 1 minute. [T1.309-1990]

1. For a periodic function, the number of cycles or events per unit time.
2. The number of cycles occurring per second of an electrical or electromagnetic wave; a number representing a specific point in the electromagnetic spectrum. [47CFR]

The degree of conformity to a specified value of a frequency.

Of an oscillator, the change in frequency, over time, caused by internal changes in oscillator parameters even when external factors, such as environment and power supply characteristics, are constant.

See allocation (of a frequency band).

See allotment (of a radio frequency or radio frequency channel).

1. Authorization, given by an Administration, for a radio station to use a radio frequency or radio frequency channel under specified conditions
2. The process of authorizing a specific frequency, group of frequencies, or frequency band to be used at a certain location under specified conditions, such as bandwidth, power, azimuth, duty cycle, or modulation. Synonym radio frequency channel assignment.

The power granted an Administration, or its designated or delegated leader or agency via treaty or law, to specify frequencies, or frequency bands, in the electromagnetic spectrum for use in systems or equipment.
Note: Primary frequency assignment authority for the United States is exercised by the National Telecommunications and Information Administration (NTIA) for the Federal Government and by the Federal… (Read More →)

1. The process by which the relative phases of precision clocks are compared for the purpose of defining a single time standard.
2. A process in which network synchronization is achieved by use, at all nodes, of oscillators that adjust their frequencies to the average frequency of the digital bit streams received from connected nodes.
Note: In frequency averaging, all… (Read More →)

See electromagnetic spectrum.

See allocation (of a frequency band).

See phase coherence.

1. Of an electronic device, the extent to which it will operate at its designed performance level in its intended operational environment (including the presence of interference) without causing interference to other devices.
2. The degree to which an electrical or electronic device or devices operating on or responding to a specified frequency or frequencies is capable of functioning with… (Read More →)

1. The difference between the instantaneous frequency of a digital signal and the long-term average frequency of that signal. [T
1. Rpt17-1993]
2. An unintentional deviation from the nominal frequency value.

1. The amount by which a frequency differs from a prescribed value, such as the amount an oscillator frequency drifts from its nominal frequency.
2. In frequency modulation, the absolute difference between (a) the maximum permissible instantaneous frequency of the modulated wave or the minimum permissible instantaneous frequency of the modulated wave and (b) the carrier frequency.
3. In frequency… (Read More →)

An electronic counter-countermeasure (ECCM) in which communications nets' operating frequencies are widely separated from each other, causing a requirement to spread jamming power over wider frequency bands and thus compelling a reduction of available jamming power on any single channel or frequency, or causing a requirement for more jamming power or more jamming equipment. [From Weik '89]

The end-to-end shift in frequency that may result from independent frequency translation errors in a circuit.

Synonym amplitude-vs. -frequency distortion.

Transmission and reception in which the same information signal is transmitted and received simultaneously on two or more independently fading carrier frequencies.

An undesired progressive change in frequency with time.
Note 1: Causes of frequency drift include component aging and environmental changes.
Note 2: Frequency drift may be in either direction and is not necessarily linear.

A short-term variation, with respect to time, of the frequency of an oscillator.
Note: Frequency fluctuation, f(t), is given by where (t) is the phase angle of the sinusoidal wave with respect to time, t.

A deviation of frequency that generally results from irregular motion of the recording medium during the recording, duplication, or reproduction. [T1.401-1988] Synonym [loosely] flutter.

1. The interchanging of the frequencies of carrier channels to accomplish specific purposes, such as to prevent feedback and oscillation, to reduce crosstalk, and to correct for a high frequency-response slope in the transmission line.
Note: Frequency frogging is accomplished by having modulators, which are integrated into specially designed repeaters, translate a low-frequency group to a high-frequency group, and vice… (Read More →)

A frequency band deliberately left vacant between two channels to provide a margin of safety against mutual interference.

[The] repeated switching of frequencies during radio transmission according to a specified algorithm, to minimize unauthorized interception or jamming of telecommunications. [NIS] [INFOSEC-99]
Note: The overall bandwidth required for frequency hopping is much wider than that required to transmit the same information using only one carrier frequency.

One frequency used for one hour regardless of the number of transmitters over which it is simultaneously broadcast by a station during that hour. [47CFR]

See frequency stability.

The condition in which a frequency-correcting feedback loop maintains control of an oscillator within the limits of one cycle.
Note: Frequency lock does not imply phase lock, but phase lock does imply frequency lock.

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.
Note 1: In FM, the carrier frequency is called the center frequency.
Note 2: FM is a form of angle modulation.
Note 3: In optical communications, even if the… (Read More →)

Synonym FOT.

See FOT.
In the transmission of radio waves via ionospheric reflection, the highest effective, i.e., working, frequency that is predicted to be usable for a specified path and time for 90% of the days of the month.
Note 1: The FOT is normally just below the value of the maximum usable frequency (MUF). In the prediction of usable frequencies, the… (Read More →)

The difference between the frequency of a source and a reference frequency.

A prediction of the maximum usable frequency (MUF), the optimum traffic frequency, and the lowest usable frequency (LUF) for transmission between two specific locations or geographical areas during various times throughout a 24-hour period.
Note: The prediction is usually indicated by means of a graph for each frequency plotted as a function of time. [From Weik '89]

A continuous range or spectrum of frequencies that extends from one limiting frequency to another.
Note 1: The frequency range for given equipment specifies the frequencies at which the equipment is operable. For example, filters pass or stop certain bands of frequencies. The frequency range for propagation indicates the frequencies at which electromagnetic wave propagation in certain modes or paths… (Read More →)

See insertion-loss-vs. -frequency characteristic.

A plot of the gain or attenuation of a device, such as an amplifier or a filter, as a function of frequency.
Note: A flat curve indicates a uniform gain or attenuation over the range of frequencies for which the curve is flat. Most amplifiers have a flat frequency response over a certain band, above and below which the gain… (Read More →)

Conducting a search for signals over a band or range of frequencies by means of a manually or automatically tuned receiver.
Note: The tuning rate, i.e., the frequency change rate, may be fixed or variable, or it may be performed mechanically at low speed or electronically at high speed. Frequency scanning may be used to enable a radar to transmit… (Read More →)

The assignment to or use of the same radio frequency by two or more stations that are separated geographically or that use the frequency at different times.
Note 1: Frequency sharing reduces the potential for mutual interference where the assignment of different frequencies to each user is not practical or possible.
Note 2: In a communications net, frequency sharing does… (Read More →)

1. Any change in frequency.
2. Any change in the frequency of a radio transmitter or oscillator.
Note: In the radio regime, frequency shift is also called rf shift.
3. See frequency-shift telegraphy.
4. In facsimile, a frequency modulation system where one frequency represents picture black and another frequency represents picture white. Frequencies between these two limits may represent shades… (Read More →)

See frequency standard.

See electromagnetic spectrum.

The situation that occurs when many stations transmit simultaneously using frequencies that are close together, i.e., with insufficient width of frequency guard bands or channel spacing.
Note: Frequency spectrum congestion causes (a) difficulty in discrimination by tuning, (b) overlap of (i) a sideband and an adjacent carrier, or (ii) upper and lower sidebands, respectively, of adjacent carriers, and (c) interference… (Read More →)

The degree to which variations of the frequency of an oscillator deviate from the mean frequency over a specified period of time.

A stable oscillator used for frequency calibration or reference.
Note 1: A frequency standard generates a fundamental frequency with a high degree of accuracy and precision. Harmonics of this fundamental frequency are used to provide reference points.
Note 2: Frequency standards in a network or facility are sometimes administratively designated as "primary" or "secondary. " The terms "primary" and "secondary,"… (Read More →)

A device that produces frequencies that are phase coherent with a reference frequency.
Note: The reference frequency may be derived from an internal or external source.

1. The maximum permissible departure by the center frequency of the frequency band occupied by an emission from the assigned frequency, or by the characteristic frequency of an emission from the reference frequency. Frequency tolerance is expressed in parts per 106 or in hertz. [NTIA] [RR]
Note: In the United States, frequency tolerance is expressed in parts per 10n, in… (Read More →)

The transfer of signals occupying a specified frequency band, such as a channel or group of channels, from one portion of the frequency spectrum to another, in such a way that the arithmetic frequency difference of signals within the band is unaltered.

Data compaction accomplished by using an expression composed of a number of different frequencies of different magnitudes to represent a particular curve.
Note: An example of frequency-analysis compaction is the use of a Fourier analysis to represent an arbitrary curve, a periodic function, an aperiodic function, or a wave shape. Thus, the fundamental frequency, the amplitude of the fundamental frequency,… (Read More →)

A signaling method in which one or more discrete frequencies correspond to each desired significant condition of a code.
Note 1: The transition from one set of frequencies to the other may be a continuous or a discontinuous change in frequency or in phase.
Note 2: Frequency-change signaling may be used in both supervisory signaling and data transmission.

A channel derived by dividing an allocated or available bandwidth over a medium into two or more portions, each usable separately.
Note: A frequency-derived channel is continuously available and may be further divided on either a frequency or time basis.

The use of frequency division to provide multiple and simultaneous transmissions to a single transponder.

The deriving of two or more simultaneous, continuous channels from a transmission medium by assigning a separate portion of the available frequency spectrum to each of the individual channels.

Frequency-change signaling in which the change from one significant condition to another is accompanied by decay in amplitude of one or more frequencies and by buildup in amplitude of one or more other frequencies.
Note: Frequency-exchange signaling applies to supervisory signaling and user-information transmission. Synonym two-source frequency keying.

A signal structuring technique employing automatic switching of the transmitted frequency. Selection of the frequency to be transmitted is typically made in a pseudo-random manner from a set of frequencies covering a band wider than the information bandwidth. The intended receiver would frequency-hop in synchronization with the code of the transmitter in order to retrieve the desired information. [NTIA] [RR]… (Read More →)

Frequency modulation in which the modulating signal shifts the output frequency between predetermined values.
Note 1: Usually, the instantaneous frequency is shifted between two discrete values termed the "mark" and "yyspace" frequencies. This is a noncoherent form of FSK.
Note 2: Coherent forms of FSK exist in which there is no phase discontinuity in the output signal. Synonyms frequency-shift modulation,… (Read More →)

Synonym frequency-shift keying.

Synonym frequency-shift keying.

Telegraphy by frequency modulation in which the telegraph signal shifts the frequency of the carrier between predetermined values. [NTIA] [RR]

See FAQ file.

Synonym near-field diffraction pattern.

In optics, the reflection of a portion of incident light at a discrete interface between two media having different refractive indices.
Note 1: Fresnel reflection occurs at the air-glass interfaces at the entrance and exit ends of an optical fiber. Resultant transmission losses, on the order of 4% per interface, can be reduced considerably by the use of index-matching materials.… (Read More →)

In radio communications, one of a (theoretically infinite) number of a concentric ellipsoids of revolution which define volumes in the radiation pattern of a (usually) circular aperture.
Note 1: The cross section of the first Fresnel zone is circular. Subsequent Fresnel zones are annular in cross section, and concentric with the first.
Note 2: Odd-numbered Fresnel zones have relatively intense… (Read More →)

A measure of the thermal noise generated in the first stage of a receiver.

A programmed-logic or stored-program device that interfaces data communication equipment with an input/output bus or memory of a data processing computer.

1. [A] security filter logically separated from the remainder of an information system (IS) to protect system integrity. Synonyms [loosely] firewall, proxy. [INFOSEC-99]
2. A process that is invoked to process data according to a specified security policy prior to releasing the data outside the processing environment or upon receiving data from an external source [TCSEC].

1. Of an antenna, the gain in a specified direction, i.e., azimuth, usually that of maximum gain, compared to the gain in a direction 180° from the specified azimuth.
Note: Front-to-back ratio is usually expressed in dB.
2. A ratio of parameters used to characterize rectifiers or other devices, in which electrical current, signal strength, resistance, or other parameters, in… (Read More →)

Full Service Access Network

Abbreviation for filtered symmetric differential phase-shift keying.

Abbreviation for frequency-shift keying.

Abbreviation for file transfer, access, and management.

File Transfer Protocol

A collection of files that are available by using file transfer protocol (FTP). Synonyms file archive, file site.

A method of accessing and retrieving FTP-based files via e-mail.

Historically, the telecommunications service initiated in 1964 by the Federal government to provide a consolidated communications capability to support the agencies with voice and data services that could endure when the public switched network was congested or otherwise incapacitated. GSA has awarded and maintained the FTS network since its inception. The FTS2000 designator was used in the 1988 contract award,… (Read More →)

Abbreviation for Federal Telecommunications System
200
0. The designation for a defunct Federal telecommunications contract replaced by the contract designated by the title "FTS200
1. "

Abbreviation for Federal Telecommunications System. A contract to provide a consolidated telecommunications capability to support Federal agencies with voice and data services (including local, long-distance, and international services) that can endure if the public switched network is congested or otherwise incapacitated. The FTS2000 contract was renegotiated for the FTS2001 contract to take advantage of pricing structures and unbundling rulings.

Fiber-to-the-Curb

Fiber-to-the-Home

1. Fiber-to-the-Node,
2. Fiber-to-the-Neighborhood.

Fiber-to-the-Premises

Fiber To The “x“ where “x“ = home (“H“), premise (“P“), or curb (“C“)

A carrier that is transmitted without reduction in power, i.e., a carrier that is of sufficient level to demodulate the sideband(s).

A single-sideband emission without reduction of the carrier. [NTIA] [RR]

Full width at half maximum in which the independent variable is time. See full width at half maximum.

The peak voltage level of a nominal 400-Hz sine wave required to excite the analog-to-digital converter of the transmit channel unit to the extremes of its encoding range. [T1.305-1990]

In an analog-to-digital converter, the condition in which the input signal amplitude has just reached the threshold at which clipping begins to occur. [From Weik '89]

All processing functions required to recover the information bits from a received signal.

An expression of the extent of a function, given by the difference between the two extreme values of the independent variable at which the dependent variable is equal to half of its maximum value.
Note 1: FWHM is applied to such phenomena as the duration of pulse waveforms and the spectral width of sources used for optical communications.
Note 2:… (Read More →)

A circuit that permits simultaneous transmission in both directions.

Synonym duplex operation.

In television, a video frame update rate that provides the appearance of full motion without flicker or smear problems.
Note: Picture motion appears to be full at greater than 16 fps (frames per second). European television operates at 25 fps and North American television at 30 fps.

See network topology.

See network topology.

Connectors from one source that mate with complementary components from other sources without mechanical damage and with transmission properties maintained within specified limits.

A domain name including all higher level domain names up to the top-level domain name; for example: Paris. nisc. sri. com is a fully qualified domain name for the host at
19
2. 3
3.
3
3. 109; nisc. sri. com is the fully qualified domain name for the NISC domain.
Note: The fully qualified domain name must be unique… (Read More →)

A set of signal elements that is used to transmit or represent a function-control character that actuates a control function, such as carriage return, line-feed, letters shift, or figures shift, that is to be performed by communications devices, such as teletypewriters and teleprinters. [From Weik '89]

In intelligent networks, an elemental call-processing component that directs internal network resources to perform specific actions, such as collecting dialed digits.
Note: An FC is unique to the intelligent-network-IN/2 architecture.

A standardization document that characterizes the requirements of a standard or group of standards, and specifies how the options and ambiguities in the standard(s) should be interpreted or implemented to (a) provide a particular information technology function, (b) provide for the development of uniform, recognized tests, and (c) promote interoperability among different network elements and terminal equipment that implement a… (Read More →)

In an integrated services digital network (ISDN), signaling in which the signaling messages are unambiguous and have clearly defined meanings that are known to both the sender and receiver of the messages.
Note: Functional signaling is usually generated by the data terminal equipment (DTE).

A combination of a communications link and the associated transfer control functions.

The portion of security testing in which the advertised features of a system are tested for correct operation [TCSEC].

1. An entity of hardware, software, or both, capable of accomplishing a specified purpose.
2. A functionally distinct part of a basic component [ITSEC].

The ability of equipment to operate as expected during actual service conditions in a central office. [T1.304-1989]

A predefined set of complimentary security enforcing functions capable of being implemented in a Target of Evaluation [ITSEC].

Of a periodic wave, the sinusoidal component, i.e., Fourier component, having the lowest frequency.
Note: Every periodic waveform may be expressed as the summation of the fundamental and its harmonics. For example, a square wave may be expressed as the summation of sine waves equal in frequency to the fundamental and all odd harmonics, each frequency having an appropriate amplitude… (Read More →)

The lowest order mode of a waveguide.
Note: In optical fibers, the fundamental mode is designated LP01 or HE11.

Synonym break out.

1. A device that has as its critical component a metal wire or strip that will melt when heated by a prescribed (design) amperage, creating an open in the circuit of which it is a part, thereby protecting the circuit from an overcurrent condition.
Note: Fuses are often characterized as "fast-blow" or "slow-blow," according to the time required for them… (Read More →)

Synonym vitreous silica.

Synonym (in cryptosystems) linkage.

In fiber optics, a splice created by localized heating of the ends of the two fibers to be joined.
Note: A properly made fusion splice results in a continuous length of material with minimal discontinuities at the splice.

Free Video On Demand

Firewall

Firewall/ Network Address Translation

Abbreviation for full width at half maximum.

Abbreviation for fixed service, foreign exchange service.