Telecom Dictionary - Definitions of terms
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
F
Facet Erosion - 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.
Facility - 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 as a block or frame, an additional item of information or a constraint encoded within the protocol to provide the required control. 5. A real property entity consisting of one or more of the following: a building, a structure, a utility system, pavement, and underlying land.
Facility Assembly - A group of interconnected equipment and transmission media uniquely identified and dedicated to a specific type of service.
Facility Code - 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.
Facility Grounding System - 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.
Facility Group - The particular group of facilities to route the call.
Facility Group Member - The specific member of a trunk group or a multi-line hunt group.
Facsimile - (FACSimile) Originally called "telecopying," it is the communication of a printed page between remote locations. Fax machines scan a paper form and transmit a coded image over the telephone system. The receiving machine prints a facsimile of the original. A fax machine is made up of a scanner, printer and modem with fax signaling. (see Fax)
Fax standards were developed starting in 1968 and are classified by Groups. Groups 1 and 2, used until the late 1980s, transmitted a page in six and three minutes respectively. Group 3 transmits at less than one minute per page and uses data compression at 9,600 bps. The Group 3 speed increase led to the extraordinary rise in usage in the late 1980s. Group 3 resolution is 203x98 dpi in standard mode, 203x196 in fine mode and 203x392 in super fine mode.
Group 3 is still the standard today, but Group 4 machines can transmit a page in just a few seconds and provide up to 400x400 resolution. Group 4 requires 56 to 64 Kbps bandwidth and needs ISDN or Switched 56 circuits. See fax/modem and e-mail.Facsimile Converter - 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).
Facsimile Frequency Shift - 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.
Facsimile Picture Signal - In facsimile systems, the baseband signal that results from the scanning process.
Facsimile Receiver - In a facsimile system, the equipment that converts the facsimile picture signal into a recorded copy.
Facsimile Recorder - 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.
Facsimile Signal Level - 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.
Facsimile Transceiver - 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.
Facsimile Transmitter - 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.
Fade - 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.
Fade Margin - 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.
Fading - 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.
Fading Distribution - 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. Note 3: The fading distribution may also be measured in terms of power level, where the unit of measure is usually watts per square meter and the expression is in dB.
Fading Margin - Synonym fade margin. 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.
Fail - See failure, graceful degradation. The temporary or permanent termination of the ability of an entity to perform its required function.
Fail Safe - 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. 3. The automatic protection of programs and/or processing systems when hardware or software failure is detected. 4. Pertaining to the structuring of a system such that either it cannot fail to accomplish its assigned mission regardless of environmental factors or that the probability of such failure is extremely low
Fail-Safe Operation - 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.
Fail Soft - The selective termination of affected nonessential processing, when hardware or software failure is determined to be imminent.
Failure - The temporary or permanent termination of the ability of an entity to perform its required function.
Failure Access - An Unauthorized access to data resulting from a hardware or software failure.
Failure Control - The methods used to detect imminent hardware or software failure and provide fail safe or fail soft recovery.
Fair Queuing - 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.
Fake Sector - 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.
Fall Time - 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 time limits. Synonym pulse decay time.
False Character - See illegal character. A character, or a combination of bits, that is not valid in a given system according to specified criteria, such as with respect to a specified alphabet, a particular pattern of bits, a rule of formation, or a check code.
False Clock - 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.
False Lock - A condition where a phase-locked loop locks to a frequency other than the correct one, or to an improper phase.
Fan-Beam Antenna - A directional antenna producing a main beam having a large ratio of major to minor dimension at any transverse cross section.
Fan Out - Synonym break out. To separate the individual fibers or buffer tubes of a fiber-optic cable for the purpose of splicing or installing optical connectors.
Fanout Cable - Synonym breakout cable. A multifiber fiber -optic cable design in which individual fibers, usually tight-buffered, are surrounded by separate strength members and jackets, which are in turn enveloped by a common jacket. Note 1: The breakout cable facilitates easy installation of fiber-optic connectors. All that need be done to prepare the ends of the cable to receive connectors is to remove the outer jacket, exposing what are essentially individual single-fiber cables. Note 2: Because it tends to induce bends in the fibers, the breakout cable design usually results in slightly higher transmission losses, for a given fiber, than loose- buffer designs.
FAQ - An acronym for Frequently Asked Questions. FAQs are online documents that list and answer the most common questions on a particular subject.
FAQ File - 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.
Faraday Effect - 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.
Far-End Block Error (FEBE) - An indication returned to a transmitting node (source) that an errored block has been detected at the receiving node (sink).
Far-End Crosstalk - 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.
Far-End Customer Interface - 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.
Far-End receive Failure (FERF) - 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.
Far Field - Synonym far-field region. 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 2D 2/
from the source,
Far-Field Region - 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 2D 2/
Far-Field Diffraction Pattern - 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 s 2 /
Far-Field Radiation Pattern - A radiation pattern measured at the far field of an antenna or other emitter.
Far-Field Region - 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 2D 2/
Far Zone - Synonym far-field region. - 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 2D 2/
Fast Packet Switching - 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.
Fast Select - 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.
Fat Client - 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.
Fault - 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.
Fault Management - 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 and manipulating database information.
Fault Protection Subsystem - 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."
Fault Tolerance - 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.
Fax Tone Detection -This feature, when activated, tells fax switch to detect the presence of CNG/fax tones which may be transmitted by a calling fax machine or PC Fax card. All calls accompanied by CNG tones, whether they be from a fax machine or PC Fax card, are routed through to equipment connected to the device port labeled FAX. If no fax-type equipment is used on fax switch, simply deactivate this feature.
Fax (Telecopying) - The telephonic transmission of scanned-in printed material (text or images), usually to a telephone number associated with a printer or other output device. The original document is scanned with a fax machine, which treats the contents (text or images) as a single fixed graphic image, converting it into a bitmap. In this digital form, the information is transmitted as electrical signals through the telephone system. The receiving fax machine reconverts the coded image and prints a paper copy of the document.
Almost all modems manufactured today are capable of sending and receiving fax data. Fax/modem software generates fax signals directly from disk files or the screen. Even if a document is text only, it is treated by the computer as a scanned image and is transmitted to the receiver as a bitmap. Faxing a message online works well if the recipient wants only to read the message. However, if the document requires editing, it must be converted into ASCII text by an OCR (optical character recognition) program, or it must be retyped manually into the computer. A more efficient method of sending documents that require modification is through the e-mail system. E-mail files are already ASCII text so they can be edited immediately in any text editor or word processing program.
The Internet now provides a new and cheaper way to send faxes in some cases. A number of free and commercial companies provide arrangements for using the Internet rather than the public telephone system for most or part of the path to the fax point. Some services also provide the ability to broadcast a fax to multiple addresses. Acronym for facsimile.
Fax Board - Fax capability built onto a printed circuit board. Today, most fax boards are fax/modems, which also provide data transmission. See fax/modem.
Fax Group - An encoding format used for fax transmission. There are two types: Fax Group 3, also known as G3, and Fax Group 4, also known as G4. Fax Group 3 and 4 are two of the encoding formats for Tagged Image File Format (TIFF) files. The more commonly used format, Fax Group 3, is Recommendation T.4 of the
CCIT , now known as the ITU-T (for Telecommunication Standardization Sector of the International Telecommunications Union). Fax Group 3 supports one-dimensional image compression of black and white images, On a standard fax machine, Fax Group 3 uses redundancy reduction to enhance speed and is able to transmit a page in one minute or less. Fax Group 3 can achieve compression ratios of 10:1 for office documents and 15:1 for engineering drawings with a resolution of 200 dots per inch (dpi).Less frequently used, Fax Group 4 (G4) is ITU-T Recommendation T.6 and supports two-dimensional image compression, compressing the line width as well as the line length. Fax Group 4 can achieve compression ratios of 15:1 for office documents and 20:1 for engineering drawings with a resolution of 400 dpi. Unlike Fax Group 3, Fax Group 4 can use Integrated Services Digital Network (ISDN) for transmission.
Fax Logger - Automatically storing copies of incoming and outgoing faxes onto some storage medium.
Fax Machine (Facsimile) - A device that attaches to your telephone line and is capable of scanning a document, electronically transmitting and receiving the image, and printing the image(sometimes called "TELEFAX" or "TELECOPIER")Fax/Modem - A combination fax board and data modem available as an external unit that plugs into the serial port of the computer or as an expansion board for internal installation. It includes a switch that routes the call to the fax or data modem. Incoming faxes are printed on the computer's printer. Most all modems today are fax/modems.
A fax/modem requires software that generates the fax transmission from typed-in text, a disk file or from a screen image. Fax/modems often transmit a sharper image than a fax machine, which obtains its source material by scanning the page.
Group 3 fax/modems provide various levels of processing based upon their service class. Class 1 devices perform basic handshaking and data conversion and are the most flexible, because much of the work is done by the computer's CPU. Class 2 devices establish and end the call and perform error checking. There are a variety of de facto Class 2 implementations and one Class 2.0 standard. As PCs have become more powerful, future service classes with more features are unlikely.Fax Modem Switch - A device that allows a single phone line to be shared for a fax machine and a modem. When a call comes in and it is a fax call, the call is automatically routed to the fax machine or fax.modem. If the call is a modem call, it is routed to the correct modem.. Some devices handle voice, fax and data modem switching. May require a security access code (SAC) in the dialing string to automatically switch to the modem.
Fax over Internet Protocol (FoIP) - The fax counterpart to VoIP, available from some providers either free or at additional cost. FoIP is actually more reliable than VoIP because of its tolerance for poor latency.
Fax Phone Switch - A device that tests a phone line for a fax signal and routes the call to the fax machine. When a fax machine dials a number and the line answers, it emits an 1100Hz signal (CNG tone) to identify itself. Tone Detection Fax Phone Switches listen for this signal and if present, automatically routes the call to a fax machine, fax modem or fax printer. Calls without the fax tones are automatically routes to phones or phone system. Some devices handle voice, fax and data modem switching and may require keying in a security access code (SAC) to switch to the modem. Distinctive Ring Fax Phone Switches use a phone company feature called distinctive ring to route the calls instead of using tones. See CNG tone. Synonyms Automatic Fax Switch , Fax Switch , Phone Fax Switch , Fax Modem Switch. For more info see Fax Switch.
Fax Server - A computer in a network that provides a bank of fax/modems, allowing users to fax out and remote users to fax in over the next available modem. The fax server may be a dedicated machine or implemented on a file server that is providing other services.
A fax server (or faxserver) is a system installed in a local area network (LAN) server that allows computer users who are attached to the LAN to send and receive fax messages. Fax messages can be stored as printable word processing, graphics, database, or spreadsheet files. Scanned documents can be sent as fax messages, allowing a computer and scanner to effectively emulate a dedicated fax machine.
A fax server is composed of a computer with a fax program, a
fax modem (a modem capable of sending and receiving fax signals as well as conventional Internet data), a connection to the Internet or a telephone line, and connections to the LAN users.There are several advantages to a fax server when compared with an ordinary fax machine. A single fax server can emulate multiple fax machines (one for each network user), thereby reducing overhead. Some functions can be automated. For example, a business fax server can automatically send invoices and purchase orders to customers and suppliers at specified times. Received faxes can be automatically stored as files on the server, and retrieved later by network users. In addition, a fax server can function without paper, reducing clutter and eliminating the need to continually check paper trays.
The term "fax server" is sometimes used to describe a program that enables a computer to send and receive fax messages.
Fax Switch - A device that analyses incoming phone calls for a fax signal and routes the call to the fax machine. When a fax machine dials a number and the line answers, it emits an 1100Hz signal (CNG tone) to identify itself. A tone detection fax switch listens for these CNG tones and if present, routes the call to the fax device. Another type of fax switch is a distinctive ring fax switch, which is a device that tests a phone line for a distinctive ring signal and routes the call to a specific device (example: phone, phone system, answering machine, fax machine. fax modem). For more info see Distinctive Ring Definition and Use. Some devices handle voice, fax and data modem switching and may require keying in a security access code (SAC) to switch to the modem. See CNG tone. For more info see Fax Switch.
Fax Switches - Fax Switches test a phone line for a fax signal and routes the call to the fax machine. When a fax machine dials a number and the line answers, it emits an 1100Hz signal (CNG tone) to identify itself. Some devices handle voice, fax and data modem switching and may require keying in a security access code (SAC) to switch to the modem. See CNG tone. For more info see Fax Switches.
Fax Tone Detection-This feature, when activated, tells automatic call processors and fax switches to detect the presence of CNG/fax tones which may be transmitted by a calling fax machine or PC Fax card. All calls accompanied by CNG tones, whether they be from a fax machine or PC Fax card, are routed through to equipment connected to the device port labeled FAX. If no fax-type equipment is used on the line sharing device, simply deactivate this feature. Typically with most line sharing equipment the factory preset is "on".
FC - Abbreviation for functional component. - 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.
FCC - Federal Communications Commission. The U.S. Government board made up 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 Information Administration (NTIA).
The FCC is the regulator of telephone and telecommunications services in the United States. It's not yet known the full extent to which the FCC will regulate VoIP communications. Part of the complication lies with determining the regulation of communications that begin or end on an FCC-regulated system, such as the standard telephone service.
FCC Registration Program - 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 of Federal Regulations. This includes the assignment of identification numbers to the equipment and the testing of the equipment. Note 2: The FCC registration program contains no requirement that accepted terminal equipment be compatible with, or function with, the network.
FCS - Abbreviation for frame check sequence. See cyclic redundancy check. 1. An error - detection scheme that (a) uses parity bits generated by polynomial encoding of digital signals, (b) appends those parity bits to the digital signal, and (c) uses decoding algorithms that detect errors in the received digital signal. Note: Error correction, if required, may be accomplished through the use of an automatic repeat-request ( ARQ ) system. 2. An error checking mechanism that checks data integrity by computing a polynomial algorithm based checksum.
FDDI - Abbreviation for fiber distributed data interface. 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 X3T9.5, containing Physical Media Dependent (PMD) specifications, (b) ANSI X3T9.5, containing the Physical (PHY) specifications, (c) ANSI X3.139, containing Media Access Control ( MAC ) specifications, and (d) ANSI X39.5, containing the Station Management (SMT) specifications. Note 2: The data rate of an FDDI ring may be doubled to 200 Mb/s, with loss of redundancy. Note 3: FDDI-2 , a second- generation FDDI network standard, is under development.
FDDI-2: See fiber distributed data interface. FDDI-2, a second-generation FDDI network standard, is under development.
FDHM - See full width at half maximum. 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: The term full duration at half maximum ( FDHM ) is preferred when the independent variable is time.
FDM - Abbreviation for frequency-division multiplexing. 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.
FDMA - Abbreviation for frequency-division multiple access. The use of frequency division to provide multiple and simultaneous transmissions to a single transponder.
FDX - Abbreviation for full duplex. See full-duplex (FDX) circuit, full-duplex (FDX) operation. A circuit that permits simultaneous transmission in both directions.
Feature Code - 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).
FEC - Abbreviation for forward error correction. 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.
Federal Communications Commission - See FCC. The U.S. Government board made up 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 Information Administration (NTIA).
Federal Excise Tax - A 3% tax mandated by the federal government imposed on all telecommunications services including local, long distance and wireless bills.
Federal Networking Council (FNC) - The body responsible for coordinating networking needs among U.S. Federal agencies.
Federal Subscriber Line Charge - This is a charge paid by consumers implemented by the Federal Communications Commission (FCC). It is intended to recover some of the costs associated with a customer's local telephone line to access the interstate long distance network. It helps keep interstate long distance rates low. You pay this charge whether or not you actually make long distance calls.
Federal Telecommunications System (FTS) - A switched long-distance telecommunications service formerly provided for official Federal Government use. Note: FTS has been replaced by Federal Telecommunications Service 2000 (FTS2000).
Federal Telecommunications System 2000 Service - See FTS2000. The designation for a defunct Federal telecommunications contract replaced by the contract designated by the title "FTS2001."
Federal Universal Service Charge – See "Universal Service Fund Surcharge"
Feed - 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 as is generated in a radio or television studio, and (b) the head-end of a distribution facility, such as a broadcasting station in a network. 4. Pertaining to the function of inserting one thing into another, such as in a feed horn, paper feed, card feed, and line feed.
Feedback - 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, of the overall circuit. Note 2: If the feedback is regenerative (additive), it is called "positive feedback," which increases gain and distortion, and decreases linearity and stability. Note 3: If the feedback is degenerative (subtractive), it is called "negative feedback," which reduces the gain and distortion, and increases linearity and stability. Note 4: Feedback may occur inadvertently, and be detrimental. 2. Information returned as a response to an originating source.
Feedback Path - The signal path from the input of the bit-masking block to the output of the adaptive predictor.
Feeder Echo Noise - 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.
Feeder Link - 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.
Feed-Forward Path - 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.
FEP - Abbreviation for front-end processor. A programmed-logic or stored-program device that interfaces data communication equipment with an input / output bus or memory of a data processing computer.
Fermat's Principle - 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.
Fetch Protection - 1. [An] AIS-provided restriction to prevent a program from accessing data in another user's segment of storage. 2. [An] information-system (IS) hardware-provided restriction to prevent a program from accessing data in another user's segment of storage.
FET photodetector: A photodetector using photogeneration of carriers in the channel region of a field-effect transistor structure to provide photodetection with current gain.
Fiber - See optical fiber. A filament of transparent dielectric material, usually glass or plastic, and usually circular in cross section, that guides light. Note 1: An optical fiber usually has a cylindrical core surrounded by, and in intimate contact with, a cladding of similar geometry. Note 2: The refractive index of the core must be slightly higher than that of the cladding for the light to be guided by the fiber.
Fiber Amplifier - 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 high-powered continuous output at an optical frequency slightly higher than that of the communication signal. The signal is intensified by Raman amplification. Note 2: Because neither optical-electrical conversion nor electrical amplification takes place, this type of amplifier is well suited for a wide variety of applications, both digital and analog. Note 3: Because this type of amplifier does not require extraordinary frequency (wavelength) control of the pumping laser, it is relatively simple.
Fiber Axis - 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.
Fiber Bandwidth - See bandwidth (of an optical fiber).
Fiber Buffer - See buffer. In a fiber optic communication cable, one type of component used to encapsulate one or more optical fibers for the purpose of providing such functions as mechanical isolation, protection from physical damage and fiber identification. Note: The buffer may take the form of a miniature conduit, contained within the cable and called a loose buffer, or loose buffer tube, in which one or more fibers may be enclosed, often with a lubricating gel. A tight buffer consists of a polymer coating in intimate contact with the primary coating applied to the fiber during manufacture.
Fiber Cable - See fiber optic cable. A telecommunications cable in which one or more optical fibers are used as the propagation medium. 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 conductors is the transmission of electric power for repeaters. Synonyms optical cable, optical fiber cable.
Fiber Cutoff Wavelength (
Fiber Dispersion - See dispersion. In optical fiber communications, the incorrect terms " multimode dispersion " and " intermodal dispersion " should not be used as synonyms for the correct term " multimode distortion." Note: In classical optics, "dispersion" is used to denote the wavelength dependence of refractive index in matter, (dn/d
- material dispersion: In optical fiber communication, the wavelength dependence of the velocity of propagation (of the optical signal) on the bulk material of which the fiber is made. Note 1: Because every optical signal has a finite spectral width, material dispersion results in spreading of the signal. Note 2: Use of the redundant term " chromatic dispersion " is discouraged. Note 3: In pure silica, the basic material from which the most common telecommunication-grade fibers are made, material dispersion is minimum at wavelengths in the vicinity of 1.27
m (slightly longer in practical fibers).
- profile dispersion: In an optical fiber, that dispersion attributable to the variation of refractive index contrast with wavelength. Profile dispersion is a function of the profile dispersion parameter.
- waveguide dispersion: Dispersion, of importance only in single-mode fibers, caused by the dependence of the phase and group velocities on core radius, numerical aperture, and wavelength. Note 1: For circular waveguides, the dependence is on the ratio, a /
Fiber Distributed Data Interface (FDDI) - 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 X3T9.5, containing Physical Media Dependent (PMD) specifications, (b) ANSI X3T9.5, containing the Physical (PHY) specifications, (c) ANSI X3.139, containing Media Access Control (MAC) specifications, and (d) ANSI X39.5, containing the Station Management (SMT) specifications. Note 2: The data rate of an FDDI ring may be doubled to 200 Mb/s, with loss of redundancy. Note 3: FDDI-2, a second-generation FDDI network standard, is under development.
Fiber Optic (or "optical fiber") - Refers to the medium and the technology associated with the transmission of information as light impulses along a glass or plastic wire or fiber. Fiber optic wire carries much more information than conventional copper wire and is far less subject to electromagnetic interference. Most telephone company long-distance lines are now fiber optic.
Transmission on fiber optic wire requires repeating at distance intervals. The glass fiber requires more protection within an outer cable than copper. For these reasons and because the installation of any new wiring is labor-intensive, few communities yet have fiber optic wires or cables from the phone company's branch office to local customers (known as local loop).
Fiber Optic Bus - See bus. One or more optical fibers that serve as a common connection for a group of related devices.
Fiber Optic Cable - A telecommunications cable in which one or more optical fibers are used as the propagation medium. 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 conductors is the transmission of electric power for repeaters. Synonyms optical cable, optical fiber cable.
Fiber Optic Isolator - See optical isolator. A device that uses a short optical transmission path to accomplish electrical isolation between elements of a circuit. Note 1: The optical path may be air or a dielectric waveguide. Note 2: The transmitting and receiving elements of a fiber optic isolator may be contained within a single compact module, for mounting, e.g., on a circuit board.
Fiber Optic Link - A communications link that transmits signals by means of modulated light propagated in an optical fiber.
Fiber Optics (FO): The branch of optical technology concerned with the transmission of light through fibers made of transparent materials such as glasses and plastics. 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 of fiber optics, such as endoscopes, use flexible fiber bundles in which individual fibers are spatially aligned, permitting optical relay of an image. Note 3: Some specialized industrial applications use rigid (fused) aligned fiber bundles for image transfer; such as in the fiber optics faceplates used on some cathode ray rubes (CRTs) to "flatten" the image.
Fiber Pigtail - See pigtail. A short length of optical fiber that is permanently affixed to an active device, e.g., LED or laser diode, and is used to couple the device, using a splice or connector, to a longer fiber. 2. A short length of single-fiber cable, usually tight-buffered, that has an optical connector on one end and a length of exposed fiber at the other end. Note: The exposed fiber of the pigtail is then spliced to one fiber of a multifiber trunk, i.e., arterial, cable, to enable the multifiber cable to be "broken out" into individual single-fiber cables that may be connected to a patch panel or an input or output port of an optical receiver or transmitter. 3. A short length of electrical conductor permanently affixed to a component, used to connect the component to another conductor.
Fidelity - 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.
FidoNet - A network designed for e-mail distribution through individual bulletin board systems rather than through Internet servers.
Field - 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 a record that may contain a data item, a data aggregate, a pointer, or a link. 5. In an interlaced, raster -scanned video display, a partial frame, consisting of every nth scanning line of a complete frame, where n is an integer equal to the number of fields (usually two) in a complete frame. Note 1: For example, in the National Television Standards Committee (NTSC) television specification used in the United States, a single frame is composed of two fields, each of which has half the number of scanning lines in a complete frame. The scanning lines of a field are separated by twice the space between the scanning lines in the full frame. The two fields are interlaced, i.e. , a complete frame consists of the following traces, which are listed in the order of their appearance in the complete frame, but not the order in which scanning occurs: the first line of the first field, the first line of the second field, the second line of the first field, the second line of the second field, the third line of the first field, the third line of the second field, etc. , until completion of the full frame. The fields are scanned alternately, one complete field at a time. Thus, the flicker rate of the display is perceived by the eye to be twice as fast as that which would result if the complete frame were to be scanned in line-by-line order. Note 2: Not all scanning lines are necessarily applied to user information, i.e. , the graphic display. Certain scanning lines, not seen under ordinary viewing conditions, are often used for transmitting test signals that indicate the quality of the displayed video.
Field-Disturbance Sensor - 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.
Field Intensity - The irradiance of an electromagnetic wave under specified conditions. Note: Field intensity is usually expressed in watts per square meter
Field Strength - 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 in the horizontal plane.
Field Tag - Synonym flag. 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.
Field Wire - 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.
FIFO - Abbreviation for first-in first-out. 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.
File - 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.
File Archive - Synonym FTP archive. A collection of files that are available by using file transfer protocol (FTP). Synonym file site.
File Name Extension - 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 (graphics file)
.txt = a text file.
2. Proprietary HTML tags that are recognized by a single Web browser or by those Web browsers developed by a single company.
File-Oriented Applications - Applications concerned with the storage, manipulation, and exchange of information between application processes in the form of files.
File Protection - 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.
File Security - [A] means by which access to computer files is limited to authorized users only.
File Server - 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.
File Site - Synonym FTP archive. A collection of files that are available by using file transfer protocol (FTP).
File Transfer - In networking, a service to move a part or the whole of a file's content over a computer network.
File Transfer, Access, and Management (FTAM) - 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.
File Transfer Protocol (FTP) - A common method for sending and/or receiving files between Internet sites using a login system. Publicly accessed FTP sites are often called anonymous FTPs.
Fill - See bit stuffing. The insertion of noninformation bits into data. Note 1: Stuffed bits should not be confused with overhead bits. Note 2: In data transmission, bit stuffing is used for various purposes, such as for synchronizing bit streams that do not necessarily have the same or rationally related bit rates, or to fill buffers or frames. The location of the stuffing bits is communicated to the receiving end of the data link, where these extra bits are removed to return the bit streams to their original bit rates or form. Bit stuffing may be used to synchronize several channels before multiplexing or to rate-match two single channels to each other. Synonym positive justification.
Fill Bit - See bit stuffing. The insertion of noninformation bits into data. Note 1: Stuffed bits should not be confused with overhead bits. Note 2: In data transmission, bit stuffing is used for various purposes, such as for synchronizing bit streams that do not necessarily have the same or rationally related bit rates, or to fill buffers or frames. The location of the stuffing bits is communicated to the receiving end of the data link, where these extra bits are removed to return the bit streams to their original bit rates or form. Bit stuffing may be used to synchronize several channels before multiplexing or to rate-match two single channels to each other.
Fill Device - [A] COMSEC item used to transfer or store key in electronic form or to insert key into a crypto-equipment.
Filled Cable - 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 a dielectric material, is not considered as a filled cable.
Fill-in Area - 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).
Fill-in Signal Unit (FISU) - 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.
FILO - Abbreviation for first-in last-out. 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.
Filter - 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 frequency band
Filtered Symmetric Differential Phase-Shift Keying (FSDPSK) - 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.
Final Trunk Group - 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.
Finger - 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.
Finished Call - 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.
FIP - Acronym for Federal Information Processing.
FIP Equipment - 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.
FIP System - In the Federal government, any organized combination of FIP equipment, software, services, support services, or related supplies.
FIREFLY - [A] key management protocol based on public key cryptography.
Firewall - 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 service ); (b) making internal addresses invisible and directly unaccessible from outside and passing through authorized traffic after proper checking (a proxy service); (c) facilitating protected (encrypted) connections to cooperative parties over public networks (a tunneling service); (d) filtering outgoing traffic for security and network usage rules (filtering or monitoring service); (e) filtering incoming traffic for rogue data (viruses, spam, inappropriate data (filtering), or improper actions ( port scanning, overload prevention, etc. ; (f) blocking forbidden external services or addresses (blocking, "network nanny"-functions); (g) providing log -in services for authorized outside users and simulating the approved outside user as an inside user (proxy, log-in server ); (h) caching network traffic (cache service); (i) converting between different network protocols on different protocol levels (bridge when handling lower level protocols, gateway when handling higher level protocols); (j) traffic diverting ( e.g., for cost optimizing, accounting, network planning, monitoring); (k)providing consistent, open entry to the internal network ( portal service) and facilitating public network address and connection sharing (proxy service). 2. A system designed to defend against unauthorized access to or from a private network. Firewalls can be implemented in both hardware and software, or a combination of both.
Firmware - 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: Another example of firmware is a program embedded in an erasable programmable read-only memory (EPROM) chip, which program may be modified by special external hardware, but not by an application program. 2. A program recorded in permanent or semipermanent computer memory.
First-In First-Out (FIFO) - 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.
First-In Last-Out (FILO) - 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.
First-Route Traffic - Traffic that has not been route-advanced at any switching system.
First Window - Of silica-based optical fibers, the transmission window at approximately 830 to 850 nm.
FISINT - Acronym for foreign instrumentation signals intelligence. - 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 to signals from telemetry, beaconry, electronic interrogators, tracking/fusing/ arming/firing command systems, and video data links.
Five-Hundred (500) Service - 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.
Fixed Access - 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.
Fixed Attenuator - See pad. A network, of fixed resistors, that attenuates signals by a fixed amount with negligible distortion. Note: The resistive network is called an attenuator if the resistance is adjustable.
Fixed Loop - 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.
Fixed Microwave Auxiliary Station - 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.
Fixed-Reference Modulation - Modulation in which the significant condition for any signal element is based on a fixed reference.
Fixed-Satellite Service -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 space radiocommunication services. 2. 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 operated in the inter-satellite service; the fixed-satellite service may also include feeder links of other space radiocommunication services.
Fixed Service (FX) - A radiocommunication service between specified fixed points.
Fixed Station 1. A station in the fixed service. 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.
Fixed Storage - Synonym read-only storage. A storage device in which the contents cannot be modified, except by a particular user, or when operating under particular conditions, e.g. , a storage device in which writing is prevented by a lockout.
Fixed-Tolerance-Band Compaction - 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 unless a signal to the contrary occurs.
Flag: 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,
