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raceway: Within a building, an radar blind range: The range that corresponds to theenclosure, i.e., channel, used to situation in which a radar transmitter is on and hencecontain and protect wires, cables, or the receiver must be off, so that the radar transmittedbus bars. (188) signal does not saturate, i.e., does not blind, its own

rack: A frame upon which one ormore units of equipment are mounted. (188) Note:DOD racks are always vertical.

racon: See radar beacon.

rad: Acronym for radiation absorbed dose. Thebasic unit of measure for expressing absorbed radiantenergy per unit mass of material. Note 1: A radcorresponds to an absorption of 0.01 J/kg, i.e., 100ergs/g. Note 2: The absorbed radiant energy heats,ionizes, and/or destroys the material upon which it isincident.

rad.: Abbreviation for radian(s).

radar: Acronym for radio detection and ranging. 1.A radio detection system that transmits short bursts(pulses) of rf energy and detects their echos fromobjects (targets) such as aircraft or ships. Note: Theround-trip propagation time for the echo return maybe used to determine the target’s range (distance fromthe radar’s antenna). If the transmitting antenna hasa narrow beam (the usual case), the azimuth orelevation of the target may also be determined.Synonym primary radar. Contrast with secondaryradar. 2. A radio detection device that providesinformation on range, azimuth, and/or elevation ofobjects. [JP1] 3. A radiodetermination system basedon the comparison of reference signals with radiosignals reflected, or retransmitted, from the positionto be determined. [NTIA] [RR]

radar beacon (racon): 1. A transmitter-receiverassociated with a fixed navigational mark which,when triggered by a radar, automatically returns adistinctive signal which can appear on the display ofthe triggering radar, providing range, bearing andidentification information. [NTIA] [RR] 2. Areceiver-transmitter combination which sends out acoded signal when triggered by the proper type ofpulse, enabling determination of range and bearinginformation by the interrogating station or aircraft.[JP1]

receiver. Note: Radar blind ranges occur becausethere is a time interval between transmitted pulses thatcorresponds to the time required for a pulse topropagate to the object, i.e., to the target, and itsreflection to travel back. This causes an attempt tomeasure the range just as the radar transmitter istransmitting the next pulse. However, the receiver isoff, therefore this particular range cannot bemeasured. The width of the range value that cannotbe measured depends on the duration of the time thatthe radar receiver is off, which depends on theduration of the transmitted pulse. The return-timeinterval could be coincident with the very next radar-transmitted pulse, i.e., the first pulse following atransmitted pulse, or the second, or the third, and soon, giving rise to a succession of blind ranges. Theblind ranges are given by r = (mc)/(2fn), where r ism m

the blind range for a given value of m, m is a positiveinteger that indicates which of the blind ranges isbeing determined, c is the velocity of electromagneticwave propagation in vacuum (approximately 3 × 108

m/s), f is the radar pulse repetition rate, and n is therefractive index of the transmission medium (nearly 1for air). The radar blind range is independent of theradar radio frequency (rf) of the radar pulse. [FromWeik ’89]

radar blind speed: The magnitude of the radialcomponent of velocity of an object, i.e., a target,relative to a radar site, that cannot be measured by theradar unit. Note: Radar blind speeds occur because ofthe relationship between the transmitted pulserepetition rate (PRR) and the received pulse-repetitionrate. The Doppler pulse repetition rate is thedifference between the transmitted and received pulserepetition rates. For example, when the object isstationary with respect to the radar site, the reflectedPRR is the same as the transmitted PRR and thereforea net zero signal is indicated for the radial componentof velocity. If it happens that the Doppler PRR is thesame as the transmitted PRR, i.e., the illuminatingPRR, or it is a multiple of the transmitted PRR, a zerosignal is also obtained and hence the radar is blind tothese speeds, one for each multiple of the transmittedpulse repetition rate. It is not the absolute magnitudeof the speed of the object that is measured, but onlythe radial component of the speed. The radial

RHRs 2h � 2a

w 1.414 h � a ,

RHRk w 4.12 h � a ,

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components of blind speeds, v , are given by Second-order differentials are neglected. Theym

v = m�f/102, where v is the blind speed in knots, m contribute less than 0.1%. [From Weik ’89]m

is the multiple of the radar pulse repetition rate andthe number of the blind speed, namely a positiveinteger, 1, 2, 3, 4, . . ., for the first, second, third,fourth, and so on, blind speed, � is the wavelength ofthe illuminating radar in centimeters; f is thetransmitter pulse repetition rate in pps (pulses persecond); and the 102 is a units conversion factor.[From Weik ’89]

radar cross section: An expression of the extent towhich an object, i.e., a target, reflects radar pulses,usually with respect to their point of origin. Note:The radar cross section of an aircraft can vary by afactor of over 100, depending on the aspect angle ofthe aircraft to the radar transmitter. Radar reflectionoff the nose of the aircraft usually represents thesmallest radar cross section, while a broadsidepresentation to the signal produces the greatest crosssection. Shape, surface roughness, and reflectivematerial as well as orientation also affect the radarcross section. [From Weik ’89]

radar intelligence (RADINT): Intelligence derived with range. These are given by W = (HBW)(R/57)from data collected by radar. [JP1] and H = (VBW)(R/57), where W is the width of the

radar line-of-sight (LOS) equation: An equation thatexpresses the radar horizon range (RHR), given by

where RHR is the radar horizon range in statutes

miles, h is the antenna height in feet, and a is theobject critical altitude, i.e., the target altitude in feet, radar signature: 1. The detailed waveform of abelow which the radar cannot illuminate the object. detected radar echo. Note: Radar signatures may beNote: The RHR is also given by used to identify or distinguish among objects, i.e.,

where RHR is the radar horizon range in kilometersk

when h and a are in meters. The effective Earthradius, namely 4/3 times the actual Earth radius, isused in deriving these formulas. The effective Earthradius for LOS varies with carrier frequency.

radar mile: The time required for a radar pulse totravel 1 mile (~1.6 km) to an object, i.e., to a target;reflect; and return to the receiver. Note: A radarstatute mile is approximately 10.8 µs (microseconds);a radar nautical mile is approximately 12.4 µs. Thetime for any other radar unit distance is readilydetermined, such as the radar meter or the radarkilometer. [From Weik ’89]

radar resolution cell: The volume of space that isoccupied by a radar pulse and that is determined bythe pulse duration and the horizontal and verticalbeamwidths of the transmitting radar. Note: Theradar cannot distinguish between two separate objectsthat lie within the same resolution cell. The radarresolution cell depth (RCD) remains constantregardless of the distance from the transmittingantenna. It does not increase with range. The RCD isgiven by RCD = 150d, where the RCD is in metersand d is the pulse duration in microseconds. Theheight of the cell and the width of the cell do increase

cell, HBW is the horizontal beamwidth in degrees, Ris the range, H is the height of the cell, and VBW isthe vertical beamwidth in degrees. The range, R, isthe distance from the radar antenna to the reflectingobject, i.e., the target. The width and height willcome out in the same units in which the range isgiven. For example, if the range is given in meters,the width and height of the radar resolution cell willbe in meters. The 57 merely converts degrees toradians. If the beamwidths are given in radianmeasure, the 57 is omitted. [From Weik ’89]

targets, such as aircraft, decoys, missiles withwarheads, and chaff. [From Weik ’89] 2. Thedetailed characteristics of a radar transmission. Note:Radar signatures based upon emission analysis maybe used to identify or distinguish among specific radartypes.

RADHAZ: Acronym for electromagnetic radiationhazards.

� n2(a)k2 (5/a)2 ,

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radian (rad.): A unit of plane angle measure equal to radiation efficiency: At a given frequency, the ratio ofthe angle subtended at the center of a circle by an arc the power radiated to the total power supplied to theequal in length to the radius of the circle. Note: One radiator. (188)radian is equal to 360(/2%, which is approximately57( 17' 44.6". radiation field: Synonym far-field region.

radiance: Radiant power, in a given direction, per unit radiation-hardened fiber: An optical fiber made withsolid angle per unit of projected area of the source, as core and cladding materials that recover, within aviewed from the given direction. Note: Radiance is specified period of time, a specified percentage ofusually expressed in watts per steradian per square their intrinsic transparency after darkening frommeter. (188) exposure to a radiation pulse.

radiant emittance: Radiant power emitted into a full radiation mode: For an optical fiber, an unboundsphere, i.e., 4% sr (steradians), by a unit area of a mode. (188) Note: In an optical fiber, a radiationsource, expressed in watts per square meter. (188) mode is one having fields that are transverselySynonym radiant exitance.

radiant energy: Energy in the form of electromagneticwaves. Note 1: Radiant energy may be calculated byintegrating radiant power with respect to time. Note2: Radiant energy is usually expressed in joules.(188)

radiant exitance: Synonym radiant emittance.

radiant flux: Deprecated synonym for radiant power.

radiant intensity: Radiant power per unit solid angle,usually expressed in watts per steradian. (188)

radiant power: The rate of flow of electromagnetic radiation pattern: 1. The variation of the fieldenergy, i.e., radiant energy. Note 1: Radiant power is intensity of an antenna as an angular function withusually expressed in watts, i.e., joules per second. respect to the axis. (188) Note: A radiation pattern isNote 2: The modifier is often dropped and “power” usually represented graphically for the far-fieldis used to mean “radiant power”. Deprecatedsynonyms flux, radiant flux. fiber optics, the relative power distribution at the

radiation: 1. In communication, the emission ofenergy in the form of electromagnetic waves. (188) 2.The outward flow of energy from any source in theform of radio waves. [NTIA] [RR]

radiation angle: In fiber optics, half the vertex angleof the cone of light emitted at the exit face of anoptical fiber. (188) Note: The cone boundary isusually defined (a) by the angle at which the far-fieldirradiance has decreased to a specified fraction of itsmaximum value or (b) as the cone within which thereis a specified fraction of the total radiated power atany point in the far field. Synonym output angle.

oscillatory everywhere external to the waveguide, andwhich exists even at the limit of zero wavelength.Specifically, a radiation mode is one for which

where � is the imaginary part (phase term) of the axialpropagation constant, integer 5 is the azimuthal indexof the mode, n(a) is the refractive index, where a isthe core radius, and k is the free-space wave number,k = 2%/�, where � is the wavelength. Radiationmodes correspond to refracted rays in the terminologyof geometric optics. Synonym unbound mode.

conditions in either horizontal or vertical plane. 2. In

output of a fiber or active device as a function ofposition or angle. (188) Note 1: The near-fieldradiation pattern describes the radiant emittance(W•m ) as a function of position in the plane of the–2

exit face of an optical fiber. Note 2: The far-fieldradiation pattern describes the irradiance as a functionof angle in the far-field region of the exit face of anoptical fiber. Note 3: The radiation pattern may be afunction of the length of the fiber, the manner inwhich it is excited, and the wavelength. Synonymdirectivity pattern.

radiation resistance: The resistance that, if inserted inplace of an antenna, would consume the same amountof power that is radiated by the antenna. (188)

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radio coverage

radiation scattering: The diversion of radiation(thermal, electromagnetic, or nuclear) from itsoriginal path as a result of interaction or collisionswith atoms, molecules, or larger particles in theatmosphere or other media between the source ofradiation (e.g., a nuclear explosion) and a point somedistance away. As a result of scattering, radiation(especially gamma rays and neutrons) will be receivedat such a point from many directions instead of only radiocommunication service: A service as defined infrom the direction of the source. [JP1] this Section [of the Radio Regulations] involving the

RADINT: Acronym for radar intelligence. waves for specific telecommunication purposes. In

radio: 1. Telecommunication by modulation andradiation of electromagnetic waves. (188) 2. Atransmitter, receiver, or transceiver used forcommunication via electromagnetic waves. 3. Ageneral term applied to the use of radio waves.[NTIA] [RR]

radio altimeter: Radionavigation equipment, on boardan aircraft or spacecraft, used to determine the heightof the aircraft or the spacecraft above the Earth’ssurface or another surface. [NTIA] [RR]

radio and wire integration (RWI): The combining ofwire circuits with radio facilities. [JP1]

radio baseband: See baseband.

radiobeacon station: A station in the radionavigationservice the emissions of which are intended to enablea mobile station to determine its bearing or directionin relation to the radiobeacon station. [NTIA] [RR]

radio beam: A radiation pattern from a directionalantenna, such that the energy of the transmittedelectromagnetic wave is confined to a small angle inat least one dimension. (188)

radio channel: An assigned band of frequenciessufficient for radio communication. (188) Note 1:The bandwidth of a radio channel depends upon thetype of transmission and the frequency tolerance.Note 2: A channel is usually assigned for a specifiedradio service to be provided by a specifiedtransmitter.

radio common carrier (RCC): A common carrierengaged in the provision of Public Mobile Service,

which is not also in the business of providing landlinelocal exchange telephone service. These carrierswere formerly called “miscellaneous commoncarriers.” [47CFR]

radiocommunication: Telecommunication by meansof radio waves. [NTIA] [RR]

transmission, emission and/or reception of radio

these regulations, unless otherwise stated, anyradiocommunication service relates to terrestrialradiocommunication. [NTIA] [RR]

radio control: The remote control of an apparatus bysignals conveyed by electromagnetic waves. Note:Radio control may be used to control the movementof an aircraft, vehicle, missile, or other mobile unit,either manned or unmanned, from a radio station onthe ground or in another mobile unit. [From Weik’89]

radio-coverage diagram: A diagram that shows thearea within which a radio station is broadcasting aneffective signal strength in relation to a givenstandard. Note: An example of a radio-coveragediagram is a polar plot, in each direction from theantenna, of the distance from the antenna at which thesignal strength is equal to a specified value, i.e., it isthe locus of all points at which the signal strength isequal to a specified value. [From Weik ’89]

radio detection: The detection of the presence of anobject by radiolocation without precise determinationof its position. [JP1]

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radio detection and ranging: See radar. subdivisions, see electromagnetic spectrum and

radiodetermination: The determination of theposition, velocity and/or other characteristics of anobject, or the obtaining of information relating tothese parameters, by means of the propagationproperties of radio waves. [NTIA] [RR]

radiodetermination-satellite service: Aradiocommunication service for the purpose of radio frequency interference (RFI): Synonymradiodetermination involving the use of one or morespace stations. This service may also include feederlinks necessary for its own operation. [NTIA] [RR] radio horizon: The locus of points at which direct rays

radiodetermination station: A station in theradiodetermination service. [NTIA] [RR]

radio direction-finding [RDF]: Radiodeterminationusing the reception of radio waves for the purpose ofdetermining the direction of a station or object.[NTIA] [RR]

radio direction-finding station: A radiodeterminationstation using radio direction-finding. [NTIA] [RR]

radio equipment: As defined in Federal InformationManagement Regulations, any equipment orinterconnected system or subsystem of equipment(both transmission and reception) that is used tocommunicate over a distance by modulating andradiating electromagnetic waves in space withoutartificial guide. This does not include such items asmicrowave, satellite, or cellular telephone equipment.

radio fadeout: See flutter.

radio field intensity: Synonym field strength.

radio fix: 1. The locating of a radio transmitter bybearings taken from two or more direction findingstations, the site of the transmitter being at the pointof intersection. [JP1] 2. The location of a ship oraircraft by determining the direction of radio signalscoming to the ship or aircraft from two or moresending stations, the locations of which are known.[JP1]

radio frequency (rf): Any frequency within theelectromagnetic spectrum normally associated withradio wave propagation. (188) For designation of

associated diagram.

radio frequency assignment: See frequency assign-ment.

radio frequency channel assignment: Synonymfrequency assignment.

electromagnetic interference.

from an antenna are tangential to the surface of theEarth. (188) Note: If the Earth were a perfect sphereand there were no atmospheric anomalies, the radiohorizon would be a circle. In practice, the distance tothe radio horizon is affected by the height of thetransmitting antenna, the height of the receivingantenna, atmospheric conditions, and the presence ofobstructions, e.g., mountains.

radio horizon range (RHR): The distance at which adirect radio wave can reach a receiving antenna ofgiven height from a transmitting antenna of givenheight. Note: The radio horizon range in nauticalmiles, R, is given by the relation R = 1.23(h + h ),t r

1/2 1/2

where h and h are the heights of the transmitting andt r

receiving antennas in feet. The radio horizon range,R, in nautical miles is also given by the relation R =2.23(h +h ), where h and h are the heights of thet r t r

1/2 1/2

transmitting and receiving antennas in meters. Theeffective Earth radius, 4/3 times the actual Earthradius, is used in deriving the formulae. Second-order differentials are neglected. They are of theorder of 0.1%. [From Weik ’89]

radio interface: The common boundary between amobile station and the radio equipment in thenetwork, which is the boundary defined by functionalcharacteristics, physical interconnectioncharacteristics, signal characteristics, and othercharacteristics as appropriate.

radiolocation: Radiodetermination used for purposesother than those of radionavigation. [NTIA] [RR]

radiolocation land station: A station in theradiolocation service not intended to be used while inmotion. [NTIA] [RR]

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TABLE OF RADIOMETRIC TERMS

Term Symbol Quantity Unit

radiantenergy

Q energy joule (J)

radiantpower

Synonymopticalpower

1 power watt (W)

irradiance E powerincident per

unit area(irrespective

of angle)

W•m–2

spectralirradiance

E� irradianceper unit

wavelengthinterval at a

givenwavelength

W•m •–2

nm–1

radiantemittanceSynonymradiantexitance

W poweremitted (intoa full sphere)per unit area

W•m–2

radiantintensity

I power perunit solid

angle

W•sr–1

radiance L power perunit angleper unit

projectedarea

W•sr •m–1 –2

spectralradiance

L� radiance perunit

wavelengthinterval at a

givenwavelength

W•sr •m •–1 –2

nm–1

radiolocation mobile station: A station in theradiolocation service intended to be used while inmotion or during halts at unspecified points. [NTIA][RR]

radiolocation service: A radiodetermination servicefor the purpose of radiolocation. [NTIA] [RR]

radiological monitoring: Synonym monitoring (def.#4).

radiometry: The science of radiation measurement.See Table of Radiometric Terms.

radionavigation: 1. Radio-location intended for thedetermination of position or direction or forobstruction warning in navigation. [JP1]2. Radiodetermination used for the purposes ofnavigation, including obstruction warning. [NTIA][RR]

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radionavigation land station: A station in the (MIFR). Note: Formerly International Frequencyradionavigation service not intended to be used whilein motion. [NTIA] [RR]

radionavigation mobile station: A station in theradionavigation service intended to be used while inmotion or during halts at unspecified points. [NTIA][RR]

radionavigation-satellite service: A radiodetermina-tion-satellite service used for the purpose of radio-navigation. This service may also include feeder linksnecessary for its operation. [NTIA] [RR]

radio net: 1. An organization of radio stations that is Earth stations. The analog and digital basebandcapable of direct communication on a common arrangements are similar to satellite systems. Radio-frequency. (188) 2. An organization of radio stationsthat broadcast common programming, not necessarilysimultaneously, at different frequencies from differentlocations.

radio paging: The use of a pocket-size radio receiver transmission system in which signals are received,capable of alerting its wearer that there is a phone conditioned, and retransmitted by one or morecall, either from a displayed phone number or to a intermediate radio stations. (188)predesignated number. Note: Radio paging may beconsidered a subset of paging. Synonym beeping.

radio personal terminal: See personal terminal.

radio range: 1. The distance from a transmitter atwhich the signal strength remains above the minimumusable level for a particular antenna and receivercombination. 2. A radio aid to air navigation thatcreates an infinite number of paths in spacethroughout a given sector or azimuth angle by variousmethods of transmission and reception ofelectromagnetic waves. [From Weik ’89]

radio range station: A radionavigation land station inthe aeronautical radionavigation service providingradial equisignal zones. (In certain instances a radiorange station may be placed on board a ship.) [NTIA]

radio recognition and identification: Seeidentification, friend or foe.

Radio Regulations Board: A permanent organizationof the International Telecommunication Union (ITU)that implements frequency assignment policy andmaintains the Master International Frequency Register

Registration Board (IFRB).

radio relay: 1. The reception and retransmission by aradio station of signals that are received either fromanother radio station or from a wire, fiber optic,microwave, coaxial cable, or other link of anintegrated land line and radio communications systemcomponent. 2. A terrestrial point-to-point communi-cations system, such as a microwave-relay com-munications system or a satellite communicationssystem. Note: The siting of radio-relay stations andthe radio coverage diagrams of the antenna patternsare arranged for minimum interference with satellite

relay links may form part of the connection betweenan Earth station and a switching center. [From Weik’89]

radio relay system: A point-to-point radio

radiosonde: An automatic radio transmitter in themeteorological aids service usually carried on anaircraft, free balloon, kite, or parachute, and whichtransmits meteorological data. [NTIA] [RR]

radiotelegram: A telegram, originating in or intendedfor a mobile station or a mobile Earth stationtransmitted on all or part of its route over theradiocommunication channels of the mobile service orof the mobile-satellite service. [NTIA] [RR]

radio telegraphy: The transmission of telegraphiccodes by means of radio. [JP1]

radiotelemetry: Telemetry by means of radio waves.[NTIA] [RR]

radiotelephone call: A telephone call, originating inor intended for a mobile station or a mobile Earthstation, transmitted on all or part of its route over theradiocommunication channels of the mobile service orof the mobile-satellite service. [NTIA] [RR]

radiotelephone distress frequency: An internationaldistress and calling frequency for mobile

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radiotelephone stations, survival craft, and emergencyposition-indicating radio beacons. Note: An exampleof a radiotelephone distress frequency is 2180 kHz.[From Weik ’89]

radio telephony: The transmission of speech by means disk or tape storage. Note 3: RAM is usually volatile.of modulated radio waves. [JP1]

radio teletypewriter (RTTY): A teletypewriter pseudorandomly selected bits of a bit stream to avoidemployed in a communication system using radio long sequences of bits of the same sense. (188) Note:circuits. Note: Such systems are spoken of as RATT The same selection pattern must be used on thesystems. (188) receive terminal in order to restore the original bit

radiotelex call: A telex call, originating in or intendedfor a mobile station or a mobile Earth station,transmitted on all or part of its route over theradiocommunication channels of the mobile service orthe mobile-satellite service. [NTIA] [RR]

radio wave: An electromagnetic wave of a frequency transient disturbances with a statistically random timearbitrarily lower than 3000 GHz. Synonym Hertzianwave.

radio watch shift: Synonym area broadcast shift.

radio-wire integration: See radio and wireintegration.

RAM: Acronym for random access memory.

Raman amplifier: Synonym fiber amplifier.

Raman scattering: The generation of many differentwavelengths of light from a nominally single-wave-length source (a) by means of lasing action and inter-action with molecules, thereby creating many differ-ent excited molecular energy levels that will producephotons of various energy levels, i.e., various wave-lengths, when transitions to lower excited states occurand (b) by the beating together of two frequencies,thus inducing dipole moments in molecules at thedifference frequencies and thereby causingmodulation of laser-molecule interaction, which, inturn, produces light at side frequencies, i.e., sidewavelengths relative to the nominal wavelength.[From Weik ’89]

random access discrete address (RADA): Acommunications technique in which radio users shareone wide frequency band instead of each user’s beingassigned a narrow band.

random access memory (RAM): A read/write, non-sequential-access memory used for the storage ofinstructions and data. Note 1: RAM access time isessentially the same for all storage locations. Note 2:RAM is characterized by a shorter access time than

randomizer: 1. A device used to invert the sense of

stream. 2. [An] analog or digital source ofunpredictable, unbiased, and usually independent bits.Note: Randomizers can be used for several differentfunctions, including key generation or to provide astarting state for a key generator. [NIS]

random noise: Noise consisting of a large number of

distribution. (188) Note: Thermal noise is anexample of random noise.

random number: 1. A number selected from a knownset of numbers in such a way that each number in theset has the same probability of occurrence. 2. Anumber obtained by chance. 3. One of a sequence ofnumbers considered appropriate for satisfying certainstatistical tests or believed to be free from conditionsthat might bias the result of a calculation.

range: See radio range.

ranging: The measurement of the distance to a remoteobject (target), from a known observation or referencepoint. Note: Ranging may be accomplished bygeometric means, e.g., triangulation, or by themeasurement of the transit time of an electromagneticor acoustic signal. Ranging has application tonavigation and cartography.

raster: A predetermined pattern of scanning lineswithin a display space. Note: An example of a rasteris the pattern followed by an electron beam scanningthe screen of a television camera or receiver. (188)

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raster lines

raster count: The total number of raster scanning lineswithin a display space. [From Weik ’89]

raster density: In display systems, the number ofscanning lines per unit distance perpendicular to thescanning direction. [From Weik ’89]

raster scanning: Scanning in which the motion of thescanning spot follows a raster. (188)

rated output power: That power available at aspecified output of a device under specifiedconditions of operation. (188) Note: Rated outputpower may be further described; e.g., maximum ratedoutput power, average rated output power.

ratio-squared combiner: Synonym maximal-ratiocombiner.

ray: A geometric representation of a lightwave by aline normal to the electromagnetic wavefront; i.e., inthe direction of propagation of the wave. [FAA]

Rayleigh distribution: A mathematical statement,usually applied to frequency distributions of randomvariables, for the case in which two orthogonalvariables are independent and normally distributedwith unit variance. (188)

Rayleigh fading: In electromagnetic wave propaga-tion, phase-interference fading caused by multipath,and which may be approximated by the Rayleighdistribution. (188)

Rayleigh scattering: Of an electromagnetic wavepropagating in a material medium, scattering causedby refractive-index inhomogeneities that are smallcompared to the wavelength. (188) Note 1: Rayleighscattering losses vary as the reciprocal of the fourthpower of the wavelength. Note 2: Ionosphericscattering is caused partly by Rayleigh scattering.

ray optics: Synonym geometric optics.

RBOC: Acronym for Regional Bell OperatingCompany.

RC: Abbreviation for reflection coefficient.

RCC: Abbreviation for radio common carrier.

RDF: Abbreviation for radio direction finding.

read head: A magnetic head capable of reading only.

reading: The acquisition or interpretation of data froma storage device, from a data medium, or fromanother source.

read-only memory (ROM): A memory in which data,under normal conditions, can only be read. Synonymnonerasable storage.

read-only storage: A storage device in which the con-tents cannot be modified, except by a particular user,or when operating under particular conditions, e.g., astorage device in which writing is prevented by alockout. (188) Synonym fixed storage.

read/write opening: Synonym read/write slot.

read/write slot: An opening in the jacket of a disketteto allow access to the read/write heads. Synonymread/write opening.

ready-for-data signal: 1. A call-control signal that istransmitted by the data circuit-terminating equipment(DCE) to the data terminal equipment (DTE) toindicate that the connection is available for datatransfer between both DTEs. 2. A signal that (a) issent in the backward direction in the interexchangedata channel, to indicate that all the succeedingexchanges involved in the connection have beenthrough-connected, or (b) is sent in the forwarddirection in the interexchange data channel to

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indicate that all the preceding exchanges involved inthe connection have been through-connected. Note:The ready-for-data signal is sent by the user terminal.It corresponds to the ready-for-data state at the userinterface. [From Weik ’89]

real power: See effective power.

real time: 1. The actual time during which a physical amplitude reaches 90% of its steady-state value.process occurs. (188) 2. Pertaining to theperformance of a computation during the actual timethat the related physical process occurs, in order thatresults of the computation can be used in guiding thephysical process.

reasonableness check: A test to determine whether avalue conforms to specified criteria. Note: Areasonableness check can be used to eliminatequestionable data points from subsequent processing.Synonym wild-point detection.

receive-after-transmit time delay: The time intervalbetween (a) the instant of keying off the localtransmitter to stop transmitting and (b) the instant thelocal receiver output has increased to 90% of itssteady-state value in response to an rf signal from adistant transmitter. (188) Note 1: The rf signal fromthe distant transmitter must exist at the local receiverinput prior to, or at the time of, keying off the localtransmitter. Note 2: Receive-after-transmit timedelay applies only to half-duplex operation.

received noise power: 1. The calculated or measurednoise power, within the bandwidth being used, at thereceive end of a circuit, channel, link, or system.(188) 2. The absolute power of the noise measured orcalculated at a receive point. (188) Note: The relatedbandwidth and the noise weighting must also bespecified. 3. The value of noise power, from allsources, measured at the line terminals of telephoneset’s receiver. (188) Note: Either flat weighting orsome other specific amplitude-frequency character-istic or noise weighting characteristic must beassociated with the measurement.

received signal level (RSL): The signal level at areceiver input terminal. Note 1: The signal bandwidthand the established reference level must be specified.(188) Note 2: The RSL is usually expressed in dBwith respect to 1 mW, i.e., 0 dBm.

receive only (RO): Pertaining to a device or a mode ofoperation capable of receiving messages, but not oftransmitting messages. (188)

receiver attack-time delay: The time interval from (a)the instant a step rf signal, at a level equal to thereceiver threshold of sensitivity, is applied to thereceiver input to (b) the instant the receiver output

Note: If a squelch circuit is operating, the receiverattack-time delay includes the time for the receiver tobreak squelch. (188)

receiver lockout system: Synonym lockout (def. #4).

receiver release-time delay: The time interval fromremoval of rf energy at the receiver input until thereceiver output is squelched. (188)

recognized operating agency (ROA): Any operatingagency, as defined in the ITU Convention (Geneva,1992), which operates a public correspondence orbroadcasting service and upon which the obligationsprovided for in Article 6 of the ITU Constitution areimposed by the Member in whose territory the headoffice of the agency is situated, or by the Memberwhich has authorized this operating agency toestablish and operate a telecommunication service onits territory. Formerly recognized private operatingagency (RPOA).

reconditioned carrier reception: Synonym exalted-carrier reception.

reconstructed sample: An analog sample generated atthe output of a decoder when a specified charactersignal is applied at its input. (188) Note: The ampli-tude of the reconstructed sample is proportional to thevalue of the corresponding encoded sample.

record: 1. A set of data treated as a unit. (188) 2. Towrite data on a medium, such as magnetic tape,magnetic disk, or optical disk.

record communication: 1. A telecommunicationsprocess that produces an electronic message that istransmitted, received, stored or archived, and may beretrieved. 2. A telecommunications process, thatproduces a hard copy record of the transmission, suchas a teletypewriter printout or a facsimile printout.(188)

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recorder warning tone: A half-second burst of1400 Hz applied to a telephone line every 15 secondsto indicate to the called party that the calling party isrecording the conversation. Note: The recorderwarning tone is required by law to be generated as anintegral part of any recording device used for thepurpose and is required to be not under the control ofthe calling party. The tone is recorded together withthe conversation.

record information: All forms (e.g., narrative, RED signal: 1. [A] Telecommunications or automatedgraphic, data, computer memory) of information information system signal that would divulgeregistered in either temporary or permanent form so classified information if recovered and analyzed.that it can be retrieved, reproduced, or preserved.[JP1]

recording density: Synonym bit density.

recording spot: In a facsimile recorder, the spot thatis used to generate the recorded copy on the recordmedium. (188)

record medium: 1. The physical medium on whichinformation is stored in recoverable form. (188) 2. Infacsimile transmission, the physical medium on whichthe recorder forms an image of the object, i.e., createsthe recorded copy. (188) Note: The record mediumand the record sheet may be identical. Synonymrecord sheet.

record sheet: Synonym record medium.

record traffic: 1. Traffic that is recorded, inpermanent or quasipermanent form, by the originator,the addressee, or both. (188) 2. Traffic that ispermanently or semipermanently recorded in responseto administrative procedures or public law.

recovery: In a database management system, theprocedures and capabilities available forreconstruction of the contents of a database to a statethat prevailed before the detection of processingerrors and before the occurrence of a hardware orsoftware failure that resulted in the destruction ofsome or all of the stored data.

recovery procedure: 1. The actions necessary torestore an automated information system’s data filesand computational capability after a system failure.2. In data communications, a process whereby a data

station attempts to resolve conflicting or erroneousconditions arising during the transfer of data.

RED/BLACK concept: [The] separation of electricaland electronic circuits, components, equipment, andsystems that handle classified plain text (RED)information, in electrical signal form, from thosewhich handle unclassified (BLACK) information inthe same form. [NIS] (188)

[NIS] 2. In cryptographic systems, a signalcontaining classified information that has NOT beenencrypted.

reduced carrier single-sideband emission: A single-sideband emission in which the degree of carriersuppression enables the carrier to be reconstituted andto be used for demodulation. [NTIA] [RR]

reduced carrier transmission: A form of amplitude-modulation in which the carrier is transmitted at acontrolled level below that which is required fordemodulation, but at a level sufficient to serve as afrequency reference. (188)

redundancy: 1. In the transmission of data, the excessof transmitted message symbols over that required toconvey the essential information in a noise-freecircuit. Note: Redundancy may be introducedintentionally (as in the case of error detection orcorrection codes) or inadvertently (such as byoversampling a band-limited signal, inefficientformats, etc.). 2. In a communication system, surpluscapability usually provided to improve the reliabilityand quality of service. (188)

redundancy check: 1. A method of verifying that anyredundant hardware or software in a communicationsystem is in an operational condition. (188) 2. Acheck that uses one or more extra binary digits orcharacters attached to data for the detection of errors.(188)

redundant code: A code using more signal elementsthan necessary to represent the intrinsic information.(188) Note: The redundancy may be used for error-control purposes.

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reference antenna: An antenna that may be real, reference monitor: [An] access control concept thatvirtual, or theoretical, and has a radiation pattern thatcan be used as a basis of comparison with otherantenna radiation patterns. Note: Examples ofreference antennas are unit dipoles, half-wave dipoles,and isotropic, i.e., omnidirectional antennas. [FromWeik ’89]

reference black level: [In television,] The levelcorresponding to the specified maximum excursion ofthe luminance signal in the black direction. [47CFR]

reference circuit: A hypothetical circuit of specifiedequivalent length and configuration, and having adefined transmission characteristic or characteristics,used primarily as a reference for measuring theperformance of other, i.e., real, circuits or as a guidefor planning and engineering of circuits and networks.(188) Note: Normally, several types of referencecircuits are defined, with different configurations,because communications are required over a widerange of distances. A group of related referencecircuits is also called a reference system.

reference clock: 1. A clock with which another clockis compared. (188) 2. A clock, usually of highstability and accuracy, used to govern a network ofmutually synchronized clocks of lower stability.Note: The failure of a reference clock does notnecessarily cause loss of synchronism.

reference configuration: In ISDN, a combination andarrangement of functional groups and reference pointsthat reflect possible network topology.

reference frequency: 1. A standard fixed frequencyfrom which operational frequencies may be derived orwith which they may be compared. (188) Note: Thereference frequency may be used to specify anassigned frequency or fix a characteristic or carrierfrequency. 2. A frequency having a fixed and specificposition with respect to the assigned frequency. Thedisplacement of this frequency with respect to theassigned frequency has the same absolute value andsign that the displacement of the characteristicfrequency has with respect to the center of thefrequency band occupied by the emission. [NTIA][RR]

refers to an abstract machine that mediates allaccesses to objects by subjects. [NIS]

reference noise: The magnitude of circuit noisechosen as a reference for measurement. (188) Note:Many different levels with a number of differentweightings are in current use, and care must be takento ensure that the proper parameters are stated. SeedBa, dBa(F1A), dBa(HA1), dBa0, dBm,dBm(psoph), dBm0, dBrn, dBrnC, dBrnC0,dBrn(f -f ), dBrn(144-line), dBx.1 2

reference point: In ISDN, a logical point betweentwo, nonoverlapping functional groups. Note: Whenequipment is placed at a reference point, thatreference point is designated an interface.

reference surface: In optical-fiber technology, thatsurface of an optical fiber that is used to contact thetransverse-alignment elements of a component such asa connector or mechanical splice. Note: Fortelecommunications-grade fibers, the referencesurface is the outer surface of the cladding. Forplastic-clad silica (PCS) fibers, which have astrippable polymer cladding (not to be confused withthe polymer overcoat of an all-glass fiber), thereference surface may be the core.

reference system: A group of related referencecircuits.

reference transmission level point: See relativetransmission level, transmission level point.

reference white level: [In television,] The levelcorresponding to the specified maximum excursion ofthe luminance signal in the white direction. [47CFR]

reflectance: The ratio of reflected power to incidentpower, generally expressed in dB or percent. (188)

reflected code: Synonym Gray code.

reflecting layer: In the ionosphere, a layer that has afree-electron density sufficient to reflect radio waves.Note: The principal reflecting layers are the E, F , and1

F layers in the daylight hemisphere. Note 2: A2

critical frequency is associated with the reflection byeach layer.

RC ��������

Z1 Z2

Z1 � Z2

SWR 1SWR� 1

,

Lr 20 log10��������

Z1 Z2

Z1 � Z2

10log10

Z1 Z22

Z1 � Z22

,

Lf 10 log10

n1 n22

n1 � n22

,

n2(r) n2(a)

1 (r/a)2cos21(r)� sin2�(r) ,

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reflecting loss: See reflection loss.

reflection: The abrupt change in direction of a wavefront at an interface between two dissimilar media sothat the wave front returns into the medium fromwhich it originated. Note 1: Reflection may bespecular (i.e., mirror-like) or diffuse (i.e., notretaining the image, only the energy) according to thenature of the interface. Note 2: Depending on thenature of the interface, i.e., dielectric-conductor ordielectric-dielectric, the phase of the reflected wavemay or may not be inverted.

reflection coefficient (RC): 1. The ratio of theamplitude of the reflected wave and the amplitude ofthe incident wave. (188) 2. At a discontinuity in atransmission line, the complex ratio of the electricfield strength of the reflected wave to that of theincident wave. (188) Note 1: The reflectioncoefficient may also be established using other fieldor circuit quantities. Note 2: The reflectioncoefficient is given by

where Z is the impedance toward the source, Z is the1 2

impedance toward the load, the vertical bars designateabsolute magnitude, and SWR is the standing waveratio.

reflection loss: 1. At a discontinuity or impedancemismatch, e.g., in a transmission line, the ratio of theincident power to the reflected power. (188) Note 1:Reflection loss is usually expressed in dB. Note 2:The reflection loss, L , is given byr

where Z and Z are the respective impedances, and1 2

the vertical bars designate absolute magnitude. (188)2. In an optical fiber, the loss that takes place at anydiscontinuity of refractive index, especially at an air-glass interface such as a fiber endface, at which afraction of the optical signal is reflected back toward

the source. Note: This reflection phenomenon is alsocalled “Fresnel reflection loss,” or simply, “Fresnelloss.” At normal incidence, the fraction of reflectedpower is expressed by the formula

where n and n are the respective indices of refrac-1 2

tion.

reflective array antenna: An antenna, such as abillboard antenna, in which the driven elements aresituated at a predetermined distance from a surfacedesigned to reflect the signal in a desired direction.(188) Note: Reflective array antennas (a) usuallyhave many driven elements working in conjunctionwith an electrically large reflecting surface to producea unidirectional beam, (b) may be used to increaseantenna gain, i.e., reduce radiation in unwanteddirections, and (c) may contain parasitic elements aswell as driven elements.

reflectivity: The reflectance at the surface of amaterial so thick that the reflectance does not changewith increasing thickness, i.e., the intrinsic reflectanceof the surface, irrespective of other parameters suchas the reflectance of the rear surface. Note: The term“reflectivity” is no longer in common use. Seereflectance.

reflector: In an antenna, one or more conductingelements or surfaces that reflect incident radiantenergy. (188)

refracted ray: 1. A ray that undergoes a change ofvelocity, or in the general case, both velocity anddirection, as a result of interaction with the materialmedium in which it travels. 2. In an optical fiber, aray that is refracted from the core into the cladding.Specifically a ray having direction such that

where r is the radial distance from the fiber axis, 1(r)is the azimuthal angle of projection of the ray at r onthe transverse plane, �(r) is the angle the ray makes

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refractive index profile, multimode step-index fiber

refractive index profile, doubly clad single-modefiber

with the fiber axis, n(r) is the refractive index at r,n(a) is the refractive index at the core radius, a.Refracted rays correspond to radiation modes in theterminology of mode descriptors.

refraction: Retardation, and—in the general case—redirection, of a wavefront passing through (a) aboundary between two dissimilar media or (b) amedium having a refractive index that is a continuousfunction of position, e.g., a graded-index optical fiber. Note: For two media of different refractive indices,the angle of refraction is closely approximated bySnell’s Law.

refraction profile: Synonym refractive index profile.

refractive index (n, ��): Of a medium, the ratio of thevelocity of propagation of an electromagnetic wave invacuum to its velocity in the medium. (188) Synonymindex of refraction.

refractive index contrast: In an optical fiber, ameasure of the relative difference in refractive indexof the core and cladding. (188) Note: Refractiveindex contrast, �, is given by � = (n - n )/(2n ),1 2 1

2 2 2

where n is the maximum refractive index in the core1

and n is the refractive index of the homogeneous2

cladding.

refractive index profile: Of the cross section of anoptical fiber, the description, i.e., plot, of the value ofthe refractive index as a function of distance from thefiber axis along a diameter. (188) Synonyms indexprofile, refraction profile.

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refractive index profile, quadruply clad single-modefiber

refractive index profile, graded-index multimodefiber

reframing time: The time interval between the instantat which a valid frame-alignment signal is available atthe receiving data terminal equipment and the instantat which frame alignment is established. Note: Thereframing time includes the time required forreplicated verification of the validity of the frame-alignment signal. Synonym frame-alignmentrecovery time.

refresh: To reproduce, repeatedly, a display image ona display surface, so that the image remains visible.

regeneration: 1. In a regenerative repeater, theprocess by which digital signals are amplified,reshaped, retimed, and retransmitted. (188) Synonympositive feedback. 2. In a storage or display device,the restoration of stored or displayed data that havedeteriorated. (188) Note: For example, conventionalcathode-ray tube displays must be continuallyregenerated for the data to remain displayed. 3. Incomputer graphics, the sequence of events needed togenerate a display image from its representation instorage.

regenerative feedback: Feedback in which the portionof the output signal that is returned to the input has acomponent that is in phase with the input signal.

regenerative repeater: A repeater, designed fordigital transmission, in which digital signals areamplified, reshaped, retimed, and retransmitted.(188) Synonym regenerator.

regenerator: Synonym regenerative repeater.

Regional Bell Operating Company (RBOC): One ofthe seven holding companies formed by divestiture bythe American Telephone and Telegraph Company ofits local Bell System operating companies, and towhich one or more of the Bell System local telephonecompanies were assigned.

regional center: See office classification.

register: 1. A device, accessible to one or more inputcircuits, that accepts and stores data. (188) Note: Aregister is usually used only as a device for temporarystorage of data. 2. A temporary-memory device usedto receive, hold, and transfer data (usually a computerword) to be operated upon by a processing unit.Note: Computers typically contain a variety ofregisters. General purpose registers may performmany functions, such as holding constants oraccumulating arithmetic results. Special purposeregisters perform special functions, such as holdingthe instruction being executed, the address of astorage location, or data being retrieved from or sentto storage.

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registered jack (RJ): Any of the series of jacks, released loop: Synonym switched loop.described in the Code of Federal Regulations, Title47, part 68, used to provide interface to the publictelephone network.

registration: 1. The accurate positioning of an entityrelative to a reference. (188) 2. See FCCregistration program.

registration program: See FCC RegistrationProgram.

rekeying: The changing of one or more keys that areused for either COMSEC or TRANSEC functions.(188)

relative error: The ratio of an absolute error to thetrue, specified, or theoretically correct value of thequantity that is in error.

relative spectral width: See spectral width.

relative transmission level: The ratio of the signalpower, at a given point in a transmission system, to areference signal power. (188) Note: The ratio isusually determined by applying a standard test tone atzero transmission level point (or applying adjustedtest tone power at any other point) and measuring thegain or loss to the location of interest. A distinctionshould be made between the standard test tone powerand the expected median power of the actual signalrequired as the basis for the design of transmissionsystems.

relay: 1. To retransmit a received message from onestation to another station. 2. An electromechanical orsemiconductor switch (i.e., solid-state relay) inwhich a current or voltage applied across one port orterminal controls electrical currents or voltages thatappear across another terminal or terminals. (188)

relay configuration: An operating configuration inwhich a circuit is established between two stations viaan intermediate relay station. Two links are usedsimultaneously and the channel connections at therelay station are accomplished completely within thestation. (188)

relay station: An intermediate station that passesinformation between terminals or other relay stations.

release time: 1. The time interval between (a) theinstant that an enabling signal (as in a vogad or echosuppressor) is discontinued, and (b) the instant atwhich suppression ceases. (188) 2. The time intervalbetween (a) the instant a relay coil is de-energized,and (b) the instant that contact closure ceases (or,depending on the nature of the relay, is established).(188)

reliability: 1. The ability of an item to perform arequired function under stated conditions for aspecified period of time. 2. The probability that afunctional unit will perform its required function fora specified interval under stated conditions. (188) 3.The continuous availability of communicationservices to the general public, and emergencyresponse activities in particular, during normaloperating conditions and under emergencycircumstances with minimal disruption.

reliability assessment: 1. The process of determiningwhether existing hardware, firmware, or software hasachieved a specified level of operational reliability.2. The process of determining the achieved level ofoperational reliability of existing hardware, firmware,or software. Synonym reliability evaluation. [FromWeik ’89]

reliability evaluation: Synonym reliabilityassessment.

remote access: 1. Pertaining to communication with adata processing facility from a remote location orfacility through a data link. 2. A PABX servicefeature that allows a user at a remote location toaccess by telephone PABX features, such as access towide area telephone service (WATS) lines. Note: Forremote access, individual authorization codes areusually required.

remote access data processing: Data processing inwhich some input/output functions are performed bydevices that are connected to a computer system bymeans of data communication.

remote batch entry: Submission of batches of datathrough an input unit that has access to a computerthrough a data link.

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remote batch processing: Batch processing in which remote rekeying: The encrypted transmission of keysinput-output units have access to a computer through from a remote source. (188)a data link.

remote call forwarding: A service feature that allowscalls coming to a remote call-forwarding number tobe automatically forwarded to any answering locationdesignated by the call receiver. Note: Customersmay have a remote-forwarding telephone number ina central switching office without having any otherlocal telephone service in that office.

remote clock: 1. A clock that is remote from aparticular facility, such as a communications stationor node, with which it is associated. 2. A clock that isremote from another clock to which it is to becompared.

remote control equipment: Devices used to performmonitoring, controlling, and/or supervisory functions,at a distance. (188)

remote job entry (RJE): In computer operations, amode of operation that allows execution of jobinstructions received from a remote site and return ofthe output to the same or a different remote site via acommunications link.

remote login: A login that allows a user terminal toconnect to a host computer via a network or directtelecommunications link, and to interact with that hostcomputer as if the user terminal were directlyconnected to that host computer. Synonym remotelogon.

remote logon: Synonym remote login.

remote operations service element (ROSE) protocol: retransmission. (188)A protocol that (a) provides remote operationcapabilities, (b) allows interaction between entities in repertory dialer: A telephone set that stores a groupa distributed application, and (c) upon receiving a of numbers frequently called by a customer andremote operations service request, allows the transmits the dialing information to the central officereceiving entity to attempt the operation and reportthe results of the attempt to the requesting entity.(188)

remote orderwire: An extension of a local orderwireto a point convenient for personnel to performrequired operational and maintenance functions.(188)

remote trunk arrangement (RTA): Arrangement thatpermits the extension of TSPS functions to remotelocations. [47CFR]

REN: Acronym for ringer equivalency number.

reorder tone: See busy signal.

repeater: 1. An analog device that amplifies an inputsignal regardless of its nature, i.e., analog or digital.2. A digital device that amplifies, reshapes, retimes,or performs a combination of any of these functionson a digital input signal for retransmission. (188)Note: The term “repeater” originated with telegraphyand referred to an electromechanical device used toregenerate telegraph signals. Use of the term has con-tinued in telephony and data communications.

repeating coil: A voice-frequency transformercharacterized by a closed core, a pair of identicalbalanced primary (line) windings, a pair of identicalbut not necessarily balanced secondary (drop)windings, and low transmission loss at voicefrequencies. (188) Note: It permits transfer of voicecurrents from one winding to another by magneticinduction, matches line and drop impedances, andprevents direct conduction between the line and thedrop.

repeat-request (RQ) system: Synonym ARQ.

reperforator: In teletypewriter systems, a device usedto punch a tape in accordance with arriving signals,permitting reproduction of the signals for

by a single action. (188) Contrast with speedcalling.

reproducibility: Synonym precision (def. #1, #2, #3).

reproducible fault: In computer andtelecommunications systems, a fault that will occureach time the set of conditions causing the faultoccurs. Note: The conditions under which the fault

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occurs and the precision with which the fault occursmust be specified when determining thereproducibility of a fault.

reproduction speed: 1. In facsimile systems, the rateat which recorded copy is produced. Note: Thereproduction speed is usually expressed (a) as the areaof recorded copy produced per unit time, such assquare meters per second or (b) as the number ofpages per minute. 2. In duplicating equipment, the reserved words, while Fortran has no reserved words.rate at which copies are made. Note: Thereproduction speed is usually expressed in pages perminute. (188)

request data transfer: A signal sent by the DTE tothe DCE to request the establishment of a dataconnection.

request-repeat (RQ) signal: A signal from a receiverto a transmitter asking that a message be transmittedagain. [From Weik ’89]

request-to-send signal: A signal that is generated bya receiver in order to condition a remote transmitter tocommence transmission. [From Weik ’89]

reradiation: 1. Radiation, at the same or differentwavelengths, i.e., frequencies, of energy receivedfrom an incident wave. (188) 2. Undesirable control equipment to (b) the total number of bits, unitradiation of signals locally generated in a radioreceiver. Note: Radiation might cause interference orreveal the location of the device.

rerouting: Recommencement of route selection fromthe first point of routing control, when congestion isencountered at some intermediate switching point inthe connection that is to be established.

resale carrier: A company that redistributes theservices of a commercial carrier and retails theservices to the public.

resale service: In FCC deliberations and rulings, theright of a buyer of basic telecommunication services,such as private lines, foreign exchanges, or WATS, toresell and/or share with others the unused capacity.

reserve capacity: Installed capacity of a system whichis not normally utilized but can be made availablewhen required. [NATO]

reserved circuit service: In ISDN applications, atelecommunications service that establishes acommunication path at a preset time (requested by theuser) in response to a user-network signaling request.

reserved word: In programming languages, a keywordwhose definition is fixed by the programminglanguage and which cannot be changed by the user.Note: In Ada® and COBOL all keywords are

reset mode: The parameters initially programmed forbasic operation. (188)

resettability: A measure of the ability to duplicatecontrollable conditions. Note: An example ofresettability is the ability to reset the frequencycontrols of radio equipment. (188)

resident: Pertaining to computer programs that remainon a particular storage device.

residual error rate: Synonym undetected errorratio.

residual error ratio: 1. The ratio of (a) the number ofbits, unit elements, characters, or blocks incorrectlyreceived but undetected or uncorrected by the error-

elements, characters or blocks. [After CCITT] 2. Theerror ratio that remains after attempts at correction aremade.

residual modulation: Synonym carrier noise level.

resistance hybrid: A network of resistors to whichfour branches of a circuit may be connected to makethem conjugate in pairs. Note: The primary use of aresistance hybrid is to convert between 2-wire and 4-wire communications circuits. Such conversion isnecessary when repeaters are introduced in a 2-wirecircuit.

resolution: 1. The minimum difference between twodiscrete values that can be distinguished by ameasuring device. (188) Note: High resolution doesnot necessarily imply high accuracy. 2. The degree ofprecision to which a quantity can be measured ordetermined. (188) 3. A measurement of the smallest

f %

2 LC.

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detail that can be distinguished by a sensor systemunder specific conditions. [JP1] (188)

resolving power: A measure of the ability of a lens oroptical system to form separate and distinct images oftwo objects with small angular separation. (188)Note: The resolving power of an optical system isultimately limited by diffraction by the aperture.Thus, an optical system cannot form a perfect imageof a point.

resonance: In an electrical circuit, the condition thatexists when the inductive reactance and the capacitivereactance are of equal magnitude, causing electricalenergy to oscillate between the magnetic field of theinductor and the electric field of the capacitor. Note1: Resonance occurs because the collapsing magneticfield of the inductor generates an electric current in itswindings that charges the capacitor and thedischarging capacitor provides an electric current thatbuilds the magnetic field in the inductor, and theprocess is repeated. Note 2: At resonance, the seriesimpedance of the two elements is at a minimum andthe parallel impedance is a maximum. Resonance isused for tuning and filtering, because resonanceoccurs at a particular frequency for given values ofinductance and capacitance. Resonance can bedetrimental to the operation of communicationscircuits by causing unwanted sustained and transientoscillations that may cause noise, signal distortion,and damage to circuit elements. Note 3: Atresonance the inductive reactance and the capacitivereactance are of equal magnitude. Therefore, 7L = 1/7C , where 7 = 2%f, in which f is the resonantfrequency in hertz, L is the inductance in henrys, andC is the capacity in farads when standard SI units areused. Thus,

resonant antenna: Synonym periodic antenna.

resonant cavity: See optical cavity.

resource controller (RC): The processor(s) thatcontrol access to satellite payload communicationsresources within an individual satellite program.(188)

respond opportunity: In data transmission, the linklevel logical control condition during which a givensecondary station may transmit a response.

response: 1. A reply to a query. (188) 2. In datatransmission, the content of the control field of aresponse frame advising the primary stationconcerning the processing by the secondary station ofone or more command frames. 3. The effect of anactive or passive device upon an input signal.

response frame: In data transmission, all frames thatmay be transmitted by a secondary station.

response PDU: A protocol data unit (PDU)transmitted by a logical link control (LLC) sublayer inwhich the PDU command/response (C/R) bit is equalto “1”.

response time: The time a system or functional unittakes to react to a given input. (188) Note: Forexample, in data processing, the response timeperceived by the end user is the interval between (a)the instant at which an operator at a terminal enters arequest for a response from a computer and (b) theinstant at which the first character of the response isreceived at a terminal. In a data system, the systemresponse time is the interval between the receipt ofthe end of transmission of an inquiry message and thebeginning of the transmission of a response messageto the station originating the inquiry.

response timer (T ): In multilevel precedence andK

preemption, the device that controls the length of timethat the call receiver of the precedence call has toaccept the incoming precedence call. Note: Thelength of the time is usually set in the range of 4 s to30 s.

responsiveness: Ability of an entity to provide servicewithin the required time. Note: The term timelinessis sometimes used incorrectly to mean responsiveness.[NATO]

responsivity: In a photodetector, the ratio of theelectrical output to the optical input. (188) Note 1:Responsivity is usually expressed in amperes per watt,or volts per watt, of incident radiant power. Note 2:Responsivity is a function of the wavelength of theincident radiation and the bandgap of the material of

Lr 10 log10��������

Z1 � Z2

Z1 Z2

,

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which the photodetector is made. Deprecated optical fibers. Note 3: In a metallic transmission line,synonym sensitivity.

restart: The resumption of the execution of acomputer program using the data recorded at acheckpoint.

restitution: A series of significant conditionsdetermined by the decisions taken according to theproducts of the demodulation process. (188)

restoration: Action taken to repair and return to e.g, optical fibers, see reflection loss (def #2).service one or more telecommunications services,including repair of a damaged or impaired telecom-munications facility, that have a degraded quality ofservice or have a service outage. (188) Note:Restoration may be done by various means, such aspatching, routing, substitution of component parts, orselecting other pathways.

restricted access: A class of service in which users the loop to give an “off-hook” signal when the callmay be denied access to one or more of the system receiver answers. (188) Note: Reverse-batteryfeatures or operating levels. (188) signaling may be used either for a short period, or for

restricted area: Synonym controlled space.

restricted channel: In digital communicationssystems, a channel that has a useful capacity of only56 kb/s (kilobits per second), instead of 64 kb/s. (188)Note: The restricted channel, currently common inNorth America, was originally developed to satisfy a rf: Abbreviation for radio frequency.ones-density limitation in T1 circuits.

retrieval service: In interactive telecommunications, bandwidth.a service allowing access to and retrieval of storedinformation, e.g., the information within a database.

retrograde orbit: Of a satellite orbiting the Earth, anorbit in which the projection of the satellite’s positionon the (Earth’s) equatorial plane revolves in thedirection opposite that of the rotation of the Earth.

return loss: The ratio, at the junction of a transmissionline and a terminating impedance or otherdiscontinuity, of the amplitude of the reflected waveto the amplitude of the incident wave. Note 1: Returnloss is usually expressed in dB. (188) Note 2: Returnloss is a measure of the dissimilarity betweenimpedances in metallic transmission lines and loads,or between refractive indices in dielectric media, e.g.,

return loss is given by

where Z is the impedance toward the source and Z is1 2

the impedance toward the load, and the vertical barsindicate magnitude. Note 4: For dielectric media,

return-to-zero (RZ): A digital code having twoinformation states, e.g., “0” and “1” or “mark” and“space”, in which code the signal returns to a reststate during a portion of the bit period. (188)

reverse-battery signaling: Loop signaling in whichbattery and ground are reversed on the tip and ring of

the duration of a call, to indicate that it is a toll call.

revertive pulsing: In telephone networks, a means ofcontrolling distant switching selections by pulsing.Note: In revertive pulsing, the near end receivessignals from the far end.

rf bandwidth: See occupied bandwidth, necessary

RFI: Abbreviation for radio frequency interference.See electromagnetic interference.

rf power margin: 1. The amount of transmitter powerabove that which is computed by the link designer asthe minimum required to meet specified linkperformance. Note: The rf power margin allows foruncertainties in (a) empirical components of the signallevel prediction method, (b) terrain characteristics, (c)atmospheric conditions, and (d) equipmentperformance parameters. (188) 2. At any given timein an operational link, the reserve transmitter powerover that which is required to maintain specified linkperformance.

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ribbon cable

rf tight: Offering a high degree of electromagneticshielding effectiveness. (188)

RGB: Abbreviation for red-green-blue. Pertaining tothe use of three separate signals to carry the red,green, and blue components, respectively, of a colorvideo image. (188) Note: The image is not NTSC-encoded; RGB typically results in higher resolutionthan that specified by the National TelevisionStandards Committee.

rhombic antenna: A directional antenna that iscomposed of long-wire radiators that form the sides ofa rhombus, the two halves of which are fed equally inopposite phase at one apex. [From Weik ’89] Note:A rhombic antenna is usually terminated at the apexopposite the driven apex, which termination makes itsradiation pattern unidirectional. It is bidirectional ifthe opposite apex is unterminated.

RI: Abbreviation for routing indicator.

ribbon cable: 1. Any cable constructed as a ribbonwith parallel elements. 2. A fiber optic cable inwhich the optical fibers are held in grooves andlaminated within a flat semirigid strip of material,such as plastic, that positions, holds, and protectsthem. Note: Ribbon cables may be stacked toproduce fiber optic cables with large numbers offibers. Buffers, strength members, fillers, andjacketing are usually added to produce the final cable.[After 2196].

right-hand (or clockwise) polarized wave: Anelliptically or circularly polarized wave, in which theelectric field vector, observed in any fixed plane,normal to the direction of propagation, whilst lookingin the direction of propagation, rotates with time in a

right-hand or clockwise direction. [NTIA] [RR]Synonym clockwise polarized wave.

right-hand rule: Synonym Fleming’s rule.

ring: 1. In telephony, a signal of specific duration andcharacter that indicates to a user (customer,subscriber) that a calling party is engaged in an accessattempt. (188) 2. Synonym ring network. Seenetwork topology.

ringaround: 1. The improper routing of a call backthrough a switching center already engaged inattempting to complete the same call. 2. Insecondary surveillance radar, the presence of falsetargets declared as a result of transponderinterrogation by side lobes of the interrogatingantenna.

ringback signal: 1. In telephony, a signal, usuallyconsisting of an audio tone interrupted at a slow rate,provided to a caller to indicate that the called-partyinstrument is receiving a ringing signal. (188) Note:This signal may be generated by the called-partyservicing switch or by the calling-party switch. 2. Aringing signal returned to a caller to indicate that oneof the types of delayed automatic calling is nowringing the called party. (188)

ringback tone: Synonym audible ringing tone.

ringdown: In telephony, a method of signaling anoperator in which telephone ringing current is sentover the line to operate a lamp and cause the drop ofa self-locking relay. (188) Note 1: Ringdown (a) isused in manual operation, as distinguished fromdialing, (b) uses a continuous or pulsed ac signaltransmitted over the line, and (c) may be used with orwithout a switchboard. (188) Note 2: The term“ringdown” originated in magneto telephonesignaling in which cranking the magneto in atelephone set would not only “ring” its bell but alsocause a lever to fall “down” at the central officeswitchboard.

ringdown circuit: In telephony, a circuit in whichmanually generated signaling power is used toperform ringdown. (188)

ringdown signaling: In telephony, the application ofa signal to a line (a) to operate a line signal lamp or a

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supervisory signal lamp at a switchboard or (b) to ringa called receiver instrument. (188)

ringer equivalency number (REN): A number commutation. (188) 2. In a dc voltage, the alternatingdetermined in accordance with the Code of Federal component that is coupled into a circuit from a sourceRegulations, Title 47, part 68, which number of interference.represents the ringer loading effect on a line. Note:A ringer equivalency number of 1 represents theloading effect of a single traditional telephone setringing circuit. Modern telephone instruments mayhave a REN lower than 1. The total REN expressesthe total loading effect of the subscriber’s equipmenton the central office ringing current generator. Theservice provider usually sets a limit, e.g., 3, 4, or 5(representing “extension,” i.e., parallel-connectedtelephones), to the total REN on a subscriber’s loop.The actual number of instruments across the loop maybe greater than the service provider’s REN limit, iftheir respective individual RENs are less than 1.

ring latency: In a ring network, such as a token ringnetwork, the time required for a signal to propagateonce around the ring. Note 1: Ring latency may bemeasured in seconds or in bits at the data transmissionrate. Note 2: Ring latency includes signalpropagation delays in (a) the ring medium, (b) thedrop cables, and (c) the data stations connected to thering network. (188)

ring network: See network topology.

ring topology: See network topology.

ring transit time: See round-trip delay time.

R interface: For a basic rate access in an ISDNenvironment, the interfacing specifications coveringpre-ISDN standards (e.g., EIA-232C).

rip cord: Of an optical cable, a parallel cord of strongyarn that is situated under the jacket(s) of the cablefor the purpose of facilitating jacket removalpreparatory to splicing or breaking out. Note: The ripcord is exposed by carefully removing or severing aportion of the jacket near the end of the cable. It isthen grasped with the fingers, or usually, with a toolsuch as a pair of pliers, and pulled to sever the jacketfor the remainder of the desired distance. [AfterFAA]

ripple voltage: 1. In a dc voltage, the alternatingcomponent that is residually retained fromrectification of ac power, or from generation and

rise time: In the approximation of a step function, thetime required for a signal to change from a specifiedlow value to a specified high value. Typically, thesevalues are 10% and 90% of the step height. (188)

RJ: Abbreviation for registered jack.

RJE: Abbreviation for remote job entry.

rms pulse duration: See root-mean-square pulseduration .

RO: Abbreviation for receive only.

ROM: Acronym for read-only memory.

roofing filter: A low-pass filter used to reduceunwanted higher frequencies. (188)

room noise level: Synonym ambient noise level.

root: In computer science, the highest level of ahierarchy.

root-mean-square (rms) deviation: A single quantity,) , characterizing a function, f(x), given byrms

Note: The term “rms deviation” is also used inprobability and statistics, where the normalization,

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M , is unity. Here, the term is used in a more general0

sense.

root-mean-square (rms) pulse broadening: Thetemporal rms deviation of the impulse response of asystem.

root-mean-square (rms) pulse duration: A specialcase of root-mean-square deviation where theindependent variable is time and f(t) describes thepulse waveform.

rotary dial: A signaling mechanism—usuallyincorporated within a telephone set—that whenrotated and released, generates dc pulses required forestablishing a connection in a telephone system.

rotary hunting: Hunting in which all the numbers inthe hunt group are selected in a prescribed order.(188) Note: In modern electronic switching systems,the numbers in the hunt group are not necessarilyselected in consecutive order.

rotary switching: In telephone systems, an electro-mechanical switching method whereby the selectingmechanism consists of a rotating element using router: In data communications, a functional unit usedseveral groups of wipers, brushes, and contacts. to interconnect two or more networks. Note 1:(188) Routers operate at the network layer (layer 3) of the

rotational position sensing: [In magnetic media,] A Model. Note 2: The router reads the network layertechnique used to locate a given sector, a desired address of all packets transmitted by a network, andtrack, and a specific record by continuous comparison forwards only those addressed to another network.of the read/write head position with appropriatesynchronization signals.

round-trip delay time: 1. The elapsed time for transitof a signal over a closed circuit. (188) Note: Round-trip delay time is significant in systems that requiretwo-way interactive communication such as voicetelephony or ACK/NAK data systems where theround-trip time directly affects the throughput rate. Itmay range from a very few microseconds for a shortline-of-sight (LOS) radio system to many seconds fora multiple-link circuit with one or more satellite linksinvolved. This includes the node delays as well as themedia transit time. 2. In primary or secondary radarsystems, the time required for a transmitted pulse toreach a target and for the echo or transponder reply toreturn to the receiver. (188)

route: 1. In communications systems operations, thegeographical path that is followed by a call ormessage over the circuits that are used in establishinga chain of connections. 2. To determine the path thata message or call is to take in a communicationsnetwork. Note: In a Transmission ControlProtocol/Internet Protocol (TCP/IP) internet, each IPdatagram is routed separately. The route a datagramfollows may include many gateways and manyphysical networks. 3. To construct the path that acall or message is to take in a communicationsnetwork in going from one station to another or froma source user end instrument to a destination user endinstrument. [From Weik ’89]

route diversity: The allocation of circuits between twopoints over more than one geographic or physicalroute with no geographic points in common. (188)

route matrix: In communications network operations,a record that indicates the interconnections betweenpairs of nodes in the network, and is used to producedirect routes, alternate routes, and available routetables from point to point. [From Weik ’89]

ISO Open Systems Interconnection—Reference

routine: A computer program, called by anotherprogram, that may have some general or frequent use.

routine message: A category of precedence to be usedfor all types of messages that justify transmission byrapid means unless of sufficient urgency to require ahigher precedence. [JP1]

routing: The process of determining and prescribingthe path or method to be used for establishingtelephone connections or forwarding messages.

routing diagram: In a communications system, adiagram that (a) shows all links between all switch-boards, exchanges, switching centers, and stations inthe system, such as the links between primary relay,major relay, minor relay, and tributary stations as wellas supplementary links, (b) is used to identify the

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stations and links, and (c) is used to indicate tape-relay routes, transfer circuits, refile circuits, radiolinks, operational status, line conditions, and othernetwork information required for network operationsand management. [From Weik ’89]

routing directory: See routing table. communication service between landline central

routing indicator (RI): 1. A group of letters assignedto indicate: (a) the geographic location of a station;(b) a fixed headquarters of a command, activity, orunit at a geographic location; and (c) the generallocation of a tape relay or tributary station to facilitatethe routing of traffic over the tape relay networks. rural subscriber station: A fixed station in the rural[JP1] 2. In a message header, an address, i.e., groupof characters, that specify routing instructions for thetransmission of the message to its final destination.(188) Note: Routing indicators may also include RWI: Abbreviation for radio and wire integration.addresses of intermediate points.

routing table: A matrix associated with a networkcontrol protocol, which gives the hierarchy of linkrouting at each node.

RQ: Abbreviation for repeat-request. See ARQ.

RSL: Abbreviation for received signal level.

RTA: Abbreviation for remote trunk arrangement.

RTTY: Abbreviation for radio teletypewriter.

rubidium clock: A clock containing a quartz oscillatorstabilized by a rubidium standard.

rubidium standard: A frequency standard in which aspecified hyperfine transition of electrons inrubidium-87 atoms is used to control the outputfrequency. Note: A rubidium standard consists of agas cell, which has an inherent long-term instability.This instability relegates the rubidium standard to itsstatus as a secondary standard.

run: The execution of one or more computer jobs orprograms.

run-length encoding: A redundancy-reductiontechnique for facsimile in which a run of consecutivepicture elements having the same state (gray scale orcolor) is encoded into a single code word. (188)

rural radio service: A public radio service renderedby fixed stations on frequencies below 1000 MHzused to provide (1) Basic Exchange Telecommuni-cations Radio Service, which is public message com-munication service between a central office andsubscribers located in rural areas, (2) public message

offices and different exchange areas which it is im-practicable to interconnect by any other means, or (3)private line telephone, telegraph, or facsimile servicebetween two or more points to which it is im-practicable to extend service via landline. [47CFR]

radio service used by a subscriber for communicationwithin a central office station.

RX: Abbreviation for receive, receiver.

RZ: Abbreviation for return-to-zero.

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