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Tra.gov.eggain: The ratio of output current,
gap-loss attenuator: An optical attenuator that
exploits the principle of gap loss to reduce the optical power level when inserted in-line in the fiber path; e.g., to prevent saturation of the receiver.
Note: Gap-loss attenuators should be used in-line near the optical transmitter. [After FAA] expressed in dB, will be negative, in which casethere is a loss between input and output.
garble: 1. An error in transmission, reception,
encryption, or decryption that changes the text of a gain hit: See hit.
message or any portion thereof in such a manner that
it is incorrect or undecryptable. [JP1] 2. In a
gain medium: An active medium, device, or system
telephone circuit or channel, readily audible but in which amplification of input occurs with or unintelligible interference from another circuit or without feedback. Note: Gain media include channel. Note: Garble may, for example, take place amplifiers, lasers, and avalanche photodiodes in an FDM telephone carrier system in which an interfering signal from another channel or system isdemodulated in such a fashion that it has an gain of an antenna: Synonym antenna gain.
objectionable audio power level but is nonethelessunintelligible.
galactic radio noise: Synonym cosmic noise.
gate: 1. A device having one output channel and one
gap loss: 1. The power loss that occurs when an
or more input channels, such that the output channel optical signal is transferred from one fiber to another state is completely determined by the input channel that is axially aligned with it, but longitudinally states, except during switching transients. 2. One of
separated from it. Note: The gap allows light from many types of combinational logic elements having the “transmitting” fiber to spread out as it leaves the at least two inputs; e.g., AND, OR, NAND, and fiber endface. When it strikes the “receiving” fiber, some of the light will enter the cladding, where it is
quickly lost. [After FAA] 2. An analogous form of
gateway: 1. In a communications network, a network
coupling loss that occurs between an optical source, node equipped for interfacing with another network e.g., an LED, and an optical fiber. Note: Gap loss is that uses different protocols. (188) Note 1: A not usually significant at the optical detector, gateway may contain devices such as protocol because the sensitive area of the detector is normally translators, impedance matching devices, rate somewhat larger than the cross section of the fiber converters, fault isolators, or signal translators as core. Unless the separation is substantial, all light necessary to provide system interoperability. It also emerging from the fiber, even though it diverges, requires that mutually acceptable administrative will still strike the detector. Synonym longitudinal
procedures be established between the two networks.
offset loss. [FAA]
Note 2: A protocol translation/mapping gateway
interconnects networks with different network
protocol technologies by performing the required
protocol conversions. 2. Loosely, a computer
configured to perform the tasks of a gateway.
gating: 1. The process of selecting only those
portions of a wave between specified time intervals
or between specified amplitude limits. 2. The
controlling of signals by means of combinational
logic elements. (188) 3. A process in which a
predetermined set of conditions, when established,
gaussian beam: A beam of light whose electric field
general purpose network: See common user
intensity distribution is gaussian. Note: When such network.
a beam is circular in cross section the intensity atdistance r from the center, E(r), is given by geometric optics: The branch of optics that describes
light propagation in terms of rays. Note 1: Rays arebent at the interface between two dissimilar media, and may be curved in a medium in which the
refractive index is a function of position. Note 2:
The ray in geometric optics is perpendicular to the
wavefront in physical optics. Synonym ray optics.
where E(0) is the electrical field strength at the beamcenter, i.e., at r = 0; and w is the value of r at which geometric spreading: See inverse-square law.
the intensity is 1/e of its value on the axis.
geostationary orbit: A circular orbit in the equatorial
gaussian pulse: A pulse that has a waveform
plane, any point on which revolves about the Earth described by the gaussian distribution. (188) Note: in the same direction and with the same period as the In the time domain, the amplitude of the waveform Earth’s rotation. (188) Note: An object in a geostationary orbit will remain directly above a fixedpoint on the equator at a distance of approximately 42,164 km from the center of the Earth, i.e.,approximately 35,787 km above mean sea level.
where A is the maximum amplitude, and ) is the geostationary satellite: A geosynchronous satellite
pulse half-duration at the 1/e points.
whose circular and direct orbit lies in the plane ofthe Earth’s equator and which thus remains fixed GBH: Abbreviation for group busy hour.
relative to the Earth; by extension, a satellite thatremains approximately fixed relative to the Earth.
GCT: Abbreviation for Greenwich Civil Time. See
Coordinated Universal Time.
geostationary satellite orbit: The orbit in which a
GDF: Abbreviation for group distribution frame.
satellite must be placed to be a geostationarysatellite. [NTIA] [RR] gel: 1. A substance, resembling petroleum jelly in
viscosity, that surrounds a fiber, or multiple fibers, geosynchronous orbit: Any orbit about the Earth,
enclosed in a loose buffer tube. Note: This gel which orbit has a period equal to the period of serves to lubricate and support the fibers in the rotation of the Earth about its axis, and in the same buffer tube. It also prevents water intrusion in the sense, i.e., direction, as the rotation of the Earth.
event the buffer tube is breached. [FAA] 2. Index-
matching material in the form of a gel. [FAA]
germanium photodiode: A germanium-based PN- or
Synonym index-matching gel. See index-matching
PIN-junction photodiode. Note 1: Germanium material.
photodiodes are useful for direct detection of opticalwavelengths from approximately 1 µm to several general purpose computer: A computer designed to
tens of µm. Note 2: Germanium-based detectors are perform, or that is capable of performing, in a noisier than silicon-based detectors. Silicon-based reasonably efficient manner, the functions required detectors are therefore usually preferred for by both scientific and business applications. Note: wavelengths shorter than 1 µm. [After FAA] A general purpose computer is often understood tobe a large system, capable of supporting remote ghost: A secondary image or signal resulting from
terminal operations, but it may also be a smaller echo, envelope delay distortion, or multipath computer, e.g., a desktop workstation.
gigaflop: A billion, i.e., 10 , f
GMT: Abbreviation for Greenwich Mean Time.
Obsolete term. See Coordinated Universal Time.
gigahertz (GHz): A unit of frequency denoting
go-ahead message: Synonym go-ahead notice.
go-ahead notice: In a tape-relay communications
glare: Deprecated synonym for call collision.
system, a service message, usually sent to a relaystation or to a tributary station, that contains a glass: 1. In the strict sense, a state of matter. [FAA]
request to the operator to resume transmitting over 2. In fiber-optic communication, any of a number of
a specified channel or channels. [From Weik ’89] noncrystalline, amorphous inorganic substances, go-ahead message, start message, start
formed, by heating, from metallic or semiconductor oxides or halides, and used as the material for fibers.
Note: The most common glasses are based on silicon go-ahead tone: In communications systems, an
audible signal transmitted by a system indicating that the system is ready to receive a message or signal.
glide slope facility: In aeronautical navigation, an
instrument approach landing facility that furnishesvertical guidance information to an aircraft from its gold code: In spread-spectrum systems, a code that is
approach altitude down to the surface of the runway.
generated by summing, using modulo-two addition, the outputs of two spread-spectrum code-sequencegenerators. [From Weik ’89] global: 1. Pertaining to, or involving, the entire
world. (188) 2. Pertaining to that which is defined
Gopher: A menu-based information searching tool
in one subsection of an entity and used in at least one that allows users to access various types of other subsection of the same entity. (188) 3. In
databases, such as FTP archives and white pages computer, data processing, and communications databases. Note 1: Gopher is most often used as an systems, pertaining to what is applicable to an area Internet browser. Note 2: Gopher software uses the beyond the immediate area of consideration. Note: Examples of global entities are (a) in computerprogramming, an entity that is defined in one GOS: Abbreviation for grade of service.
subdivision of a computer program and used in atleast one other subdivision of that program and (b) GOSIP: Acronym for Government Open Systems
in personal computer systems and their software Interconnection Profile. A definition of Federal
packages, a setting, definition, or condition that Government functional requirements for open applies to the entire software system. [From Weik systems computer network products, including a common set of Open System Interconnection (OSI)data communication protocols that enables systems global address: In a communications network, the
developed by different vendors to interoperate and predefined address that is used as an address for all enable the users of different applications on these users of that network, and that may not be the systems to exchange information. Note 1: The OSI address of an individual user, or subgroup of users, protocols were developed primarily by ISO and CCITT. Note 2: The GOSIP is a subset of the OSIprotocols and is based on agreements reached by global status: 1. The set of attributes of an entity,
described at a particular time, when that set is participating in the National Institute of Standards extended to every occurrence of that entity within a and Technology (NIST) Implementors Workshop.
prescribed boundary. (188) 2. The complete set of
Note 3: The GOSIP is described in the latest version attributes necessary to describe an entity at a Government Open Systems Interconnection
transported via analog circuits, equalization for Profile: See GOSIP.
graceful degradation: Degradation of a system in
grandfathered systems: Systems, including but not
such a manner that it continues to operate, but limited to, (a) PBX and key telephone systems, provides a reduced level of service rather than directly connected to the public switched telephone network on June 1, 1978, that may remainpermanently connected thereto without registration graded-index fiber: An optical fiber with a core
unless subsequently modified, and (b) systems that having a refractive index that decreases with are of the same type as those connected to the public increasing radial distance from the fiber axis. (188) switched telephone network on July 1, 1978, that Note: The most common refractive index profile for were added before January 1, 1980, and that may a graded-index fiber is very nearly parabolic. The remain permanently connected thereto without parabolic profile results in continual refocusing of registration unless subsequently modified.
the rays in the core, and compensates for multimodedistortion.
grandfathered terminal equipment: Terminal
equipment (other than PBX and key telephonesystems) and protective circuitry connected to thepublic switched telephone network before July 1,1978, that may remain connected thereto for lifewithout registration unless subsequently modified.
graphical user interface (GUI): A computer
program or environment that displays options on thescreen as icons, i.e., picture symbols, by which usersenter commands by selecting an icon. Note: Iconsmay be selected, e.g., by pressing the <ENTER> keyon the keyboard, by “clicking” a computer mouse button, or by touching the icon on a touch pad.
graphic character: 1. A visual representation of a
graded-index profile: In the core of an optical fiber,
character, other than a control character. 2. In the
a plot of the variation of refractive index such that ASCII code, a character other than an alphanumeric the refractive index decreases with increasing radial character, intended to be written, printed, or otherwise displayed in a form that can be read byhumans. Note 1: Graphic characters are contained grade of service (GOS): 1. The probability of a
in rows 2 through 7 of the ASCII code table.
call’s being blocked or delayed more than a Note 2: The space and delete characters are con- specified interval, expressed as a decimal fraction.
(188) Note: Grade of service may be applied to thebusy hour or to some other specified period or set of graphics: The art or science of conveying
traffic conditions. Grade of service may be viewed information through the use of display media, such independently from the perspective of incoming as graphs, letters, lines, drawings, and pictures.
versus outgoing calls, and is not necessarily equal in (188) Note: Graphics includes the transmission of each direction. 2. In telephony, the quality of
service for which a circuit is designed or conditionedto provide, e.g., voice grade or program grade.
Gray code: A binary code in which consecutive
Note: Criteria for different grades of service may decimal numbers are represented by binary include equalization for amplitude over a specified expressions that differ in the state of one, and only band of frequencies, or in the case of digital data one, one bit. Synonym reflected code.
gray scale: An optical pattern consisting of discrete
ground loop: In an electrical system, an unwanted
steps or shades of gray between black and white.
current that flows in a conductor connecting two points that are nominally at the same potential, i.e.,ground, but are actually at different potentials.
great circle: A circle defined by the intersection of
Note 1: For example, the electrical potential at the surface of the Earth and any plane that passes different points on the surface of the Earth can vary through the center of the Earth. Note: On the by hundreds of volts, primarily from the influence of idealized surface of the Earth, the shortest distance the solar wind. Such an occurrence can be between two points lies along a great circle.
hazardous, e.g., to personnel working on longgrounded conductors such as metallic Greenwich Civil Time (GCT): Synonym Greenwich
telecommunications cable pairs. Note 2: A ground Mean Time (GMT). Obsolete term. See
loop can also exist in a floating ground system, i.e., Coordinated Universal Time.
one not connected to an Earth ground, if theconductors that constitute the ground system have a Greenwich Mean Time (GMT): Mean solar time at
relatively high resistance, or have, flowing through the meridian of Greenwich, England, formerly used them, high currents that produce a significant voltage as a basis for standard time throughout the world.
(“I•R”) drop. Note 3: Ground loops can be (188) Obsolete term. Synonym Greenwich Civil
detrimental to the operation of the electrical system.
Time. See Coordinated Universal Time.
Contrast with ground current.
ground: 1. An electrical connection to earth through
ground plane: An electrically conductive surface that
an earth-electrode subsystem. (188) 2. In an
serves as the near-field reflection point for an electrical circuit, a common return path that usually antenna. Note: A ground plane may consist of a (a) is connected to an earth-electrode subsystem and natural (e.g., Earth or sea) surface, an artificial (b) is extended throughout a facility via a facility surface of opportunity (e.g., the roof of a motor ground system consisting of the signal reference vehicle), or a specially designed artificial surface subsystem, the fault protection subsystem, and the (e.g., the disc of a discone antenna). (188) lightning protection subsystem. 3. In an electrical
circuit, a common return path that (a) may not
ground potential: The zero reference level used to
necessarily be connected to earth and (b) is the zero apply and measure voltages in a system. Note: A voltage reference level for the equipment or system.
potential difference may exist between this referencelevel and the ground potential of the Earth, which ground absorption: The dissipation of rf energy by
varies with locality, soil conditions, and ground constants: The electrical parameters of earth,
ground-return circuit: 1. A circuit using a common
such as conductivity, permittivity, and magnetic return path that is at ground potential. Note: Earth permeability. Note 1: The values of these may serve as a portion of the ground-return circuit.
parameters vary with the local chemical composition 2. A circuit in which there is a common return path,
and density of the earth. Note 2: For a propagating electromagnetic wave, such as a surface wavepropagating along the surface of the Earth, these ground start: A method of signaling from a terminal
parameters vary with frequency and direction. (188) or subscriber loop to a switch, in which method oneside of a cable pair is temporarily grounded. (188) ground current: In the presence of an electrical
fault, the current that flows in the protective ground ground wave: In radio transmission, a surface wave
wire of a power distribution system. Contrast with that propagates close to the surface of the Earth.
Note 1: The Earth has one refractive index and theatmosphere has another, thus constituting aninterface that supports surface wave transmission.
These refractive indices are subject to spatial and velocity, to travel a given distance. Note: For temporal changes. Note 2: Ground waves do not optical fiber dispersion measurement purposes, the include ionospheric and tropospheric waves.
quantity of interest is group delay per unit length,which is the reciprocal of the group velocity of a group: 1. In frequency-division multiplexing, a
particular mode. The measured group delay of a specific number of associated voice channels, either signal through an optical fiber exhibits a wavelength within a supergroup or as an independent entity.
dependence due to the various dispersion mech- Note 1: In wideband systems, a group usually consists of 12 voice channels and occupies thefrequency band from 60 kHz to 108 kHz. Note 2: group delay time: In a group of waves that have
this is CCITT group B. Note 3: CCITT Basic Group slightly different individual frequencies, the time A, for carrier telephone systems, consists of 12 required for any defined point on the envelope (i.e., channels occupying upper sidebands in the 12-kHz the envelope determined by the additive resultant of to 60-kHz band. Basic Group A is no longer the group of waves) to travel through a device or mentioned in CCITT Recommendations. Note 4: A supergroup usually consists of 60 voice channels,i.e., 5 groups of 12 voice channels each, occupying group distribution frame (GDF): In frequency-
the frequency band from 312 kHz to 552 kHz. (188) division multiplexing, a distribution frame that Note 5: A mastergroup consists of 10 supergroups or provides terminating and interconnecting facilities at 600 voice channels. (188) Note 6: The CCITT the group level, i.e., group modulator output and standard mastergroup consists of 5 supergroups.
group demodulator input circuits of FDM carrier The U.S. commercial carrier standard mastergroup equipment. Note: The basic spectrum of the FDM consists of 10 supergroups. Note 7: The terms “supermaster group” or “jumbo group” are
sometimes used to refer to 6 mastergroups. 2. A set
group index (N): In fiber optics, for a given mode
of characters forming a unit for transmission or propagating in a medium of refractive index , the velocity of light in vacuum, c, divided by the groupvelocity of the mode. (188) Note: For a plane wave group address: In a communications network, a
of wavelength , the group index may also be predefined address used to address only a specified set of users. Synonym collective address.
group alerting and dispatching system: A service
feature that (a) enables a controlling telephone toplace a call to a specified number of telephonessimultaneously, (b) enables the call to be recorded, where n is the phase index of wavelength .
(c) if any of the called lines is busy, enables theequipment to camp on until the busy line is free, and grouping factor: Synonym blocking factor.
(d) rings the free line and plays the recordedmessage.
group 1. . . 4 facsimile: See facsimile.
group busy hour (GBH): The busy hour for a given
group patch bay: See patch bay.
group velocity: 1. The velocity of propagation of an
group delay: 1. The rate of change of the total phase
envelope produced when an electromagnetic wave is shift with respect to angular frequency, d/d7, modulated by, or mixed with, other waves of through a device or transmission medium, where different frequencies. (188) Note: The group is the total phase shift, and 7 is the angular velocity is the velocity of information propagation frequency equal to 2%f, where f is the frequency. 2.
and, loosely, of energy propagation. 2. In optical
In an optical fiber, the transit time required for fiber transmission, for a particular mode, the optical power, traveling at a given mode’s group reciprocal of the rate of change of the phase constantwith respect to angular frequency. Note: The groupvelocity equals the phase velocity if the phaseconstant is a linear function of the angularfrequency, 7 = 2%f, where f is the frequency. 3. In
optical-fiber transmission, the velocity of themodulated optical power.
G/T: Abbreviation for antenna gain-to-noise-
guard band: See frequency guard band, time
guarded frequency: A transmission frequency that is
not to be jammed or interfered with because of thevalue of the information being derived from it.
Note: For example, a guarded frequency will not bejammed when the tactical, strategic, and technicalinformation that can be obtained from thetransmissions outweighs the potential operationalgain achieved by jamming. [From Weik ’89] guided mode: Synonym bound mode.
guided ray: In an optical fiber, a ray that is confined
primarily to the core. Note: A guided ray satisfiesthe relation given by where is the angle the ray makes with the fiber axis, r is the radial position, i.e., radial distance, ofthe ray from the fiber axis, n is the refractive index at the radial distance r from the fiber axis, and n is the refractive index at the core radius, a, i.e., at the
core-cladding interface. Guided rays correspond to
bound modes, i.e., guided modes, in terms of modes
rather than rays. (188) Synonyms bound ray,
guided wave: A wave having (a) energy concentrated
near a boundary, or between substantially parallelboundaries, separating materials of differentproperties and (b) a direction of propagationeffectively parallel to these boundaries. (188)
WEEKLY COMMENTARY 29 NOVEMBER 2010 Overview European markets extended their losses last week amid uncertainty about the fate of peripheral Eurozone countries. Bank shares fell sharply on fears that even the highest-ranked bondholders may be faced with losses. Bank troubles in Ireland culminated in a formal request for international aid, in which the European Uni