Fiber Optics Illustrated Dictionary - Part 41 potx

Fiber Optics Illustrated Dictionary GAC See Global Area Coverage. gadolinium A light, silvery, crystallizing, ferromag- netic rare earth metal isolated from yttrium in the late 1800s. Gadolinium has been used in the production of phosphors in color cathode-ray tubes (CRTs), and for making gadolinium yttrium garnets used in mi- crowave technologies. See europium, yttrium. gaff The spike that is attached to a utility pole climber's iron. See boomer. gage Performance indicator. See gauge. Gaia Global Astrometric Interferometer for Astro- physics. See interferometer. gain Increase in power ofatransmission, usually in- dicated in decibels (dB) when applied to audio gain. Gain is sometimes intentionally created by using vari- ous means to boost a signal. Unfortunately, doing so typically also increases noise and interference in ana- log systems. Gain is descriptive of an antenna's ca- pability to increase its effective radiated signal, rela- tive to a reference like an isotropic antenna or a cen- ter-fed, half-wave dipole antenna. galena A bluish-gray lead sulphide mineral com- monly used as a sensitive radio wave detector in crys- tal detectors in the early 1900s. Sometimes the ga- lena was thinly coated with other materials to improve its properties. gallium arsenide GaAs. Asemiconductor substance used to produce electronic components, such as com- puter chips and solar panels (when combined with germanium). It is sometimes used in place ofsilicon for high speed devices. It withstands heat and radia- tion well, making it suitable for orbiting satellite ap- plications. If used alone, the bandgap of GaAs is too high for use as semiconductor lasers, so the material is impreg- nated (doped) with other chemical elements and, as such, is the main active material used to fabricate semiconductor diode lasers, emitting pulsed light in the infrared frequency spectrum. GaAs lasers can be used at room temperature and cooler temperatures and, in general emit higher wave- lengths at higher temperatures. GaAs lasers emit a wider, more diffused beam than gas lasers, but they are small, inexpensive, versatile, and rugged and suit- able for many applications. See homojunction laser, indium gallium arsenide nitride, semiconductor la- ser. Galvani, Luigi (1737-1798) An Italian physicist, educator and physician who experimented with minute levels ofelectricity in the leg nerves offrogs around 1786. Galvani 's wife had observed twitching in a recently killed frog when a nerve was touched and pointed it out to her husband; Galvani followed up her observation with further experiments leading to a better understanding of nerve impulse transport in biological systems. His name has been applied to measuring instruments (galvanometer) and small lev- els ofelectricity on skin surfaces (galvanic skin re- sponse). galvanic Related to or producing a direct electrical current through chemical rather than electrostatic means. See galvanometer. 392 galvanic cell A power cell that produces electricity through electrochemical rather than through electro- static means. See battery. Luigi Galvani - Physicist Luigi Galvani didnumemus experiments innonbio- logical andbiological electricalimpulses. The galva- nometer is named after him. galvanometer Named after Luigi Galvani, an instru- ment for detecting low levels of electric current through the use of a magnetic needle or coil sus- pended within a magnetic field. The basic concept of a galvanometer is that very low levels of current, when channeled through a magnetic coil, can influ- ence the magnetic field sufficiently to deflect the coil (or needle) in one direction or the other, depending upon the polarity of the current. The magnitude of the deflection (torque) is proportional to the amount of current. Thus, the torque can be read and measured when compared against a calibrated scale associated with the receiver, indicating the direction and strength of any current that may be present. The historic development of the galvanometer fol- lowed from principles described by 0rstedt and Ampere and was furthered by Johann Schweigger, who presented a paper on the galvanometer multiplier in July 1820. Halfa decade later, Ampere developed a working galvanometer, as did Nobili, who used two needles, each with its own separate coil, to reduce in- terference from the Earth's magnetic field. Nobili's innovation made it possible to position the device without worrying about the direction of the Earth's magnetic meridian, thus creating astatic galvanom- eter. It also made it possible to use a longer needle, thus increasing the size of the gauge and the ease of getting an accurate reading. Nobili galvanometers designed by Ruhrnkorff were popular in the latter 1800s. Most of the early galvanometers, known as tangent galvanometers, were constructed with a com- pass integrated into a surrounding electromagnetic coil. In 1858, William Thomson (Lord Kelvin) refined the technology and created the astatic galvanometer, the basis of more modern galvanometers. In 1880, D' Arsonval further improved upon the technology, by integrating a small coil with the metering needle, both housed within the field ofa permanent magnet. © 2003 by CRC Press LLC In telecommunications, galvanometers have many uses, including the testing and diagnosis of circuits. Thomson's mirror galvanometer, for example, was used for reading currents on long submarine commu- nications cables. Following World War II, a dynamo transformer, a type of torque motor, based upon the moving-iron galvanometer, was patented by Mueller, an American inventor. The versatile galvanometer is now also used in aero- nautics, train, and power plant applications. A number of scientific instrument museums include historic galvanometers in their collections, including the Robert A. Paselk Scientific Instrument Museum in Arcata, CA. Traditional galvanometers have been partly replaced by solid state current meters for in- dustrial current-measuring use; however, mechanical galvanometers are still commonly used in schools to help teach the principles of electromagnetism. Com- mercial galvanometers vary in size and shape but most are about the size of a travel alarm clock and have a semicircular or vertical scale (similar to postal meters) for reading the measurements in amps, volts, or other relevant units. Electronic optical scanning galvanometers are becoming important in the scan- ning and printing industries. See galvanic; Galvani, Luigi; Schweigger, Johann. Historic Galvanic Power Cell A historic electrochemical power galvanic cell named afterItalian physicist Luigi Galvani. galvanometer, ballistic A type of galvanometer pat- ented by the Leeds & Northrup Co. in the early 1900s intended to measure the total charge (as opposed to peak charge) or ofa burst or short duration pulse of current. When the duration of the impulse to the coil is short, the coil gives a short twist proportional to the magnitude and duration of the current. Ballistic galvanometers are designed with a higher inertia coil. Some of the practical applications ofballistic galva- nometers include the testing of various configurations in a prototype circuit board (e.g., combinations of capacitors) and the experimental determination of hysteresis curves for various substances or devices. See galvanometer. galvanometer, D'ArsonvalAhistoric, common coil- based galvanometer, consisting ofa narrow, rectan- gular coil, suspended so that it can move between the poles ofa permanent magnet to register a reading of direct current. This version of the galvanometer, de- veloped by D'Arsonval in 1880, made the historic compass-based galvanometers obsolete. They were designed with compact, more reliable casings than the tangent galvanometers, since an external circu- lar coil around the instrument was not used. Later adaptations of thermocouples or rectifiers to the D'Arsonval galvanometer permitted the conversion ofalternating current (AC) to direct current (DC) in order to measure alternating current. See galvanom- eter. galvanometer, mirrorA device for measuring very low levels of current developed by Poggendorff in the 1820s and later refined by William Thomson (Lord Kelvin) in the 1850s that was a departure from the early compass needle style galvanometers. The mirror or reflecting galvanometer was used for mea- suring current in submarine communications cables in the late 1870s. There were two main systems in a mirror galvanometer, the galvanometer with a mir- ror that reflected a beam of light whose direction and extent was influenced by the polarity ofa tiny amount of current, and a lamp at the receiving end with a cali- brated scale that registered the light reflected from the galvanometer, shifting to the right or to the left depending upon the direction ofpolarity and amount of current. See galvanometer. galvanometer, resonant A newer form ofpatented galvanometer technology that is being used in the printing industry for scanning images onto printing plates. This somewhat revolutionary technology uses computer electronics to control a raster-based laser scanner without the use of motors or rotating mirrors. Instead, the scanning mirror is associated with a tor- sion bar that is influenced by electromagnetic coils. Thus, in practical use very high scanning speeds are possible and there are no significant mechanical parts to wear out. See galvanometer. gamma ferric oxide Ferric oxide is found as dark synthetic pigments and as natural red or black hema- tite. Gamma ferric oxide has been used since the 1940s to provide configurable magnetic recording surfaces, first on magnetic tapes, later on floppy dis- kettes. gamma camera A device for detecting and record- ing gamma ray emissions. The basic components in- clude a collimator, for preprocessing the gamma ray emissions entering at desired angles through gamma ray absorbing materials, a detector crystal (gamma ray scintillator), an array ofphotomultiplier tubes for converting the photonic energy into electrical energy while amplifying the electron emissions, output and logic circuits, and a processing unit (computer) for interpreting the data into meaningful information. Gamma cameras are used in radiopharmaceutical imaging for detecting radiation that has passed through bodily organs to reveal internal structures and anomalies. 393 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary gamma testing The testing of a product by out-of- house testers who fit the profile of endusers who would actually purchase or use the product being tested. It is the step before User Acceptance Testing (UAT) or delta testing and after beta testing (in-house testing). Gamma testers understand that the product is essentially finished but there may still be a few op- portunities for user input into the final design (an important aspect of software design). The testers also understand that the product is considered to be bug- and defect-free but that a bug-free state is not 100% assured because people outside the company haven't used the product in a real life environment. See beta testing, User Acceptance Testing. gamut I. A range or series. 2. In imagery, the color gamut is the range of colors that can be perceived or reproduced, usually within the context ofa particu- lar situation or technology. For example, the gamut of an RGB cathode-ray tube (CRT) monitor is quite different from the gamut of printing inks or process color perceptual combinations of dots. The gamut range of videotaped images is narrower than that of film-based images. It is important to understand the differences in order to adapt the technologies to one another. See dynamic range. 3. The range of wave- lengths within a spectrum that are usable, viewable, or of scientific interest. GAN See global area network. Gandalf FZA Compression Protocol One of sev- eral mechanisms proposed in the mid-1990s to en- able compression of PPP encapsulated packets. Gandalf is based on FZA, which was developed by David Carr at Gandalf Data Ltd. and enhanced as FZA + by Abbie Barbir. It is a derivative of LZ that optimizes at the expense of CPU cycles and memory in order to achieve high performance compression, available on a fee or royalty basis. See Compression Control Protocol, Deflate Protocol, Point-to-Point Protocol, RFC 1993. gang To group or aggregate cables, components, ob- jects, or picture elements. To mechanically or elec- trically combine components or devices so they can be controlled from one source. Gang of Nine Nine vendor companies who formed a group in 1989 to promote and develop the industry standard architecture (ISA) which is commonly used for computer peripheral device connections on Intel- based microcomputers. Their work resulted in the 32- bit Extended ISA (EISA) standard. gap Opening, space, small distance between objects or signals, small distance ofa less dense material than the surrounding materials. GAP See Generic Access Profile. gap, electrical An opening in an electrical connec- tion, which may close to allow a circuit connection or, more commonly, over which a spark will jump to provide a brief connection or discharge through the air, as the gap in a spark plug on an engine. An un- planned gap, through breakage, can interrupt an op- tical or electrical connection, thus interfering with a transmission. gap, pickup The distance between a reading/recording 394 head and the medium with which it interacts. The dis- tance is often very precise, as in hard drive read/write heads and compact disc pickups, where a slight ad- justment allows a much greater density of recorded pits in the disc. gap, timeAn informational space or time gap inserted to indicate a stopping and/or starting point in recorded material or in a coded transmission. gap loss The loss in signal strength that occurs when crossing a gap. Even very tiny gaps may substantially affect the quality ofa transmission, and gaps are apt to occur at comers and junctions where transmission media change and in couplers. garbage 1. In computing, meaningless information, spurious characters, nonsensical output. 2. A mean- ingless signal or electrical interference. See interfer- ence, noise. garbage in/garbage out GIGO. colloq. A means of saying that you can't get something good out if you have put something bad into a system. In computer terms, it means that if you supply bad input, you're not going to get good output. In terms of hardware, a weak or poor signal at the origin is not going to re- sult in a good signal at the receiving end. In program- ming terms, feeding the computer the wrong instruc- tions or the wrong data is not going to result in the software performing in a correct or desired manner. In management terms, providing bad instructions and motivations to subordinates is not going to result in good work even if they are capable professionals. garble A communication or signal in which some portion of the content has been changed to be unde- cipherable, unintelligible, out of sequence, or other- wise undesirably "scrambled." The change is usually in terms of the strength or content of the signal. A phone conversation may sound garbled if the speed of transmission is inconsistent with the speed of the spoken message, resulting in words running together or pauses that are inappropriate. It may also sound garbled if there are power fluctuations causing the sound level to significantly fade in and out or if there are other signals overlaying the desired signal, mak- ing it unintelligible (e.g., party line noise, crosstalk). Thus, in voice and radio communications, the term tends to be associated with reduced intelligibility re- lated to informational timing problems, power fluc- tuations, or multiple signals overlaying portions of one another. In data communications, the term tends to be associ- ated with portions ofa communication arriving out of sequence or interspersed with nonsensical or scrambled data. It can also occur in encrypted mes- sages if the decryption algorithms do not work cor- rectly. A file or data communication may be garbled if packets are reassembled in the wrong order or have inappropriate portions merged into existing packets or between the appropriate packets. As in voice com- munications, garbled data can result from power fluc- tuations but it can also arise from programming bugs or programming deficiencies, such as insufficient or inappropriate error checking. Surge suppressors, power conditioners, robust and appropriate (for the © 2003 by CRC Press LLC task) error checking, good decryption algorithms, and data redundancy are all strategies for eliminating or mitigating problems associated with garbled. Garden Valley Telephone Company GVTel. The oldest telephone cooperative in the United States, chartered in Minnesota in 1912 and still operating after more than 88 years. Garfield, Oliver An author and engineer, in 1955 Garfield wrote a 63-page book Simple Electronic Brains and How to Make Them as a practical embodi- ment and complement to Edmund C. Berkeley's 1949 book Giant Brains or Machines that Think. The two men partnered for a while to produce computing mechanisms such as the Geniac, in the mid-1950s. Unfortunately, there were disputes and a lawsuit; Garfield and Berkeley ended up selling the comput- ing devices as the Brainiac and Garfield got the name Geniac. The original Geniac (later the Brainiac) was an innovative computing device that could be con- figured to play simple games. While the author of this text couldn't find hard evi- dence of wrongdoing, Garfield's business practices may not have been entirely legal. For a while Gar- field used the Geniac name to promote his GENIAC Pocket Calculator. It was a repackaged Otis King cal- culator (a cylindrical slide rule) sold after the breakup with Berkeley through the Oliver Garfield Co., Inc. The Otis King calculators were serial numbered and shipped from England. Some of the Garfield calcu- lators have all the original Otis King markings re- moved or, more likely, Garfield stole the design and cloned it without the identifying marks. It is unlikely he had permission from Otis King to distribute their calculators without attribution, so perhaps this sheds some insight as to why his dealings with Berkeley didn't work out. See Berkeley, Edmund; Geniac. garnetA red, more or less transparent semiprecious mineral often used in jewelry and industrial applica- tions. It somewhat resembles ruby but is generally a little less transparent and a deeper, muddier shade of red. Synthetic garnets can be manufactured from ox- ides of some of the rare earths. Lasers and some types of computer memory that use magnetic film are made from garnet. See gadolinium, laser. GARP See Global Atmospheric Research Program. gas laser A laser in which a gas or vapor is used as the active medium. The gas may be excited by a high- frequency oscillator or direct current. Ion lasers use noble gases such as argon. Apulse of voltage is used to ionize the gas and direct current (DC) can be used to maintain the state of ionization. Gas lasers were pioneered by A. Javan in 1960 and the argon laser was developed in the mid-1960s by William Bridges. See laser, laser history. gas maserA maser in which a gas or vapor interacts with microwaves. Gas masers are found in scientific oscillators such as atomic clocks. See atomic clock; Dicke, Robert; laser history; maser. gas plasma display See plasma display panel. gas tubeA type of electron tube that is not completely evacuated. Early electron tubes burned out quickly because of the gas inside the bulb. Later tubes were designed to last longer by being evacuated. In spe- cialized applications, a trade-off is used and a small amount of gas is left in the tube to promote ioniza- tion to enhance current flow. Gassner, Carl,Jr. A German-born inventor who first created a commercially practical dry cell, based on a sealed zinc container that, for the most part, super- seded the wet cell. In November 1887, Gassner was granted U.S. Utility Patent #373,064 for his inven- tion. Dry cells were welcomed because they didn't have the problems of leakage associated with wet cells, and they could be made smaller and more por- table. They were an important innovation and are still in use today in the fonn ofcarbon-zinc batteries. See dry cell; Leclanche, Georges; Plante, Gaston. gaston A random noise modulator sometimes used as an antij amming communications transmitting de- vice. gastroscope Developed around the 1930s as one of the historic fiber optic medical imaging technologies, the gastroscope makes it possible to peer inside the gastric (digestive) system. It is especially useful for locating and illuminating structures such as suspected tumors in the stomach. GAT See Generic Addressing and Transport Protocol. gate In an electrical circuit, in its broadest sense, a junction that selectively controls whether current gets through, when it gets through, or how much of it gets through. gate, security In a software program, an input or pro- cess point that selectively lets users or other processes through, as a security gate, login gate, or system gate- way for different types ofinformation or protocols (network traffic, mail, etc.). In the more specific con- text of programming, a circuit that performs a basic logic operation and provides a single output from that operation. See firewall, gateway, proxy. gate, telephone In telephone call distribution sys- tems, aphysical or virtual trunk through which calls are handled by a group of operators or agents accord- ing to some characteristics specified for each gate. Gates, William Henry, HI (1955- ) Bill Gates is a prominent success story in the personal computer in- dustry and has a major influence on the direction and type of software that is available to consumers around the world today. In the 1980s he went from entrepre- neur to software magnate, earning billions of dollars by investing in technology and selling computer op- erating systems and basic business software tools. Gates began programming seriously in Seattle, Wash- ington, while still in grade school, along with his friend and business partner, Paul Allen, who was two years older. Gates came from a privileged family with many solid business contacts, and Allen and Gates were both precocious entrepreneurs, successfully winning commercial programming contracts at a young age. Their first business partnership, based upon traffic analysis software, was called Traf-O-Data, founded around 1972. The economic success ofMicrosoft began with the signing of the IBM OSIBASIC contract. Ofparticu- lar importance is the fact that Gates reserved the right 395 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary to market the results of the development (sold by mM as PC-DOS) in competition with IBM, a contractual loophole that Gates had also achieved with MITS, who were dismayed because they thought they had bought the exclusive rights to Microsoft BASIC for the Altair. Gates' father was a lawyer and Gates had a long-standing interest in contracts and business deals, which probably accounts for the Microsoft- fa- vorable outcome of the two pivotal contracts. Times have changed; today large corporations have teams of lawyers to develop and scrutinize contracts but, two decades ago, many deals were still established on trust and a handshake or on less extensive paper- work and scrutiny than is common now. Since Gates and Allen didn't have an operating sys- tem to sell to ffiM, they bought QDOS, developed by Tim Paterson. In one of computer history's great- est ironies, Tim Paterson acknowledged that he had created QDOS by using a mid-1970s version of the documentation for Gary Kildall's CP/M. Microsoft then hired Paterson to quickly develop it into PC- DOS. QDOS was syntactically and functionally simi- lar to Kildall's CP/M. Microsoft's version of a PC operating system, sold in competition with the prod- uct they produced for ffiM, became known as MS- DOS. In addition to operating systems, Microsoft began developing business tools, word processors, spreadsheets, etc., and buying up competitive prod- ucts and companies including FoxPro, Stacker, Altamira Composer, Vxtreme, Vermeer (now known as Frontpage), Web Mapper, Softimage, Web ~ and others. Microsoft also now has stakes in several broadcast and cable companies. In 1982, Kildall's Digital Research Inc. sued Micro- soft Corporation and ffiM for copyright infringement of the CP/M operating system. Digital Research won, but by this time Microsoft's momentum was so great, few people heard about the suit and Kildall's com- pany lost its majority market share. The situation was still of consequence almost twenty years after QDOS was purchased, however, as Caldera, the new own- ers ofKildall's early and later operating systems tech- nology, pursued legal avenues against Microsoft. In July 1996, Caldera, Inc. filed suit against Microsoft Corporation for damages and injunctive relief under U.S. antitrust laws for "illegal conduct calculated to prevent and destroy competition in the software in- dustry." Allen left Microsoft in 1983 for health reasons and to pursue other investments through his own com- pany, but he maintained close personal ties with Bill Gates. He served on the Board of Directors of Micro- soft for a time, announcing his intention to resign and become a strategy advisor as of November 2000. In the late 1990s, Gates was still head of the organiza- tion that had grown from a small group ofhalfa dozen programmers and clerical staff to a campus in Red- mond with tens of thousands of employees and as- sets in the billions. The controversy did not die down, however. In May 1998, the United States of America filed a complaint against Microsoft. Thus, Gates' ac- tions as CEO came under severe scrutiny, aposition 396 he resigned in January 2000. He continued to hold the position of Chairman, however. Gates has spun offa number ofother businesses, in- cluding a multimedia company and the Teledesic In- ternet in the Sky project that he is co-developing with Steve McCaw. He is clearly interested in expanding into the broadcast and telecommunications fields and heavily promotes the use of Microsoft's Web browser. Gates is one of the richest people in the world, and one of the most focused, aggressive, and successful business and marketing giants in the software indus- try. Allegations of antitrust violations are part of an ongoing investigation of Microsoft by the U.S. Jus- tice Department on behalf of hundreds of software developers who don't feel they can compete against a company allegedly succeeding because of unfair business practices. Whatever the results of the inves- tigation, part of Bill Gates' success is due to his am- bition, tenacity, and all-encompassing competitive drive. Nonetheless, there is much controversy over his ethics, methods, and acquisition of products from other sources that he has marketed as his own. gateway A transmission connection between net- works that handles information flow and typically performs bandwidth and protocol adjustments and conversions, as needed. It may also combine (aggre- gate) network transmissions from several devices connected to a smaller number of network connec- tions. Gateways are commonly used between dissimi- lar networks such as between local area networks (LAN s) and the Internet (proxy servers), and between land services and satellite services, etc. When local nets are connected with external nets, the gateway may also perform security functions. Gateways are used on both wired and wireless networks. Wireless gateway networks use radio transceivers rather than physical connections for wire or fiber optic cables. Wireless networks also tend to have additional secu- rity features and encryption schemes to compensate for the fact that it's sometimes difficult to determine if someone is intercepting wireless transmissions. Consumer-oriented gateways that are available as peripheral devices may include Web server software and other utilities to facilitate Internet connections and firewall, logging, or other security schemes to protect data transmissions or specific devices from unauthorized access. A gateway differs from a proxy in that a gateway handles requests as though the requests originated from the gateway and not from the original client, thus serving as a server-side portal in a firewall. See fire- wall, proxy. Gateway to Gateway Protocol GGP. A historic, ex- perimental TCP lIP network transport layer routing protocol used to convey routing information through a distributed shortest path computation. The proto- col was primarily used for gateway-related tasks such as routing datagrams. It is now considered obsolete and developers are cautioned not to implement it. See RFC 1009, RFC 1812. gating 1. Selectively allowing certain waveforms, frequencies, or portions of waves to pass through a © 2003 by CRC Press LLC gate point. 2. Performing electronic switching by ap- plication ofa certain current or waveform. 3. Using logic to control the passage of current or information through a system. gauge An instrument or other indicator for measur- ing or testing. An indicator of the thickness or thin- ness of a substance or object, especially applied to wires and cabling. Position relative to another, as in the distance between the sides ofa railroad track. See American Wire Gauge (Brown and Sharpe), Birmington Wire Gauge, Steel Wire Gauge. gaussA centimeter-gram-second (CGS) unit of mag- netic flux density. For example, if one line of mag- netic force passes through one square centimeter, the field intensity is said to be one gauss. Named after Karl Friedrich Gauss. See lines of force, magnetic field. Gauss - Mathematician &Astronomer Aportraitfrom a Germanpostage stampcommemo- rates the achievements of Carl (Karl) Gauss who mathematically described important basic concepts in magnetism, surveying, and mathematics. Gauss, Jobann Karl Friedrich (1777-1855) A bril- liant German mathematician and astronomer who devised the heliotrope, an instrument that could re- flect sunlight over long distances, providing a means for making straight lines and calculations related to the Earth's swface. He investigated terrestrial mag- netism in cooperation with W. Weber in 1831 and published some significant papers several years later. In 1833, he constructed an electric telegraph, just as similar devices began to be developed in the United States. The gauss unit for magnetic flux density is named after him. Gauss's law As it applies to dielectrics (without get- ting into integrals), the total electric flux ofa closed surface (a surface without holes) equals the charge enclosed divided by the permittivity. Gauss's law fa- cilitates the assessment of a stationary enclosed charge associated with asurface by mapping the sur- face field outside the charge distribution. See Ampere's law, Coulomb's law, dielectric, flux, Gaussian surface, Maxwell's equations. Gaussian curve, normal curveA Gaussian curve is often called a bell curve due to its shape, and a nor- mal curve due to its experimentally observed or theo- retical distribution (depending upon context). The concept and observations on larger statistical sets to confirm the concept were developed over a couple of centuries, with A. de Moivre noting in the 1730s that the binomial distributions described earlier by 1. Bernoulli took on the characteristics ofa continuous curve when developed using increasingly large sample populations. Around the late 1700s, 1. Karl Gauss enlarged on the concept, finding many appli- cations for its use. He thus popularized the bell curve ~£~E~i~~ ~ia~:~~U::d~~o:~~e~i~=~~ ill representation that resembles the outline of the curve ofa bell. Its structure is based upon a combination of observed population distribution (in the statistical, not the human sense) and assumptions about its generalizability. In a diagrammatic representation of the curve, the majority of occurrences of a phenom- enon fall within the center and highest point of the curve (the mean and mode). The changes in the di- rection of the curve and dispersion of frequencies are symmetric to either side of the mean and mode and are described in terms ofstandarddeviations. An interesting demonstration of the shape and dis- tribution of elements in a Gaussian curve can be seen in a number of science museums. It is set up with ver- tical channels and ping pong balls (or ball bearings), in which the balls are dropped into the top ofa de- vice where they randomly roll down into a line of channels that can be viewed through a transparent panel. After many hundreds of balls have fallen down through the mechanism, the shape of the curve will emerge, with the majority ofballs in the center, and fewer as you move left or right out to the edges (the tails of the distribution) due to the lower statistical probability of the balls moving farther and farther from the main center of the path. Gaussian curve models are at the heart of many ex- periments and statistical theories. Relationships such as that between optical intensity and frequency will often fit Gaussian models, though they may be skewed in one direction or the other due to environ- mental effects. Conformance to a normal "bell" curve is frequently an underlying assumption for the design and scoring of tests. Unfortunately, it is sometimes used as ajus- tification for describing populations where the size of the sample being evaluated is not mathematically sufficient to justify assumptions about its relationship to the normal curve. Gaussian minimum shift keying GMSK. A type of wave modulation from the frequency shift keying family used in wireless communications such as cel- lular phone systems and, notably, the Global System for Mobile Communication (GSM). GMSK is a com- promise solution, as it is less efficient than some types of modulation, but it is popular for its cost benefit. In GMSK, a digital signal is modulated onto the analog 397 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary carrier frequency as the phase of the carrier is varied by the signal information. A Gaussian filter is applied before modulation. Most of the power is concentrated at 250 kHz and there is low incidence of channel in- terference. Commercial applications of GMSK for mobile telephony were described in the early 1980s and later put into practical use in GSM. In 1996, Thierry Turlette authored a frequently cited paper on GMSK "GMSK in a nutshell." In the late 1990s, more efficient algorithms for GMSK were suggested by re- searchers. See phase shift keying. Gaussian noise Noise or other electromagnetic in- terference that conforms to aprobability pattern con- sistent with expectations based on Gaussian statistics. Noise that is somewhat random across a range offre- quencies is sometimes known as white noise or Gaussian noise. Gaussian surface Atheoretical surface providing a geometry analogous to a physical surface to facili- tate modeling and calculations related to electric fields. See Gauss's law. Gauthey, Dom A French monk who invented a tube system for channeling acoustics, in essence a "speak- ing tube" or historic manual telephone conduit (ap- parently derived from ship-based speaking tubes). It consisted basically ofa tube with funnel shapes on the ends for speaking and listening. The interesting aspect of the idea is that it was suggested the tubes could be organized in relay, with human speakers (re- lay agents) at the junction of each length of tube. Thus, it would be theoretically possible to commu- nicate a message more than 500 kilometers in less than an hour. He presented his invention to the l'Academie des sciences (Academy of Sciences) ca. 1782, transmitting sound over a distance of 760 meters. See telephone history. Gb, Gbyte gigabyte. See giga GB gigabit. See giga GBCS See Global Business Communications Sys- tems. GBIC Gigabit Interface Converter. A small, some- times swappable, fast gigabit network converter de- vice that attaches to a port connection. GBR ground-based radar. See radar. GCA 1. See game control adapter. 2. ground-con- trolled approach. Aradar-based aircraft landing sys- tem. GCI Ground Control ofInterception. A radar-based technique for directing aircraft in the interception of approaching craft. GCMD See Global Change Master Directory. GCRA See generic cell rate algorithm. GCS 1. Government Communication Systems. 2. Great Canadian Scientists. A project to increase awareness of great scientists with Canadian affilia- tions and roots originating from a lack ofprint mate- rials on the subject. Many of the profiled scientists have contributed to the telecommunications industry. GCT See Greenwich Civil Time. GDF group distribution frame. See distribution frame. GDG See Global Development Gateway. 398 GDI See graphics device interface. Geissler tube A type of sealed dual-electrode gas- filled tube that glows when current passes through it. The color of the glow varies with the types of gases used, and the wave characteristics can be influenced by the amount and type ofcurrent applied. Historic versions of the Geissler tube, named after the inven- tor J. Heinrich Geissler, resembled glass lanterns or candles mounted on a metal or wood base with a straight or spiral illumination up through the center of a second, protective glass bulb (sometimes filled with a colored liquid to enhance the effect of the pri- mary illumination in the inner tube). Some of the smallest, earliest tubes lacked a stand and protective bulb but came in a variety ofcreative and charming shapes resembling short strings of hollow glass beads. Early Geissler-style tubes were used for signs and lamps, more recent variations are used as scientific research and calibration instruments. Over the de- cades, Geissler tubes have played a role in many pio- neer aspects ofelectronics and telecommunications leading to the development of the light bulb, flash bulbs, a number ofprojection technologies, and the discovery of cathode rays. In contemporary calibration tubes, the central region of the tube is usually narrower than the ends. The very narrow region in the center induces strong spectral lines for sample comparisons. The Geissler tube is useful for calibrating optical instruments and as a ref- erence tool. It has also been used in conjunction with imaging technologies as alow-cost experimental ro- tating mirror photodetection device. Educational versions of the Geissler tube often have more than one tube, each with different contents. These are useful for teaching about gases, induction, fluorescence, and other related concepts. For ex- ample, an energized Geissler-style tube can be used to illustrate magnetic field influences on charged par- ticles. Geissler tube effects may be observed by the unaided eye or with scientific instruments such as spectroscopes. See cathode-ray tube, Crookes tube. Geissler, Johann Heinrich Wilhelm (1814-1879) A German physicist and glassblower who established a workshop in Bonn, where he crafted scientific ap- paratus. One of his more significant inventions was a type ofmercury air pump that is still in use today for evacuating the air from bulbs and various labora- tory apparatus. In collaboration with Julius Pliickers, Geissler did experiments to measure the density of water. He also created instruments for the measure- ment of vapor. Modem refinements of the Geissler tube, that he developed in the late 1850s, are still used for scientific calibration. See Geissler tube. GEM See Graphics Environment Manager. GEMINAX Global Enhanced Multiport integrated ADSL Transceiver. An integrated voice and data chipset provided by Infineon Technologies, GEMINAX was selected for the North American Litespan next generaltion network digital loop car- rier multiservice broadband access platform. The chipset can be integrated into cost effective, very high density linecards for voice and DSL-based data © 2003 by CRC Press LLC network services. See Litespan. GEMS See Global Environmental Monitoring Sys- tem. gender A designation widely used to cable connec- tors to indicate whether they are female "innies," or male "outies," that is, whether they have holes or ex- tended pins. If it is a simple round or squarish con- nector like a switchboard or composite video connec- tor, the female end is usually called a plug while the male end is usually called ajack. Most common switchboxes for computer data con- nections have female connectors. Male and female connectors are both found on the backs of comput- ers, and vary from platform to platform and some- times even from brand to brand. This variation is in- convenient for users, who often have to pay extra money for gender changers, but cab Ie and connector manufacturers don't seem to mind the extra business. Gender BendingAdapters Gender benders are commonly used to make con- nections between cableswith the samemale or female contacts facing one another. Some common gender benders used with serial cables include (A) DB-25 regular; (B) DB-25 slimline; (C) DB-9 regular. The slimline models are convenient for portable devices, such as laptops, for connectingto modems or printers. gender bender/changer/converter A small con- necter designed to change the gender ofa plug or re- ceptacle in order to enable connection to another plug or receptacle. The male end is the one in which the contact points protrude from the connecter. The fe- male end is the one in which the contacts are de- pressed. Thus, a simple gender bender has two female ends or two male ends. Switchboxes and adaptors sometimes also perform gender bending functions. Adapters/extenders (male on one side, female on the other) are sometimes erroneously called gender bend- ers, because they superficially resemble them, but have different genders. Gender benders are usually passive devices that do not influence the signal pass- ing through the device. See adapter, extender, switch box. GeneralInstrumentCorporation GIC. A broadcast technology corporation which is significant because it was the first to suggest an all-digital broadcast sys- tem to the Advisory Committee on Advanced Tele- vision Service (ACATS) for consideration for recom- mendations to the Federal Communications Commis- sion (FCC) and the U.S. Congress. Subsequent to the GIC proposal, the focus on digital systems greatly increased, and ACATS and other advisory bodies brought the thinking about television technologies into closer alignment with recent digital advance- ments. In a separate but related matter, General Instrument Corporation sought, through the U.S. courts, to hold the FCC to the mandate to ensure "Competitive Avail- ability ofNavigation Devices" (e.g., cable set-top boxes) to maintain the right of competitors other than cable companies to produce and distribute these vir- tual navigation devices. However, as of June 2000, the court decision was to reject GIC's challenge to an FCC separation requirement for hybrid navigation devices. See Advisory Committee on Advanced Tele- vision Service. GeneralMagicA California-based commercial ven- ture established in 1989 that focuses on providing innovative, cost-effective computer-Internet-tele- phony products for mobile applications. Products in- clude Portico, a development name for integrated voice/data communications and information services, and DataRover integrated voice/data hardware de- vices General Packet Radio Service GPRS. A wireless high-speed data communications standard operating over Global System for Mobile Communications (GSM) networks. GPRS is a packet-based air inter- face using existing circuit-switched GSM networks. GPRS offers enhancements to basic GSM. It provides functional connections with the Internet that were not possible with earlier systems. It can operate at speeds ranging from 9.6 Kbps to 115 Kbps (with plans for rates up to 384 Kbps) and offers live connections to mobile users such that users can be online continu- ously, without paying minute-by-minute fees other than when uploading or downloading information. The higher data rates possible with GPRS not only reduce connect time costs but enable broader-band services, such as videoconferencing, to be imple- mented on mobile devices. Full implementation of these higher data rates are somewhat dependent upon the evolution of the underlying GSM technologies but will likely be realized over the next two years or so. Many see GPRS as a bridge between GSM and 3G mobile services. GeneralProtectionFault GPF. A common fault con- dition encountered by users of Microsoft Windows software when applications memory conflicts occur. At the very least, applications should be closed up. Unfortunately, it may also be necessary to reboot the system. GeneralRadiotelephone OperatorLicense GROL. A lifetime operator's license granted by the Federal Communications Commission (FCC) upon success- ful completion of competency requirements. The li- cense is required for individuals who adjust, main- tain, or service FCC-licensed marine, aviation, and international radiotelephone transmitters. It conveys the operating authority of the Marine Radiotelephone Operator License and requires the Written Element 1 and Written Element 3 exams to be passed. 399 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary Some related FCC radiotelephone authorizations in- clude the First, Second, and Third Class Radiotele- graph Operator Certificates. These require exams, in some cases Morse Code competency, and are valid for five-year terms (renewable). A GROL-licensee may also be granted a Ship Radar Endorsement on qualifying and passing the Written Element 8 exami- nation. This permits the repair, maintenance and in- ternal adjustment of ship radar equipment. There are also licenses specific to the Global Maritime Distress and Safety System. See GMDSS Radio Operator Li- cense. General Switch Management Protocol GSMP. An IETF standards-track packet network administration protocol to control a frame- or cell-based label switch. GSMP is an asymmetric protocol supporting master (controller) and slave (switch) interactions. GSMP provides a means to query and report connection, port, switch, and Quality of Service (QoS) informa- tion and statistics for MPLS label switch devices from or to a third party controller. Thus, GSMP can be used to query switches, to establish and release connec- tions, to modify amulticast connection, and to man- age switch ports. It can also notify the controller of asynchronous events. Multiple instantiations of a single controller can be used to control multiple switches and partitioning is supported for the control ofa single switch by multiple controllers. The capability to query and report switch-related con- figuration and statistical status is particularly valu- able for remote switch operations and, as the proto- col evolves, is desired for optical network configu- rations as well. Initially, GSMP was developed to work with static switch partitions; however, dynamic forwarding to multiple administrative domains might be feasible for future versions of GSMP. GSMP does not make significant assumptions about the underlying hardware over which it is transmitted and thus can be implemented in avariety of types of networks. As a separate standards-track document, packet encapsulations for GSMP transport have been defined for ATM, Ethernet, and TCP networks: In ATM networking, GSMP packets are vari- able length and encapsulated directly in ATM AAL-5 with an LLC/SNAP header. • For Ethernet, GSMP packets are transmitted after the Ethertype Ox880C identifier up to a maximum length of 1492 bytes. In TeP/IP, GSMP is transmitted after a prepended TLV header field of type Ox88-0C and an integer indicating the length of the fol- lowing GSMP message. The message is pro- cessed after its successful receipt. TCP/IP en- capsulation can also be transmitted with au- thentication. With the evolution of GSMP towards an industry standard in the late 1990s, there has been interest from the commercial and developer communities in defin- ing GSMP for other environments, including experi- mental switches and patented, proprietary switches. Thus, GSMP for FSR switches (VTT Information 400 Technology) and ForeRunner (Sprint) switches are ofinterest to developers. See flow, Ipsilon Flow Man- agement Protocol, RFC 1987, RFC 2026. Generalized TrunkProtocol GTP. Atelephony pro- tocol enabling complex Channel Associated Signal- ing (CAS) and Common Channel Signaling (CCS) protocols to be executed in peripheral devices in or- der to remove some of the processing load from the main processor. generator In its basic sense, a machine that is de- signed to convert mechanical energy into electrical energy, or one that converts direct current (DC) into alternating current (AC). Dynamo. Generic Access Profile GAP. Aprofile is defined by the Open Systems Interconnection (OSI) model as a combination of one or more base standards and as- sociation classes, necessary for performing aparticu- lar function. The GAP specifies well-defined com- patibility levels for DECT products, as an extension of an ETSI-published Public Access Profile (PAP) incorporated into Digital European Cordless Tele- communications. (DECT). See Digital European Cordless Telecommunications. Generic Addressing and Transport Protocol GAT. A digital telephony protocol for exchanging Appli- cation Protocol data units (APDUs) between service provision points. It may be used between a terminal and a network or within or among networks. The rec- ommendations for GAT use with ISDNIB-ISDN is described in ITU- T Q.860. generic cell rate algorithm GCRA. In ATM net- working, an algorithm used to enforce a particular performance level with regard to cell traffic. The GCRA evaluates the cell to determine whether it con- forms to the established cell traffic contract. In anet- work switch, the UPC function will typically incor- pot'ate an algorithm such as GCRA to enforce con- formance with the specified parameters. See leaky bucket for a fuller explanation and example. See cell rate for related concepts. generic flow control GFC. In ATM networks, a means ofcontrolling traffic flow. A field in the ATM header can be used to designate flow control param- eters. This field is evaluated en route, as appropriate, and is not included in the final delivered communi- cation. See cell rate. generic flow control field GFC. In ATM network- ing, traffic flow control is an essential aspect ofmov- ing cells from one place to another. In the ATM header, there are priority bits which can be set to in- form the end-station that congestion control may be implemented by the switcher. See cell rate. Generic Security Service Application GSSA. An IETF elective proposed general Internet standard. See RFC 2078. GENIAC Genius Almost-Automatic Computer (in the tradition of the UNIVAC, ENIAC naming con- vention). The GENIAC was a personal computing device designed by Edmund C. Berkeley and possi- bly also Oliver Garfield in the mid-l 950s. Berkeley was an insightful author, robotics entrepreneur, and the designer of what was likely the first desktop © 2003 by CRC Press LLC computer ever invented, the Simon. Garfield was an author, engineer, and business person in much the same vein as Berkeley. Unfortunately, the partnership ended up in disputes and Garfield ended up with the name Geniac while Berkeley continued marketing computing devices under the name Brainiac. The GENIAC kit was originally sold through Ber- keley Enterprises, Inc., documented by Oliver Garfield's GENIACS: Simple Electric Brain Ma- chines, and How to Make Them bound with the Manual for Geniac Electric Brain Construction kit No.1. Once assembled, it could play simple games and do basic computations. The kit sold for about $15.95 to $19.95 (about two days' wages). Logical functions were carried out electromechanically, through cascading rotary switches that could be con- figured for different computing experiments. For in- formation on the GENIAC Calculator, see Garfield, Oliver. See Berkeley, Edmund C.; Brainiac; Simon. geographic information system GIS. Any system in which terrain infonnation is gathered, processed, and stored, usually for later retrieval for analysis, long-term comparisons, mapping, navigation, etc. An enormous amount of geographic infonnation is gath- ered by orbiting satellites, geocoded, and stored on high storage-capacity computer systems, much of which is accessible through public computer net- works. Land-based tracking of networks, utilities, and transportations systems is also carried out with GIS systems. See geoInterface, Landsat. geographic interface This term has two meanings: (1) interfaces designed for users to access and ma- nipulate geographic data, and (2) an evolutionary step in computer user interfaces which models the world in a simulated 3D environment as visual objects or func- tional constructs. The second meaning represents a relatively new ap- proach to computer user interfaces. The idea has been around for a while, but the resources to implement it have been cost prohibitive until recently. In the early 1970s, microcomputer user interfaces consisted of dipswitches for input and small blinking lights for output (see Kenbak-l and Altair). They were replaced by simple monochrome, text-based interfaces by 1975 (see SPHERE System). In the early 1980s, de- velopers began producing graphical user interfaces (based largely on 1970s research at Xerox PARC), and it was not long after that the first experimental geographic interfaces began to appear. See geoInterface, graphical user interface, object-ori- ented, Open Systems Interconnection. geographic north The region on the Earth called the North Pole from which imaginary lines of longitude emanate to meet again on the other side at geographic south, as established by convention. Geographic north is the general direction in which the north-seeking needle on a compass points but it is not exactly the same as magnetic north, which changes as large geo- logical formations change. See magnetic north. Georgia Rural Telephone Museum Located in a former 18,000- ft cotton warehouse, built in 1911, the Georgia Rural Telephone Museum opened officially in 1995 in Leslie, Georgia. The building was estab- lished across the street from the Citizen's Telephone Company. It includes about 2,000 historic telephones and other examples of communications equipment. http://www.sowega.net/ museum! Geostationary Meteorological Satellite GMS. A geostationary satellite system of the Japan Meteoro- logical Association (JMA) and the National Space Development Agency (NASDA) that is affiliated with World Weather Watch (WWW). The GMS system senses the region over Asia and the western Pacific at 140 degrees E longitude. It is similar to the U.S. GOES system. The first GMS was launched from the ~:~~~~;£: ~~~::&~~~:~~~~~i~~~e~r~~ i~~~ ill GMS-5, which has been operational since the mid- 1990s, provides data on cloud patterns (including volcanic activity), water vapor distribution, and sea surface patterns to more than two dozen countries. The Japan Weather Association provides hourly GMS images online. GMS systems also serve as commu- nications relays for forwarding information obtained from ships, aircraft, and communications buoys and provide assistance in emergency search and rescue operations. By the late 1990s, the GMS system was being designed to take on a broader role, serving not only as a meteorological sensing system and relay station, but also as an air traffic control support system. In February 2000, the GMS-4 system, launched in 1989, was taken out of service and moved out of the way into a higher region for its final orbit. The GMS- 5 system, launched in 1995, is still operational and apparently in good working order, but a transition is being made to a new system of satellites, the Multi- functional Transport Satellite (MTSAT) series, begin- ning with MTSAT-IR and MTSAT-2. Despite its age, GMS-5 is expected to be able to operate until the MTSAT platfonns come online around 2003. See Multifunctional Transport Satellite, National Space Development Agency. Geostationary OperationalMeteorological Satel- lite GOMS. Also known as Elektro, the GOMS sys- tem is atbree-axis-stabilized imaging satellite that is part of the Russian Federation Planeta-C Meteoro- logical Space System. The first of the series of satel- lites was launched in October 1994, with each plat- form expected to last at least three years. GOMS or- bits over the Earth's equator at longitude 76°50' E. GOMS senses infrared images of the Earth's surface and cloud cover, provides continuous coverage of atmospheric patterns, detects potentially hazardous phenomena, measures seasurfacetemperattrres, and monitors space-borne energy particles. Aboard the satellite, a radiometric line scanner im- ages the Earth, digitally encodes the information, and transmits it to a ground station for preprocessing and eventual dissemination as satellite products. The com- munications portion of GOMS includes satellite-to- ground transmissions, ground-station intercommu- nication relays, and transmission to users on an operational basis. 401 © 2003 by CRC Press LLC . GIC's challenge to an FCC separation requirement for hybrid navigation devices. See Advisory Committee on Advanced Tele- vision Service. GeneralMagicA California-based commercial ven- ture established in 1989 that focuses on providing innovative, cost-effective computer-Internet-tele- phony products for mobile applications. Products in- clude Portico,. OperationalMeteorological Satel- lite GOMS. Also known as Elektro, the GOMS sys- tem is atbree-axis-stabilized imaging satellite that is part of the Russian Federation Planeta-C Meteoro- logical Space System. The first of the series of satel- lites was launched in October 1994, with each plat- form expected to last at least three years. GOMS or- bits over the Earth's equator at longitude 76°50' E. GOMS senses infrared images of the Earth's surface and cloud cover, provides continuous coverage of atmospheric patterns, detects potentially hazardous phenomena, measures seasurfacetemperattrres, and monitors space-borne energy particles. Aboard the satellite,. called Traf-O-Data, founded around 1972. The economic success ofMicrosoft began with the signing of the IBM OSIBASIC contract. Ofparticu- lar importance is the fact that Gates reserved the right 395 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary to market the results of the development (sold by mM as PC-DOS) in competition with IBM, a contractual loophole that Gates had also achieved with MITS, who were dismayed because they thought they had bought the exclusive rights to Microsoft BASIC for the Altair. Gates' father was a lawyer and Gates had a long-standing interest in contracts and business deals, which probably accounts for the Microsoft- fa- vorable outcome of the two pivotal contracts. Times have changed; today large corporations have teams of lawyers to develop and scrutinize contracts but, two decades ago, many deals were still established on trust and a handshake or on less extensive paper- work and scrutiny than is common now. Since Gates and Allen didn't have an operating sys- tem to sell to ffiM, they bought QDOS, developed by Tim Paterson. In one of computer history's great- est ironies, Tim Paterson acknowledged that he had created QDOS by using a mid-1970s version of the documentation for Gary Kildall's CP/M. Microsoft then hired Paterson to quickly develop it into PC- DOS. QDOS was syntactically and functionally simi- lar to Kildall's CP/M. Microsoft's version of