Fiber Optics Illustrated Dictionary JosefMurgas - Telegraphy Pioneer Josef Murgas, pastor of the Sacred Heart Church. [Photo portrait courtesy of the /t)Joming Historical and Geological Society. copyright expired by date.} Museum of Radio and Technology A nonprofit, volunteer-assisted antique radio technology museum, located in aconverted elementary school in Hunting- ton, West Virginia. It includes crystal radio sets, vacuum tube technologies, schematics, vintage books and magazines, and other educational resources and exhibits. Museum ofTelevision and Radio A nonprofit, New York-based preservation and education institution es- tablished in 1975 by William S. Paley. Its goal is to collect and preserve historic radio and television pro- grams and make them available for public education and use. In 1991, it was moved to the William S. Paley building. It houses over 60,000 programs selected for OJ I'J:f/.4. I '~';"J~ A "quenched spark" device from one of Joseph Murgas' patents ./i'Om 1911. [U.s. patent diagram, public domain.} I' "a inquisitive and set up a laboratory in the attic for ex- periments. Over the years, he received numerous pat- ents for his devices; he transferred these to a syndi- cate called the Universal Aether Telegraph Company. In 1904, Murgas patented a tone system ofwireless telegraphy with a rotary spark for transmitting faster than the traditional Morse code system. He then built a high transmitting tower which was hailed in the lo- cal newspaper as the "World's First Telegraphy Tower." Many prominent citizens witnessed a test demonstration in September 1905 and apublic dem- onstration in November 1905, after which Murgas traveled to New York to meet with Guglielmo Mar- coni and Reginald Fessenden. Unfortunately, gale force winds destroyed Murgas' transmitting tower and other bad luck befell him soon after. He was get- ting on in years and having financial difficulties, so he sold his important invention to Guglielmo Mar- coni, to prevent his discoveries from being lost to humanity. Murgas' achievements have not gone entirely unrec- ognized. President Calvin Coolidge honored him by appointing him to the National Radio Commission. Liberty ship #2881 was named after him during World War II. A U.S. Senate Bill adopted I October 1985 urged the Citizen Stamp Advisory Committee of the U.S.P.S. to issued a commemorative stamp of Father Murgas to celebrate Slovak Heritage Month. See Marconi, Guglielmo. Murphy's law Reportedly stated by Edward A. Murphy as "If there are two or more ways to do some- thing, and one of those can result in catastrophe, then someone will do it." and also reported as "Ifthere is any way to do it wrong, he will." However it was originally worded, Murphy's apropos observation was quoted a few days later, in a news conference, by Dr. John Stapp, a surgeon and research subject in studies of human tolerance to high-velocity ejections and gravity forces (Gs). The statement is often re- stated more simply as "Ifsomething can go wrong, it will." See Murphy, Edward. Murphy, Edward A. An American engineer in- volved in human testing of some spectacular ac- celeration/deceleration experiments in the U.S. Air Force in the 1950s. Following his observations about the configuration of sensors, he is best known for a prescient observation about catastrophes now known as Murphy's law. See Murphy's law. Murray loop test A type of diagnostic procedure which uses resistance through a bridge to locate an "open" in a length ofcircuit. It is similar to a Varley loop test, except that instead ofadjustable dials, one arm is eliminated and a variable resistance arm con- nected in its place, and a third wire is not required. See Varley loop test, Wheatstone bridge. Museum of Independent Telephony In Abilene, Kansas, the home of the United Telephone Company from 1898 to 1966, one of its former presidents, Carl A. Scupin, helped found the Dickinson County His- torical Society and Museum. The Museum of Inde- pendent Telephony now shares premises with this museum. 662 © 2003 by CRC Press LLC their historic, artistic, and cultural value. The collec- tion adds about 3000 programs per year. The museum works in conjunction with the Museum of Television and Radio in L.A. , California. Both institutions spon- sor seminars and exhibitions. Museum of Television and Radio in L.A. Also known as the West Coast Museum of Television and Radio, it was established in 1995 in Los Angeles. This museum is named after Leonard H. Goldenson, con- sidered a pioneer of the broadcasting industry. It works in conjunction with the original Museum of Television and Radio in New York. music on hold Background music on a phone line that is heard when a caller is put on hold. It can be set up to play music from a radio, cassette tape, or CD player, usually with a simple RCAjack near the phone panel. Recorded music is generally better, as most radio stations play advertising, which is not ap- preciated by most callers. Some people don't care for background music while on hold, but it's probably better than not knowing whether or not you've been cut off: Musical InstrumentDigital Interface MIDI. MIDI is a standard protocol for communication of sound information through a number of specified param- eters. Functions provided on MIDI-capable instru- ments are assigned numeric values which can be digi- tally intercommunicated and remotely or locally con- trolled. MIDI capabilities are built into many musi- cal editing and sequencing software programs. MIDI-compatible instruments generally have DIN plugs for interconnecting the various MIDI devices, and usually include MIDI in, MIDI out, and some- times MIDI through. A simple example ofa MIDI setup would be a keyboard connected to the fast serial port or MIDI port of a computer with MIDI- compatible software. There may also be separate speakers, since most computer and keyboard speak- ers tend to be minimally useful for sound reproduc- tion. MIDI allows the songs from the keyboard to be communicated to the computer and stored and edited. Conversely, compositions created on the computer, sometimes including custom sound patches, can be communicated back to the keyboard. MIDI is not the only music protocol, but it's definitely the most widespread and best supported. It is built into numerous synthesizers, keyboards, drums, and software music editing and sequencing programs. Musschenbroek, Pieter van See van Musschen- broek, Pieter. MUT See MultiUser Talk. mute A feature or device that allows sound to be turned off or lowered in volume. A mute button on a phone can cut out the sound to the mouthpiece so something can be said in the background without be- ing transmitted over the connected call (handy if you have to call the dog or ask a co-worker a sensitive question). A mute on a stringed instrument dampens the vibrations of the bridge so that the sound of the instrument is much softer. mutual capacitance Capacitance is the capability or inherent tendency of an object or substances to store electrical charge. This characteristic is related to the composition and structure of the object or substance, but also to the environment within which the entity exists. Influences from other objects will affect the capacitance of an object and increase its capacitance as they draw nearer to that object, hence the phrase mutual capacitance. As a somewhat imprecise ex- ample, but one that helps illustrate this idea, think of a satellite orbiting in space. As it draws nearer the Earth, the greater is its tendency to be pulled by the Earth's gravitational field. Similarly, with objects, the nearer they draw to another object, the greater is the tendency for capacitance, the capability to store a charge. Capacitance is also affected by the medium that exists between objects. Objects covered in plas- tic or a gel will have a different capacitance in rela- tion to one another than objects separated by air. Thus, capacitance may be expressed as it applies to a particular object but must also be taken into con- sideration as it applies to the atomic interactions be- tween two (or more) objects. If the objects come into contact with one another, or are connected by a con- ducting substance, then the capability to store up an electrical charge with relation to one other changes in that the conducting surface effects a discharge or balancing of charges between the two objects. In general, electrical conductors have higher capaci- tance than, say, a block of wood, but even people store up electrical charges. The human body acts as a ca- pacitor when it picks up electrical charges through friction contact with carpets, for example. The next time you touch a conducting surface after storing up a charge, you may feel a spark as the excess electri- cal energy in your body is rapidly discharged. The extra charge is not always discharged quickly, how- ever. If you hang around without generating a lot of friction with your feet nor having any contact with highly-conducting surfaces, you will still gradually discharge the stored up charge as it "leaks" more slowly into lesser-conducting materials such as the air, and wood or vinyl floors. See grounding, static electricity, triboelectricity. MUX See multiplexer. MVIP Multi-Vendor Integration Protocol. See Multi- Vendor Integration Protocol. MVL 1. Man Vehicle Laboratory. A lab within the Center for Space Research (CSR) at the Massachu- setts Institute of Technology, founded in 1962. 2. See Multimedia Virtual Laboratory. 3. Multimedia and Visualization Laboratory. See Multimedia Learning Laboratory. 4. See Multiple Virtual Line. MVP multichannel video programming. Any of a variety of types of multiple-channel video program- ming genres, including television, network anima- tions, Internet streaming video, or video program- ming delivered through traditional or fast data-rate phone lines. Due to the continued need to review, as- sess, and regulate video programming, the Federal Communications Commission prepared a report in 1999 on MVP that was released in January 2000. In its report, the FCC described a number of aspects of video programming, including the market share of 663 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary different means of delivering programming, and reiterated the belief that competition was the best way to promote broadbased access to video programming and competitive rates for the general public. MVPD multichannel video programming distributor/ distribution. A broadcast distributor ofa number of video programming channels, usually provided through cable TV or satellite feeds. Broadband In- ternet is now considered to be a viable distribution 664 channel. See MVP. MVS Multiple Virtual Storage. MXR 1. mixer. 2. multiplexer. myriametric Myriametric waves are associated with the very low frequency (VLF) transmission range (3 to 30 KHz) and occur naturally in auroral phenom- ena. In the late 1980s, Home described the plasma- based terrestrial generation of myriametric waves. MZI Mach-Zehnder Interferometer. © 2003 by CRC Press LLC n 1. abbrev. nano See nano 2. In mathematics, a symbol for a numerical quantity used to denote that any number can be substituted in place of the nor, quite commonly, n will represent any value within a stated number set such as any positive integer (whole numbers greater than zero). It is usually written in ital- ics in lower or upper case. Scalable solutions to net- work configurations or database data sets are some- times called n solutions to indicate that the system can be expanded to handle exceedingly large num- bers or quantities far in excess of what might be needed in any given situation. See N definition #4. 3. symb. refractive index. N 1. abbrev. noise, usually as it pertains to signal in- terference. Thus, SIN represents signal-to-noise ra- tio and C/N represents carrier-to-noise ratio. 2. abbrev. "north," on a magnet or compass. The north-seeking end of a compass needle points to a region near the Earth's North Pole called magnetic north. 3. symb. "on," with F as the corresponding symbol for "off." 4. symb. the last component, value, routine, link, or other virtual, conceptual, or physi- cal aspect ofa multipart system. In this context, it is usually written in italics. In a database, for example, N may be the largest conceivable number of records that might be expected to be needed or entered. In a distributed network, N may represent the largest num- ber of hops that might be expected for a data trans- mission path. N is an important concept in both pro- gramming and physical topologies. The concept of N as a theoretical maximum enables planners to de- sign and construct systems with the view of making the system efficient within the perceived constraints of N. See n definition #2. See N definition #1.4. In a Central Office telephone code, any integer between 2 and 9. See NXX. NconnectorA standardized medium-power, barrel- shaped cable/device coupler for interconnecting com- ponents in a system or devices on a network. N se- ries connectors and adaptors come in a variety of shapes and configurations from simple connectors to extend the length ofa cable to adaptors to change the "sex" of the cable between male and female to ter- minators for establishing the end link in a series of connections. N connectors are selectively coated in nickel, silver, or synthetics over brass, phosphor bronze, or be- ryllium copper and typically support 50-ohm sig- nals (though 70-ohm versions are available). They are widely used for connecting radio frequency (RF) co- axial components. F or Ethernet connections, 10Base-5 "thick" Ethernet cables with N connectors are becoming less common in favor of1 OBase-2 "thin" Ethernet cables with BNC connectors or 1 OBase- T twisted-pair phone-style RJ- 45 connectors. See F connector. N port, node port. A port that enables an endstation device (peripheral, computer, etc.) to be connected as a node in a Fibre Channel network. The N port is connected to the switched fabric port or F port. The N port is assigned a higher address than FL and NL ports and thus would have lower loop control prior- ity compared to these ports. A name server in the Fi- bre Channel fabric switch typically uses a discovery process to determine the fabric topology to obtain the addresses of other N ports for port logins. The N port may be built into the connected device or may be contained on an interface board, such as a PCI-compatible board in a computer. High bandwidth devices, such as broadband storage devices, may have multiple Fibre Channel ports. See F port, FL port, NL port. n region In a semiconductor, a region in which the conduction-electron density exceeds the hole density. The n materials interact with the p materials (the re- gion with corresponding "holes") at the p-n junction in p-n semiconductors. See p region, p-n junction. NSeries RecommendationsA series oflTU-T rec- ommendations providing guidelines for the mainte- nance of international sound programming and tele- vision transmission circuits. These guidelines are available for purchase from the lTU- T. Since lTU-T specifications and recommendations are widely fol- lowed by vendors in the telecommunications indus- try, those wanting to maximize interoperability with other systems need to be aware of the information disseminated by the lTU- T. A full list of general cat- egories is listed in Appendix C and specific series topics are listed under individual entries in this dic- tionary, e.g., K Series Recommendations. See N Se- ries Recommendations chart. N-l, N-minus-one The second-to-Iast or penultimate 665 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary node, device, link, router, hop, subroutine, loop, or other virtual or physical link or component. This con- cept is important in many respects. The second-to- last link in a programming loop, aphysical or virtual network or other multipart system may have to be handled or configured differently, given that the next virtual or physical component in the system is the last. The penultimate item or data bit is often significant in programming routines. For example, in computer sorting algorithms, the number of iterations required in aparticular function is frequently equal to N-l. The handling of software stacks, dynamic groupings of stored data, also is related to the concept of the penultimate item or data grouping in the stack. In rou- tines where the program ends ifit reaches the last or N data set, an awareness ofreaching the penultimate 666 © 2003 by CRC Press LLC set may be important to restarting, backtracking, or otherwise looping back and continuing program ex- ecution. See N definition #4. n-ary A structure or element that may have n num- ber of multiple applications or conditions or a speci- fied limit that can be expressed as apositive integer greater than one (1) in some situations and greater than two (2) in others. The limit may be explicitly stated as ternary (three), quaternary (four), etc. If the number is large, the actual number may be used, as in 16-ary code in which 16 significant conditions ex- ist. The term is often used as a synonym for "many" or "more than two" in general discussions where the n may be undesignated or unknown. n-ary tree A data structure with multiple branching hierarchies with a maximum limit ofn children in a node. N-ISDN Narrowband ISDN, Narrowband Integrated Services Digital Network. Definitions vary but, in general, Narrowband ISDN is used to refer to earlier installations of ISDN providing lower data rates through copper wires as opposed to newer Broadband ISDN providing higher data rates through fiber op- tic cables. See ISDN for a fuller explanation. N-scope A type of radar display in which the target appears as a pair of vertical blips coming from a hori- zontal time base. The direction of the target is inferred by the amplitudes of the related vertical blips. A tar- get distance can also be determined by comparison to a pedestal signal along the base line. NA 1. See naming authority. 2. network administra- tor/administration. 3. See Night Answer. 4. night at- tendant. 5. North America. NAB 1. See National Alliance of Business and Na- tional Association ofBroadcasters in Appendix G. NABTS See North American Basic Teletext Speci- fication. NAC 1. Network Access Center. 2. See Network Access Control. 3. See Network Applications Con- sortium. 4. See Numbering Advisory Committee. 5. See null attachment concentrator. NACIC See National Counterintelligence Informa- tion Center in Appendix G. NACN See North American Cellular Network. NADC See North American Digital Cellular. NADF 1. See North American Directory Plan. 2. North Atlantic Directory Forum. nadir In satellite imaging, apoint on the ground cen- tered vertically below a remote sensing platform. name resolutionA means ofassociating an assigned name with its origin, location, or other relevant char- acteristics. In a network where a name has been used as a mnemonic alias to allow easy recognition of an address, application, or process, there needs to be a mechanism to resolve the name into a form that can be easily recognized and subsequently located by the system. In other words, mysite.com has to be trans- lated into a machine-readable address of the location of the host site for mysite.com. This is done through name resolution, usually through a lookup table or larger database. Sometimes the name itself will pro- vide some information about its origin or date of es- tablishment, e.g., the name is a set of alphanumeric characters assigned according to a system that can be understood by humans. See naming authority. naming authority 1. Alegislative or organizational body that assigns names, usually as unique identifi- ers. Various types of naming structures include hier- archical, flat, random, etc. There are many well- known naming authorities: the U.S. Library of Con- gress; R.R. Bowker (ISBN); lANA (Internet). On the Internet, the various registered domains may assign subauthorities and subnames for local machines. See lANA. 2. In a hierarchical document management system, a tree of entities which provides a unique identifier to each document. This task may be shared by subauthorities. NAMPS Narrowband Analog Mobile Phone Service. An analog cellular communications technology which provides triple the capacity of an analog cel- lular voice channel by splitting the channel into 10 kHz bandwidth narrow bands. Narrowband standards were released by the Telecommunications Industry Association (TIA) in 1992 (IS-88, IS-89, IS-90). Digital mobile phone services are gaining ground on traditional analog systems. See AMPS, DAMPS, code division multiple access, time division multiple access. NAMTS See Nippon Advanced Mobile Telephone System. NANC See North American Numbering Council nano- (abbrev. - n) A unit prefix for one billionth (North American system), or 10- 9 , that is, .000 000 001. See nanometer. NANOG See North American Network Operators Group. nanometer (abbrev. - n) In the SI system, a length measure corresponding to one billionth (10- 9 ) of a meter. Ananometer is one thousandth ofa micron. Nanometers are often used to describe the size of tiny particles (e.g., chemical substances) or electromag- netic wave phenomena (e.g., laser wavelengths) Light waves at 534 nm are in the visible spectrum (appearing yellow to human senses; wavelengths are also commonly expressed in microns). Smoke par- ticles range from about 10 to 1000 nIn. Electron mi- croscopes image up to maximum ranges of about 5 to 0.5 nanometers. With increasing miniaturization, the trend in the semi- conductor industry is to use nanometers instead of microns, with a number of major vendors announc- ing an official changeover in spring 2002. In synthetic materials fabrication, the region of 1 to 100 nanometers is ofparticular interest as it is less well understood and is subject to interesting interac- tions between molecular and macroscopic prop- erties. Distances traveled by certain phenomena such as seis- mic waves may be described in terms of nanometers per second (nm/sec). See nano- NANP See North American Numbering Plan. NANPA See North American Numbering Plan Ad- ministration. NAP See Network Access Point. 667 ; ••. ~" •. ~., •• • " • •• l • _. ;>~,;> > ;. ::~::;. :". ;;~~ . © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary NAPP See National Aerial Photography Program in AppendixG. N APT Native American Public Telecommunications, Inc. narrative traffic A military term for transmitted se- cured or unsecured natural language communica- tions. For example, in military space programs, the Special Communications Systems is a realtime, au- tomated communications system on which narrative messages can be composed and edited. The Global Command and Control System (GCCS) is a secured system capable of handling narrative and data traf- fic. During times of emergency when traffic over net- works is suppressed, narrative traffic may alternately be sent by other means such as courier. narrowband 1. A term which varies in definition depending upon the industry and its bandwidth needs, and on the current state of technology. Narrowband usually represents the lower end of the available ca- pacity or spectrum ofa system. In some cases it is used to denote a single band within a multiplexed group of bands sent more-or-Iess simultaneously. In traditional telephony, it represents a sub-voice-grade line. In cellular communications, it represents one division of the broadcast spectrum consisting of a channel frequency (CF) of about 30 kHz, usually ac- complished through frequency division duplexing (FDD). See AMPS, NAMPS. Narrowband Analog Mobile Phone Service See NAMPS. narrowband ISDN ISDN services at basic channel speeds up to 64 kbps, which is fine for voice and some data communications, but only adequate for applica- tions like full-motion video, or video and sound. Ef- forts are being made to incorporate new standards into broadband ISDN (B-ISDN) that will remove the fixed channel structure limitation of narrowband ISDN. narrowcasting A type of program delivery that tar- gets specific people and often specific services to those people. Ifbroadcasting is considered to be pro- gram delivery to a wide and sometimes scattered au- dience, from one to many, then narrowcasting can be seen as one to one or one to few. For example, elec- tronic industries' personnel might subscribe to pro- gramming on circuit board fabrication. At an even more specific level is "pointcasting," that is, program services which target user-selected information, a type of electronic clipping service providing elec- tronic information on specified topics of interest. NARTE See National Association of Radio and Tele- communications Engineers in Appendix G. NAS See network-attached storage. NASA See National Aeronautics and Space Admin- istration in Appendix G. nasa7 A double-precision Systems Performance Evaluation Cooperative (SPEC) benchmark used in scientific and engineering applications. A benchmark tends to be a specific quantitative measure ofa par- ticular aspect of system functioning, and by itself conveys a limited picture of overall system perfor- mance. However, in the specific context for which it is intended, a benchmark can provide valuable infor- 668 mation for design engineers, researchers, and manu- facturers. Nasa 7 generates input data, performs one of seven floating point-intensive kernel routines, and compares the results against an expected reference measure. It is used to evaluate performance, memory, VO operations, and networking factors. See bench- mark, Rhealstone, Whetstone. NASD Project Network-Attached Storage Devices Project. A project of the National Storage Industry Consortium (NSIC) to explore, validate, and docu- ment the technologies needed to enable the deploy- ment of network-attached storage device systems and subsystems. The project was initiated because the trend towards large distributed networks is causing people to rethink the most efficient ways to imple- ment storage capabilities, and more networks are us- ing remote rather than local storage to handle large data repositories. Fibre Channel is seen as one of the technologies appropriate for fast-access remote stor- age. See National Storage Industry Consortium. National See Appendix G for a long list of commu- nications-related organizations prefaced with "N a- tiona!." National CenterforSupercomputingApplications NCSA. A research center at the University of Illinois, best known for the development ofNCSA Mosaic, the historic Web information browser that preceded Netscape Navigator. National CodeChangeA designated day in the U.K. when old telephone codes and numbers were changed to revamp the system. New codes and telephone num- bers became available in August 1994 and the Code Change took place in April 1995. On the same day, the dialing code for international calls originating in the U.K. changed from 010 to 00. National Electrical Code NEC. A code developed to safeguard public safety and property from hazards associated with the use of electricity. This includes wiring and electrical device construction, materials, installation, and maintenance and is adopted in many parts of the country as law for various building, equip- ment, and utility pole (below supply space) installa- tions. The Code is developed by the American Na- tional Standards Institute (ANSI) and is published by the National Fire Protection Association (NFPA). See National Electrical Safety Code. NationalElectricalSafety Code NESC. A code gov- erning electrical facilities located in public rights-of- way to ensure the safety of the public and installa- tion/maintenance professionals. It is published by the Institute of Electrical and Electronics Engineers (IEEE). See National Electrical Code. National Geophysical Data Center NGDC. One of three data and information centers of the U.S. Na- tional Environmental Satellite, Data and Information Service (NESDIS). National ID Card An identification concept pro- posed many times over the decades for a variety of © 2003 by CRC Press LLC reasons. In the U.S., there has been much opposition to the concept, with concerns about security breaches (people using the information in unethical ways to access private information in centralized databases), loss, replacement, forgeries, and more. In a sense, National ill Cards already exist for non-American legal residents (and a National ill Card doesn't solve the problem of illegal residents). The commonly called Green Card (Immigration Visa for Resident AlienslPermanent Residents) is a bio- metric national identification card issued over the course of many decades that includes a photo and a fingerprint (biometric identifier) tied to a federal da- tabase that already serves the purposes most people want a National ID Card to cover. To get a Green Card, you have to provide birth, background, educa- tional, and other personal information to the U.S. fed- eral government and be approved through a back- ground check and interview, which is usually repeated approximatelyevety 10 years. Asking evety U.S. citi- zen to also carry a National ill Card in addition to the many driver's license/passport/birth certificate/ social security documents already· issued calls to question why yet another card should be issued and how it would be any different or better than the docu- ments already routinely carried. Some people have even compared it somewhat radically to skin brand- ing. A National ID Card can be easily lost, as with any other card, and fall into the wrong hands. Wrongdo- ers often use forged or stolen documents; this might give them one more document to forge or steal and may not have any substantial security benefits in re- lation to the increased security risks associated with the loss of the card. Nevertheless, after the events of September 11, 2001, the issue of National ill cards has again been brought fOlWard and will no doubt be debated for a long time. In the world of electronics, where the infonnation on the ill card may be directly linked to a powerful central database, it must be care- fully weighed whether a National ID Card program should be undertaken, especially given that, once the database exists, it may over time be commandeered for other purposes by future governments, or even- tually be used by law enforcement agencies to track and profile individuals without their knowledge. Stranger things have happened in the past. National Information Infrastructure NIL The name for the political, administrative, and physical underpinnings of an interconnected collection of pub- lic and commercial national narrowband and broad- band data networks. One of the biggest stakeholders in the NIT is the National Information Infrastructure Advisory Council (NIIAC), established in 1994 through a 1993 executive order. The NlIAC is respon- sible for advising the government on a national strat- egy for promoting development of the Nil and the Global Information Infrastructure (Gil). The NIl is a physically and regionally diverse sys- tem which is considered as a whole, mainly on the basis of interconnectivity. It includes small and large networks, wireless and wireline connections, public and private systems, and many sizes and types of or- ganizations and individuals. The Nil is also known by the catchphrase "Information Superhighway," al- though this describes the communications aspect of the NIl and could be considered a subset. National Public Broadcasting Archives NPBA. Housed at the University of Maryland in the Hornbake Library, the NPBA started as a coopera- tive project of several broadcasting and educational institutions. It was initiated by Donald R. McNeil, a Public Broadcasting System (PBS) board member, and officially dedicated in June 1990. NPBS provides an archival record of major documents and selected programming from U.S. noncommercial broadcast- ing history. http://www.lib.umd.edulUMCP/NPBAI National Public Radio NPR. A major award-win- ning producer and distributor of public radio broad- cast programs developed by independent producers. Based in Washington, D.C., NPR provides popular shows such as All Things Considered, Car Talk, and Morning Edition plus NPR hourly news on the In- ternet. It also hosts lively discussion groups online about issues raised on NPR programs. See Public Radio International. http://www.npr.org/ National SpatialDataInfrastructure NSDI. A U.S. ~~~~~~h~~!:~~i:~11~;:i:~~~:~f:t~~:~I. new geospatial data collected or produced, either di- rectly or indirectly, using the Federal Geographic Data Committee (FGDC) standard. NationalTelevision System Committee See NTSC. NATOA See National Association ofTelecommuni- cations Officers and Advisors in Appendix G. natural antenna frequency An antenna's lowest natural resonance frequency when operated without external capacitance or inductance. natural frequency The frequency at which an oth- elWise uninfluenced or unimpeded body will oscil- late when stimulated to move. Knowledge of natural frequencies is important in structural engineering and scientific research. The collapse of "Galloping Gertie," the Tacoma Nar- rows bridge is one of the more spectacular examples of how natural frequencies must be considered when building large or safety-oriented structures. The Tacoma Narrows bridge collapsed because of the in- teraction ofa windstorm with the natural frequency of the bridge's movements. Without holes in the sidewalls to let the wind pass through, the accumu- lation of the bridge oscillations from the wind caused a resonance wave so great, it tore the bridge apart. Natural frequencies aren't always harmful. They can be helpful tools for sensing devices. Many structures exhibit natural frequency vibrations that can be sensed with seismic instruments or light-based sen- sors. It has been proposed that fiber optic sensor ar- rays could be built into bridges and buildings to pro- vide readouts of natural frequencies over time. In fi- ber optic sensors with micromechanical resonators (e.g., those made from metallic glass), a measured 669 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary parameter (temperature, pressure, force, etc.) is ex- pected to change the micro resonator's natural fre- quency which may be both excited by and detected by light. This, in tum, provides data about the phe- nomenon or object sensed. natural logarithm See logarithm. natural magnet There are two types of permanent magnets. One is a substance that exhibits and retains magnetic properties without application ofa current after it has been magnetized with another magnetic source. The second is a substance which exhibits magnetic properties as it comes out of the ground, without needing to be exposed to magnetic influences for it to become a magnet. The second type of per- manent magnet is called a natural magnet. See lode- stone. natural wavelength The wavelength that corre- sponds to an antenna's natural frequency. Matching an antenna's resonant frequency to the characteris- tics of the wave being received (or transmitted) is an important aspect of antenna design. NAVSTAR A series of Global Positioning System (GPS) satellites operated by the U.S. Department of Defense, whose navigational signals are available to civilian users. See Global Positioning System (GPS), GLONASS, Standard Positioning Service. NAVTEX An international, automated weather and maritime navigational warning distribution system. NAVTEX sends warnings to ships as they move in and out of areas for which broadcast information is available that may be relevant to marine safety. See Global Maritime Distress and Safety System. Navy Navigation Satellite System NNSS. A system ofsatellites moving in polar orbits about 700 miles above Earth, which preceded the Global Positioning System (GPS) used today. NNSS Doppler technol- ogy could compute group positions on or around the Earth to about I-meter accuracy by means of mul- tiple readings. The long time between transits over the same location (about 90 minutes), and the diffi- culty of determining instantaneous velocity led to the development of the GPS system. See Global Position- ing System. NBC See National Broadcasting Company in Appen- dixG. NBFCP See NetBIOS Frames Control Protocol. NBFM narrowband frequency modulation. NBMA nonbroadcast multiple access. NCACHE, DNS NCACHE Negative caching is a part of the DNS specification that deals with cach- ing the nonexistence ofa domain name or RRset, thus reducing message load and response time for nega- tive answers. With the growth of network traffic and increased need for quick and frequent resolution of domain names, the importance of negative caching has grown to the point where it was suggested by Andrews and others that negative caching be routine rather than optional. See negative caching, RFC 1034, RFC 2308. NCCS Network Control Center System. NCIA native client interface architecture. An SNA applications-access architecture developed by Cisco 670 Systems. NCIA encapsulates SNA traffic on a client computer, preserving the user interface from the na- tive SNA system so that the end-user can work in a familiar environment and also have direct TCP/IP ac- cess. NAVSTAR GPS Satellite The 19th NAVSTAR satellite was launched in 1993. on board an Air Force Delta 11 craft. The NAVSTAR satellites are usedfor GPSdata and geodesic research. [NASA/Marshall images.} NClTS See National Committee for Information Technology Standardization. NCO See National Coordination Office for Comput- ing, Information, and Communications in Appendix G. NCOP Network Code OfPractice. NCSA 1. See National Center for Supercomputing Applications in Appendix G. 2. National Computer Security Association. Now the International Com- puter Security Association. NCSA Mosaic A well-known Internet information browser and World Wide Web client developed at the National Center for Supercomputing Applications. Mosaic was the predecessor to Netscape Navigator distributed by Netscape Communications. Navigator was later declared open source software. See Mosaic for a fuller history; see Netscape Navigator. NDIS See Network Driver Interface Specification. NDSI See National Spatial Data Infrastructure. NDT I. network downtime. In telephony, the elapsed time from when network managers become aware of a problem until the moment at which the subscriber's service is restored. In computer networking, the time during which normal processes are unable to execute due to electrical outages, software crashes, network link disconnections, processing overload, malicious tampering, or unintentional bugs that interfere with processes outside of the application that has the bugs. 2. No Dial Tone. © 2003 by CRC Press LLC NE See network element. near end crosstalk NEXT. When wires are packed tightly together, and signals are traveling through most or all of the wires, especially in two directions, the signals originating at one end can exceed or in- terfere with weaker signals coming from the other end, resulting in crosstalk. With much higher speed transmissions media, such as gigabit Ethernet, which involve bidirectional signals in more complex sys- tems of aggregated wires, this can be a severe impedi- ment. One means ofcompensating for NEXT is to include a NEXT canceler, which detects and adjusts for noise in the circuit. See far end crosstalk. near-infrared NIR. A region of the optical portion of the electromagnetic spectrum that has slightly shorter wavelengths than the visible spectrum per- ceived by humans as the color red. Certain snakes and insects have infrared-sensing receptors. Humans tend to sense infrared as thermal energy (heat). In general, near-infrared has frequencies ranging from about 700 to 3000 nm. Commonly-available commercial ach- romatic lenses are generally in the 700 to 1500 om range. There are many filters designed to selectively include or exclude infrared radiation and some pho- tographic filters selectively admit infrared radiation for specialized applications. Infrared light is suitable for many types of data trans- fer and is commonly found in wireless remote con- trols and light-based wireless computer networks. It is widely used in remote sensing applications such as astronomy and in fiber optic communications sys- tems. NIR-based spectroscopy is useful for materi- als analysis in a wide range ofchemical and pharma- ceutical applications. See infrared. nearfield, nearfield In propagating electromagnetic or acoustic waves, the region near a source wave or reflected wave that is less than the length of one wave- length. Since there may be many wavelengths present, a specific frequency may be selected (which may be the strongest, the most central, or the most relevant to a particular task), or an average or other estimate ofa range ofwavelengths may be calculated to provide a nearfield estimate. If a range of wave- lengths is being studied, the concept of nearfield is sometimes broadened to include the median or long- est wavelength within the range and the interactions that occur between the wavelengths (e.g., diffraction). Thus, the nearfield is context-specific but, in general, inversely related to the wavelengths of interest. Concepts ofnearfield are important in observing or scanning radiant energy at very close ranges as there are special problems associated with collecting undistorted data from incomplete or interacting wave- lengths. In laser technologies, measures such as beam width and beam separation or divergence from the intended path are also more difficult to calculate in the nearfield, but these calculations may be impor- tant in tasks such as aligning fiber optic light sources. See nearfield imaging, nearfield diffraction. nearfield imaging Observing or recording an image at very close range. In electromagnetic imaging, it is a region in which the observing/recording device is so close to the source ofpropagating waves that the wavelengths may interfere with the process (e.g., by interacting with one another) or may be longer than the distance between the sample and the observing/ recording device. This poses special problems in achieving undistorted viewing. Nearfield imaging is achallenge in many fields, including microscopy and spectroscopy. Many of the same nearfield imaging issues apply to the monitoring ofacoustic phenomena very near to the source of the sound waves. There are a number of ways to tackle the challenge ofnearfield imaging. Imaging at a range of frequen- cies and combining and processing the data may yield averages or patterns that provide information about the imaged sample. Hypercooling may reduce mo- lecular movement, thus removing or reducing poten- tial sources of interference. Using a fiber optic probe or taper to draw the image away from the surface is another strategy. See diffraction, Rayleigh scattering. nearfield diffraction, Fresnel diffraction Diffrac- tion in which electromagnetic waves incident upon an obstruction are diffracted in spherical waves origi- nating from a point source. Since spherical waves overlapping any type ofwaves results in some com- plicated interactions, it can be challenging to calcu- late and mathematically model Fresnel diffraction. Fresnel diffraction must be taken into consideration in the design of antennas, imaging technologies (e.g., nearfield spectroscopes), and other devices in which there are radiant or reflective elements that are proxi- mate and likely to have radiating energy that overlaps. F or experimental purposes, a laser light source can be converted to a spherical light source by use ofa lens and a small opening to spatially filter the light down to apoint light source. See diffraction, Fresnel region. NEC See National Electrical Code. NECA See National Exchange Carrier Association. neck The narrow portion ofa cathode-ray tube (CRn at the end where the electron beams are emitted from the cathode. negative acknowledge, negative acknowledgment NAK A commonly used international communica- tions control character which indicates that data was not received, or not received so that it could be un- derstood. This is common to handshaking protocols, in which an acknowledgment is required before the sender can continue. See acknowledge. negative bias In an electron tube, voltage applied to a control grid to make it hold more of a negative charge than the electron-emitting cathode. Manipu- lation of the control grid is what makes it possible to control the flow of electrons from the cathode to the anode, and thus to create different types of circuits and effects. negative caching The storage ofinformation about the nonexistence of an object, entity, or service. The availability of this information can reduce the time it takes to determine the components or configuration of a system or file. Negative caching statistics are commonly stored in tables or headers, depending on 671 © 2003 by CRC Press LLC . of general cat- egories is listed in Appendix C and specific series topics are listed under individual entries in this dic- tionary, e.g., K Series Recommendations. See N Se- ries Recommendations chart. N-l, N-minus-one The second-to-Iast or penultimate 665 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary node, device, link, router, hop, subroutine, loop, or other virtual or physical link or component. This con- cept is important in many respects. The second-to- last. of what might be needed in any given situation. See N definition #4. 3. symb. refractive index. N 1. abbrev. noise, usually as it pertains to signal in- terference. Thus, SIN represents signal-to-noise ra- tio and C/N represents carrier-to-noise ratio. 2. abbrev. "north," on a magnet or compass. The north-seeking end of a compass needle points to a region near the Earth's North Pole called magnetic north. 3. symb. "on," with F as the corresponding symbol for "off." 4. symb. the last component, value, routine, link, or other virtual, conceptual, or physi- cal aspect ofa multipart system. In this context, it is usually written in italics. In. can be sensed with seismic instruments or light-based sen- sors. It has been proposed that fiber optic sensor ar- rays could be built into bridges and buildings to pro- vide readouts of natural frequencies over time. In fi- ber optic sensors with micromechanical resonators (e.g., those made from metallic glass), a measured 669 ©