Fiber Optics Illustrated Dictionary - Part 70 pot

In other words, for any given line or plane, there is a relation-ship that is perpendicular to that line or plane for any given point of reference.. For example, if you moved the flagpol

Fiber Optics Illustrated Dictionary

Mellon, and the University of Michigan The

original NeXT was grayscale, with color added in

later versions The first NeXT was cube-shaped, with

later hardware resembling more conventional

desk-top flat systems, known as NeXT stations

The first NeXT was based on the Motorola 68030

processor with a built-in 68882 math coprocessor, and

it came standard with 8MBytes ofRAM At the time,

most computers had 1 to 4 MBytes of RAM The

original price was $6500 and marketing efforts were

aimed at higher education institutions, although

busi-ness owners expressed early interest due to the

net-working capabilities of the system

The frrst edition of CRC's Telecommunications

Il-lustrated Dictionary was written on a NeXT

com-puter, and even though the basic technology is over

10 years old, the computer hardware and operating

system have stood the test of time in essentially

their original form The simple, stunningly aesthetic

graphical user interface still beats most systems

hands-down; the powerful object-oriented

Unix-based operating system and shell connect seamlessly

with the Internet, and the multitasking operating

sys-tem allows dozens ofprocesses to run happily at the

same time.Inover 3 years of 24-hour a day

opera-tions running multiple desktop publishing, Web

browsing, and illustration programs at the same time,

the author's machine didn't crash once That's an

enviable track record After using a dozen different

types of computers daily for over 20 years, the

au-thor has seen few systems that equal it (Sun systems

provide similar performance)

The NeXT is an excellent networking computer,

con-necting easily to the Internet, other NeXT systems,

and other types of computers through TCPlIP It is

also an excellent Internet portal, with a full

comple-ment of Unix tools, including Telnet, FTP, and

oth-ers easily downloadable from the Net OmniWeb, by

Lighthouse Design, Ltd., is a powerful Internet

graphical browser for NeXTStep that preceded many

well-known graphical browsers

In 1997, Apple Computing, Inc bought out NeXT,

Inc and continued developing the operating system

software under the development name of Rhapsody,

now better known as MacasX See Jobs, Steven

Next Generation Digital Loop Carrier NGDLC

Developed in the 1980s as an evolution of Digital

Loop Carrier systems, NGDLC is based on very large

scale integration (VLSI) technology ISDN was

de-veloped and promoted at about the same time that

NGDLCs were implemented, so many were

devel-oped to accommodate ISDN Whereas Digital Loop

Carriers were designed to provide services over

tra-ditional copper phone lines, NGDLC was designed

to work in conjunction with fiber optic cables or

fi-ber/copper hybrid systems See Digital Loop Carrier

Next Generation Internet NGI AU.S federal

mul-tiagency research and development initiative

estab-lished in 1997 NGI works with industry and

academia to develop, test, and demonstrate advanced

networking technologies and applications The

fol-lowing federal networks are used as testbeds for the

NGI initiative:

• NSF's very high performance Backbone Net-work Service (vBNS)

• NASA's Research and Education Network (NREN)

• DoD's Defense Research and Education Net-work (DREN)

• DoE's Energy Sciences network (ESnet) (pro-posed beginning in FY 1999)

NGI is coordinated by the NGI Implementation Team, coordinated by the Large Scale Networking Work-ing Group of the Subcommittee on ComputWork-ing, In-formation, and Communications (CIC) research and development of the U.S White House National Sci-ence and Technology Council's Committee on Tech-nology http://www.ngi.gov/

Next Hop Resolution Protocol NHRP.An internet-working architecture, which runs in addition to rout-ing protocols and provides the information that en-ables the elimination of multiple Internet Protocol (IP) hops when traversing a Next Hop Resolution Protocol network Aims at resolving some of the la-tency and throughput limitations ofClassicalIP See Next Hop Server, ROLC, NBMA

Next Hop Server NHS In an NHRP networking en-vironment, the Next Hop Server locatesanegress point near a given destination and resolves its ATM address, enabling the establishment of a direct ATM connection See Next Hop Resolution Protocol NGDLC See Next Generation Digital Loop Carrier NGI See Next Generation Internet

NGSO nongeostationary orbit

NGSO FSS nongeostationary orbit fixed satellite service

NHRP See Next Hop Resolution Protocol

NICI See National Information and Communications Infrastructure in Appendix G

nickel metal hydride NiMH Arechargeable battery commonly used in portable devices Hydride is a hy-drogen compound

nickel-cadmium cell NiCd, NiCad Avery common, sealed, rechargeable power cell that works well in low temperatures The positive electrode is nickel and oxide, and the negative electrode is cadmium, with the plates immersed separately in a potassium-hy-droxide electrolyte solution NiCad batteries have been used in many small, portable telecommunica-tions devices but have the disadvantage ofa"memory effect," that is, they will not fully recharge unless first fully discharged, thus reducing the useful time ofthe

battery

nicknameAneasy-to-use, easy-to-remember substi-tute or secondary name In most cases, it's a short name, generally one easy to remember because it is familiar or matches the personality or properties of the person or object for which it is designated Anick-name can also be a Anick-name given as a term of intimacy and affection between two people who are closely acquainted Nicknames may also be names that are easy to type, to save time, as on public discussion areas of the Internet See handle, NICname

Chat (IRC), a name that can be set with /nick

<putnamehere> Only one person can have a specific

nickname at anyone time on IRC See Internet

Re-lay Chat, WhoIs

Nicol, William (ca 1768-1851) A Scottish educator

and physicist who developed the Nicol prism from

Iceland spar There are few records about his early

life, but he began publishing his research in 1828 and

spent the latter part of his life studying crystals and

fossils He apparently developed his own lenses and

invented new methods for grinding samples for

mi-croscopic inspection Nicol's sister, who was about

five years younger, married Edward Sang, a

promi-nent mathematician and engineer

Nicol prism A refractive component consisting of

two blocks of Iceland spar (calcspar) cemented

to-gether along the diagonal plane with Canada balsam,

a material derived from bark ooze that was a

com-mon bonding agent in optics for about 200 years The

Nicol prism was one of two common birefringent

prisms, along with the Ahrens prism

The unusually distinct birefringent properties

ofIce-land spar were described in 1670 by Rasmus

Bartholin, but the mathematics of its properties were

not worked out until almost 150 years later, by

Tho-mas Young

William Nicol put two equally shaped calcspar blocks

together to produce the Nicol prism, described in

1828 The device was used in polarimeters as early

as the 1840s Historic polarimeters consisted of a

sample tube mounted horizontally between an

ana-lyzing Nicol prism and a polarizing Nicol prism

Monochromatic light could be shone through the tube

with the analyzing prism rotated to produce two light

sources for comparison

polarizers into European scientific microscopes, be-ginning around the 1850s or 1860s A rotating Nicol prism polarization analyzer could be mounted be-tween the microscope nosepiece and the objective lens or over the eyepiece, depending upon the instru-ment By selectively rotating the prism and the sample, the polarizing characteristics of the sample could be discerned Nicole prisms continued to be common in microscopes as recently as the 1950s

In the 1880s, William Thompson (Lord Kelvin) used

a Nicol prism in his lectures and demonstrations on the polarization of light Edwin Land credits his in-vention ofpolarizers at the age of 19 to a demonstra-tion he saw as a schoolchild ofa Nicol prism His in-vention led to a patent and the establishment of the Polaroid Corporation

Polarization is now typically accomplished with films and coatings Polarizing beam splitters somewhat resemble Nicol prisms, having two blocks combined with a refractive coating layer, but the blocks are equi-lateral triangles and the resulting component is cubi-cal See Bartholin, Rasmus; Iceland spar; polariza-tion, Wollaston prism

NIDS See network intrusion detection system

NIF See network interface function

ordinate, and regulate private sector participation in the provision of telecommunications services http://www.ncc.gov.ng/

NIMBUS A satellite program initiated in the early 1960s by the National Aeronautics and Space Admin-istration (NASA), and now operated jointly with the Oceanic Atmospheric Administration (NOAA)

Nicol Birefringent Polarizing Prism

Iceland spar is a doubly-refractive (birefringent) mineral with interesting prismatic properties TWo calcspar blocks

can be bonded along the diagonal with a material ofslightly lower refraction index (b) toform a Nicol prism which

makes it possible to more widely separate the two courses oflight through the material and thus isolate the one of interest In constructing the prism, the natural rhombus angle of-72 0can be ground down to68 0(a) for more

effective results.

In this example, incident light (I) enters the material and is split into two beams, one slightly stronger than the

other The ordinary beam (0) is reflected off the seam due to its angle and the fact that it has a slightly lower

refractive index than the bonding material (much as light reflects off the cladding in fiber optic filaments) The

"extra-ordinary"beam (E) hits the seam almost straight on and passes essentially unimpeded across the bonded

seam Thus, the plane polarized light (E) exits in the same general direction as the incident light.

Fiber Optics Illustrated Dictionary

NIMBUS is used for research and development by

atmospheric and Earth scientists

NiMH See nickel metal hydride

Nimrod Routing ArchitectureA scalable network

routing architecture intended to support dynamic,

heterogenous intemetworks ofarbitrary size, Nimrod

was originally suggested by Noel Chiappa It was

thereafter refined by the IETF Nimrod Working

Group and formally described in the mid-1990s

Nimrod achieves scalability by representing and

ma-nipulating routing information at multiple levels of

abstraction to accommodate expanding, diversifying

networks Nimrod is characterized by maps that

rep-resent internetwork connectivity and services, user

route generation and selection, and user packet

for-warding along established paths It is applicable to

routing within single and multiple routing domains

in TCP/IP and OSI environments See RFC 1992

NIODNetwork Inward/Outward Dialing

Nipkow Disc - Historic Image Scanner

This Nipkow disc shows the spiral series of holes

through which the light is beamed as the disc rotates.

This historic example isfrom the American Radio

Mu-seum collection [Classic Concepts photo.}

Nipkow, Paul GottliebAGerman experimenter who

developed a rotating dial with a spiral arrangement

ofholes that he patented in 1884 It was an early

elec-tromechanical television system This was later

in-corporated into television transmitting and receiving

units See Nipkow disc

Nipkow discA rotating disc with a sequential

heli-cal pattern of holes used by many early television

experimenters to attempt the projection oftelevision images The perforated disc wasrotated in front of

the image to be transmitted in order to quantize the signal, in a primitive sense, by segmenting the im-age into lines The photosensitive material selenium was placed behind the disc to register the dark and light areas of the image Unfortunately, systems for amplifying the signal for transmission didn't exist at the time, and didn't become practical until other tech-nological developments occurred The disc is named after its inventor, Paul Nipkow

Modem versions of the Nipkow disc are used in a variety of applications and typically are fabricated from plastic or glass, with thousands of pinholes or microlenses embossed into the substrate They re-semble translucent CDs and are used in optical scan-ners and confocal microscopy In a confocal micro-scope capable ofresolving very tiny images, the per-forated disc rotates between a beam-splitter and a lens, providing expanded depth imaging through a form of optical sectioning A rotation of the disc en-ables an XY section of the specimen to be acquired

in realtime Height can be evaluated through grab-bing a frame and processing the image and Z data combined with it to provide a 3D topographical

"map" ofthe microscopic specimen See Baird, John Logie; television history

Nippon Advanced Mobile Telephone System NAMTS.Anearly, first-generation, analog FM-based mobile phone system with digital processing, first introduced in Japan Communication Services Lim-ited (CSL) made the system publicly available in 1984

Nippon Telephone and Telegraph Corporation NTT The major Japanese telephone company and largest phone company in the world In 1997, deregu-lation allowed NTT to begin operating internation-ally, and its first international subsidiary, NTT World-wide Telecommunications Corporation, began servic-ing overseas corporate customers See Arcstar; Japan Telecom Co Ltd.; KDDI Corp

NIS1 Network Imaging Server 2 See Network In-formation Service

NISDN 1See National ISDN-l in Appendix G NISTSee National Institute of Standards and Tech-nology in Appendix G

NITFNational Image Transfer Format

NIUFSee North American ISDN Users Forum NJE See Network Job Entry

NL port, end loop portIn a Fibre Channel network,

a port on an endstation that enables it to be connected

to the Fibre Channel loop The NL port is assigned the lowest addresses and thus has the highest prior-ity in terms ofobtaining control ofa loop See F port,

FL port, N port

NLASee Network Layer Address

NLANRNational Laboratory for Applied Network Research

NLCSee nematic liquid crystal

NLPIDNetwork Layer Protocol ID

NMAANational Multimedia Association ofAmeri-can http://www.nmaa.org/

Emily Noether - Mathematician

Emily Noether developed mathematical group

theo-ries that are still widely used by physicists.

NMACS Network Monitor and Control System

NMD See nonintrusive measurement device

NMP 1 See Network Management Processor 2 See

Network Management Protocol

NMR See nuclear magnetic resonance

NMS Network Management System

NNI 1 network node interface 2 Nederlands

Normalisatie-Instituut A Netherlands standards

or-ganization established in 1959, located in Delft

NNTP See Network News Transfer Protocol

NOAASee National Oceanic and Atmospheric

Ad-ministration

noble gasA rare or inert gas Examples include

ar-gon, krypton, neon, and helium These gases are

use-ful in illuminated signs and laser technologies See

argon, krypton, neon

nodal clockIna network, a reference clock source

for major timing functions associated with a node A

valid clock reference may be extracted from a

vari-ety of sources, including a Primary Linkage and

Co-ordination Program (PLCP) The best nodal clock in

a facility can be selected to provide a unified timing

source for Building-Integrated Timing Supply (BITS)

such that a group of network switches would appear

as a node in the hierarchical network scheme

nodeJunction, confluence, meeting point, terminal,

intersection Aconnection point in a network, which

may consist ofarouter, switcher, dialup modem,

com-puter, or other interconnecting device supporting the

same protocol, or converting to the needed protocol

Together the nodes, equipment, and pathways

con-node portSee N port

Noether,Emily "Emmy"(1882-1935)A brilliant German-born mathematician, Emily Noether devel-oped mathematical group theories which underlie many subsequent representations ofmodem physics

Einstein praised her contributions and offered to write her obituary Noetherian Rings are named after her and grandmaster chess player Emanuel Lasker proved some Noetherian algebraic concepts (Lasker-Noether decomposition theorem)

noiseMeaningless or otherwise unwanted sounds or signals interfering with the desired information or transmission in electromagnetic or acoustic commu-nication systems Noise can arise from bad shield-ing, wires too close together, overlapping transmis-sions, weather disturbances, irregular/reflective ter-rain, incorrect operation, deliberate human interfer-ence, random varying velocity, or faulty or incom-patible hardware

Noise in fiber optic networks is different from noise

in wired networks Electrical disturbances, voltage surges, and ground loops can have a significant pact on wired networks but may have little or no im-pact on fiber optic cables, especially end-to-end op-tical networks

thermal noiseor noise from back reflection and are vulnerable to noise anywhere there is ajunction with electrical components Thermal noise may be espe-cially problematic in systems using p-i-n

photodetec-tors Fiber optic networks may experience beat noise

at the receiving end from amplification, depending

upon the frequencies or from relative intensity noise

from fluctuations in the emissions from the source illumination

Another source ofnoise in optical networks is modal noise,which arises when the emitted light (e.g., la-ser light) travels through a multimode fiberinslightly different reflective paths, resulting in slightly

vary-ing distances for the total path or phase delay The

light reaching the output end may exhibit fluctuat-ing interference patterns and may obscure whether the light pulse is on or off Microbends and pits may increase modal noise Modalpartition noiseresults from a fluctuation in intensity from the laser source affecting the longitudinal modes of a multimode transmission Dispersion of the different modes can result in varying speeds along the travel path, caus-ing fluctations at the destination

Intersymbol interference noisemay result from un-even fluctuations of light pulses that overlap in the process oftraveling toward the destination Quantum noise resulting from the particle nature of light can

contribute to shot noise There is Poisson variance in

the number of photons received in any given bit pe-riod such that the photonic energy fluctuates This may increase as the optical power increases See crosstalk, garbage, interference, loss (includes dia-grams), intersymbol interference

Fiber Optics Illustrated Dictionary

noise, modal See dispersion, noise

noise canceling Techniques and technology to reduce

or eliminate noise This may be background noise or

noise on the transmissions pathway Noise

cancella-tion can be through digital algorithms which analyze

the information and screen out calculated noise (a

feature now found on digital cellular phones), or may

be through conditioning circuits in transmitters or

receivers Noise cancellation is sometimes achieved

by adding noise, creating a "white" noise that may

be less objectionable than bursty, intermittent noise

noise filterAnelectrical circuit designed to detect

or evaluate and exclude extraneous signals passing

through a circuit Indigital circuits, fairly

sophisti-cated analysis may take place In analog circuits,

simple exclusions of particular patterns or

frequen-cies may be used

non-facility-associated signaling NFAS In ISDN

networks, a type of signaling in which the D channel

is at a separate primary rate interface (PRI) from an

associated set ofB channels Multiple PRI lines can

be supported through a single D channel using NFAS

In contrast, in facility-associated signaling, the D

channel is at the same PRI as the associated B channels

nonintrusive measurement device NMD A device

used to measure various parameters in analog voice

transmissions over communications networks

Mea-sured parameters include noise level, speech level,

echo path loss, and echo path delay

nonionizing That which does not cause ionization or

change the ion environment around it A number of

transmissions media, including visible light rays and

radio waves, do not cause ionization, but can be

propagated by ionized particles with which they come

in contact

nonlinear distortion In an optical waveguide, the

distortion that occurs over distance when more than

one wavelength, with different transmission

charac-teristics, or more than one pulse, which may reflect

at different angles in the waveguide, travels at

dif-ferent speeds Thus, a signal sent together doesn't

always arrive at its destination in synch with its other

components and the effect is cumulative over

dis-tance

The gradual loss of synchronization can have

delete-rious effects not only at the destination point, but en

route, as well, where crosstalk may result from

non-linear waveform interaction Nonnon-linear distortion is

influenced by the character of the original pulse, the

breadth of the waveguide, the composition of the

wavelengths (which may be prone to chromatic

dis-persion), the number of bends or obstacles (doping)

in the lightguide, and the means of amplification See

chromatic dispersion, Raman scattering See noise

nonreturn to zero NRZ A simple binary encoding

scheme in which ones and zeros are represented by

high and low voltages, and there is no return to a zero

level between successive encoded bits, hence the

name Since transitions mayor may not occur at each

successive bit cell, the NRZ signal has spectral

en-ergy and, consequently, a direct current (DC)

com-ponent that is a nonzero energy at DC It is thus one

type of baseband signal See Manchester encoding nonvolatile memory Circuits or components that retain their data, even if the electrical current is shut off In computer circuitry, volatile memory is installed

in greater quantities than nonvolatile memory Non-volatile memory is typically used for configuration settings (e.g., video parameters) See EPROM, read-only memory Contrast with dynamic random access memory

nonwireline carrier Also called an A Block carrier, for alternate carrier; that is, a competitive phone services carrier that is not the established local phone company (usually a Bell carrier, hence B Block car-rier)

NORC Network Operators Research Committee normal An imaginary line in a direction describing the perpendicular to another line or plane In other words, for any given line or plane, there is a relation-ship that is perpendicular to that line or plane for any given point of reference

The term "normal" is unfamiliar to many people and the word "perpendicular" is often substituted The use

of the word "normal" appears to date back to an Old English term for "rectangular" or "right." Since a right angle is 90° perpendicular to the reference angle

by definition, this may account for the evolution of the term as it is now used

For simplicity, picture a very slender flagpole an-chored squarely in a flat concrete slab; assuming that any point in the center of the flagpole at a specified distance from the slab is equidistant from the slab in any direction (imagine invisible equal-length guy wires all the way around the pole), it is considered

normalto the slab, even if the slab is removed from the ground and tilted in different directions - as long

as the flagpole remains firmly anchored in the same position relative to the surface of the slab, it is con-siderednormalto the plane of the slab If you took away the flagpole and substituted an imaginary line, this line expresses the slab'snormalgeometry, even ifthe line were extended out the other side of the slab (poking into the ground like a pylon representing the negative direction of the normal vector)

While normal is usually visualized as a line, it should

be remembered that the line could be imagined as being anywhere perpendicular to the reference sur-face, not just in the middle For example, if you moved the flagpole from the center of the concrete slab to the edge, while still keeping it straight (i.e., maintaining the even lengths of the imaginary guywires), the flagpole is still considered normalto

the plane of the slab.Thus,jor some shapes,normal can be seen as a planar concept expressed as a line in the context of a specific given point of intersection with the reference plane To understand the planar aspect, imagine walls in a house and how they are set at 90° angles relative to the plane ofthe floor You can pick any point of intersection with the floor along the bottom of the baseboard of a wall and there will

be an imaginary line normal to the floor concurrent with the plane ofthe wall The relationship holds true for other selected points along the wall The wall

as an anchor, and any other point where the wall

touches the floor in its new orientation will still be

normal to the floor However, the pivoting

relation-ship between the wall and the floor only holds

con-sistently for flat surfaces

It is fairly straightforward to grasp the concept of

normal for straight lines or flat planes, but what ifthe

reference line or surface is curved? Imagine a

tooth-pick sticking partway into a perfectly round orange

Ifthe line ofthe toothpick is perpendicular to the

tan-gent plane of the orange relative to where the

tooth-pick intersects the curved surface of the orange, the

toothpick isnormalto the surface of the orange,

whether it's the outside convex surface ofthe orange

or the inside concave surface In a perfect sphere, the

relationship holds ifthe toothpick passes through the

center and pokes out the other side However, if the

line of the extra long toothpick is offcenter, or the

orange isn't perfectly round, normal cannot be

as-sumed to be the same on both sides of the orange

through a single line Normal must be calculated

rela-tive to one point of intersection on a single reference

surface ifthe calculations are tobegeneralizable to any

surface.Ifyou're having trouble visualizing the angle

at which the toothpick must pierce the round orange

to be normal, imagine equal-length guywires around

the toothpick as you did with the flagpole Now

pic-ture the stakes holding the guywires as spinning

around the toothpick to mark a circle like a compass

and slicing off a chunk of orange through the marks

Ifyou place the round piece of orange on your

table-top, the toothpick will now be sticking straight up,

perpendicular (normal) to the surface ofthe table For

a natural, asymmetric orange (or eggplant), normal

will be related to the contours on the fruit's surface

where the toothpick pierces the skin

Determining normal for a point on a bumpy surface

like the Earth's terrain or an optical diffraction

grat-ing is a little more complicated, since it will change

every few inches orJlm,but here is a way to

visual-ize the relationship Imagine flying a small aircraft

(or a flight simulator) a few feet offthe ground in the

desert and maintaining that distance from the ground

over a series ofsand dunes As you pull back, the nose

ofthe aircraft pulls up As you push forward, the nose

of the aircraft pushes down The relationship of the

steering stick may not be perfectly perpendicular to

the surface ofthe sand beneath it (due to lag), but it's

close and it gives you a way to picture approximately

where normal is for a given surface on a complex

plane like desert terrain

The concept of normal, when applied to bumpy

sur-faces, has a fractal nature in the sense that bumpy

surfaces often appear more complex as they are more

closely examined Benoit Mandelbrot used the

ex-ample of a coastline to describe this relationship in

fractal geometry and he developed equations based

upon self-similarity leading to the observation that

the closer you look at a coastline, the longer it gets,

due to the fact that slight indentations and protrusions

can be more readily seen Determining normal for a

surface is scrutinized at the point where you want to determine thenormalrelationship, the more the quan-tity or shapes of the bumps and indentations might influence the angle of an imaginary steering stick or toothpick

Thus, normal is dependent, in part, upon the scale and type of measuring apparatus (and geometry) used to determine the relationship ofthe point ofintersection

to the reference plane Returning to the guywire anal-ogy, imagine a toothpick placed normal to the surface ofan irregular eggplant rather than a perfectly round orange; the angle of the toothpick would likely be different if the guywires were very close to the pick as opposed to some inches away from the tooth-pick

The concept of normal, which is a way of conceiv-ing perpendicular relationships in 3D space in any orientation, is essential in many aspects ofgeometry, theoretical physics, robotics, industrial fabrication (especially telescopes and microscopes), mapping, geology, computer-aided design and drafting, and much more It is frequently used to describe grating surfaces, layered semiconductor structures, and other industrial fabrications The angle of incidence of a re-flected wave is generally described using surface normal as a reference Thus, normal is useful for de-scribing light paths, reflectivity, and diffraction Sur-prisingly, many technical references gloss over or don't mention the term at all See incidence, normal wave

normal distribution Atheoretical construct based upon observations of the distribution of certain traits

in sufficiently large populations From these obser-vations, it is possible to create a statistical represen-tation offrequency distribution to form a bell-shaped curve with certain consistent mathematical proper-ties across the curve It is also called a Gaussian dis-tribution after the observations of Karl Gauss Thus, relationships such as the mode and the mean fall in the center of the curve and are equal and frequency tails off to either side through a number of symmet-ric standard deviations until it becomes zero Once it had been observed that many traits seem to follow a general statistical distribution pattern (many

of which came out of studies or assumptions about human intelligence), the normal distribution or nor-mal curvewas then assumed to apply to many other frequency distributions, with this assumption then being built into tools designed to measure traits in a population (which has some self-fulfilling and circu-lar aspects that may interfere with the development

of objective measuring instruments) Thus, it is used

as a basis for describing probabilities (though some might say possibilities) Many students ask profes-sors if a class is being graded on a "bell curve."In fact, with small class sizes, there aren't sufficient numbers in the population set to justify the assump-tion of a normal curve but many instructors apply normal curve concepts to assigning grades anyway (or get nervous if exam results don't naturally fol-low characteristics of a normal curve)

Fiber Optics Illustrated Dictionary

Inits most general sense,ina sufficiently large, natural

population, a normal distribution describes a sample

set in which there are many members with similar

traits, then a gradually lessening number with slightly

different traits diverging in either direction from the

mean For example, there may be a large number of

men who are 5'10" tall in the U.S., with

diminish-ing numbers who are smaller or taller until a point is

reached where there are no more people outside the

sample set When plotted in Cartesian coordinates,

this trait maybe geometrically illustrated as a

statis-tical curve resembling a symmetric bell shape, with

the mean (average) and mode (most frequent)

cen-tered around those who are 5' 10' ,

In communications, the concept may be useful for

some aspects of assessing, estimating, or predicting

network demographics, peak time use, etc

normal wave Energy in wave form (e.g., radio

waves) that travelsnormal(perpendicular) to a

ref-erence plane or line Since normal is a theoretical

re-lationship (an imaginary line), the concept of a

nor-mal wave is not dependent upon whether the wave

impacts the reference surface which may, in fact, be

imaginary In practical applications, a normal wave

may fail to impact, reflect from, or travel through a

reference surface (e.g., a receiving antenna) If the

reference surface is reflective, and the wave reaches

the surface, the wave would be reflected back in the

direction from which it came, a situation called a

Littrow condition See normal

Norman, RobertAresearcher who published a clear

statement of the laws governing magnetic attraction

and repulsion in 1581 See magnet

Normes Europeenne de Telecommunications NET.

An organization providing compliance testing for

commercial telecommunications products for sale

throughout the European Union to determine whether

they conform to mandatory standards

NortelNorthern Telecom Limited A leading global

digital network provider providing commercial data,

voice, and video services Nortel is a dominant

pub-lic switching equipment supplier in Canada

de-scended from Northern Electric It is also known for

manufacturing and distributing radar sets based on

magnetron tube technology, particularly during the

second world war Nortel technology is leased by

other companies See Qwest

North American area codesSee the Appendix for a

chart ofarea codes for Canada, the U.S., and U.S

ter-ritories

North American Basic Teletext Specification

NABTS.AnElectronic Industry Association (EIA)

and lTU standard that describes a means to

modu-late data onto a vertical blanking interval (VBI), the

transition time when the electron beam in a video

dis-play travels from bottom right to top left with the

elec-tron beam turned off so as not to interfere with the

image that is currently displayed This is usually

as-sociated with an NTSC signal, as is standard in North

American television broadcasting

NABTS can be adapted to transmit Internet Protocol

(IP) data so that broadcast companies can send

vari-ous data services along with a television signal RFC

2078 describes a one-way 36-byte packet structure that can be encoded into a single horizontal scanline

of a television signal Synchronization packets are

located at the beginning, followed by address, index,

and parameter information, followed by 26 bytes of user data, finally ending with forward error correc-tion (FEC) data

The full NABTS specification is described in

EIA-516 The entire NABTS specification is not always implemented See NTSC, RFC 2728

North American Cellular NetworkNACN Acom-mercial provider of international cellular roaming services through their network backbone, serving over 7500 cities worldwide Supported protocols are System Signaling 7 (SS7), X.24, GSM and IS41

North American Digital CellularNADC A com-mercial digital mobile phone service launched in

1991, NADC was introduced as a second-generation system IS-54 supports data rates of48 kbps at a band-width of 30 kHz using digital phase shift keying (DPSK) modulation IS-136 is based upon time di-vision multiple access (TDMA) See DAMPS, time division multiple access

North American Directory PlanNADP An X.500-based client/server Directory System for providing global electronic directory and address book capabil-ity, distributed by ISOCOR

North American ISDN Users ForumNIUF See ISDN associations

North American Network Operators Group

NANOG An association oflntemet Service Provid-ers which meets several times a year to discuss tech-nical issues regarding the administration and opera-tion of Internet-connected services

North American Numbering CouncilNANC A Federal Advisory Committee established and char-tered with the U.S Congress in 1995 by the Federal Communications Commission (FCC) to assist in adopting a model for administering the North Ameri-can Numbering Plan (NANP) This identification scheme is used for many telecommunications net-works around the world NANC advises the FCC and other NANP member governments on general num-ber issues and on issues of numnum-ber portability (e.g., for mobile telephones) See North American Num-bering Plan http://www.fcc.gov/ccb/Nanc/

North American Numbering PlanNANP Asystem ofassigned codes and conventions introduced in 1947 for routing North American (World Number Zone 1) calls through the various telephone trunks ofthe pub-lic telephone network In 1995, significant changes were made to the NANP, mainly due to increased demand for area codes, including changing the middle digits from 1 and 0 to 2 through 9 See Area Codes chart in the Appendix

North American Numbering Plan Administration

NANPA Aworking group that develops and advises the North American Numbering Council (NANC) on processes for selecting a neutral NANP Administra-tor It oversees a number of task forces and coordi-nates with them on issues related to cost recovery for

North American Telephone AssociationNATA.

Now known as the MultiMedia Telecommunications

Association, this is an open public policy, market

development, and educational forum for

telecommu-nications products and services developers and

resell-ers http://www.mmta.org/

north geographic poleThe point at which the

imagi-nary lines of latitude converge at the north pole

rela-tive to the shape of the Earth and its alignment in its

orbit around the Sun The general direction in which

north-seeking compass needles point is near

"geo-graphic north" in northern Canada See north

mag-netic pole

north magnetic poleA point in northern Canada,

near the north geographic pole, to which the

north-seeking tip ofa compass points What is called

mag-netic north could be seen as Earth's south pole, ifthe

"north" end of a magnet were used to determine

"north" on a compass or alternately as the north pole

if a north-seeking (south) pole of a compass is used

to determine the direction If that sounds confusing,

consider that the designation of north or south on a

magnet is not an absolute measure but one assigned

relative to the polarity ofthe Earth, for which we have

already designated north and south geographic poles

Thus, "magnetic north" is the direction toward which

a north-seeking (south) pole ofa compass points The

north magnetic pole is not the same as the Earth's

north geographic pole, despite its proximity, because

the planet is a dynamic ecosystem whose magnetic

properties change over time, whereas geographic

north is a cartographically fixed point See north

geo-graphic pole

NOTIFY,DNS NOTIFY A mechanism for the

prompt notification ofnetwork zone changes that was

proposed as a Standards Track Comment in 1996

NOTIFY is a DNS opcode that enables a master

server to advise slave servers of a change in data so

that they may initiate a query to discover the new data

Traditionally many networks were configured to poll

the server in order to discover any changes within the

zone This was a trade-off in terms ofload on the

sys-tem vs the currentness of information A NOTIFY

transaction, on the other hand, establishes a means

to initiate and expedite the update process when SOA

RR changes occur (and, theoretically, other RR

changes), thus reducing delay without imposing

ex-cess load on the system NOTIFY uses a subset of

the fields in the DNS Message Format See RFC

1035, RFC 1996

NOTIFY SetIn distributed networks using DNS

NOTIFY, the NOTIFY Set encompasses servers to

be notified if changes to a zone have occurred that

should be queried to enact updates The set defaults

to those listed in the NS RRset but, in some cases,

additions or overrides may be possible to

accommo-date special circumstances or stealth servers that are

not listed in the NS RRset See NOTIFY

NOVNews Overview

NovellOne of the significant companies providing

networking software (Novell Netware) to the

busi-by a buyout ofNDSI busi-by Ray Noorda in 1983 In 1998, Novell began promoting Novell Directory Service (NDS) as a means to tie different networking plat-forms together In the 2000s, Novell acquired Cam-bridge Technology Partners and SilverStream Software

NOWTNetherlands Observatory for Science and Technology (Nederlands Observatorium van Wetenschap en Technologie)

Noyce, Robert N.(1927-1990)AnAmerican elec-tronics engineer and significant pioneer of semicon-ductor technology, Noyce received the first Ameri-can semiconductor patent (#2,981,877) and more than

a dozen other patents Early in his career, Noyce did research at the Philco Corporation In 1956, he joined the Shockley Semiconductor Laboratory where he worked with transistors and soon met Gordon Moore, his longtime associate and business partner Together they founded Fairchild Semiconductor and later, in

1968, Intel Corporation Noyce was president ofIntel until 1975 and then served as chairman of the board

Noyce narrowly missed winning the Nobel Prize in physics Although his patent was the first to be awarded for a pioneer integrated circuit (IC) inven-tion, a patent application and verifiable invention by Jack Kilby at Texas Instruments was determined to predate Noyce's by just a few months Kilby was awarded the Nobel Prize in 2000, a decade after Noyce's death Nevertheless, Noyce made a mean-ingful contribution with his version of the new con-cept, as his design was commercially practical and his company, Intel, grew to be one of the foremost chip design and manufacturing firms in the world The Robert N Noyce award is presented annually to outstanding contributors by the IEEE society See in-tegrated circuit; Intel Corporation; Kilby, Jack; Moore, Gordon

NPA 1 National Pricing Agreement AT&T agree-ment 2 See Numbering Plan Area Athree-digit area code NPAsinclude special, reserved, and unassigned numbers

NPR See National Public Radio

NPSTC See National Public Safety Telecommuni-cations Council

NRC 1 See National Research Council 2 See Net-work Reliability and Interoperability Council 3 non-recurring charge

NREN See National Research and Education Network NRIC See Network Reliability and Interoperability Council

NRSC National Radio Systems Committee NRZSee nonreturn to zero

NSAI National Standards Authority of Ireland A standards body for Ireland established in 1961, lo-cated in Dublin

NSAP network service access point

NSFSee National Science Foundation

NSFNETNational Science Foundation Network A network established by the Office ofAdvanced Sci-entific Computing through the National Science Foundation, which is used for the civilian computing

Fiber Optics Illustrated Dictionary

operations of the U.S Department of Defense See

National Science Foundation

NSIESee Network Security Infonnation Exchange

NSlnetNASA Science Internet, a network of the

National Aeronautics and Space Administration

NSP 1 See National Internet Services Provider

2 Native Signal Processing

NSSN National Standards Systems Network

http://www.nssn.org/

NSTACNational Security Telecommunications

Ad-visory Committee

NTNorthern Telecom, Inc

NTSC National Television System Committee.An

organization fonned by the Federal Communications

Commission (FCC) which set black and white

stan-dards for the emerging television broadcast industry

in 1941 By 1953, after the proposal and

consider-ation ofseveral television systems, the FCC adopted

a 525-line color standard developed by Radio

Cor-poration ofAmerica (RCA), which was downwardly

compatible with previous black and white

technolo-gies This is, in part, why luminance and chrominance

infonnation are carried separately This system was

accepted by the FCC and is widely used in North

America and parts of South America

In NTSC broadcasts, color, intensity, and

synchroni-zation infonnation are combined into a signal and

broadcast as 525 scan lines, in two fields of 262.5

lines each (Europe typically uses 625 lines) Only 480

lines are visible; the rest occur during the vertical

re-trace periods at the end of each field NTSC is

con-sidered to run at 30 frames per second, although, in

color television broadcasts, the actual playing rate is

approximately 29.97 frames per second See High

Definition TV, PAL, SECAM

NuBusNuBus is a simple Apple Computer 32-bit

backplane card slot standard (ANSI/IEEE P1196) for

the connection of peripherals to Apple Macintosh

computers The clock is derived from a 10-MHz

ref-erence NuBus backplane space is limited to

74.55 x 11.90 mm (even though some models have

larger slots) NuBus slots can support up to 13.9W

ofpower per card, although more can be used ifother

slots are not filled

nuclear magnetic resonanceNMR A technology

used to reveal the inside of structures or biological

organisms through a series of magnetic scanners or

a magnetic field enveloping the body It is used in

addition to, and as an alternative to, X-rays in

medi-cal research and diagnostic imaging

nullEmpty, having no value.Adummy value,

char-acter, symbol, or marker Null values are sometimes

used as delimiters to indicate the beginning and/or

end of a value or data stream Null characters

some-times are used as padding, to even out the size of

blocks or to provide extra time for synchronization

Null is a very useful concept, regularly usedin

pro-gramming and network transmissions protocols

null attachment concentratorNAC In a Fiber

Dis-tributed Data Interface (FDDI) network, there are a

number of types of node configurations, including

single, dual, and null attachment concentrators Anull

attachment concentrator does not contain any A, B,

or S ports but is configured with multiple M ports The NAC may be used in a simple tree configura-tion It does not support a secondary path for redun-dancy and thus cannot be inserted into a dual ring network See Fiber Distributed Data Interface

null modemA serial transmissions medium which functions in many ways as a modem, as it uses the same software, protocols, and serial transmissions media, except that there is no modem In other words, instead of the signal going from a computer to a mo-dem through a phone line to another momo-dem and to the destination computer, the signal goes from the fIrst computer through a serial cable with no modem con-nected to the second computer, and back again The transmit (Tx) and receive(Rx) lines are swapped (usually lines 2 and 3) This provides fast local file transfer capabilities between machines

null modem cableThere are many ways to config-ure a modem cable,as long as the two computers talk-ing to each other are talktalk-ing the same language (trans-missions protocol), but the most common configu-ration for a null modem cable is to take a standard RS-232c cable and cross (swap) the transmit and re-ceive lines on one end, that is, lines 2 and 3 Or, rather than taking apart a cable, it is usually easier to get a null modem connector that swaps the lines It looks very similar to an extender or other small coupler See null modem

number portabilityNP A service which enables subscribers to retain a geographic or nongeographic telephone number when they change their location, their services provider, or their type of service This is defined with regard to switching services in the Telecommunications Act of 1996, and published

by the Federal Communications Commission (FCC), as:

" the ability ofusers oftelecommunications ser-vices to retain, at the same location, existing tele-communications numbers without impainnent of quality, reliability, or convenience when switch-ing from one telecommunications carrier to an-other."

See Federal Communications Commission, Telecom-munications Act of 1996

Numbering Advisory CommitteeNAC This name

is used by a number oftelecommunications advisory bodies worldwide including Australia, Hong Kong, Zaire, and others.In general, these committees pro-vide forums for the exchange of views on number-ing issues, includnumber-ing assignment, reassignment, stor-age, access, and the dissemination ofpublic and gov-ernmental infonnation for developing Number Plans Recently, these committees have given increased at-tention to the allocation and availability of numbers for mobile telecommunications services

Numbering Plan AreaNPA A three-digit geo-graphic telephony area code NPAs include special, reserved, and unassigned numbers Within each NPA, there are 800 possible NXX Codes (also known as central office codes) NPAs are divided into two general categories:

Category Description

Geographic NPA The Numbering Plan

Area code associated with a specific region

Service Access Code Nongeographic NPAs

associated with specialized services that may be offered over multiple area codes, such

as toll free numbers, 900 numbers, etc

numeric keypadAny compact block offunctionally

related touchtone telephone, typewriter, calculator, or

computer input keys The most common type

ofnu-meric keypad is a group of about 10 to 18 nuofnu-merical

or function keys arranged in a block These are

usu-ally physicusu-ally organized to facilitate touch-typing or,

in some cases, physically organized to slow down

typ-ing! On early touchtone phone systems, there was no

point in entering numbers quickly as the switching

on the network could not be accomplished as quickly

as the numbers could be typed, so the digits were

re-versed to slow down digit entry

The numeric keypad on a computer keyboard

typi-cally consists of 18 keys, with the numerals zero

through nine, and symbols, usually consisting

ofpe-riod, plus, minus, asterisk (star), and enter keys The

remaining three keys differ widely on various

com-puter platfonns, but usually include symbols such as

the tilde, slash, or pipe (vertical bar) See keymap,

keypad

numerical apertureNA In a fiber lightguide, a

quantitative description of the lightguiding

capabili-ties of the "light pipe." If fibers were made of just

one pure light-propagating material and were always

straight and perfectly aligned with the incoming light

source (also assuming there is no back reflection from

the endface), the numerical aperture would probably

be expressed in terms ofthe diameter ofthe fiber

fila-ment However, fiber optic cables may be made from

a number ofmaterials (e.g., glass or plastic) with

dif-ferent refractive indexes and are not perfectly straight

nor necessarily perfectly aligned with the source light

Cladding is laminated around the conducting core to

reflect the light back into the filament and has a

dif-ferent refractive index from the conducting core

Mathematically expressing these different factors in

relation to one another provides a numerical aperture

rating that gives an idea of the light-guiding

capac-ity of a fiber cable assembly See acceptance angle

Numeris, NumerisThe name given to their line of

data telecommunications services by France

Telecom Numeris is based upon Reseau Numerique

al'integration de Service (RNIS) standards to

pro-vide its customers " service that opens doors the

world over for intelligent telephony, fast Internet

ac-cess, and the efficient transfer of information." Data

circumstances) Access to Numeris can be established through D ISDN (16 Kbps) or B ISDN (dual 64 Kbps) channels Numeris Duet offers dual lines for simul-taneous phoning and data communications (e.g., fac-simile or Internet) Numeris Commerce offers D channel services for ecommerce applications such as bank card transactions

nutating fieldIn radar tracking, an oscillating feed from an antenna that produces an oscillating deflec-tion of the radar beam

Nutt, Emma N.Credited as the first female telephone operator See operator, telephone, for additional in-formation and history

nuvistorA type of electron tube in a ceramic enve-lope with cylindrical, closely spaced electrodes

nVabbrev nanovolt.

NV See Network Video

nW abbrev nanowatt.

Nx64A digital network channelized data transmis-sions system As an example, a Tl line can be split into multiple Nx64k circuits for transmission across different ATM-based virtual circuits (Ves) When implemented through High-bit-rate Digital Sub-scriber Line (HOSL), it enables a network access pro-vider to provide data services via two pairs of local

~:~~~::~E~fr~~~ri~!~~iA~:~~£;~~;~~ :. Nx64 interfaceA hardware network interface that

enables Nx64-compliant connections at speeds be-tween 64 and up to about 2048 Kbps, in multiples of

64 Kbps This type of interface, in conjunction with Nx64 data formats, is commercially promoted to pro-vide high bandwidth access to packet-switched back-bone networks such as Frame Relay, X.21, and X.25

Thus, it is ofinterest, for example, to businesses with Frame Relay access to the Internet Anumber

ofITU-T V Series Recommendations relate to Nx64 stan-dards (e.g., V.35) See Nx64

NXX NXX is also known as Central Office Code, or

CO Code.Itis an industry abbreviation designating the three digits of a phone number preceding the last four (EXTN) A ten-digit number is expressed with symbolic characters as: NPA-NXX-EXTN NXX is

a reference to the exchange that services that specific area N refers to any integer between 2 and 9 and X refers to any integer between 0 and 9 Each NXX Code contains 10,000 station numbers See North American Numbering Plan, RNX

NYNEX Corporation One of the Regional Bell Operating Companies (RBOCs) formed as a result of the mid-1980s AT&T divestiture, Nynex comprised several related companies, including the New York Telephone company (NY), the New England Tele-phone company (NE), and others (X) such as NYNEX Information Resources, NYNEX Mobile Communications, NYNEX Business Information Systems, and more

In the early 1990s, NYNEX was developing interac-tive video network technology in cooperation with other vendors In 1994, NYNEX representatives