Fiber Optics Illustrated Dictionary - Part 69 pdf

On computer networks, for example, storage of the nonexistence of certain servers or ma-chines can lead to more efficient polling or routing of processes or network services.Ifcertain pr

Fiber Optics Illustrated Dictionary

the application On computer networks, for example,

storage of the nonexistence of certain servers or

ma-chines can lead to more efficient polling or routing

of processes or network services.Ifcertain printers

or fax servers are offline for maintenance, negative

caching information can be used to prevent

overflow-ing queues Ifcertain hosts are offline, routing of

packets can be renegotiated through other servers If

certain elements of an image file do not exist,

nega-tive caching can be used to prevent expensive

pro-duction tasks on a printing press or milling machine

holding up the line See NCACHE

negative feedbackThe propagation of an acoustic

or electromagnetic signal in the general opposite

di-rection of the source signal This often results from

backreflection ofthe outgoing signal or from the

sig-nal being circularly fed to the source through another

source (e.g., a second microphone).In

slower-mov-ing phenomena (e.g., sound), the delay between the

original source output and the feedback can magnify

the effects of the phenomenon and cause echo

Uncontrolled negative feedback may create

undes-ired loss ofgain, distortion, echoes, or other

interfer-ence but it is not detrimental in all circumstances.In

electronics, negative feedback in a circuit (sometimes

caned shunt feedback because the circuit is looped

back upon itself) can help condition a signal When

configured as inverse or degenerative feedback, it

may help reduce distortion, nonlinearity, and signal

instability in an amplified signal Optical negative

feedback has been proposed as a means to reduce

spectrallinewidth and noise in frequency modulated

(FM) systems

negative glowA luminous glow which can be

ob-served between an electron-emitting cathode and the

Faraday dark space in a cold-cathode discharge tube

See Faraday dark space

negative imageAnimage in which the dark and the

light values are reversed, or in which the

comple-ments of the colors are displayed instead ofthe

nor-mal colors; also called an inverse image

Photo-graphic negatives contain a negative image In

desk-top publishing, negative images are sometimes

cre-ated so the printout can be processed some way in

manufacturing For example, an image printed on

film for subsequent exposure to aprinting plate might

be printed in negative Negative images are often used

for posterization and other special effects.In

mono-chrome television display systems, a negative image

may arise from reversal of the polarity of the signals

negative plate, negative terminalIn a storage

bat-tery, the grid and any conductive material directly

attached to the negative terminal, that is, the

termi-nal that emits electrons when the circuit is active

negative-going video Ina four-field analog video

sequence, a reference point in the subcarrier cycle (the

other being positive-going) that is related to the start

of an NTSC video frame The positive-going and

negative-going cycles alternate in sequence to form

the video field

A video frame is constructed by drawing scanlines

in a sequential, repeating pattem, usually from left

to right and top to bottom at a specified rate (e.g., 30 frames per second) When the electron beam is mov-ing from right to left to begin the next line (or from bottom right to top left when it has finished the full screen) it is turned off or "blanked" so as not to in-terfere with the image on the screen In an interlaced system, it takes two screen images to makeup the fun frame since only the odd or even lines are drawn with each half-frame The process happens so fast that the human eye resolves two half-frames as a full image (although a bit of flicker may be noticed)

A horizontal drive (H drive) triggers a low-voltage negative-going pulse at the beginning ofthe horizon-tal blanking point (in standard systems this is at the right edge of the screen, the trailing edge of the scan-line that has just been drawn) and ending where the edge of the sync for the next line begins

Subcarrier/horizontal (SCIH) phase resolution is syn-chronization between the zero crossing point of the subcarrier sine wave and the negative-going (lead-ing) edge of the horizontal sync in the first field and

a specified line at the halfway point This aids in re-solving phase issues that are important in video tape recording The timing provided by the leading edge

of a negative-going pulse to the leading edge of the subsequent negative-going pulse can be used as a start-stop mechanism Similarly, negative-going and positive-going edges of the same pulse can be useful for timing and integration of signals from multiple video components

Some display monitors expect horizontal and verti-cal sync polarities to conform to certain specifications and, thus, some graphics output devices win include

a hardware switch to output the signal with

negative-going polarities A grab pulse can be a

positive-go-ing or negative-gopositive-go-ing polarity output pulse for synching video to a component such as a frame grab-ber

Negroponte, Nicolas(1943- ) Outspoken author, philosopher, and educator, Negroponte is well known

for his lectures and Wired magazine back-page

edi-torials He is the founder and director of the Massa-chusetts Institute of Technology's celebrated Media Laboratory, established in the late 1980s Prio'r to that,

he founded MIT's Architecture Machine Group, a think tank and research lab for discussing new ap-proaches to human-computer interfaces

neighborsAnetworking term used to describe nodes attached to the same link See node

nematic liquid crystalNLC Nematics are rod-like organic molecules and nematic liquid crystals are mesomorphic (between liquid and solid) structures that show clumps of thread-like flaws when stressed/ fractured, from which the name is derived

Room temperature NLCs were developed by creat-ing eutectic mixtures ofMBBA combined with other compounds to broaden the effective temperature range, but their stability and dielectric properties were not suitable for commercial components G.W Gray

of Hull University discovered cyanobiphenyl mate-rials with room-temperature nematic phases with use-ful birefringent and dielectric properties Nematic

that exhibit some properties of solids, such as

gen-eral orientation ofmolecules, and some properties of

liquids, such has not having a specific positional

or-der to the molecules, unor-der certain circumstances

(while il1 a thermotropic liquid crystal phase) There

is an even more specific phase in which the molecules

buddy up to each other but are not symmetric in

re-flection This slightly skewed orientation is called a

chiral nematic phase Chiral nematic liquid crystals

have a helical internal structure with interesting

cir-cular birefringent properties Thus, circir-cularly

polar-ized light entering the material will travel at

differ-ent speeds, depending upon the direction of the

po-larization and the wavelength, in relation to the

ori-entation of the chiral NLC Linearly polarized light

will similarly be affected, causing the angle of

po-larization ofthe two beams of refracted light to

pro-gressively change as they move through the crystal

NLCs are used in optical scanners with birefringent

thin films and large imaging surfaces NLCs are the

most common type of liquid crystal used in display

devices See multiplexed optical scanner technology,

Schadt-Helfrich effect, smectic liquid crystal

NENA See National Emergency Number Association

neon gas(symb - Ne)Aninert gas with many

in-dustrial and commercial applications When ionized,

neon glows red.Itwas popularly used to illuminate

signs in the 1940s and 1950s, and is still used for this

purpose, along with other gases that emit other colors

neon lampA long glass illuminating tube with an

electrode at each end and low-pressure neon gas

in-side, which may be angled into interesting shapes

When illuminated, it produces a red-orange light that

can be seen in daylight and can penetrate fog better

than most conventional types oflights Neon has also

been used in older tubes in the broadcasting

indus-tries, in simple oscillating circuits, and in

commer-cial signs

neper(pron - nay-per, symb - Np ) A

dimension-less mathematical unit for expressing relative

mea-surements It is used to express ratios that are useful

inphysics and electronics, as for voltage and current

relationships

The neper is similar to the decibel except that it is

established upon a base of2.718281828 ; quantities

expressed by nepers are based upon natural

(Napierian) logarithms rather than base 10

loga-rithms The neper is not a Systeme Intemationale (SI)

unit, but it is widely used and thus 1Np has been

as-signed an SI equivalent value of 1 In terms of

deci-bels, 1Np= 8.686 dB

The neper is named after the Scottish mathematician

John Napier (Thone Neper) who did historic research

on logarithms See decibel; Neper, Thone

Neper, Jhone(1550-1617) A Scottish

mathemati-cian, now more commonly known as John Napier,

who did pioneer work in logarithms and published

Mirifici logarithmorum canonis descriptioin Latin,

in 1614 There were no computers in those days, so

logarithmic tables had to be methodically calculated

and inscribed by hand Neper published a followup

ing calculations using ivory numbering rods (Napier's bones) marked with numbers (a physical calculating device that facilitates computations just as a slide rule facilitates computations) Neper's logarithmic dis-coveries were important fundamentals for many fu-ture discoveries in mathematics, physics, and as-tronomy

nephelometerAninstrument for measuring or esti-matingli~ht-scatteringcoefficients in fine particulate

"clouds.' Nephelometers are used to assess the prop-erties of aerosols, dust, allergens, microbes, liquid suspensions, and other small groupings of fine par-ticles by measuring light attenuation by scattering and absorption over distance

Nephelometers incorporate many optical compo-nents, including a light trap to provide a dark refer-ence against which scattered light may be assessed They may also include concentrating or diffracting lenses, one or more photomultiplier tubes, and band-pass filters If the light is to be separated into wave-lengths, they may also include prismatic components such as dichroic filters A Ronchi grating or "chop-per" may be used for calibration See dichroic, nephelometry, Ronchi grating

nephelometryThe science of light scattering or, stated another way, the study of "cloudiness" or of microscopic particles or surfaces that influence the passage and direction of travel of light Nephelom-etry is useful in the study of weather, atmospheric pollution, drug solubility, immunology, allergens, electromagnetic wave propagation, dust, and mi-crobes

Lasers have become important components in nephelometers for measuring biosystem "clouds." Thus, laser/fiber optic nephelometers are useful in-struments for counting fine particles and characterizinng suspended particles, tasks that are difficult by any other means See nephelometer; Tyndall, John

Nernst effectA potential difference (electromotive force) develops in a metal band or strip when heated This is a transverse thermomagnetic effect, Le., the force is perpendicular to the magnetic field The ef-fect is named after Walther Nernst (1864-1941) who described the third law of thermodynamics (the Nemst heat theorem) in 1905

Nernst lampA continuous source of near-infrared radiation developed byW Nemst in the 1890s It is useful in fields such as spectroscopy

NESCSee National Electrical Safety Code NESDISNational Environmental Satellite, Data and Information Service

Net Citizen, Net DenizenSee Netizen

Net PoliceA generic term for the various individu-als who moderate communications on the net for ap-propriateness, tact, good taste, honesty, and fair use Although some resent the activities ofthe Net Police, for the most part, these folks are committed, caring, hard-working volunteers who want to see the broadest possible access to the Internet, and who encourage voluntary compliance with Netiquette in order to try

Fiber Optics Illustrated Dictionary

to prevent government regulation of the Internet's

open communications forums See Netiquette

NETIROM A packet radio communications

proto-col which has largely superseded AX.25 It provides

support for a wider variety of types of packets with

automatic routing See AX.25

NetBIOS Frames Control ProtocolNBFCP

Origi-nally the NetBEUI protocol, NBFCP establishes NBF

Protocol to run over Point-to-Point Protocol (PPP)

NBFCP enables an end system to connect to a peer

system or to the local area network (LAN) in which

the peer is located.Itis not suitable for

interconnect-ing LANs NBFCP defines a method for

encapsulat-ing multiprotocol datagrams, a link control protocol

(LCP) for establishing and configuring the data link

connection, and a family of network control

proto-cols (NCPs) for establishing and configuring

differ-ent network-layer protocols See RFC 2097

NETBLT NETwork BLock Transfer Protocol This

is a transport level networking protocol intended for

the fast transfer oflarge quantities of data It provides

flow control and reliability characteristics, with

maxi-mum throughput over different types of networks It

runs over Internet Protocol (IP), but need not be

lim-ited to IP

The protocol opens a connection between two clients,

transfers data in large data aggregates called

"buff-ers," and closes the connection Each buffer is

trans-ferred as a sequence ofpackets Enhanced Trivial File

Transfer Protocol (ETFTP) is an implementation of

NETBLT See RFC 998

NetcastBroadcasting through the Internet, for

ex-ample, through streaming video See Webcast

NetiquetteNewsgroup etiquette, Network etiquette.

Animportant, well-respected voluntary code of

eth-ics and etiquette on the Internet Many people have

contributed to Netiquette, but it was mainly

devel-oped by Rachel Kadel at the Harvard Computer

So-ciety, and subsequently maintained by Cindy Alvarez

The whole point of having Netiquette is so that

net-work citizens can enjoy maximum freedom by not

abusing the rights and sensibilities of others, so that

the Net will remain largely unregulated and

unre-stricted This freedom depends upon the cooperation

of everyone

In the early days of BBSs, in the late 1970s, most

systems were completely open and not password

pro-tected Gradually the constant vandalism and lack of

consideration for others caused passwords to be

implemented Eventually, by the mid-1980s, even this

was not sufficient to curtail childish or destructive

be-havior and many of the system operators (sysops)

gave up trying to maintain the systems

Many ofthe same unfortunate patterns of abuse have

damaged the USENET newsgroup system, which

used to be a fantastic open forum for discussion, with

many scientific and cultural leaders participating

un-der their real names in the mid-1980s Unfortunately,

this system is now abused by bad language,

inappro-priate remarks, and get-rich-quick come-ons

Conse-quently, many groups have been forced to close up

or go to moderated status, and most celebrities now

use assumed names Ifmembers of the Internet com-munity realize that it is completely possible to vol-untarily appreciate and respect the rights of others, the Internet can remain an open resource for all

It's a good idea to read Netiquette Its adherents

en-courage people to choose voluntary self-restraint and freedom over regulation See emoticon, Frequently Asked Question, Netizen Also, Arlene H Rinaldi's

"Net User Guidelines and Netiquette" in text format

is available at many sites on the Internet, including: ftp://ftp.lib.berkeley.edu/pub/net.trainingIFAU/netiquette.txt

NetizenNet citizen or Net denizen Aresponsible user

of the Internet Many founders and users of the

In-ternet consider themselves members of a new type

of global community that shares and promotes a vi-sion ofan open, freely accessible, self-governed com-munications venue in which participants voluntarily deport themselves with responsibility, integrity, char-ity, and tolerance toward the many diverse opinions expressed online A Netizen is one who contributes

to the positive evolution ofthe Net and respects online Netiquette One could also more broadly say that any-one who uses the Net is a Netizen, although some people online have less polite terms for those who abuse their freedoms and those of others on the Net See Netiquette

netmaskA symbolic representation of an Internet Protocol (IP) address that identifies which part is the host number and which part is the network number through a bitwise-AND operation The result of this logical operation is the network number Netmasks are specified for different classes of addresses, and are used in classless addressing as well See name resolution

NetRangerAnintrusion detection utility from Cisco Systems now known as the Cisco Secure Intrusion Detection System Aservice pack was issued to sup-port the detection system sensor component to reduce the chance of the system being circumvented by an encoding vulnerability See CodeRed, virus

NETS See Normes Europeenne de Telecom-munications

Netscape CommunicationsOriginally Mosaic com-munications, Netscape Communications was the original developer and distributor of Netscape Navi-gator, the best-known open-source browser on the In-ternet The company was founded by Mark Andreessen and some very experienced business people from Silicon Graphics Corporation and McCaw Cellular Communications It had one of the highest profile public offerings in the computer in-dustry See Andreessen, Mark

Netscape NavigatorThe most broadly distributed and used Web browser on the World Wide Web, and the name of its related server software Descended from Mosaic, the browser was developed by Nets-cape Communications and widely distributed as shareware until late 1997 At that point, Netscape made the decision, in 1998, to freely distribute the software as open source software and concentrate on marketing their server software The first beta release was distributed in 1994

fabric, or structure A logical, physical, or electrical

grouping in which there is some electromagnetic or

biological intercommunication between some or all

of the parts A broadcast network is a physical and

communications association ofdirectors, actors,

pro-duction personnel, and technologies which together

cooperate and are used to create and distribute

pro-gramming to its viewers A computer network is one

in which computers are able to intercommunicate and

share resources by means of wireless and/or wired

connections and transmissions protocols A cellular

communications network is one in which a

coopera-tive system of wireless communications protocols,

geographically spaced transceivers, relay and

control-ling stations, and transceiving user devices are used

to interconnect callers while moving within or among

transceiving cells

network-attached storageNAS In general terms,

a dedicated file storage device or system of

associ-ated devices on a network server The NAS is

in-tended to take the storage burden off the processing

server so that a greater amount of storage and more

specialized storage-related resources can be

concen-trated within the NAS In more specific terms, NAS

is the implementation of a storage access protocol

over a network transmissions protocol (e.g., TCP/IP)

such that the storage resources are concentrated and

separate from the process server (and may even be

in a remote location)

The advantage ofNAS is that storage devices can be

placed where it is convenient to install or maintain

them and large storage closets can be established for

high-end storage needs The disadvantage is that the

burden ofthe transmissions between remote users and

the NAS is handled across the network, increasing

traffic over what would occur if the storage devices

were associated with individual workstations and

decreasing access times, depending upon the distance

and the relative load on the network

NAS is often implemented within a storage area

net-work (SAN), which is a broader concept, and may

be designated as SANINAS See NASD Project,

Na-tional Storage Industry Consortium, storage area

net-work

network, broadcastn A commercial or amateur

ra-dio or television broadcast station A few examples

of well-known broadcast networks include CBC

(Canada), BBC (Britain), ABC, NBC, and PBS

Amateurs often run local or special-interest radio,

television, or slow-scan television broadcasts See

ANIK

network, computern 1 Asystem comprising nodes

and their associated interconnected paths 2 A

sys-tem of interconnected communications lines,

chan-nels, or circuits Asmall-scale computer network

typi-cally consists of a server, a number of computers,

some printers, modems, and sometimes scanners, and

facsimile machines The highway system is a type of

network, as is the very effective train system in

Eu-rope See local area network, wide area network

network access control NAC Network policies,

the data transmissions to a server, switching/routing component, network, workstation, or peripheral de-vice Password accounts, dedicated workstations and peripherals, gateways, firewalls, and employee passcards are examples ofNAC components and pro-cedures

NAC policies and systems are of particular interest

at institutions where sensitive information or expen-sive services must be handled efficiently or protected from tampering or misuse NAC is important in busi-ness and educational local area networks and particu-larly important in classified government and military systems, especially on systems where links to the outside world through the Internet are desired with-out compromising internal security In some cases biometrics (e.g., iris scans) may be used to control access to computer terminals or rooms Monitors and logs may be implemented to oversee general use and

to provide an audit trail to check back through un-usual activities See authentication, firewall, gateway

Network Access PointNAP Amajor backbone point which provides service to ISPs and is designated to exchange data with other NAPs NAP was a devel-opment in the mid-1990s which arose from the change in the U.S Internet from a single, dominant backbone to a shared backbone across four NAPs (California, Illinois, New Jersey, Washington, D.C.)

See MAE East, MAE West, Metropolitan Area Eth-ernet, Public Exchange Point

network addressAnidentifier for a physical or logi-cal component on a network Components often have

a fixed hardware address, but may also have one or more logical addresses Logical addresses may change dynamically as the network is altered physi-cally, or as the network software is tuned or proto-cols changed Network addresses are typically asso-ciated with nodes and stations See address resolu-tion, domain name, Media Access Control

network administrator I The human in charge of the installation, configuration, customization, secu-rity, and lower level operating functions of a com-puter network On larger networks, these tasks may

be divided among a number of professionals See SysOp 2 A software program that handles details of the job of a human network administrator Activities automated with network administration software in-clude monitoring, archiving, and system checks See daemon, dragon

Network Applications ConsortiumNAC A trade organization seeking to support and promote gener-ally accepted standards rather than a large number of fragmented proprietary standards for network appli-cations in order to promote interoperability

http://www.netapps.org/

Network Control ProtocolsNCP The Point-to-Point Protocol handles assignment and management of Internet Protocol (IP) addresses and other functions through a family of Network Control Protocols (NCPs) which manage the specific needs oftheir as-sociated network-layer protocols See Point-to-Point Protocol, RFC 1661

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Fiber Optics Illustrated Dictionary

network driveA drive accessible to multiple users

on a computer network On some network systems,

users have to specify and access a particular drive to

take advantage ofthe shared storage space On other

systems, the shared arrangement can be set up so that

it is transparent to the user and, in fact, a volume may

traverse several drives Network drives are sometimes

configured for data redundancy in case one drive or

partition becomes corrupted See redundant array of

inexpensive disks

Network Driver Interface SpecificationNDIS A

network protocol/driver interface jointly developed

by Microsoft Corporation and 3Com Corporation

NDIS provides a standard interface layer that receives

information from network transport stacks and

net-work adapter card software drivers The transport

pro-tocols are thus hardware-independent

network elementNE This is defmed in the

Telecom-munications Act of 1996, and published by the

Fed-eral Communications Commission (FCC), as:

" a facility or equipment used in the provision

ofa telecommunications service Such term also

includes features, functions, and capabilities that

are provided by means of such facility or

equip-ment, including subscriber numbers, databases,

signaling systems, and information sufficient for

billing and collection or used in the transmission,

routing, or other provision of a

telecommunica-tions service."

See Federal Communications Commission,

Telecom-munications Act of 1996

networkfax serverA workstation equipped with

facsimile or fax/modem hardware and software so

multiple users of the network can route a fax in and

out through the server This removes the necessity of

having a fax system attached to each computer The

fax server can then also be located nearer its

associ-ated phone line There are fax servers that can use

Internet connections (T1, frame relay, etc.) rather than

phone lines to send and receive messages

network filterA transducer designed to separate

transmission waves on the basis of frequency

Network Information ServiceNIS A client/server

protocol de.veloped by Sun Microsystems for

distrib-uting system configuration data among networked

computers, formerly and informally known as

Yel-low Pages NIS is licensed to other Unix vendors

network interfaceNI Ajunction or reference point

in a network that supports or represents a change in

the physical and/or logical structure of a link or, in

some cases, represents a jurisdictional change (even

ifthere is no physical change or data conversion) The

point at which a phone service line connects to a

subscriber's premises is a network interface and

vari-ous aspects of this connection have been

standard-ized For example, the network interface electrical

characteristics and interactions for an analog

connec-tion between a telecommunicaconnec-tions carrier and the

customer premises are described in ANSI

T1.401-1993

network interface card, network interface

control-lerNIC APC board that provides a means to

physi-cally and logiphysi-cally connect a computer to a network For microcomputers, typically these cards are equipped with BNC and/or RJ-45 sockets facing the outside ofthe computer and edge card connectors that fit into the expansion slots inside a computer The cables resemble video cables, or fat phone cables, depending upon the type used

Most systems require a physicalterminatoron the physical endpoints ofthe network (ifthe network isn't working, it may be because termination is missing

or incorrectly installed) Separate software, not in-cluded with the computer operating system, may be required to use the specific card installed

Many workstation-level computers come with net-work hardware and software built in, and Macintosh users are familiar with the built-in AppleTalk hard-ware and softhard-ware The trend is for microcomputers

to useTCP/IPnetworking over Ethernet

Network Integration Verification TestNIVT A test designed to evaluate and improve three different Front End Processors (PEPs) handling routing and transport protocols in mixed high-performance rout-ing systems with large Topology Databases to assess scalability Information on NIVT and actual test re-ports are available through the ffiM Web site

network interface functionNIF A function associ-ated with a specific interface link in a network For example, there may be specific translation functions

in the interface between a subscriber's computer and the Network Interface Device (NIC) supplied by a service provider, e.g., in ISDN networks

network intrusion detection system NIDS Ameans

or set ofprocedures and/or programs designed to alert the system administrator or individual users about vandalistic attacks or unauthorized access to a com-puter network There are many types of intrusion, including system flooding, virus insertion, account access, file access, and physical access NIDS more often refers to the first four categories (physical ac-cess to the electronics inside a computer may be tected by video cameras, marks, fingerprints, or de-tection chemicals, but this type of intrusion is less prevalent than day-to-day attempts by unauthorized users to view, steal, or compromise data on a system.)

An intrusion detection system is rarely just one ap-plication or device, but rather the coordinated imple-mentation ofa collection ofpolicies, procedures, and tools to ensure system security

In general, NIDS refers to systems that actively de-tect signs of intrusion (e.g., a utility that dede-tects re-peated entries of incorrect passwords) as opposed to passive systems that primarily deter intrusion (e.g.,

a password to access an account)

As networks and databases with sensitive informa-tion are increasingly connected to the Internet, they become more accessible and vulnerable to outside in-truders Electronic commerce sites on the Web are particularly vulnerable, as there are people who search for credit card numbers, bank accounts, per-sonal identification, and other commodities that are recorded on computer systems Two of the more im-portant intrusion detection mechanisms include:

cent statistics and events On older

sys-tems and mainframes, monitors

com-monly represent data as text displays

ar-ranged in columns On some of the

newer systems, graphical tables and

graphs are also available System

moni-tors are often bundled with operating

systems to allow sysops to view CPU

usage, connection requests, numbers of

users, entries and exits to the system,

locations of machines being accessed,

numbers or types of packets being

transferred, URLs of users accessing

Web servers, etc Operators use a

com-bination of live audio/visual

monitor-ing and software utilities to generate an

alert when anomalous patterns occur

logs Records of activities The data

gener-ated by monitors are often kept in

run-ning logs that can be archived

indefi-nitely or stored for a period ofhours or

months, depending on the need In

ad-dition to system monitors, software

in-stallation and system reconfiguration

activities are often logged to record

when changes were made, which files

were added or deleted, and where the

files were installed Intruders are not

al-ways high-tech computer experts; often

they are employees snooping or

steal-ing data with little understandsteal-ing ofthe

electronic trail they leave when they

en-gage in unauthorized access Even if

they do search for logs, with the

inten-tion ofchanging or deleting them, they

may be unsuccessful if the system is

configured to duplicate log entries on

another computer or a protected

direc-tory

One of the more difficult types of intrusion to detect

is access by someone who has stolen a legitimate

password Since the intruder isn't breaking into the

system, but logging on normally, the intrusion may

go unnoticed for a long time However, even this type

of activity can sometimes be detected with a

combi-nation ofmonitors and logs IfCPU usage during the

night or lunch hour is usually low, and the various

monitors show John Doe's account becomes active

during times when John isn't at his desk, there is

rea-son to investigate the anomalous patterns Intrusion

detection systems are, in large part, dependent upon

the ability of the system administrator and the

capa-bility of the system to determine normal usage

pat-terns and variations from the norm

The most difficult type ofintrusion to detect is

unau-thorized activity by a system administrator or

pro-grammer A small percentage of sysops take

advan-tage of their privileged positions for personal gain

Since a high-level administrator or systems

program-mer has access to almost everything on a network,

unethical use of network resources They are also expert at hiding a data trail when using one system

to access another or when snooping on password-pro-tected file systems These types ofintrusion often go unnoticed until funds disappear or until strange things happen after the individual leaves a project or firm The primary ways to reduce system administrator in-trusions are careful employee screening, built-in ac-countability policies and procedures, and good em-ployee relations For the most part, system adminis-trators are intelligent, dedicated professionals, proud

of their systems and concerned about maintaining good system security Contrary to what might be ex-pected, the majority ofintrusions are probably not by system administrators, but by curious or mischievous programmers on the one hand and professionals try-ing to divert funds or information or save a buck on the other (statistics suggest that a surprising propor-tion of computer-related theft is by doctors and businesspeople as opposed to university students and teenagers)

Network intrusion detection is not a simple configu-ration that can be set up and used indefinitely Com-puter security requires a responsive approach to a dynamically changing environment, like a farmer adapting to constantly changing weather and market conditions A system administrator must monitor, fine-tune, and reconfigure on an ongoing basis to achieve network security See cracker, firewall, hacker, virus, worm

Network Job EntryNJE A communications proto-col developed by IBM that arose out of the wide-spread use ofRemote Job Entry(RJE)protocol used for the remote submission of computer processing jobs.RJEcould be used in conjunction with the main-frame Job Entry Subsystem (JES) to enable RJE-en-abled workstations to submit jobs to a centralized mainframe system Network Job Entry grew out of JES, extending JES and the functionality ofRJE NJE enables two JES subsystems on different host com-puters or in different local partitions to intercommu-nicate, thus supporting peer-to-peer communications ofcommands andjob submissions on IBM host sys-tems NJE was developed at the time when mainframe prices were coming down and multiple mainframes began to be installed in separate locations It enabled specialization ofmainframe computing functions and efficient use ofcomputers with different capabilities While the protocol has been around for quite a while,

it is less well known thanRJE.BITNET was an im-portant historical precursor to the Internet based on the NJE protocol See BITNET

Network Layer PacketNLP In High Performance Routing on packet networks, a basic message unit that carries data over the path See datagram

Network Management ProcessorNMP Anetwork switch processor module used to control and moni-tor the switch

Network Management ProtocolNMP Aset ofpro-tocols developed by AT&T to control and exchange information with various network devices

Fiber Optics Illustrated Dictionary

Network Management System NMS.An

adminis-trative service tool for subscriber networks that

en-ables the system administrator to adjust performance

characteristics and to set bit rates and user settings

according to the levels of service available to

sub-scribers

Network News Transfer Protocol NNTP Asoftware

application developed in the mid-1980s to provide a

way to more quickly and efficiently query, retrieve,

and reference information from newsgroups through

NNTP servers It also facilitates list management of

newsgroup discussions NNTP is a network news

transport service Newsgroups may be accessed

through the Web from local clients using the NNTP

URL scheme as follows:

nntp://<host>:<port>/<newsgroup-name>/

<article-number>

For global access to newsgroups, the news: scheme

is preferable See news, RFC 977, RFC 1738

Network Operations Center NOC A centralized

around-the-clock facility for monitoring and

main-taining a network, which may remotely service

smaller centers such as POPs NOCs typically

pro-vide a number of technical support and accounting

services as well Most large networks (computer,

phone, broadcast) have a core staff dedicated to the

physical and logistical tasks of keeping the system

running, well-maintained, and current One of the

most prominent NOCs is the U.S Air Force NOC,

formerly the Air Force Network Control Center

network prefIXes Identifiers used to aggregate

net-works Networks are divided into classeswith the

ability to serve up to a certain number of hosts The

prefix identifies the class, and hence the number of

possible hosts

Network Reliability and Interoperability Council

NRIC.Anadvisory committee formed to provide

rec-ommendations to the Federal Communications

Com-mission (FCC) and the telecommunications

indus-tryregarding network reliability and interoperability

of public telecommunications networks The

origi-nal charter was filed in 1992 The most recent

man-date was to operate until January 2002 The NRIC

works through a number of focus groups and

subteams See Committee Tl, New Wireline Access

Technologies http://www.nric.org/

Network Security Information Exchange NSIE A

forum for identifying issues ofnetwork security such

as unauthorized or malicious entry or tampering that

might affect national security and emergency

pre-paredness telecommunications systems Members

exchange information on viruses, threats, incidents,

and other attacks on public telecommunications

net-works

network service point NSP Cisco Systems

technol-ogy that provides native SNA network service point

support

Network Solutions, Inc NSI.In1993, this company

was awarded the contract for registering Internet

domain names with the InterNIC by the National

Science Foundation NSI was acquired by Scientific

Applications International Corporation (SAIC) in

1995 See InterNIC

Network Terminal Number NTN.Anidentification number assigned to a tenninal on a public network by the public network administrator The ITU-T recom-mends that public voice/data and digital voice net-works also assign NTNs The NTN is a designation within the Data Network Identification Code (DNIC) for public networks interconnected with X.75 See Data Network Identification Code, X Series Recom-mendations

Network Video NV A freely distributable Sun SPARC-, DEC-, SGI-, HP-, orffiMRS6000-based videoconferencing system developed at Xerox PARC, which supports video, audio, and whiteboard-ing over Mbone networks

Network Voice Protocol NVP The historical fore-runner ofthe Voice File Exchange Protocol proposed for the ARPANET in the mid-1980s, the NVP was submitted in November 1977 by Danny Cohen on behalfofa cooperative effort ofthe ARPA-NSC com-munity

We tend to think ofvoice carried over computer net-works as a development ofthe late 1990s, but the idea has its roots much earlier and has been active on ex-perimental systems since the 1970s and on some com-mercial systems since the mid-1980s NVP was first implemented in December 1973, and was subse-quently used for local and remote realtime voice com-munications over the ARPANET at some of the ma-jor research facilities in the U.S

The development of secure, low-bandwidth, two-way, high-quality, realtime, digital voice communi-cations was a major objective of the ARPA Network Secure Communications (NSC) project It was, at the time, a high-priority military goal, intended to facili-tate command and control (C2) activities By imple-menting the concept with digital technologies, en-cryption could be used to help protect the content of communications NYP consists of a control pro-tocol and a data propro-tocol See Voice File Exchange Protocol, RFC 741

Neumann, John von See von Neumann, Janos neural computer A computing system theoretically designed to behave like the human brain in terms of performing logical, intelligent problem-solving and inferential "thinking" activities, which also may structurally mimic the interconnective structural to-pology ofbiological neurons in a centralized nervous system Aneural computer, like the human brain, con-figures itselfthrough experientialleaming, feedback, and internal reorganization over time Neural com-puters are not entirely theoretical, except in their most ideal form There have been many efforts and suc-cesses in the design ofneural and bionic systems since the early 1960s, with worldwide efforts by major companies to design and implement practical neural computers on a small scale since the 1970s and on a large scale since the late 1980s and early 1990s A neural computer is a specialized type of super-computer, since "supercomputer" implies the state of the art in computing at anyone time, and existing

processing and problem-solving speeds.

Neural net architectures tend to be highly parallel,

withmultiple registers, several layers, and a high level

of interconnection between nodes The concepts of

neural computers date back to the 1940s, to the work

ofW McCulloch, W Pitts, A Rosenblueth, and N

Wiener See artificial intelligence; bionics; neural

network; Wiener, Norbert

neural network In a broad sense, a type of network

organization that mimics the human nervous system,

particularly the brain, in physical structure and

con-nectivity or neural functioning as it relates to

think-ing, or both Simulation ofneural networks, and

mod-eling ofthe complex reasoning, generalizations, and

inferences characteristic ofhuman thinking have long

been ofinterest to programmers and scientists

study-ing artificial intelligence While the creation of

an-droids, humanoid intelligent robots, is probably some

time in the future, some interesting advances in

pro-gramming have resulted from studies of neural

net-work functioning Software that has the ability to

gen-eralize and make choices, react, and further

config-ure itself in response to feedback is being developed

with practical applications in many areas, including

robotics Neural networks can aid machines and

hu-mans in unfamiliar environments

Speculation about neural networks and "thinking

machines" has been around at least since Ada

Love-lace proposed, in the 1800s, that intelligent machines

might someday produce art and poetry In the late

1940s, Norbert Wiener, Arturo Rosenblueth, and their

colleagues were discussing concepts related to

"cy-bernetics," a tenn popularized by Wiener in

Cyber-netics: or, Control and Communication in the

Ani-mal and the Machine.In 1963, inElectronics World,

Ken Gilmore described the work on bionic

comput-ers being carried out at Wright-Pattcomput-erson Air Force

Base in Ohio and modeling ofindividual neuronal

cir-cuits by companies like Bell Laboratories and the

Ford Motor Company In the 1950s and early 1960s

there were already many experimental

implementa-tions of various aspects of neural networks,

includ-ing electronic maze-runninclud-ing mice,

pattern-recogniz-ing machines, self-organizpattern-recogniz-ing machines, and

simu-lations of human vision systems See artificial

intel-ligence; bionics; Harmon, L.D.; Melpar model;

MIND; pattern matching; perceptrons; Sceptron;

Wiener, Norbert

neuroeleetrieity The very minute level

electromag-netic fields generated by the activities of biological

neurons See neural network

neuronIna biological system, cells specialized to

code and conduct an electromagnetic impulse are

called neurons Anetwork ofinterconnecting neurons

is called a nervous system, and a network of

inter-connecting neurons with a main processing center is

called a central nervous system, with the main

pro-cessing center called the brain

Neuron Chip A commercial microcontroller chip

with the LONTalk automation control protocol

em-bedded into the chip This enables the chip to be used

dustrial and residential devices, including fans, switches, motors, motion sensors, valves, and more The Chip includes three 8-bit inline central process-ing units, two of which are dedicated to LONTalk protocol processing, with the third dedicated to the node application program The chip has built-in memory and 11 general-purpose input/output pins for interfacing with circuits

Neuron Chips are programmed in Neuron C and can access the built-in LONTalk communications soft-ware and network management functions, as well as schedulers, and arithmetic/logic application runtime libraries Neuron C is an object extension to ANSI C LONTalk is an open standard for control automation networks The Neuron Chip is available through Cy-press Semiconductor and Toshiba Corporation See LONWORKS, LONTalk

neutral In stasis, in equilibrium, stable, balanced, normal, unaffected, neither positive nor negative, not tending to one side or the other, nor one state or an-other Neither acid nor base

neutrodyne In early radios, an amplifying circuit used in tuned receivers Voltage was fed back by a capacitor to the circuit to neutralize it See hetero-dyne, superheterodyne

New England Museum of Wireless and Steam Located in Rhode Island, this museum preserves the original Massie station, the oldest surviving, origi-nally equipped wireless station

New Haven District Telephone Company Ahistoric exchange that welcomed its first subscriber, Rev John

E Todd, in 1878 By February 21, 1878, the company's first telephone directory included almost

50 subscribers, primarily physicians and businesses, listed according to professions No numbers were assigned to the subscribers, as operators handled the calls and phone numbers did not come into use in this area until 20 years later

NewleoFormerly ICO Global Communications (est 1995), a London-based satellite communications ser-vice, spun off from the Inmarsat Project 21 Hughes Electronics has a large interest in the company, and Hughes Telecommunications and Space Company is building the satellites Other ICO Global investors in-cluded COMSAT Corporation, Beijing Maritime, Singapore Telecom, Deutsche Telecom, and VSNL (India)

The original plan was to launch ten satellites plus two spares, into medium Earth orbits (MEO) at 10,000 Ianusingbent pipeanalog transponders The satel-lites would be divided between two orbital planes, inclined 45° relative to the Earth's equator, orbiting once every 6 hours Some innovations are planned; the solar wings carry gallium arsenide rather than sili-con solar cells and the propulsion system is hydra-zine-based Thennal control is achieved in part with

a sun nadir steering system, which orients the panels toward the sun, and the radiating surfaces away from the sun C- and S-band capabilities will support 4500 simultaneous phone conversations

Six ICONET satellites were scheduled to come online

Fiber Optics Illustrated Dictionary

in the initial stages to interface with 12 Earth stations

Start of service was scheduled for the year 2000 but

has been adjusted to 2003 for the New ICO voice and

packet-data services New ICO is a McCaw-led

ac-quisition that has resulted in an updated version of

the ICO Global Communications project with some

modifications to the satellites in production and the

inclusion of third-generation (3G) wireless services

in the new plans

New Wireline Access Technologies NWAT AFocus

Group subteam of the Network Reliability Council

established to examine reliability in key services

de-ployed over the Public Switched Network (PSN)

NWAT endeavored to identify, define, and clarify

potential selVice reliability issues associated with new

wireline technologies and to provide

recommenda-tions and potential solurecommenda-tions The project ran from

August to December 1995 Of particular concern

were Hybrid Fiber/Coax (HFC) and

Fiber-to-the-Curb (FTTC) access networks, which were evaluated

against Digital Loop Carrier (DLC) and cable

televi-sion (CATV) as benchmarks Participants came from

many key fmns in the industry, including Bellcore,

Cable Labs, Motorola, NYNEX,u.s. West, Time

Warner, and others

New York and Mississippi Valley Printing

Tele-graph Company An early American

communica-tions business organized by Hiram Sibley in 1851

which, as it expanded westward, came to be called

Western Union, a name suggested by Sibley's

asso-ciate, Ezra Cornell Western Union subsequently

in-stalled the first transcontinental line in 1861

newbie A telecommunications greenhorn; a new or

inexperienced user There's nothing wrong with

be-ing a newbie, but new users must read the

introduc-tory information, charters, and FAQs (Frequently

Asked Questions) associated with the activity they

wish to pursue It's OK to ask questions on the Net,

but the first question should always be "Where can I

read the FAQ for this channellnewsgroup/discussion

list?" Reading the FAQ will conserve bandwidth, save

time, and can spare an individual a great deal

ofper-sonal or professional embarrassment See Netiquette

news, Web access There are a number of ways in

which programmers have implemented access to

in-ternet newsgroups through Web interfaces

Tradition-ally, news has been read through Unix command line

text interfaces, and many still read the various

news-groups this way There are also dedicated newsreaders

which run on individuals' machines

When a browser is designed to support the display of

newsfeeds, newsgroup articles can be accessed

through the Web with two types ofUnifonn Resource

Locators (URLs) as follows:

news:<newsgroup-name>

e.g., news:comp.sys.1inux

news:<message-id>

News URLs are location-dependent See NNTP, RFC

1036, RFC 1738

newsgroup Aprivate or public online forum, the

larg-est of which is the USENET system USENET has

more than 35,000 newsgroups, covering every

con-ceivable topic from a/t.religion to a/t.bondage Most

newsgroups function on a subscription basis; current software makes it reasonably easy to subscribe at the moment at which you would like to read the mes-sages Not everyone has access to the same USENET newsgroups; it depends partly on what topics your Internet Services Provider has downloaded for its subscribers Postings on various newsgroup forums can range from one or two messages a day to several

thousand a day A newsreader software program can help sort out the topic threads.

Ina text-based newsreader, the various newsgroups will be listed alphabetically; in graphical newsreaders, they may be hierarchically organized

in menus The following simple text-based excerpt shows the general format of newsgroup names

alt.humor alt.humor.best-of-usenet alt invest

comp.sys.mac.advocacy comp.sys.next.software comp.theory.info-retrieval humanities.philosophy.objectivism misc.business.marketing.moderated misc.entrepreneurs.moderated misc legal

misc.legal.moderated sci.astro

The above names have a hierarchical structure from general to more specific The general topics listed

above include alternate, computer, humanities,

mis-cellaneous, recreation, and science Anyone can cre-ate a newsgroup, given sufficient community support and interest Creation ofa new USENET newsgroup requires a body ofvoters to ferry a proposal through

a lengthy submission/acceptance process, which may take 4 to7 months This is necessary as a deter-rent to frivolous group creation

Some newsgroups are moderated Unfortunately, due

to inappropriate postings, open newsgroups are de-creasing in number This puts an unfair burden on moderators, who are generally volunteers, but at least

itis a way to keep a forum alive When youpost to a

moderated group, the posting is previewed for adher-ence to the topic, or content, or both Some news-group moderators reserve the right to edit actual post-ings (although this is rare) Read the charter before you post if you don't wish to have your postings al-tered If the message meets the requirements for the group,itis then posted by the moderator This pro-cess can take from a few hours to a few days, some-times even up to a week and a half

Ifyou are offended by the topic ofa group, don't read the postings Newsgroups have evolved with a very strong commitment to the tenets of free speech, and their participants vehemently guard their right to ex-press and discuss their views online in the appropri-ate forum

Netiquettehas been developed to provide guidelines

to the effective and courteous use of the USENET

system Read Netiquette and the charter for each

group before posting; then enjoy; USENET is the

to the sum total ofhuman knowledge at anyone time.

It is a living, breathing "expert system" where you

can seek answers and support on any topic, any time

of day or night See Call for Votes, Netiquette,

USENEI

newsreader A software program for accessing,

dis-playing, searching, and posting articles to public

In-ternet newsgroups, particularly USENET You need

access to the Internet to read the postings on

news-groups Newsgroups have certain customs and

tra-ditions, and you should read the newsgroup

Neti-quette before posting, as well as the Frequently Asked

Questions (FAQ) document for that particular

news-group It is also wise to read the existing postings for

several days before contributing, to understand the

format and content oftypical postings, and not to

end-lessly repeat a topic that may have been fully

dis-cussed A good newsreader program will enable you

to follow threads, conversations on a particular topic.

There are usually many discussion threads within any

given newsgroup Pine, a popular Unix-based email

program developed at the University ofWashington,

can be used as a newsreader, as can a Web browser

Google Groups now provides searchable access to a

huge historic newsgroups archive See newsgroup

newton Aunit offorce in the meter-kilogram-second

(MKS) system of physical units of a size that will

influence a body of a mass of 1 kg to accelerate 1 m

per second per second Named after Sir Isaac

New-ton

Newton, Isaac (1642-1727)AnEnglish scientist and

mathematician acknowledged as one of the greatest

contributors of basic knowledge of our universe

through his descriptions of the laws of motion and

theory of gravitation (Philosophiae Naturalis

Principia Mathematica, 1687) and the idea that

earthly and celestial events might obey the same laws

He also studied the nature of light (Optics, 1692),

described the nature ofwhite light and its component

colors, and laid much of the foundation for modem

calculus

Newton's rings Aring-shaped interference

phenom-enon that results from reflected radiant energy

asso-ciated with transparent surfaces held very close

to-gether with a fine layer ofair in between The center

of the rings is dark, with alternating dark and light

bands with subtle colors emanating outward in

con-centric rings

Robert Boyle was the first to describe and explain

the phenomenon and Robert Hooke reported in

Micrographia (1667) that he had observed the rings.

Isaac Newton made use of the phenomenon to

pol-ish lenses After carrying out experiments with

prisms, Newton presented theories on the nature of

color that were more accurate than Hooke's, which

may be why the rings are called Newton's rings and

not Hooke's rings, but perhaps they shouldn't be

called Newton's rings either, because Newton

ac-tively discounted the significance of the rings,

say-ing they were "not necessary for establishsay-ing the

Properties of Light." Thomas Young, on the other

some important mathematical explanations for the rings In 1801, Young interpreted the interference as resulting from light interaction in the air between the reflecting/refracting surfaces, strong support for the wave nature of light

You can generate the rings ifyou put a flat or convex transparent glass almost touching a convex piece of glass Now carefully move one of the pieces closer and farther away from the other to vary the thickness

of the layer of air At the point where the air between the sphere and flat surface is of the same order as the wavelength ofthe light, the colored rings will appear through the glass

Newton's rings are an interesting way to illustrate diffraction and are useful in polishing and checking lenses Sometimes the phenomenon is undesirable,

so there are various ways to reduce/eliminate the rings, including changing the distance between or ori-entation of the two proximate surfaces, using glass-less carriers for darkroom work, or using a light dust

of talcum powder on the glass lens See dIffraction, interference

NEXT See near end crosstalk

NeXT Unix-Based Workstation

The NeXT cube was promoted as the computer for the 1990s when it was released in 1988 Surprisingly, this marketing hype has held true, even though the NeXT is no longer manufactured Many corporations are adopting Unix as their standard, as educational institutions havefor years; graphical user interfaces are now ubiquitous, and Display PostScript still pro-vides one ofthe best WYSIWYG solutions on any sys-tem Many NeXTStep aspects are now in Mac OS X

NeXT computer The NeXT computer was unveiled

in early October 1988 by Steve Jobs' company NeXT, Inc It included the first commercial erasable optical drive and incorporated VLSI technology The pro-grammable digital signal processor (DSP5600 1) came built in The operating system was Unix-based, with a gorgeous graphical display interface incorpo-rating Display PostScript The fonts and graphics are all beautifully rendered in high resolution The NeXT had some inspired input from Stanford,