Fiber Optics Illustrated Dictionary - Part 69 pdf

Fiber Optics Illustrated Dictionary the application. On computer networks, for example, storage of the nonexistence ofcertain servers or machines can lead to more efficient polling or routing of processes or network services. If certain printers or fax servers are offline for maintenance, negative caching information can be used to prevent overflow- ing queues. If certain hosts are offline, routing of packets can be renegotiated through other servers. If certain elements of an image file do not exist, negative caching can be used to prevent expensive production tasks on a printing press or milling machine holding up the line. See NCACHE. negative feedback The propagation of an acoustic or electromagnetic signal in the general opposite direction of the source signal. This often results from backreflection of the outgoing signal or from the signal being circularly fed to the source through another source (e.g., a second microphone). In slower-moving 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 of gain, distortion, echoes, or other interference but it is not detrimental in all circumstances. In electronics, negative feedback in acircuit (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 glow A luminous glow which can be observed between an electron-emitting cathode and the Faraday dark space in acold-cathode discharge tube. See Faraday dark space. negative image An image in which the dark and the light values are reversed, or in which the comple- ments of the colors are displayed instead ofthe normal colors; also called an inverse image. Photo- graphic negatives contain anegative 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, anegative image may arise from reversal of the polarity of the signals. negative plate, negative terminal In a storage bat- tery, the grid and any conductive material directly attached to the negative terminal, that is, the terminal that emits electrons when the circuit is active. negative-going video In a 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 672 to right and top to bottom at a specified rate (e.g., 30 frames per second). When the electron beam is moving 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 offlicker may be noticed). A horizontal drive (H drive) triggers a low-voltage negative-going pulse at the beginning of the horizontal 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 (leading) 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 ofa 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 ofsignals 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. Agrab pulse can be a positive-going or negative-going 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 ofTechnology'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. neighbors Anetworking term used to describe nodes attached to the same link. See node. nematic liquid crystal NLC. Nematics are rod-like organic molecules and nematic liquid crystals are mesomorphic (between liquid and solid) structures that show clumps ofthread-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 materials with room-temperature nematic phases with useful birefringent and dielectric properties. Nematic © 2003 by CRC Press LLC liquid crystals are anisotropic crystalline materials that exhibit some properties of solids, such as general orientation of molecules, and some properties of liquids, such has not having a specific positional order to the molecules, under 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, circularly polarized light entering the material will travel at different speeds, depending upon the direction of the po- larization and the wavelength, in relation to the orientation of the chiral NLC. Linearly polarized light will similarly be affected, causing the angle of po- larization of the two beams ofrefracted 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 ofliquid 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) An inert gas with many in- dustrial and commercial applications. When ionized, neon glows red. It was 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 lamp A long glass illuminating tube with an electrode at each end and low-pressure neon gas inside, 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 of lights. Neon has also been used in older tubes in the broadcasting indus- tries, in simple oscillating circuits, and in commercial 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 in physics 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 logarithms. The neper is not a Systeme Intemationale (SI) unit, but it is widely used and thus 1 Np has been assigned an SI equivalent value of 1. In terms of deci- bels, 1 Np = 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 mathematician, now more commonly known as John Napier, who did pioneer work in logarithms and published Mirifici logarithmorum canonis descriptio in 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 document in 1617 describing a means ofsimplify- 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 discoveries were important fundamentals for many future discoveries in mathematics, physics, and as- tronomy. nephelometer An instrument for measuring or esti- mating li~ht-scattering coefficients in fine particulate "clouds.' Nephelometers are used to assess the properties ofaerosols, dust, allergens, microbes, liquid suspensions, and other small groupings of fine particles by measuring light attenuation by scattering and absorption over distance. Nephelometers incorporate many optical components, including a light trap to provide a dark reference 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. nephelometry The science of light scattering or, stated another way, the study of"cloudiness" or of microscopic particles or surfaces that influence the passage and direction oftravel oflight. Nephelom- etry is useful in the study ofweather, atmospheric pollution, drug solubility, immunology, allergens, electromagnetic wave propagation, dust, and microbes. 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. N ernst effect A 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 effect is named after Walther Nernst (1864-1941) who described the third law of thermodynamics (the Nemst heat theorem) in 1905. Nernst lamp A continuous source of near-infrared radiation developed byW. Nemst in the 1890s. It is useful in fields such as spectroscopy. NESC See National Electrical Safety Code. NESDIS National Environmental Satellite, Data and Information Service. Net Citizen, Net Denizen See Netizen. Net Police A generic term for the various individuals who moderate communications on the net for ap- propriateness, tact, good taste, honesty, and fair use. Although some resent the activities of the 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 673 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary to prevent government regulation of the Internet's open communications forums. See Netiquette. NETIROM A packet radio communications protocol which has largely superseded AX.25. It provides support for a wider variety of types ofpackets with automatic routing. See AX.25. NetBIOS Frames Control Protocol NBFCP. 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. It is not suitable for interconnecting LANs. NBFCP defines a method for encapsulat- ing multi protocol datagrams, a link control protocol (LCP) for establishing and configuring the data link connection, and a family of network control protocols (NCPs) for establishing and configuring different 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 maximum 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 transferred as a sequence of packets. Enhanced Trivial File Transfer Protocol (ETFTP) is an implementation of NETBLT. See RFC 998. Netcast Broadcasting through the Internet, for example, through streaming video. See Webcast. Netiquette Newsgroup etiquette, Network etiquette. An important, well-respected voluntary code of eth- ics and etiquette on the Internet. Many people have contributed to Netiquette, but it was mainly developed by Rachel Kadel at the Harvard Computer So- ciety, and subsequently maintained by Cindy Alvarez. The whole point of having Netiquette is so that network 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 protected. 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 of the 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 under their real names in the mid-1980s. Unfortunately, this system is now abused by bad language, inappropriate 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 674 use assumed names. Ifmembers of the Internet community realize that it is completely possible to voluntarily 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 encourage 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 Netizen Net citizen or Net denizen. A responsible 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 vision of an open, freely accessible, self-governed communications 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 of the Net and respects online Netiquette. One could also more broadly say that anyone 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. netmask A 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. NetRanger An intrusion detection utility from Cisco Systems now known as the Cisco Secure Intrusion Detection System. Aservice pack was issued to support 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 Communications Originally Mosaic communications, Netscape Communications was the original developer and distributor of Nets cape 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 industry. See Andreessen, Mark. Netscape Navigator The 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. © 2003 by CRC Press LLC network An interconnected or inter-related system, fabric, or structure. Alogical, 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 of directors, actors, production 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. Acellular communications network is one in which a cooperative 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 storage NAS. In general terms, a dedicated file storage device or system of associated devices on a network server. The NAS is intended to take the storage burden off the processing server so that a greater amount of storage and more specialized storage-related resources can be concentrated 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 of the 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 network (SAN), which is a broader concept, and may be designated as SANINAS. See NASD Project, Na- tional Storage Industry Consortium, storage area network. network, broadcast n. A commercial or amateur radio 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, computer n. 1. A system comprising nodes and their associated interconnected paths. 2. A system of interconnected communications lines, chan- nels, or circuits. A small-scale computer network typically 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, configurations, and administrative steps that control the data transmissions to a server, switching/routing component, network, workstation, or peripheral device. Password accounts, dedicated workstations and peripherals, gateways, firewalls, and employee passcards are examples ofNAC components and procedures. NAC policies and systems are ofparticular interest at institutions where sensitive information or expensive services must be handled efficiently or protected from tampering or misuse. NAC is important in business and educational local area networks and particularly 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. NetworkAccess Point NAP. A major backbone point which provides service to ISPs and is designated to exchange data with other NAPs. NAP was a development 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. networkaddressAn identifier for a physical or logical 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 protocols changed. Network addresses are typically associated with nodes and stations. See address resolution, domain name, Media Access Control. network administrator I. The human in charge of the installation, configuration, customization, security, and lower level operating functions of a computer network. On larger networks, these tasks may be divided among a number ofprofessionals. See SysOp. 2. A software program that handles details of the job ofa human network administrator. Activities automated with network administration software include monitoring, archiving, and system checks. See daemon, dragon. Network Applications Consortium NAC. A trade organization seeking to support and promote generally accepted standards rather than a large number of fragmented proprietary standards for network applications in order to promote interoperability. http://www.netapps.org/ NetworkControl Protocols NCP. 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 associated network-layer protocols. See Point-to-Point Protocol, RFC 1661. 675 ~:'.' •• " .••. ~ •.• : ••. ' •• X • l .::/ , © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary network drive A drive accessible to multiple users on a computer network. On some network systems, users have to specify and access aparticular drive to take advantage of the 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 Specification NDIS. 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 network adapter card software drivers. The transport protocols are thus hardware-independent. network element NE This is defmed in the Telecom- munications Act of 1996, and published by the F ed- eral Communications Commission (FCC), as: " a facility or equipment used in the provision ofatelecommunications service. Such term also includes features, functions, and capabilities that are provided by means ofsuch facility or equipment, including subscriber numbers, databases, signaling systems, and information sufficient for billing and collection or used in the transmission, routing, or other provision ofa telecommunications service." See Federal Communications Commission, Telecom- munications Act of 1996. network fax server A 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 associated phone line. There are fax servers that can use Internet connections (T 1, frame relay, etc.) rather than phone lines to send and receive messages. network filter A transducer designed to separate transmission waves on the basis of frequency. Network Information Service NIS. Aclient/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 interface NI. 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 ajurisdictional change (even if there 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 various aspects of this connection have been standard- ized. For example, the network interface electrical characteristics and interactions for an analog connection between a telecommunications carrier and the customer premises are described in ANSI T1.401-1993. network interface card, network interface controller NIC. A PC board that provides a means to physi- 676 cally and logically connect a computer to a network. For microcomputers, typically these cards are equipped with BNC and/or RJ-45 sockets facing the outside of the 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 physical terminator on the physical endpoints of the network (if the network isn't working, it may be because termination is missing or incorrectly installed). Separate software, not included with the computer operating system, may be required to use the specific card installed. Many workstation-level computers come with network hardware and software built in, and Macintosh users are familiar with the built-in AppleTalk hardware and software. The trend is for microcomputers to use TCP/IP networking over Ethernet. Network Integration Verification Test NIVT. Atest designed to evaluate and improve three different Front End Processors (PEPs) handling routing and transport protocols in mixed high-performance routing 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 function NIF. A function associated 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. A means or set of procedures and/or programs designed to alert the system administrator or individual users about vandalistic attacks or unauthorized access to a computer 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 access to the electronics inside a computer may be detected by video cameras, marks, fingerprints, or detection chemicals, but this type of intrusion is less prevalent than day-to-day attempts by unauthorized users to view, steal, or compromise data on asystem.) An intrusion detection system is rarely just one application or device, but rather the coordinated implementation ofa collection ofpolicies, procedures, and tools to ensure system security. In general, NIDS refers to systems that actively detect signs ofintrusion (e.g., a utility that detects 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 information are increasingly connected to the Internet, they become more accessible and vulnerable to outside intruders. Electronic commerce sites on the Web are particularly vulnerable, as there are people who search for credit card numbers, bank accounts, personal identification, and other commodities that are recorded on computer systems. Two of the more important intrusion detection mechanisms include: © 2003 by CRC Press LLC monitors Applications that display realtime or recent statistics and events. On older systems and mainframes, monitors commonly represent data as text displays ar- ranged in columns. On some of the newer systems, graphical tables and graphs are also available. System monitors 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 monitoring and software utilities to generate an alert when anomalous patterns occur. logs Records of activities. The data generated by monitors are often kept in running logs that can be archived indefinitely or stored for a period of hours or months, depending on the need. In ad- dition to system monitors, software installation 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 always high-tech computer experts; often they are employees snooping or steal- ing data with little understanding of the electronic trail they leave when they en- gage in unauthorized access. Even if they do search for logs, with the inten- tion of changing or deleting them, they may be unsuccessful if the system is configured to duplicate log entries on another computer or a protected directory. 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 of monitors and logs. If CPU 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 patterns and variations from the norm. The most difficult type of intrusion to detect is unauthorized activity by a system administrator or pro- grammer. A small percentage of sysops take advantage of their privileged positions for personal gain. Since a high-level administrator or systems program- mer has access to almost everything on a network, it's very difficult for others to detect tampering or 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-protected file systems. These types of intrusion 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 intrusions are careful employee screening, built-in ac- countability policies and procedures, and good employee relations. For the most part, system administrators are intelligent, dedicated professionals, proud of their systems and concerned about maintaining good system security. Contrary to what might be ex- pected, the majority of intrusions are probably not by system administrators, but by curious or mischievous programmers on the one hand and professionals trying 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 configuration 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 Entry NJE. A communications protocol developed by IBM that arose out of the wide- spread use of Remote Job Entry (RJE) protocol used for the remote submission of computer processing jobs. RJE could be used in conjunction with the mainframe Job Entry Subsystem (JES) to enable RJE-enabled 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 computers or in different local partitions to intercommunicate, thus supporting peer-to-peer communications of commands andjob submissions on IBM host systems. 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 of mainframe computing functions and efficient use of computers with different capabilities. While the protocol has been around for quite a while, it is less well known than RJE. BITNET was an important historical precursor to the Internet based on the NJE protocol. See BITNET. Network Layer Packet NLP. In High Performance Routing on packet networks, a basic message unit that carries data over the path. See datagram. NetworkManagement Processor NMP. A network switch processor module used to control and monitor the switch. NetworkManagementProtocol NMP. A set of protocols developed by AT&T to control and exchange information with various network devices. 677 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary Network Management System NMS. An administrative service tool for subscriber networks that enables the system administrator to adjust performance characteristics and to set bit rates and user settings according to the levels of service available to subscribers. Network News TransferProtocol NNTP. A software 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 news group 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> F or 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 maintaining a network, which may remotely service smaller centers such as POPs. NOCs typically provide a number oftechnical support and accounting services as well. Most large networks (computer, phone, broadcast) have a core staff dedicated to the physical and logistical tasks ofkeeping 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 networks. Networks are divided into classes with the ability to serve up to a certain number of hosts. The prefix identifies the class, and hence the number of possible hosts. NetworkReliabilityandInteroperabilityCouncil NRIC. An advisory committee formed to provide rec- ommendations to the Federal Communications Com- mission (FCC) and the telecommunications industry regarding network reliability and interoperability ofpublic telecommunications networks. The original 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 SecurityInformation Exchange NSIE. A forum for identifying issues of network 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 networks. network service point NSP. Cisco Systems technology that provides native SNA network service point support. NetworkSolutions, Inc. NSI. In 1993, this company was awarded the contract for registering Internet domain names with the InterNIC by the National Science Foundation. NSI was acquired by Scientific 678 Applications International Corporation (SAIC) in 1995. See InterNIC. NetworkTerminalNumber NTN. An identification number assigned to atenninal on a public network by the public network administrator. The ITU -Trecom- mends that public voice/data and digital voice networks 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-, or ffiM RS6000-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 of the 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 of the ARPA-NSC community. We tend to think of voice carried over computer networks as a development of the late 1990s, but the idea has its roots much earlier and has been active on experimental systems since the 1970s and on some commercial systems since the mid-1980s. NVP was first implemented in December 1973, and was subsequently used for local and remote realtime voice communications over the ARPANET at some of the major research facilities in the U.S. The development of secure, low-bandwidth, two- way, high-quality, realtime, digital voice communications was a major objective of the ARPA Network Secure Communications (NSC) project. It was, at the time, ahigh-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 protocol and a data protocol. 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 topology ofbiological neurons in acentralized nervous system. A neural computer, like the human brain, con- figures itself through experientialleaming, feedback, and internal reorganization over time. Neural computers are not entirely theoretical, except in their most ideal form. There have been many efforts and suc- cesses in the design of neural 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 supercomputer, since "supercomputer" implies the state of the art in computing at anyone time, and existing © 2003 by CRC Press LLC neural computers have demonstrated extremely fast processing and problem-solving speeds. Neural net architectures tend to be highly parallel, with multiple 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 thinking, or both. Simulation of neural networks, and modeling of the complex reasoning, generalizations, and inferences characteristic of human thinking have long been of interest 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 network 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, in Electronics World, Ken Gilmore described the work on bionic computers being carried out at Wright-Patterson Air Force Base in Ohio and modeling of individual neuronal circuits 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, including electronic maze-running mice, pattern-recogniz- ing machines, self-organizing machines, and simu- lations of human vision systems. See artificial intelligence; bionics; Harmon, L.D.; Melpar model; MIND; pattern matching; perceptrons; Sceptron; Wiener, Norbert. neuroeleetrieity The very minute level electromagnetic fields generated by the activities of biological neurons. See neural network. neuron In a biological system, cells specialized to code and conduct an electromagnetic impulse are called neurons. A network of interconnecting neurons is called a nervous system, and a network ofinter- connecting neurons with a main processing center is called a central nervous system, with the main processing 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 as acost-effective controller for a wide variety of in- dustrial and residential devices, including fans, switches, motors, motion sensors, valves, and more. The Chip includes three 8-bit inline central processing 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 software 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 another. 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, originally equipped wireless station. New Haven District Telephone CompanyA historic 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. New leo Formerly ICO Global Communications (est. 1995), a London-based satellite communications service, 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 included 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 Ian using bent pipe analog transponders. The satellites 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 silicon 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 679 © 2003 by CRC Press LLC 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. A Focus 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 solutions. 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 television (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 communications 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 installed the first transcontinental line in 1861. newbie A telecommunications greenhorn; a new or inexperienced user. There's nothing wrong with being a newbie, but new users must read the introduc- tory information, charters, and F AQs (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 of personal or professional embarrassment. See Netiquette. news, Web access There are a number of ways in which programmers have implemented access to internet newsgroups through Web interfaces. Tradition- ally, news has been read through Unix command line text interfaces, and many still read the various newsgroups 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 A private or public online forum, the larg- est of which is the USENET system. USENET has 680 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 messages. Not everyone has access to the same USENET news groups; it depends partly on what topics your Internet Services Provider has downloaded for its subscribers. Postings on various news group 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. In a 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 create a newsgroup, given sufficient community support and interest. Creation ofa new USENET newsgroup requires a body of voters to ferry a proposal through a lengthy submission/acceptance process, which may take 4 to 7 months. This is necessary as a deter- rent to frivolous group creation. Some newsgroups are moderated. Unfortunately, due to inappropriate postings, open newsgroups are decreasing in number. This puts an unfair burden on moderators, who are generally volunteers, but at least it is a way to keep a forum alive. When you post to a moderated group, the posting is previewed for adher- ence to the topic, or content, or both. Some newsgroup moderators reserve the right to edit actual postings (although this is rare). Read the charter before you post if you don't wish to have your postings altered. If the message meets the requirements for the group, it is then posted by the moderator. This process can take from a few hours to a few days, sometimes even up to a week and a half. If you 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 express and discuss their views online in the appropri- ate forum. Netiquette has 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 © 2003 by CRC Press LLC closest individuals have ever come to having access to the sum total of human 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, US ENE I. 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 newsgroups. 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 newsgroup. It is also wise to read the existing postings for several days before contributing, to understand the format and content of typical 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 aparticular topic. There are usually many discussion threads within any given newsgroup. Pine, a popularUnix-based email program developed at the University of Washington, can be used as a newsreader, as can a Web browser. Google Groups now provides searchable access to a huge historic news groups archive. See news group. newton A unit offorce in the meter-kilogram-second (MKS) system ofphysical units of a size that will influence a body of a mass of1 kg to accelerate 1m per second per second. Named after Sir Isaac New- ton. Newton, Isaac (1642-1727) An English 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 oflight (Optics, 1692), described the nature of white light and its component colors, and laid much of the foundation for modem calculus. Newton's rings Aring-shaped interference phenomenon that results from reflected radiant energy associated with transparent surfaces held very close together with a fine layer of air 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 actively discounted the significance of the rings, say- ing they were "not necessary for establishing the Properties of Light." Thomas Young, on the other hand, revisited Newton's observations and made 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 if you 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 of the 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 orientation of the two proximate surfaces, using glass- less carriers for darkroom work, or using alight 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, andDisplay PostScriptstillpro- vides one of the best WYSIWYG solutions on any system. 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, Camegie- 681 © 2003 by CRC Press LLC . system, which used to be a fantastic open forum for discussion, with many scientific and cultural leaders participating under their real names in the mid-1980s. Unfortunately, this system is now abused by bad language, inappropriate 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 674 use assumed names. Ifmembers. 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 of lights. Neon has also been used in older tubes in the broadcasting indus- tries, in simple oscillating circuits, and in commercial 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 in physics and electronics, as for voltage and current relationships. The neper is similar to the decibel. Protocols (NCPs) which manage the specific needs oftheir associated network-layer protocols. See Point-to-Point Protocol, RFC 1661. 675 ~:'.' •• " .••. ~ •.• : ••. ' •• X • l .::/ , © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary network

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