N

.name - Pronounced dot name.The Internet generic Top Level Domain (gTLD) reserved exclusively for individuals.This is an unsponsored domain. See also Internet, gTLD, and unsponsored domain.

.net (network) - Pronounced dot net. Originally, the Internet generic Top Level Domain (gTLD) reserved exclusively for network access providers, such as Internet Service Providers (ISPs). The domain is now unrestricted.This is an unsponsored domain. See also Internet, gTLD, ISP, and unsponsored domain.

(NNCSS) Nortel Networks Certified Support Specialist - A wellknown industry certification/training program that is offered by Nortel Networks. This certification recognizes a fundamental level of post-sales technical expertise required to deploy, operate, and troubleshoot Nortel Networks products. This certification requires industry experience points, as well as Nortel Networks training. Information regarding Nortel Networks’ certification programs can be found at http://www.nortel networks.com.

n (nano-) - One billionth (10 ^-9 , or 1 ⁄1,000,000,000). A nanometer, or one-billionth of a meter, is the measurement of an optical wavelength.

N × 64 (Number times 64 kbps channels) - Bandwidth of N DS-0 channels of 64 kbps each. Synonymous with bonding, channel aggregation, dynamic bandwidth allocation. See bonding and DS-0.

N-AMPS (Narrowband Advanced Mobile Phone Service) - An improvement on the AMPS 1G analog cellular radio technology that tripled system capacity, by splitting each 30 kHz channel into three 10 kHz voice channels. Very few cellular providers in the United States deployed N-AMPS. See also 1G, analog, cellular radio, channel, and AMPS.

N-ISDN (Narrowband ISDN) - In the terminology of the integrated services digital network (ISDN), narrowband refers to bandwidth at the level of DS-1 or less. According to North American standards, a DS-1 translates to an ISDN primary rate interface (PRI), which runs over a T1 facility, which has a signaling rate of 1.544 Mbps.According to European standards, a DS-1 translates to ISDN primary rate access (PRA), which runs over an E-1 facility, which has a signaling rate of 2.048 Mbps. N-ISDN is in contrast to broadband ISDN (B-ISDN), which operates at a rate greater than the primary rate. See also B-ISDN, broadband, DS-1, E-1, ISDN, narrowband, PRA, PRI, signaling rate, and T1.

N-PCS (Narrowband Personal Communications Services) - See PCS.

N-Type Connector - A connector used to fit RG-8 coax. N-type connectors are used in microwave radio applications where the indoor radio unit connects to an outdoor dish unit via a coaxial cable feed. These connectors are also very popular in cellular/PCS/paging radio applications.

N - 1. In mathematics, an indefinite whole number. In telecommunications, for example, N × 64 refers to some number of 64-kbps channels. 2. The symbol for newton. See newton.

N2 - A parameter setting of mechanical cycles (usually 10 or 20) in the X.25 protocol that determines how many times a sending device (DCE device) will poll a receiving device (DTE device). The poll is sent because the far equipment is not responding. After the N2 is reached, a Set Asynchronous Balanced Mode (SABM) will be transmitted by the polling device, which will ultimately reset the entire link.

NA (Numerical Aperture) - See numerical aperture.

NA-TDMA (North American Time Division Multiple Access) - A digital cellular radio standard better known as Digital Advanced Mobile Phone Service (D-AMPS). See D-AMPS.

NADN (Nearest Active Downstream Neighbor) - In token-ring or IEEE 802.5 networks, the closest downstream network device from any given device that is still active.

nailed-up circuit - Dedicated circuits sometimes are referred to as nailed-up circuits because, in bygone days, the twisted-pair copper physical circuits were literally hung from nails driven in the walls of the carrier’s wire centers. See also dedicated circuit and wire center.

NAK - The ASCII control-code abbreviation for negative acknowledge. The binary code is 0101001 and the hex is 51.

Naked Call - An incoming call that receives no greeting message and no call menus or flexible routing before it is routed into an ACD queue.

NANC (North American Numbering Council) - An impartial body chartered in 1995 with oversight responsibility for the North American Numbering Plan (NANP). See also NANP.

nano- (n) - A metric prefix meaning one billionth (10 ^-9). See n.

nanometer (nm) - See nm.

NANP (North American Number Plan) - See Area Code.

NAP (Network Access Point) - An official Tier 1 site at which an Internet service provider (ISP) can access the Internet backbone and exchange traffic with other ISPs. Some NAPs are known as Internet Exchanges (IXs) and some as MAEs. NAP locations include San Francisco, California; Chicago, Illinois; Miami, Florida; and New Jersey. See also Internet, ISP, IX, and MAE.

Narrowband AMPS (N-AMPS) - See N-AMPS.

Narrowband ISDN (N-ISDN) - See N-ISDN.

Narrowband PCS (Narrowband Personal Communications Services or N-PCS) - See PCS.

Narrowband TACS (NTACS) - See NTACS.

Narrowband Total Access Communications System (NTACS) - See NTACS.

narrowband - 1.Voice grade bandwidth. In analog transmission systems, a narrowband channel has nominal bandwidth of 4 kHz, which is the standard for analog voice. In digital systems, a narrowband channel is 64 kbps, which is the fundamental standard for PCM digitized voice. 2. A channel or circuit of less than voice grade bandwidth. 3. Narrowband also is used to describe some number of 64 kbps channels (N × 64 kbps), but less than a T1 or E-1.T1 is a North American standard for a transmission system comprising 24 64-kbps channels and with a total signaling rate of 1.544 Mbps. E-1 is a European standard for a transmission system comprising 30 64-kbps information-bearing channels and with a total signaling rate of 2.048 Mbps. Narrowband ISDN (N-ISDN), for example, comprises two information bearing channels of 64 kbps, plus a signaling and control channel of 16 kbps, for a total of 144 kbps. 4. A circuit or channel offering relatively little bandwidth. See also bandwidth, broadband, and wideband.

narrowcast - Referring to transmission from one device to a limited number of other devices on a network. Cable television (CATV), direct broadcast satellite (DBS), and satellite radio use narrowcast transmission, as only subscribers to various channels, especially premium channels, are able to receive those transmissions. Internet content providers that operate on a subscription basis use a narrowcast model.The term is applied to Internet content providers who use push technology to send content to a subset of users on a network who have subscribed to or registered for a service.The terms narrowcast and multicast sometimes are used interchangeably. However, narrowcast refers to the business model, whereas multicast refers to the underlying transmission mode. See also broadcast, CATV, channel, DBS, Internet, multicast, push, and satellite.

NAS - 1. Network Access Server.A host computer on a local area network (LAN) dedicated to serve the needs of end users seeking access to internal computer resources or perhaps to the Internet through an Internet service provider (ISP). An NAS generally is associated with a Remote Authentication Dial-In User Service (RADIUS) server that performs authentication and accounting functions to ensure network security. See also authentication, ISP, LAN, RADIUS, RAS, and security. 2. Network-Attached Storage. A simple storage technology in which one or more disk arrays or other storage devices are associated with a server that exists as a node on a LAN.The storage server assumes the responsibility for all data storage and for making the data available to all users with access privileges. A storage area network (SAN) is a much more sophisticated approach. See also LAN, node, SAN, and server.

NAT (Network Address Translation) - A protocol that translates a private Internet Protocol (IP) address used in private domain, such as a LAN, into a public IP address that can be used in a public domain, such as the Internet.The translation process takes place in a router that interfaces to both domains, and operates on a symmetric basis, with translations taking place in both directions for the duration of a public session. NAT software allows the LAN-attached host to protect the privacy of its local identity as it accesses the Internet. NAT is specified in RFC 3022 from the Internet Engineering Task Force (IETF). See also domain, IETF, Internet, LAN, private IP address, protocol, public IP address, router, and symmetric.

National Access Fee - A Federal tax placed on telecommunications services provided by telephone companies.

National Bureau of Standards (NBS) - Now the National Institute of Standards and Technology (NIST). See NIST.

National Do-Not-Call Registry - See do-not-call registry.

National Electrical Code (NEC) - See NEC.

National Exchange Carrier Association (NECA) - See NECA.

National Information Infrastructure (NII) - See NII.

National Institute of Standards and Technology (NIST) - See NIST.

National Internet Registry (NIR) - See NIR.

National Research and Education Network (NREN) - See NREN.

National Science Foundation (NSF) - See NSF.

National Television Standards Committee (NTSC) - See NTSC.

nationalize - To transfer ownership of a commercial enterprise from private interests to the government. Also known as legalized theft of private property. See also privatize.

Native Protocol - The format of the LAN that is being transmitted over a WAN. For instance, if a LAN is Ethernet and it connects to a remote LAN via a frame-relay network, the native protocol is Ethernet, and the connection protocol is frame relay.

native - 1. Pertaining to something in its original, natural form.As examples, voice and video are analog in their native forms, whereas computer-to-computer communications are digital. 2. Referring to program code or an application written for a specific operating environment, such as an operating system (e.g., DOS or UNIX) or processor.

natural monopoly - A concept developed by political economist John Stuart Mill (1806–1873) and referring to utility services that are so capital-intensive and right-of-way intensive that it just doesn’t make sense to have more than one provider. Natural monopolies include transportation infrastructure such as roads, bridges, ferries, subways, and railroads, as well as utility infrastructure such as water, natural gas, electricity, sewer, cable television, and wireline telephone. In the United States, the Graham-Willis Act (1921) established telephone companies as natural monopolies. Cable television (CATV) and wireline telephone infrastructure used to be considered natural monopolies, but it’s not quite that simple any longer. See CATV, monopoly, right of way, Telecommunications Act of 1996, utility, and wireline.

NAUN (Nearest Active Upstream Neighbor) - In token-ring or IEEE 802.5 networks, the closest upstream network device from any given device that is operational.

NBS (National Bureau of Standards) - Now the National Institute of Standards and Technology (NIST). See NIST.

NCC (Network Control Center) - Also known as network operations center (NOC). See NOC.

NCP (Netware Core Protocol) - The heart of the Novell NetWare operating system. It is a set of programmed instructions that enables communication to occur between software programs on a workstation and a file server’s operating system. It manages the high-level aspects of communication, including: user account authorization, file retrievals, and remote printing services. Furthermore, NCP is a connection-oriented service. It acknowledges packets that have been received and requests retransmissions of lost or discarded packets.

NCSA Mosaic - See Mosaic.

NDIS (Network Driver Interface Specification) - A standard datalink layer (OSI level 2) protocol within the TCP/IP family that enables multiple protocols and multiple network (physical layer) adapters to exist on the same computer. NDIS allows all upper layer protocols to use the same Network Interface Card (NIC).

NDSF (Non Dispersion-Shifted Fiber) - The earliest type of single-mode fiber (SMF). NDSF improved considerably on multimode fiber (MMF) with respect to distance limitations. However, chromatic dispersion and material dispersion were discovered to be issues. NDSF runs in the O-Band, specifically in the 1,300–1320 nm range, where the effects of material dispersion are lowest in a standard single-mode fiber. Dispersion-shifted fiber (DSF) shifts the optimal dispersion point. See also dispersion, chromatic dispersion, DSF, material dispersion, MMF, O-Band, SMF, and window.

NDT (No Dial Tone) - An abbreviation frequently used on telephone company repair orders and by service personnel.

NE (Network Element) - A device attached to a network via hardware or software that performs a service or function to the network. A network element can be a router, a host, a workstation, a hub, a central office switch, a private branch exchange switch, a voice-mail system, a firewall/security program, or any other network-servicing entity.

near line-of-sight (near LOS) - See near-LOS.

Near-End Cross Talk (NEXT) - The uncommon phenomena of signals sent over twisted copper pairs bleeding onto each other via magnetic fields produced at cross connections, or within defective electronic equipment. The near end refers to the problem occurring between a switch and a DSLAM or other device within a central office/node. For a diagram, see Far-End Cross Talk.

near-LOS (near Line-Of-Sight) - Not LOS, but nearly so. Microwave and other high frequency terrestrial radio communications generally require LOS.WiMAX and some other microwave radio technologies can tolerate near-LOS.

near-realtime (nrt) - Referring to communications that does not occur in realtime (i.e., not at the precise moment as the event, itself) but nearly so. See nrt.

NEC (National Electrical Code) - A set of standards published by the National Fire Protection Association (NFPA) for the safe installation of electrical wiring and optical fiber and equipment on the premises.The NEC is approved by the American National Standards Institute (ANSI) as ANSI NFPA 70, and its use is commonly mandated by state and local law.The NEC is updated and published every three years. See also ANSI.

NECA (National Exchange Carrier Association) - A not-for-profit organization of U.S. incumbent local exchange carriers (ILECs), NECA administers the FCC’s access charge plan that determines the fees that interexchange carriers (IXCs) pay ILECs to complete calls. NECA also administers the Telecommunications Relay Service (TRS) fund that supports telecommunications services for individuals who are speech and/or hearing impaired. The subsidiary Universal Service Administrative Company (USAC) administers programs that provide support for ILEC companies in high-cost areas, assistance for low income subscribers, discounts for telecommunications service to schools and libraries, and discounts to rural health care providers. See also FCC, ILEC, IXC, TRS, and USAC.

negative acknowledgement (NAK) See NAK.

negative - 1. Something with the same charge (–) as an electron, opposite of the positive (+) charge of a proton. 2.The part of a circuit towards which electrons flow from the positive point. (The flow is opposite inside the current source.) See also null, positive, and potential. 3. No.

Neighboring Routers - A reference to routers that are adjacently connected within a network. In multiple-protocol networks, neighbors are dynamically discovered by the OSPF Hello protocol.

nerd - Someone, usually a techie gone over the edge, who is so overly intellectual and abstruse as to be regarded as socially inept, unsophisticated, awkward, unattractive, or otherwise exceedingly obnoxious, odd, or unpleasant.The word first appeared in Dr. Seuss’s book If I Ran the Zoo (1950) as the name of an imaginary animal. In the book, the narrator Gerald McGrew plans to collect a number of imaginary animals for his imaginary zoo. McGrew states,“And then, just to show them, I’ll sail to Ka-Troo And Bring Back an It-Kutch a Preep and a Proo A Nerkle a Nerd and a Seersucker, too!”. A good techie can be invaluable.A nerd can also be invaluable, even though obnoxious. See also geek and techie.

nest egg - 1. A real or artificial egg placed in a hen’s nest or nesting box to encourage it to continue laying eggs in the same place. 2. Money put aside as a reserve for future expenses or leaner times.

Net (Interneto) - See Internet.

net (network) - See network.

Net neutrality (InterNet neutrality) - The principle that the cost of Internet access should not be sensitive to the nature of the content. As Internet content has become increasingly stream-oriented and bandwidth-intensive, the demands on the network for bandwidth and congestion management have become more pronounced. Service providers have responded with increased bandwidth and various quality of service (QoS) mechanisms that prioritize various traffic types, such as audio, video, and voice. Net neutralists oppose price differentials associated with prioritized traffic types.Those opposed suggest that neutrality will discourage innovation and investment. See also bandwidth, congestion, Internet, QoS, and stream-oriented.

NetBIOS (Network Basic Input/Output System) - A set of instructions within the Novell NetWare protocol stack that extend a PC’s BIOS instructions to include those that enable communicating beyond its own hardware and into a network.

Netscape Communicator - A software suite that includes the Netscape Navigator Web browser, an editing program, voice conferencing, an e-mail client, and a calendaring system. See also browser, client, conference call, e-mail, Netscape Navigator, and We b.

Netscape Navigator - A Web browser featuring simultaneous image loading and continuous documentstreaming speed performance.The software was developed at Netscape Communications Corp. by a team led by Marc Andreessen, the creator of the original Mosaic browser, and was first commercially available in late 1994. Netscape Navigator subsequently was packaged in the Netscape Communicator application software suite and lost its individual identity. In 1998, Netscape began work on an open source version known as Mozilla. In 1999, Netscape was acquired by America Online (AOL), which packaged Netscape software as part of AOL service. See also browser, Mosaic, Mozilla, software, and We b.

NetWare Core Protocol (NCP) - The heart of the Novell NetWare operating system. It is a set of programmed instructions that enables communication to occur between software programs on a workstation and a file server’s operating system. It manages the high-level aspects of communication, including: user account authorization, file retrievals, and remote printing services. Furthermore, NCP is a connection-oriented service. It acknowledges packets that have been received and requests retransmissions of lost or discarded packets.

NetWare Loadable Module (NLM) - A Novell trademark. An individual program or application that can be loaded into memory and function as part of the Novell NetWare NOS (Network Operating System).

NetWare Shell - A function in the Novell Netware Protocol Stack. The NetWare Shell or “requestor shell” stays resident in a workstation or server’s memory. It decides whether or not to send data/instructions entered by the user (or application) to the network. Each time the workstation user executes a command, the NetWare Shell software program determines whether the call/instruction is for the user’s PC or for a remote server on the network.

NetWare - A trademark of Novell. Netware is a widely utilized network operating system software that was developed by Novell from the XNS (Xerox Network Systems) architecture, which was originally released in 1981. The Netware protocol suite is defined in the top five layers of the OSI, and can be made to run on virtually any data-link and physical layer system.

Network 10 address - More commonly known as a private Internet Protocol (IP) address, a Network 10 address is so called in reference to the first field in the first address range, 10.0.0.0 to 10.255.255.255. See also IP, IP address, and private IP address.

Network Access Point (NAP) - See NAP.

network access server (NAS) - See NAS.

Network Address Translation (NAT) - See NAT.

Network Architecture - The combination of software and hardware type of a network. Each network architecture can have one or more protocols within it.

network control center (NCC) - Also known as network operations center (NOC). See NOC.

Network Control Program (NCP) - See NCP.

Network Control Protocol (NCP) - See NCP.

Network Element (NE) - A device attached to a network via hardware or software that performs a service or function to the network. A network element can be a router, a host, a workstation, a hub, a central office switch, a private branch exchange switch, a voice-mail system, a firewall/security program, or any other network-servicing entity.

Network File System (NFS) - As commonly used, a distributed filesystem protocol suite developed by Sun Microsystems that allows remote file access across a network. In actuality, NFS is simply one protocol in the suite. NFS protocols include NFS, RPC, XDR, and others. These protocols are part of a larger architecture that Sun refers to as ONC. See also ONC.

Network Interface (NI) - Also called a Standard Network Interface (SNI), demarcation point, or lightning protector. The device that contains carbons to protect a phone line from being overloaded by lightning and acts as the separation point between the telephone company’s wire and the customer’s wire, which is also called the IW (Inside Wire). For a photo, see Standard Network Interface.

Network Interface Card (NIC) - An expansion board that plugs into a motherboard via an ISA or PCI expansion socket/slot. The network interface card provides the electronic and the physical interface for the network of its type. Network types include, but are not limited to, Ethernet and token ring. For a photo of a PCI Ethernet NIC, see NIC.

network interface device (NID) - Synonymous with network interface unit (NIU). See NID.

network interface unit (NIU) - Synonymous with network interface device (NID). See NID.

Network Layer - A layer in a communications protocol model. In general, the network layer does the job of switching and routing of the data being transmitted within the protocol. A central-office switch would be a good example of a network layer function. The latest model (guideline) for communications protocols is the OSI (Open Systems Interconnect). It is the best model so far because all of the layers or functions work independently of each other. For a diagram of the OSI model and its layers, see Open Systems Interconnection.

network management system (NMS) - See NMS.

network management - Referring to a broad range of functions associated with the management and control of a network, particularly one large and complex in nature. Network management functions include fault management, configuration management, accounting management, performance management, and security management. Some of those functions are real-time, whereas others are purely administrative. Real-time network management functions include the aspects of fault management, configuration management, performance management, and security management that require virtually instantaneous identification, analysis, and action to ensure the performance and integrity of the network. Accounting management is a purely administrative function that includes inventory management, data collection, cost allocation, and billing. Some aspects of configuration management and performance management are nonrealtime and administrative in nature, as well, including data collection, traffic analysis, and network optimization. Telemanagement is a subset of network management concerned with the administrative management of voice networks. Real-time network management systems (NMSs) include element management systems (EMSs) that deal with alarms and alerts from devices of the same type and manufacturer, and managers of managers (MOMs) that deal with alarms and alerts from multiple types of network elements (NEs). See also accounting management, bandwidth, configuration management, EMS, fault management, load balancing, MOM, NE, network optimization, performance management, security management, TMN, and traffic analysis.

network neutrality - Referring to Internet neutrality. See Net neutrality.

Network Node Interface (NNI) - In the ATM world, this type of connection provides 4096 virtual paths and 65,536 virtual connections within each path for a total of 268,435,456 channels between two ATM networks, switches, or users that are physically connected over a UNI (User Network Interface).

Network Operating System (NOS) - A software that manages communications of devices. An administrator sets access and security privileges to users of a network and monitors network performance via this software. In Novell networks, the NOS provides sockets at OSI level 4, which provide the link between software applications and lower network layers. Network operating systems are distributed file systems. Examples include Novell NetWare, NFS (Network File System for UNIX), Windows NT, and Banyan VINES.

network operations center (NOC) - Also known as network control center (NCC). See NOC.

network optimization - The process of striking the best possible balance between network performance and network costs, in consideration of grade of service (GoS) requirements. See also GoS.

Network Service Access Point (NSAP) - The logical, software, or virtual interface between the OSI (Open Systems Interconnect) network layer (3) and transport layer (4). This is known as a socket in Novell networks.

Network Service Provider (NSP) - A company that provides telecommunications services such as frame relay, ADSL, HDSL, ATM, Internet Access or other services via their own switching equipment, or leased switching equipment. NSP’s usually provide services by utilizing a local telco or CAP for the last mile (local loop). They also link their nodes via high capacity circuits, and have interconnection agreements with other telecommunications companies.

Network Termination (NT) - See NT.

Network Termination 1 (NT1) - See NT1.

Network Termination 2 (NT2) - See NT2.

Network Termination Equipment (NTE) - The generic term for DCE and DTE (Data Communication Equipment and Data Termination Equipment). With newer transmission methods, such as those provided in the xDSL family, DCE and DTE are replaced with near-end NTE and far-end NTE. The near end is the central office transmission interface and the far end is the xDSL router.

network topology - See topology.

Network Transit-Time Delay - The amount of time (in milliseconds) that it takes for a data packet to traverse across a network. Transit time delay is often rated based on a data packet making a round trip via a ping command. A typical round-trip transit time delay across a very robust network that stretches from Tokyo to New York is 200 ms. Transit time delay is increased by the number of routing or switching devices that a packet passes through. A concern for network designers is to have enough route redundancy to ensure that alternate routes can be taken by packets when connections fail. The disadvantage to having redundancy is that more switching and routing equipment is required, which increases transit-time delay.

network-attached storage (NAS) - See NAS.

network-to-network interface (NNI) - See NNI.

Network - A group of devices that communicate back and forth using a set of rules or a set of protocols (called a protocol stack in data communications). The medium that the devices communicate through can be copper wire (UTP), fiber optic, coax, fiber optic, air/vacuum (radio), or light (infrared).

NeuStar - A commercial enterprise that provides certain administrative and clearinghouse services. NeuStar was appointed by the Federal Communications Commission (FCC) in 1997 as the administrator of the North American Numbering Plan (NANP). NeuStar also currently administers a number of Internet domains, including .biz (bizness), .tw (Taiwan), and .us (United States). See also FCC and NANP.

Neutral - Also called common or floating ground. Neutral/common is a reference point and is ungrounded. It is usually a signal return or DC reference coupling for transmission circuits.

newb (newbie) - In reference to someone new at something such as computer usage, programming, or, most especially, the Internet.

newsgroup - A forum on the Internet for textual discussions of specific subjects.A newsgroup essentially is a discussion group that generally involves an article that serves as a stimulus for message postings that form conversational threads.

newton (N) - The unit of force that will impart an acceleration of one meter per second to a mass of one kilogram.The newton is named for Sir Isaac Newton (1642–1727), the English scientist who invented calculus, discovered gravitation, formulated the laws of motion, and discovered that white light is a combination of all colors in the visible light spectrum. (Not bad for an alchemist.)

NEXT (Near-End Cross Talk) - The uncommon phenomena of signals sent over twisted copper pairs bleeding onto each other via magnetic fields produced at cross connections, or within defective electronic equipment. The near end refers to the problem occurring between a switch and a DSLAM or other device within a central office/node. For a diagram, see Far-End Cross Talk.

Next Generation Internet (NGI) - See NGI.

Next-Hop Resolution Protocol (NHRP) - A set of instructions used by routers that enables them to automatically discover the physical-layer address of other routers and hosts connected to a NonBroadcast MultiAccess (NBMA) network. Data routed with NHRP can then directly address sections of the network. This allows users/devices to communicate without traffic having to use an intermediate hop, increasing performance in ATM, frame-relay, SMDS, and X.25 environments.

NFAS (Non-Facility Associated Signaling) - A signaling and control technique by which the signaling and control information associated with a communications channel is not carried within the communications channel, itself, or in a separate channel permanently associated with that communications channel. Rather, that signaling and control information is carried in a separate channel, perhaps over a separate subnetwork. NFAS typically refers to an ISDN technique in which signaling and control functions for multiple primary rate interface (PRI) trunks is accomplished using a common Signaling System 7 (SS7) D channel associated with one of them, thereby freeing the D channels associated with the other trunks and allowing them to be used as B channels for user payload transmission. SS7 is a Common Channel Signaling (CCS) system. Contrast with CAS (Channel-Associated Signaling). See also B channel, CCS, channel, D channel, ISDN, NFAS, PRI, signaling and control, SS7, and trunk.

NFPA 70 - National Fire Protection Association (NFPA) publication 70. Synonymous with National Electrical Code (NEC). See also NEC.

NFS (Network File System) - As commonly used, a distributed filesystem protocol suite developed by Sun Microsystems that allows remote file access across a network. In actuality, NFS is simply one protocol in the suite. NFS protocols include NFS, RPC, XDR, and others. These protocols are part of a larger architecture that Sun refers to as ONC. See also ONC.

NGI (Next Generation Interneto) - A initiative of the U.S. federal government intended to develop the technologies and applications that will form the future Internet.The NGI initiative is in parallel to the university-led Internet2. See also Internet and Internet2.

NHRP (Next Hop Resolution Protocol) - A set of instructions used by routers that enables them to automatically discover the physical-layer address of other routers and hosts connected to a NonBroadcast MultiAccess (NBMA) network. Data routed with NHRP can then directly address sections of the network. This allows users/devices to communicate without traffic having to use an intermediate hop, increasing performance in ATM, frame-relay, SMDS, and X.25 environments.

NI (Network Interface) - See Network Interface.

Nibble Coding - It takes four binary bits to make a decimal number, so two decimal numbers can be fit into one byte. X.25 uses a method referred to as nibble coding, which breaks overhead bytes into nibbles to help make it easier to understand the addressing of the packets. Back when X.25 was new (1970s), dynamic memory was very costly, so compacting addresses into nibbles was more efficient and cost effective.

Nibble - Four bits, or 1/2 of a byte.

NIC (Network Interface Card) - An expansion board that plugs into a motherboard via an ISA or PCI expansion socket/slot. The network interface card provides the electronic and the physical interface for the network of its type. Network types include, but are not limited to, Ethernet and token ring.

NID (Network Interface Device) - Also known as a network interface unit (NIU). A device that serves as the demarcation point (demarc) and interface between the public carrier network and the customer premises. An NID includes some form of protector that insulates the premises from potentially disastrous high voltage current caused by lightening strikes on outside copper cable plant. An NID also generally contains a chipset that supports remote testing of the local loop from a centralized Network Operations Center (NOC).

Nigerian Connection - See 419 Advance Fee Fraud.

Nigerian Scam - See 419 Advance Fee Fraud.

Night Service - A feature of PBX and hybrid key systems that allows the lines ringing into an office to be handled differently during certain times of the day. The phone system is programmed as two different systems, usually a day system, and a night, or after-hours system. If a user would like all calls that come into the office after hours to ring to a voice-mail system, or be forwarded to security, it can be done with the night-mode feature. Some systems are equipped with software that allows the nightmode feature to activate automatically at certain times of the day.

NII (National Information Infrastructure) - A program of the United States government to encourage the development of an advanced and seamless high-speed web of public and private communications networks, interactive services, interoperable hardware and software, databases, and other elements in support of voice, data, video, fax, and multimedia transmission, storage, processing, and display. The NII encompasses a wide range of interactive databases, functions, and services interconnected in a technologyneutral manner. See also Information Superhighway.

NIR (National Internet Registry) - The national organization responsible for assigning Internet Protocol (IP) addresses to Local Internet Registries (LIRs) that, in turn, assign them to Internet Service Providers (ISPs).The NIR receives address assignments from a Regional Internet Registry (RIR). In some nations, there is no NIR, so an RIR assigns IP addresses directly to the LIRs. See also IANA, IP, IP address, ISP, LIR, and RIR.

NIST (National Institute of Standards and Technology) - nee National Bureau of Standards (NBS). An agency of the United States Department of Commerce, NIST has the stated mission of promoting U.S. innovation and industrial competitiveness by advancing measurement science, standards, and technology in ways that enhance economic security and promote the quality of life.As an example, NIST developed the Advanced Encryption Standard (AES), a highly secure encryption algorithm used the United States government for sensitive unclassified documents.AES also is used in a number of commercial applications. See Appendix A for contact information. See also AES.

NIU (Network Interface Unit) - Synonymous with network interface device (NID). See NID.

NLM (Netware Loadable Module) - A Novell trademark. An individual program or application that can be loaded into memory and function as part of the Novell NetWare NOS (Network Operating System).

NLOS (Non-Line-Of-Sight) - A radio transmission system that can support effective communications without optical LOS.The higher the frequency of the signal, the more important is LOS. Cellular telephones and pagers, for example, operate in MHz (e.g., 800 and 900 MHz ranges) and the lower end of the GHz ranges (e.g., 1.8 and 1.9 GHz), and operate quite effectively in NLOS mode. Higher frequency signals, such as microwaves, generally require LOS, yet WiMAX, for example, is a wireless local loop technology operating in the 2-11 GHz range in both LOS and non-LOS (NLOS) modes. See also LOS and near-LOS.

nm (nanometer) - One billionth (10 ^-9 , or 1 ⁄1,000,000,000) of a meter. The wavelength of an optical signal is measured in nanometers.The wavelength of a typical optical signal in a long haul fiber optic transmission system (FOTS) is in the 1550 nm window, for example. Just to put it in perspective, an average molecule is about a nanometer in diameter, a human DNA molecule is about 2.5 nm wide, and a human hair is in the range of 5,000–10,000 nm in diameter.A human fingernail grows about 1 nm per second. If you watch your fingernails grow for about 25 minutes and 50 seconds, you’ll have a sense for how long a wavelength is at 1550 nm. Note: It is much more exciting to watch grass grow, or even paint dry.

NMC (Network Management Center) - A place where large or public telephone networks are managed, monitored, and maintained from a central location.

NMS (Network Management System) - A system comprising software, firmware, and hardware used to manage a large and complex network. An NMS, also known as a manager of managers (MOM), may receive alarms and alerts from multiple element management systems (EMSs), each of which manages one or more specific intelligent network elements (NEs), i.e., devices of the same type (e.g., modems or multiplexers) and generally of the same manufacturer. See also EMS, firmware, hardware,MOM, NE, network management, and software.

NMT (Nordic Mobile Telephone) - A 1G analog cellular radio technology developed and placed into service in the early 1980s in Scandinavian countries, including Denmark, Finland, Norway, and Sweden. NMT 450 operates in the 450 MHz band, which yields excellent signal propagation and, therefore, is especially appropriate for sparsely populated areas supported by few cell sites. NMT 900 operates in the 900 MHz range. NMT largely has been replaced by GSM. See also 1G, analog, cellular radio, propagation, GSM, NMT 450, and NMT 900.

'NMT 450 (Nordic Mobile Telephone 450 MHz) - A 1G analog cellular radio technology developed and placed into service in the early 1980s in Scandinavian countries. NMT 450 operates in the 450 MHz band, employing frequency division multiple access (FDMA) to derive 200 channels with a width of 25 kHz. NMT 450 employs frequency division duplex (FDD) to achieve bidirectional communications, with the downlink in the 463–468 MHz band and the uplink in the 453–458 MHz band.Within each channel, frequency modulation (FM) is employed. See also 1G, analog, cellular radio, channel, downlink, FDD, FDMA, FM, and uplink.

NMT 900 (Nordic Mobile Telephone 900 MHz) - A 1G analog cellular radio technology developed and placed into service in the early 1980s in Scandinavian countries. NMT 900 operates in the 900 MHz band, employing frequency division multiple access (FDMA) to derive 1999 channels with a width of 12.5 kHz. NMT 900 employs frequency division duplex (FDD) to achieve bidirectional communications, with the downlink in the 935-960 MHz band and the uplink in the 890-915 MHz band. Within each channel, frequency modulation (FM) is employed. See also 1G, analog, cellular radio, channel, downlink, FDD, FDMA, FM, and uplink.

NN (Network Neutrality) - Referring to Internet neutrality. See Net neutrality.

NNCDE (Nortel Networks Certified Design Expert) - A well-known industry certification/training program that is offered by Nortel Networks. This certification recognizes an advanced level of network design, planning, and optimization using Nortel Networks products. It requires industry experience as well as Nortel training. Information regarding Nortel Networks’ certification programs can be found at http://www.nortelnetworks.com.

NNCNA (Nortel Networks Certified Network Architect) - A wellknown industry certification/training program that is offered by Nortel Networks. This advanced certification not only requires learned technical knowledge, but also industry experience. Students seeking this certification are required to obtain a required number of points in certification-related areas. A specific number of points are obtained through job experience and a number are obtained by taking Nortel Networks courses. Information regarding Nortel Networks’ certification programs can be found at http://www.nortelnetworks.com.

NNCSE (Nortel Networks Certified Support Expert) - A well-known industry certification/training program that is offered by Nortel Networks. This certification recognizes an advanced level of technical post sales expertise required to implement, support, troubleshoot, and optimize Nortel Networks products. This certification requires industry experience points as well as Nortel Networks training. Information regarding Nortel Networks’ certification programs can be found at http://www.nortelnetworks.com.

NNI (Network Node Interface) - In the ATM world, this type of a connection provides 4096 virtual paths and 65,536 virtual connections within each path for a total of 268,435,456 channels between two ATM networks, switches or users that are physically connected over a UNI (User Network Interface).

NNI (Network-to-Network Interface) - The boundary or point of interaction between network service providers.The NNI is both a physical and logical point of demarcation.The NNI serves the technical boundary where protocol issues are resolved and as the point of division between the responsibilities of the individual service providers. NNIs are defined for asynchronous transfer mode (ATM) and frame relay, as examples. See also ATM, logical, frame relay, physical, and protocol.

NOC (Network Operations Center) - A place where large or public telephone networks are managed, monitored, and maintained.

NOD (Network Outward Dialing) - See Network Outward Dialing.

Node - 1. In local-area networking, any entity or device attached to a network that possesses a MAC (Media-Access Control) address. 2. In widearea networking, a node is a router or switch that serves as a control point in a network, and those control points (routers/switches) incorporate a routing protocol to communicate network information and to route traffic through the network. 3. In voice networking, a node is a device that has switching capability, or a central office. 4. In general, it is common for a node to be used as a reference for any device that is connected to a communications network via a copper wire, fiber-optic, radio link, or infrared light. These devices include routers, bridges, terminals, computers, hubs, controllers, and switches.

Noise Canceling - Noise canceling is accomplished by filtering a sample of the noise from a preamp stage of a circuit, then inverting the signal 180 degrees and adding the inverted noise signal to the original signal containing the noise. The noise combined with the inverted sample of the noise cancel each other out (electronically add to 0 V). When the original noise signal goes positive in its cycle the noise sample goes negative and the resultant output is 0 V. A good application of noise canceling is in the radio headsets that aircraft pilots use. The cockpit noise is sampled and fed into the radio system, inverted, re-fed into the amplification system, and the surrounding noise is canceled out.

Noise - Noise is any kind of distortion or unwanted signal. The two main categories of noise are electromagnetic interference and ambient noise. Electromagnetic Interference is caused by a radio signal or other magnetic field inducing itself onto a medium (twisted-/nontwisted-pair wire) or device (telephone or other electronics). The world we live in is full of radio waves that are emitted from electric appliances, such as blenders, automobile engines, transmitters, and even fluorescent lights. Even though we take preventative measures to avoid receiving these unwanted signals, they sometimes find their way into places that they are not wanted. Electromagnetic Interference is usually caused by one of two things. The first is when a wire connected to a device acts like an antenna and receives the EMI, which is then passed on to the electronics inside the device and amplified. The second is when an electronic component inside a device acts like an antenna because of poor design, poor shielding, or because the component is defective. Ambient noise is noise caused by the random movement of electrons in an electronic circuit when the power is off or by the random movement of air.

nominal - In name only, but not in reality.A T1 circuit sometimes is described as having a nominal transmission rate of 1.5 Mbps, although in reality the signaling rate is 1.544 Mbps and its payload is 1.536 Mbps. It is easier to say one point five Megabits per second or one and a half Megabits per second than one point five four four Megabits per second. It is not exact, but it is close enough for all but the most obnoxious purists. Similarly, an E-1 is generally described as having a transmission rate of 2 Mbps, although in reality the signaling rate is 2.048 Mbps and the payload is 1.92 Mbps. See also payload, signaling rate, and transmission rate.

non dispersion-shifted fiber (NDSF) - See NDSF.

non real-time variable bit rate (nrt-VBR) - See nrt-VBR.

non-blocking - A switch that provides a guaranteed talk path for every terminal; in other words, there exists a 1:1 (one-to-one) relationship between ports and time slots. Such a configuration is expensive, generally considered excessive and, therefore, unusual in all but the most intense applications scenarios, such as call center ACDs and backbone data switches. See also ACD, backbone, blocking, and call center.

non-deterministic - 1. Non-predictive. Referring to the inability to objectively predict an outcome or result of a process due to lack of knowledge of a cause and effect relationship or the inability to know initial conditions. 2. In telecommunications switching and routing, the unpredictability of a path between nodes. See also node, path, route, and switch. 3. In local area networks (LANs) a contentious medium access control (MAC) technique that does not allow a node to predict when it will be allowed to gain access to the network. Carrier sense multiple access (CSMA), which is used in 802.3 Ethernets, is non-deterministic. See also 802.3, CSMA, deterministic, LAN, MAC, and node.

non-dialable toll points - A location that a caller cannot dial directly, but must call with operator assistance. Such locations are very remote and may be beyond the reach of cable systems and may be too low and sheltered to be reached via satellite, but can be reached via special radio circuits. In the United States, there remain a large number of non-dialable toll points, generally in deep valleys and canyons.

non-facility associated signaling (NFAS) - See NFAS.

non-line-of-sight (NLOS) - See NLOS.

non-real-time (nrt) - See nrt.

non-repudiation - Referring to a mechanism that proves that the originating node sent a message and that the receiving node received it.Therefore, the sender cannot deny sending the message and the receiver cannot deny having received it. Non-repudiation can be effected through digital signatures, confirmation receipts, and timestamps. See also digital signature.

non-return-to-zero (NRZ) - See NRZ.

non-wireline carrier - Also known as an A Carrier.A provider of cellular radio service that is not a traditional landline telecommunications services.The distinction between wireline and non-wireline carriers was made primarily for purposes of segregating bidders for radio spectrum assignment during the FCC cellular spectrum auctions.The initial approach toward spectrum assignment was designed to ensure that there was one wireline (i.e., telephone company) and one non-wireline carrier per market. See also carrier, cellular, FCC, landline, radio, spectrum, and wireline carrier.

nonpersistent carrier sense multiple access (Nonpersistent CSMA) - See CSMA.

Nonpersistent CSMA (Nonpersistent Carrier Sense Multiple Access) - See CSMA.

NonReturn To Zero Inverted (NRZI) - Signals that maintain constant voltage levels with no signal transitions (no return to a zero-voltage level), but interpret the presence of data at the beginning of a bit interval as a signal transition and the absence of data as no transition. See also NRZ.

Nordic Mobile Telephone (NMT) - See NMT.

normal - 1. Conforming to an accepted, usual, or typical form, model, or pattern. 2. In geometry and mathematics, the transverse or perpendicular, i.e., a right angle, which is 90 degrees from a plane or surface. Frankly, this seems decidedly abnormal to me, as I have known a lot of people who seemed to be at right angles compared to normalcy. See also counterintuitive, critical angle, out-of-phase, and total internal reflection.

Nortel Networks Certified Design Expert (NNCDE) - A well-known industry certification/training program that is offered by Nortel Networks. This certification recognizes an advanced level of network design, planning, and optimization using Nortel Networks products. It requires industry experience as well as Nortel training. Information regarding Nortel Networks’ certification programs can be found at http://www.nortelnetworks.com.

Nortel Networks Certified Network Architect (NNCNA) - A wellknown industry certification/training program that is offered by Nortel Networks. This advanced certification not only requires learned technical knowledge, but also industry experience. Students seeking this certification are required to obtain a required number of points in certification-related areas. A specific number of points are obtained through job experience and a number are obtained by taking Nortel Networks courses. Information regarding Nortel Networks’ certification programs can be found at http://www.nortelnetworks.com.

Nortel Networks Certified Support Expert (NNCSE) - A well-known industry certification/training program that is offered by Nortel Networks. This certification recognizes an advanced level of technical post sales expertise required to implement, support, troubleshoot, and optimize Nortel Networks products. This certification requires industry experience points as well as Nortel Networks training. Information regarding Nortel Networks’ certification programs can be found at http://www.nortelnetworks.com.

Nortel Networks Certified Support Specialist (NNCSS) - A wellknown industry certification/training program that is offered by Nortel Networks. This certification recognizes a fundamental level of post-sales technical expertise required to deploy, operate, and troubleshoot Nortel Networks products. This certification requires industry experience points, as well as Nortel Networks training. Information regarding Nortel Networks’ certification programs can be found at http://www.nortel networks.com.

North American Area Codes - See Area Codes.

North American Numbering Council (NANC) - See NANC

North American Numbering Plan - See Area Codes.

North American Time Division Multiple Access (NA-TDMA) - A digital cellular radio standard better known as Digital Advanced Mobile Phone Service (D-AMPS). See D-AMPS.

NOS (Network Operating System) - A software that manages communications of devices. An administrator sets access and security privileges to users of a network, and monitors network performance via this software. In Novell Networks, the NOS provides sockets at OSI level 4, which provide the link between software applications and lower network layers. Network operating systems are distributed file systems. Examples include Novell NetWare, NFS (Network File System for UNIX), Windows NT, and Banyan VINES.

notation - The use of signs or symbols to represent numbers, words, phrases, or even complete concepts in fields such as language, mathematics, chemistry, and music. See also binary notation and hexadecimal notation.

Notch Filter - A filter that is designed to pass or block a specific band of frequencies. The three types of filters are low pass/block, high pass/block, and notch pass block. What determines if the filter is a pass or block filter is how the filter is arranged. If the filter is set in series with a circuit, then it passes the desired frequencies down the line. If it is connected to ground, it will pass the desired frequencies to ground, thus preventing them from continuing through the circuit to block them.

NPA (Number Plan Area) - Also called an Area Code. Each area code contains central offices and each central office has a set of prefixes (first three digits of a seven-digit number) that identify that central office to all other central offices within the associated area code. Some people actually sit around and plan what numbers will belong to which central office.

NPAC (Number Portability Administration Center) - In the United States, the Federal Communications Commission (FCC) established the NPAC to supervise and perform clearinghouse functions in support of local number portability (LNP) and local routing numbers (LRNs). See also LNP and LRN.

NREN (National Research and Education Network) - The first (1990) asynchronous transfer mode (ATM) network in the United States, NREN was a test-bed gigabit network sponsored by the Advanced Research Project Agency (ARPA) and the National Science Foundation (NSF). Previously (1987), a consortium of European carriers, end users, and universities sponsored a similar project known as the Research for Advanced Communications in Europe (RACE) project 1022 (1987). See also RACE.

nrt-VBR (non real-time Variable Bit Rate) - In asynchronous transfer mode (ATM), a class of traffic that is bursty, with periods of intense activity and periods of low or no activity, and of a non real-time nature that is not dependent on loss or delay because there is time to recover through retransmission.Traffic parameters include peak cell rate (PCR), cell delay variation tolerance (CDVT), sustainable cell rate (SCR), maximum burst size (MBS), and burst tolerance (BT).The quality of service (QoS) parameter is cell loss ratio (CLR). ATM also defines available bit rate (ABR), constant bit rate (CBR), real-time Variable Bit Rate (rt-VBR), unspecified bit rate (UBR), and variable bit rate (VBR) traffic classes. Examples of nrt-VBR traffic include data traffic such as X.25, frame relay, transaction processing, LAN-to-LAN, and non real-time buffered voice and video traffic. See also ABR, ATM, BT, CBR, CDVT, CLR, compression, frame relay, LAN, MBS, PCR, QoS, realtime, rt-VBR, SCR, time slot, UBR, and VBR, and X.25.

nrt - 1. near-realtime. Referring to a quality of service (QoS) level designed for applications that do not require transmission to take place in real time, but nearly so.That is to say the transmission must take place within a reasonably short time from the exact moment as the event itself takes place in the real world. Near-realtime QoS is essential in many applications directly involving humans and their perception of time.Transaction processing, for example, must take place in near-realtime to avoid customer dissatisfaction. See also QoS and realtime. 2. non-realtime. Referring to a quality of service (QoS) level designed for applications that do not require transmission to take place in real time, that is to say that the transmission need not take place at the exact moment and in the exact sequence as the event itself takes place in the real world. Internet access, for example, need not be available instantly on demand. e-mail need not be sent across a network to be received instantly, but can tolerate a considerable level of error, latency, loss of sequence, loss of data, and retransmission. See also latency, QoS, and realtime.

NRZ (NonReturn to Zero) - 1. In a physical medium, signals that maintain constant voltage levels with no signal transitions (no return to a zerovoltage level) during a bit interval. See also NRZI. 2. A binary encoding method used to write information to hard-disk drives in computers.

NRZI (NonReturn to Zero Inverted) - 1. In a physical medium, signals that maintain constant voltage levels with no signal transitions (no return to a zero-voltage level), but interpret the presence of data at the beginning of a bit interval as a signal transition and the absence of data as no transition. See also NRZ. 2. A binary encoding scheme used to write information to hard-disk drives in computers.

NSAP (Network Service Access Point) - The logical, software, or virtual interface between the OSI (Open Systems Interconnect) network layer (3) and transport layer (4). This is known as a socket in Novell networks.

NSF (National Science Foundation) - An independent agency of the United States government formed in 1950 “to promote the progress of science; to advance the national health, prosperity, and welfare; to secure the national defense, according to the NSF…” The mission of the NSF includes support for all fields of fundamental science and engineering. In telecommunications, the NSF has taken the initiative projects such as the development of the very-high-speed Backbone Network Service (vBNS), which formed the initial backbone infrastructure for Internet2. See also Internet2 and vBNS.

NSP (Network Service Provider) - A company that provides telecommunications services such as frame relay, ADSL, HDSL, ATM, Internet Access or other services via their own switching equipment, or leased switching equipment. NSP’s usually provide services by utilizing a local telco or CAP for the last mile (local loop). They also link their nodes via high capacity circuits, and have interconnection agreements with other telecommunications companies.

NT (Network Termination) - In ISDN networks, a set of functions accomplished through the use of programmed logic variously embedded in the carrier network and the customer premises equipment (CPE). NT devices operate to interface the four-wire customer wiring to the physical two-wire UTP local loop, performing functions similar to those provided by digital service units (DSUs) and channel service units (CSUs) in non-ISDN digital networks. See also CPE, CSU, DSU, four-wire circuit, ISDN, NT1, NT2, and two-wire circuit.

NT1 (Network Terminal 1) - Another reference for an ISDN terminal adapter.

NT2 (Network Termination 2) - An interface to an intelligent ISDN-compatible device (e.g., PBX or router) responsible for the user side of the connection to the network, performing such functions as multiplexing and switching. Such functions correspond to Layer 2 (Data Link Layer) of the OSI Reference Model. An NT2 commonly is actually an NT1/2 device, performing the combined functions, and operating at Layers 1, 2, and 3 of the OSI Reference Model. See also ISDN,NT,NT1, and OSI Reference Model.

NTACS (Narrowband Total Access Communications System) - A narrowband version of the TACS 1G analog cellular radio technology developed for use in the United Kingdom. NTACS operates in the 900 MHz band, employs frequency modulation (FM), and supports 400 channels of 12.5 kHz. As an analog system,TACS derives channels using frequency division multiple access (FDMA) and bidirectional communications is achieved through frequency division duplex (FDD) with the downlink in the 860–870 MHz band and the uplink in the 915–925 MHz band. See also 1G, analog, cellular radio, downlink, ETACS, FDD, FDMA, FM, narrowband, TACS, and uplink.

NTE (Network Termination Equipment) - The generic term for DCE and DTE (Data Communication Equipment and Data Termination Equipment). With newer transmission methods, such as those provided in the xDSL family, DCE and DTE are replaced with near-end NTE and far-end NTE. The near end is the central office transmission interface and the far end is the xDSL router.

NTSC (National Television Standards Committee) - The initial standard (1953) for broadcast television, NTSC was named for the committee that established it in the United States. NTSC is characterized as analog in nature, with 525 interlaced scan lines. There are 640 pixels per line, 485 of which are dedicated to the active picture.The frame rate is 30 fps, 60 fields interlaced, and the aspect ratio is 4:3.As an early analog standard that is viewed by some as overly complex and ineffective in a contemporary digital context, NTSC sometimes is referred to by its detractors in the pejorative as Never The Same Color. NTSC is defined in ITU-R Recommendation 1125 and served as the baseline for subsequent standards, Phase Alternate Line (PAL) and SECAM (SÉquential Couleur Avec Mémoire). See also analog, aspect ratio, broadcast television, frame, frame rate, interlaced scanning, ITU-R, PAL, pixel, and SECAM.

NUL - The ASCII control-code abbreviation for null. The binary code is 0000000 and the hex is 00.

Null Modem - A communications cable, such as an RS-232 cable, that has the transmit and receive wires switch places in pin-out from one end to the other. These cables are used to connect DCE (Data Communications Equipment) with DTE (Data Termination Equipment), so the transmit of one reaches the receive of the other.

Null-Modem Adapter - An adapter that is used to convert a straightthrough cable into a null-modem cable. Null-modem adapters are available in many different pin-outs and connector types.

null - 1. Valueless; amounting to nothing; zero. 2. In some computer programs, a field into which nothing is entered, not even a zero (0). In such programs, even a 0 can affect calculations. See also negative and positive.

Number Crunching - A reference to data processing or data manipulation done by a PC, server, or mainframe.

Number Portability Administration Center (NPAC) - See NPAC.

Number Portability - Number portability is still in the legal, financial, and architectural planning process. When it is completed (different places will be implemented at different times, the goal for starting was 1998), there will be a national data base that stores every phone number subscribed to by every user. The ultimate goal is to automate the ability of a customer to switch telephone companies and take their phone number to whichever exchange area (within an area code) they wish. If a customer decides to switch companies, their number must first be disconnected by the old company, then reconnected/reactivated by the new. If both numbers are active at the same time, the telephone network will become confused and most likely not complete calls. With the planning and implementation of CTI (Computer Telephone Integration), it will be possible for a company to enter into a data base (operated by a third party company), the order to disconnect, and when another company enters the connect, a computer will make the actual switch with no outage of service. This will eliminate the possibility of one telephone company interfering with a customer’s change-over by failing to disconnect service at the proper time. Competition in the telecommunications industry is hampered by the fact that no customer can switch local telephone companies and take their phone number with them (1-800/888 long-distance service is a different story. Customers can transfer those numbers.). The cost to re-advertise phone numbers for business is too costly and too inconvenient for the patrons of businesses. The estimated cost to implement number portability is 100 million dollars per LATA (area code). The legal argument at the writing of this definition is that the new phone companies do not want to pay for the number portability upgrade because the cost would outweigh the profit. The RBOCs don’t want to pay for it because they are regulated by the government, which means that any increase in costs of the phone network are passed on to the subscribers/rate payers. It seems unfair that telephone customers would have to pay for huge corporate investments—especially if they are not clients/patrons of the particular company that is receiving the benefit of the investment.

numbering plan administration (NPA) - See NPA.

Numbering Plan Area (NPA) - See NPA.

Numbering Plan - A plan of what numbers will be used where. In a local phone company, each central office has its own numbering plan or range of numbers. In a PBX or key system, numbering plans are implemented to ease the complexity of accounting, and sometimes they aid in remembering what a person’s extension number is. For example, sales can be extensions that range from 3000 to 3999, manufacturing can be extensions that range from 4000 to 4999, off-premises extensions can range from 5000 to 5999, etc. Numbering plans can be formed any way that a user/administrator likes with the following exceptions: Usually no extension on a PBX starts with 9 because 9 as a first digit is used to access outside lines, so 9000 to 9999 is not used in a numbering plan. Zero (0) is also restricted from a numbering plan because it is often used to dial the attendant or operator. A good numbering plan will make call accounting much easier. Call reports can be sorted by department if every department has its own unique numbering plan.

numerical aperture (NA) The light-gathering ability of an optical fiber, as determined by the square root of the difference of the squares of the refractive indexes of the core (n ₁ ) and the cladding (n ₂ ), and as expressed in the equation: NA = (n ¹ ₂ - n ² ₂ ) ^1⁄2 Fiber optic transmission systems (FOTS) are based on the principle of total internal reflection, meaning that all light injected into the fiber is retained in the fiber.The objective is to retain all components of the optical signal in the core. However, a light source naturally injects some light rays into the core at angles less than the critical angle, which is perpendicular to the plane of the core/cladding interface. At such severe angles, the incident light rays penetrate the interface and enter the cladding, where they may be lost. The numerical aperture essentially is an indication of how well an optical fiber accepts and propagates light. Optical fiber with a small NA (top) requires more directional, i.e., collimated, light, whereas fiber with a large NA (bottom) does not.The higher NA allows the fiber to accept more light and propagate more modes.The NA is mathematically equal to the sine of the angle of acceptance. Note:The NA is important in multimode fiber (MMF). It is not, however, a critical measurement in single-mode fiber (SMF), as the small core supports only a single mode of propagation and, therefore, the light is neither reflected nor refracted.The light-accepting ability can also be defined in terms of the cone of acceptance, which is the maximum angle at which the fiber will accept incident light, represented in three dimensional view. See also angle of acceptance, collimation, cone of acceptance, critical angle, MMF, SMF, and total internal reflection

NVRAM (NonVolatile RAM) - Random Access Memory that retains its contents when a unit is powered off.

NXX - The central office (CO) prefix, also known as the central office exchange (COE) code is a threedigit number that identifies the central office and the associated geographic carrier serving area (CSA). The CO prefix specifies the dialing pattern NXX, with N indicating that only numbers 2–9 are allowed, as 0 or 1 would confuse the network, and X indicating that any number is allowed. A call within an area code requires that the caller enter only the CO prefix and the line number, i.e., NXX.xxxx, unless there is an overlay area code. The line number can consist of any four digits (xxxx), and corresponds with a port on a switch that connects to a circuit or channel over a local loop that serves the physical premises of a subscriber. In the case of a cellular telephone number, there is no local loop, as such, and the number is associated with a handset, rather than a physical premises. See also CO, CSA, GSTN, NANP, overlay area code, and PSTN.

NYNEX (New York New England Exchange) - One of the original seven regional Bell Operating Companies that was divested from AT&T.

Nyquist Theorem - A theory that states that any analog signal to be converted to a digital signal (ADC conversion) must be sampled at twice the frequency of the top end of the bandwidth of the signal to be converted. If you would like to convert a high-fidelity recording to a compact disc, you would need to sample the audio at a minimum of 36 kHz (36,000 times per second) because the bandwidth of high-fidelity music is 18 kHz (18,000 cycles per second). This sample rate would give two samples per cycle at the highest frequency of human hearing, which is 18 kHz. A DSO channel in a channel bank samples a voice at 8000 times per second (8 kHz). This gives a Nyquist standard sample up to 4 kHz, which is sufficient to sample all sounds in the voice range.

Nyquist, Harry (1889–1976) - A physicist and engineer at AT&T Bell Telephone Laboratories, where he did important work in areas such as thermal noise, telegraphy, facsimile systems, and television. Nyquist also did significant work that laid the foundations for information theory, as was subsequently developed by Claude Shannon. In 1928, Nyquist published a paper entitled Certain Topics in Telegraph Transmission Theory, in which he expressed what is now known as the Nyquist theorem. In telecommunications, the Nyquist theorem forms the basis for pulse code modulation (PCM), the fundamental method for converting analog voice to digital format. See also Nyquist theorem and PCM.

NZDF (Non Zero Dispersion-Shifted Fiber) - A type of dispersion-shifted single-mode fiber (SMF) that shifts the optimal dispersion point by adjusting the refractive index profile of the core and the cladding. There are two types of dispersion-shifted fiber (DSF). Zero Dispersion-Shifted Fiber (ZDSF) shifts the point of zero dispersion by increasing material dispersion to the point that it cancels out chromatic dispersion at 1550 nm, rather than 1310 nm. Dense Wavelength Division Multiplexing (DWDM) and Erbium-Doped Fiber Amplifiers (EDFAs) both work in this higher window, which can create yet another noise problem in the form of four-wave mixing (FWM), a phenomenon by which wavelengths interact to create additional wavelengths.The EDFAs amplify those signals, and superimpose them on the DWDM channels. Non Zero Dispersion-Shifted Fiber (NZDF) addresses this issue by shifting the optimal dispersion point slightly above the range in which EDFAs operate. See also chromatic dispersion, cladding, core, dispersion, DSF, DWDM,EDFA, FWM,material dispersion, noise, refractive index, SMF, wavelength, window, and ZDSF.