N type or N connector - A medium-size threaded coaxial connector for use with direct current through 11 GHz with Series-8, thicknet, and Series-11U coaxial cables. It features a characteristic 50 ohm impedance structure. N-type connectors have a center pin that must be installed over the cable's center conductor.

nanofarad (nF) - A unit of capacitance equal to one billionth of a farad (0.000000001 farad).

narrowband electrical noise - Electrical disturbance from an outside source on a single channel (with a carrier wave of a certain modulated frequency).

narrowband - Any analog signal or analog representation of a digital signal whose essential spectral content is limited to that which can be contained within a voice channel of nominal 4 kHz bandwidth. Narrowband radio uses a voice channel with a nominal 3 kHz bandwidth.

National Television System Committee (NTSC) - An analog television display standard used primarily in the United States and Japan. NTSC scans the cathode ray tube 525x horizontally.

near-end crosstalk (NEXT)loss - 1. The unwanted signal coupling between pairs. It is measured at the end of a cable nearest the point of transmission. Contrast with far-end crosstalk. 2. The signal transfer between circuits at the same (near) end of the cable.

nearest active upstream neighbor (NAUN) - A reference point for communications control and for station addressing on a token ring LAN. The NAUN is the device that transmits a token or a frame to the next active station on the ring.

near-field radiation pattern - Distribution of the irradiance over an emitting surface (over the cross-section of an optical waveguide).

near infrared - Part of the electromagnetic spectrum near the visible spectrum, typically 700 nm to 1500 nm or 2000 nm; it is not rigidly defined.

NetBIOS Extended User Interface (NetBEUI) - A fast, non-routable protocol that requires minimal configuration.

network - A series of controllers, all connected via a telecommunications cable.

network access device - Equipment used to interconnect stations, servers, and shared peripherals devices on a LAN or internetwork.

network address - A Layer 3 address used to uniquely identify each LAN connected to an internetwork. See also media access control (MAC) address.

network administration - The set of tasks performed to provide secure and reliable access to selected network resources.

network-attached storage (NAS) - A form of data storage where shared data is placed on a high-capacity storage device with a built-in network interface card.

network-attached storage (NAS) appliance - A specialized device optimized for network data storage.

network computer (NC) - A device similar to a personal computer with respect to processing power, memory capacity, and graphics capabilities but lacking any storage capabilities (no built-in diskette or hard disk drives). See also thin client.

network diameter - The distance between the two data terminal equipment devices farthest apart in the same collision domain. Also called a collision diameter.

Network Equipment Building System (NEBS) - A series of standards originally developed and maintained by Telcordia Technologies that specify rigorous environmental requirements that must be met for equipment to be installed in a service provider's (SP) central office or other facility. NEBS requirements help ensure the integrity of the SP's network by establishing physical and electromagnetic compatibility for a wide range of equipment types. While NEBS is mainly a requirement of North American local exchange carriers, these standards may be employed by any SP or end user that requires an extreme level of reliability.

network identification (netid) - Part of the Open Systems Interconnection Layer 3 address. It identifies the LAN broadcast domain. See also host identification (hostid).

network interface (NI) - 1. The point of connection between a user terminal and a private or public network. 2. The point of interconnection between the public switched network and a privately owned terminal.

network interface card (NIC) - Circuitry in a device that provides the means to physically connect to a network.

network interface device (NID) - The point of connection between networks. (TIA)

Network layer - The Open Systems Interconnection Reference Model layer responsible for internetwork message transfer (e.g., between LANs on an internetwork). Also called Layer 3.

network management - The combination of planning, procedures, hardware, software, and personnel needed to maintain network operations at maximum efficiency at all times.

network management center (NMC) - An operations center used to manage network resources (e.g., mobile switching centers, location registers, base stations).

network operating system (NOS) - An integrated collection of software programs designed to control and coordinate all access to network resources. It enables the sharing of software applications, peripheral devices, communications services, and user-created files by authorized network users.

network operations center (NOC) - The physical space from which all aspects of a network are managed, monitored, and supervised.

network termination equipment -See network interface device. (TIA)

newsgroup - An Internet-based messaging environment in which all messages and replies are posted for shared viewing.

newsreader - Software used to read, compose, and post newsgroup messages.

nibble - Data unit made up of 4 bits. Also called a quartet (sometimes spelled nybble).

node - Addressable point on the network with processing abilities (e.g., personal computer, terminal, printer).

noise - An unwanted electrical signal on a wire that provides a random or persistent disturbance that interferes with the clarity or quality of the expected signal and alters the shape of the signal.

noise weighting - An objective method for the assessment of interference coupled into telephone lines that uses a frequency of 800 Hz as reference. The alternating voltages are adjusted until the interference is the same for each key frequency within the frequency range of interest so that the frequency 800 Hz has the interference weight of 1 (or 1,000 to simplify calculations); in dB, the weight at 800 Hz is 0. The weights indicate how much more or less a voltage at any key frequency within the range of interest interferes than the same voltage at 800 Hz.

nominal size (trade size) - Approximate value rather than precise value.

nominal velocity of propagation (NVP) - The coefficient used to determine the speed of transmission along a cable relative to the speed of light in a vacuum.

nomograph - Chart showing three or more scales across which a straightedge may be held in order to read off a graphical solution to a three-variable equation.

nonblocking - The ability of a device or network to successfully provide a communications path between any available devices.

noncollusion statement - A document often required with the submission of a bid certifying that the bidder has not conferred, conveyed, or otherwise communicated with another party in an attempt to restrict competition.

noncorrosive atmosphere - An environment that is not subject to gradually wearing, changing, or destroying the texture or substance of a body (e.g., corrosive action of an acid).

non-fail-safe - A lock or electric strike that remains locked or latched on loss of power. Same as fail-secure.

non-power limited (NPL) - Refers to 115 volts alternating current power circuits.

non-power-limited fire alarm (NPLFA) - In the United States, a fire alarm system using 115 volts alternating current power circuits for control rather than reduced voltage.

nonreflective break - When an optical fiber is cut or broken, the end may shatter so that the angle at where the light hitting the end may not reflect at all.

nonrepudiation services - Network security processes that provide proof that a message was sent from a specific source, thereby preventing that source from denying having sent the message.

nonrepudiation services - An encoding method that generates a digital signal from a bit string. The digital signal encodes bits one at a time. For example, a high-voltage level during a bit interval encodes a one, and a low-voltage level during a bit interval encodes a zero. This encoding method does not use zero volts as a valid logic state.

non-return-to-zero inverted (NRZ!) - An encoding method that generates a digital signal from a bit string. The digital signal encodes bits one at a time. For example, a transition at the beginning of a bit interval encodes a one and the lack of a transition at the beginning of a bit interval encodes a zero.

nonzero dispersion shifted - A type of optical fiber designed to introduce a small amount of dispersion without a zero point crossing being in the wavelength division multiplexer passband. With this type of optical fiber, it is possible to eliminate or at least greatly reduce the degradation due to four-wave mixing, a distortion mechanism that requires the spectral components to be phase matched along the optical fiber.

notice of award - The owner may issue a notice of award if preparation of the actual contract might be delayed. This procedure is required when a challenge period is required by statute. A notice of award establishes the beginning of any challenge period. (CSI)

notice to proceed - Establishes the beginning date of construction and directs the contractor to begin the project. (CSI)

notification appliance circuit (NAC) - A circuit or path directly connected to a notification appliance(s).

null - Area where signal strength has zero magnitude.

null modem - A specially designed cable that allows a user to connect two computers directly to each other via their communications ports (RS-232 ports) without modems or other communications devices (data communications equipment) between them. Null modems are particularly useful with portable computers because they enable the portable computer to exchange data with a larger system.

null virtual local area network (VLAN) - The zero VLAN identifier. A VLAN identifier (VID) of zero indicates that the frame does not contain VLAN identification.

numerical aperture (NA) - 1. A number that expresses the light-gathering ability of an optical fiber, defining the maximum angle to the fiber axis at which light will be accepted and propagated through the fiber. NA = sin q, where q is the acceptance angle. 2. Describes the angular spread of light from a central axis, as in exiting a fiber, emitting from a source, or entering a detector.

nylon - An abrasion-resistant thermoplastic with good chemical resistance.