Nagle's algorithm

Actually two separate congestion control algorithms that can be used in TCP-based networks. One algorithm reduces the sending window; the other limits small datagrams.


negative acknowledgment. Response sent from a receiving device to a sending device indicating that the information received contained errors. Compare to acknowledgment.

Name Binding Protocol

See NBP.

name caching

Method by which remotely discovered host names are stored by a router for use in future packet-forwarding decisions to allow quick access.

name resolution

Generally, the process of associating a name with a network location.

name server

Server connected to a network that resolves network names into network addresses.


network access point. Location for interconnection of Internet service providers in the United States for the exchange of packets.


See baseband.

Narrowband ISDN


National Bureau of Standards

See NBS.

National Institute of Standards and Technology


National Research and Education Network


National Science Foundation

See NSF.

National Science Foundation Network


native client interface architecture



network addressable unit. SNA term for an addressable entity. Examples include LUs, PUs, and SSCPs. NAUs generally provide upper-level network services. Compare with path control network.


nearest active upstream neighbor. In Token Ring or IEEE 802.5 networks, the closest upstream network device from any given device that is still active.


nonbroadcast multiaccess. Term describing a multiaccess network that either does not support broadcasting (such as X.25) or in which broadcasting is not feasible (for example, an SMDS broadcast group or an extended Ethernet that is too large). See also multiaccess network.


Name Binding Protocol. AppleTalk transport-level protocol that translates a character string name into an internetwork address.


National Bureau of Standards. Organization that was part of the U.S. Department of Commerce. Now known as NIST. See also NIST.


native client interface architecture. SNA applications-access architecture, developed by Cisco, that combines the full functionality of native SNA interfaces at both the host and client with the flexibility of leveraging TCP/IP backbones. NCIA encapsulates SNA traffic on a client PC or workstation, thereby providing direct TCP/IP access while preserving the native SNA interface at the end-user level. In many networks, this capability obviates the need for a standalone gateway and can provide flexible TCP/IP access while preserving the native SNA interface to the host.


Network Control Program. In SNA, a program that routes and controls the flow of data between a communications controller (in which it resides) and other network resources.

NCP/Token Ring Interconnection



neighborhood discovery. Process that runs on the NP of each LightStream 2020 ATM switch in the ATM network. For call routing purposes, every node in the network needs to know about changes in network topology, such as trunks and ports going up or down. ND learns about such changes at the chassis level and forwards this information to the GID process, which sends the information throughout the network. Sometimes referred to as neighborhood discovery daemon, or NDD. See also GID.


neighborhood discovery daemon. See ND.


network driver interface specification. Specification for a generic, hardware- and protocol-independent device driver for NICs. Produced by Microsoft.

nearest active upstream neighbor



Regional network in New England (United States) that links Boston University, Harvard University, and MIT. Now part of BBN Planet. See also BBN Planet.

negative acknowledgment

See NAK.

neighborhood discovery

See ND.

neighborhood discovery daemon

See ND.

neighboring routers

In OSPF, two routers that have interfaces to a common network. On multiaccess networks, neighbors are dynamically discovered by the OSPF Hello protocol.


network entity title. Network addresses, defined by the ISO network architecture, and used in CLNS-based networks.


Short for network.


Network Basic Input/Output System. API used by applications on an IBM LAN to request services from lower-level network processes. These services might include session establishment and termination, and information transfer.


Cisco network management application that provides an easy-to-use GUI for monitoring RMON statistics and protocol analysis information. NETscout also provides extensive tools that simplify data collection, analysis, and reporting. These tools allow system administrators to monitor traffic, set thresholds, and capture data on any set of network traffic for any segment.


IBM network management architecture and related applications. NetView is a VTAM application used for managing mainframes in SNA networks. See also VTAM.


Popular distributed NOS developed by Novell. Provides transparent remote file access and numerous other distributed network services.

NetWare Link Services Protocol


NetWare Loadable Module

See NLM.


Collection of computers, printers, routers, switches, and other devices that are able to communicate with each other over some transmission medium.

network access point

See NAP.

network access server

See access server.

network address

Network layer address referring to a logical, rather than a physical, network device. Also called a protocol address. Compare with MAC address.

network addressable unit

See NAU.

network administrator

Person responsible for the operation, maintenance, and management of a network. See also network operator.

network analyzer

Network monitoring device that maintains statistical information regarding the status of the network and each device attached to it. More sophisticated versions using artificial intelligence can detect, define, and fix problems on the network.

Network Basic Input/Output System

See NetBIOS.

Network Control Program

See NCP.

network driver interface specification


network entity title

See NET.

Network File System

See NFS.

Network Information Center

See NIC.

Network Information Service

See NIS.

network interface

Boundary between a carrier network and a privately-owned installation.

network interface card

See NIC.

network layer

Layer 3 of the OSI reference model. This layer provides connectivity and path selection between two end systems. The network layer is the layer at which routing occurs. Corresponds roughly with the path control layer of the SNA model. See also application layer, data link layer, physical layer, presentation layer, session layer, and transport layer.

network management

Generic term used to describe systems or actions that help maintain, characterize, or troubleshoot a network.

Network Management Processor

See NMP.

network management system

See NMS.

network management vector transport


Network-to-Network Interface

See NNI.

network node

See NN.

Network Node Interface

See NNI.

Network Node Server

SNA NN that provides resource location and route selection services for ENs, LEN nodes, and LUs that are in its domain.

network number

Part of an IP address that specifies the network to which the host belongs.

network operating system

See NOS.

Network Operations Center

See NOC.

network operator

Person who routinely monitors and controls a network, performing such tasks as reviewing and responding to traps, monitoring throughput, configuring new circuits, and resolving problems. See also network administrator.

network processor card

See NP card.

network service access point



Connecting of any collection of computers, printers, routers, switches, and other devices for the purpose of communication over some transmission medium.

neutral wire

Circuit wire that is connected to an earth ground at the power plant and at the transformer.

Next Hop Resolution Protocol



Network File System. As commonly used, a distributed file system 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 (External Data Representation), and others. These protocols are part of a larger architecture that Sun refers to as ONC. See also ONC.


Next Hop Resolution Protocol. Protocol used by routers to dynamically discover the MAC address of other routers and hosts connected to a NBMA network. These systems can then directly communicate without requiring traffic to use an intermediate hop, increasing performance in ATM, Frame Relay, SMDS, and X.25 environments.


1. network interface card. Board that provides network communication capabilities to and from a computer system. Also called an adapter. See also AUI.


Network Information Service. Protocol developed by Sun Microsystems for the administration of network-wide databases. The service essentially uses two programs: one for finding a NIS server and one for accessing the NIS databases.


Narrowband ISDN. Communication standards developed by the ITU-T for baseband networks. Based on 64-kbps B channels and 16- or 64-kbps D channels. Contrast with BISDN. See also BRI, ISDN, and PRI.


National Institute of Standards and Technology. Formerly the NBS, this U.S. government organization supports and catalogs a variety of standards. See also NBS.


NetWare Loadable Module. Individual program that can be loaded into memory and function as part of the NetWare NOS.


NetWare Link Services Protocol. Link-state routing protocol based on IS-IS. The Cisco implementation of NLSP also includes MIB variables and tools to redistribute routing and SAP information between NLSP and other IPX routing protocols. See also IS-IS.


Network Management Processor. Processor module on the Catalyst 5000 switch used to control and monitor the switch.


network management system. System responsible for managing at least part of a network. An NMS is generally a reasonably powerful and well-equipped computer such as an engineering workstation. NMSs communicate with agents to help keep track of network statistics and resources.


network management vector transport. SNA message consisting of a series of vectors conveying network management specific information.


network node. SNA intermediate node that provides connectivity, directory services, route selection, intermediate session routing, data transport, and network management services to LEN nodes and ENs. The NN contains a CP that manages the resources of both the NN itself and those of the ENs and LEN nodes in its domain. NNs provide intermediate routing services by implementing the APPN PU 2.1 extensions. Compare with EN. See also CP.


Network-to-Network Interface. ATM Forum standard that defines the interface between two ATM switches that are both located in a private network or are both located in a public network. The interface between a public switch and private one is defined by the UNI standard. Also, the standard interface between two Frame Relay switches meeting the same criteria. Compare with UNI.


Network Operations Center. Organization responsible for maintaining a network.


1. Endpoint of a network connection or a junction common to two or more lines in a network. Nodes can be processors, controllers, or workstations. Nodes, which vary in routing and other functional capabilities, can be interconnected by links, and serve as control points in the network. Node is sometimes used generically to refer to any entity that can access a network, and is frequently used interchangeably with device. See also host.
2. In SNA, the basic component of a network, and the point at which one or more functional units connect channels or data circuits.


Undesirable communications channel signals.

nonbroadcast multiaccess


nonreturn to zero

See NRZ.

nonreturn to zero inverted


nonseed router

In AppleTalk, a router that must first obtain, and then verify, its configuration with a seed router before it can begin operation. See also seed router.

non-stub area

Resource-intensive OSPF area that carries a default route, static routes, intra-area routes, interarea routes, and external routes. Nonstub areas are the only OSPF areas that can have virtual links configured across them, and are the only areas that can contain an ASBR. Compare with stub area. See also ASBR and OSPF.

nonvolatile random-access memory


normal mode

Term used to describe problems between the hot and neutral wires on a power line. See common mode.

normal response mode

See NRM.

Northwest Net

NSF-funded regional network serving the Northwestern United States, Alaska, Montana, and North Dakota. Northwest Net connects all major universities in the region as well as many leading industrial concerns.


network operating system. Generic term used to refer to what are really distributed file systems. Examples of NOSs include LAN Manager, NetWare, NFS, and VINES.

Novell IPX

See IPX.

npadmin account

One of the four default user accounts that are created in the factory on each LightStream 2020 ATM switch. The npadmin account is for privileged users. Its default interface is the CLI.

NP card

network processor card. Main computational and storage resource for the LightStream 2020 ATM switch. Each LightStream 2020 switch has one or two NPs. The second card, if present, serves as a backup for the first. Each NP is associated with a floppy disk drive for loading software and a hard disk drive for storing software and configuration data. Each NP also has an access card that provides an Ethernet port.

NP TCS monitoring module


NP module

On a LightStream 2020 ATM switch, the combination of the NP card, the NP access card, and the disk assembly. See also access card, disk assembly, and NP card.


NP TCS monitoring module. Process that runs on the NP of every LightStream 2020 ATM switch in an ATM network. NPTMM monitors the health of the system through the TCS and coordinates switch cutover when redundant switch cards are present. See also TCS.


National Research and Education Network. Component of the HPCC program designed to ensure U.S. technical leadership in computer communications through research and development efforts in state-of-the-art telecommunications and networking technologies. See also HPCC.


normal response mode. HDLC mode for use on links with one primary station and one or more secondary stations. In this mode, secondary stations can transmit only if they first receive a poll from the primary station.


nonreturn to zero. NRZ signals maintain constant voltage levels with no signal transitions (no return to a zero-voltage level) during a bit interval. Compare with NRZI.


nonreturn to zero inverted. NRZI signals 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. Compare with NRZ.


network service access point. Network addresses, as specified by ISO. An NSAP is the point at which OSI Network Service is made available to a transport layer (Layer 4) entity.


National Science Foundation. U.S. government agency that funds scientific research in the United States. The now-defunct NSFNET was funded by the NSF. See also NSFNET.


National Science Foundation Network. Large network that was controlled by the NSF and provided networking services in support of education and research in the United States, from 1986 to 1995. NSFNET is no longer in service.


NCP/Token Ring Interconnection. Function used by ACF/NCP to support Token Ring-attached SNA devices. NTRI also provides translation from Token Ring-attached SNA devices (PUs) to switched (dial-up) devices.

null modem

Small box or cable used to join computing devices directly, rather than over a network.


nonvolatile RAM. RAM that retains its contents when a unit is powered off. In Cisco products, NVRAM is used to store configuration information.


Network in New York (United States) with a T1 backbone connecting NSF, many universities, and several commercial concerns.