North American Directory Forum

Collection of organizations that offer, or plan to offer, public directory services in North America, based on the CCITT X.500 Recommendations.

Nearest Active Downstream Neighbour

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

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.

A line rented from the phone company for exclusive use, 24 hours per day, seven days per week. The connection exists between two predetermined points and cannot be switched to other locations. A nailed-up line is also called a leased line.

Negative Acknowledgement

A packet sent from a receiver to a sender, informing the sender that the data is missing or corrupt. When a device receives a packet, it sends back a packet to the sending device. If all the data arrived without corruption, the packet is an acknowledgement (ACK). If some of the data is missing or corrupt, a NAK results requesting that the sender retransmits the data.

In data communications, a server connected to a network that transforms host names into network addresses.

North American Network Operator's Group

Primary forum for information exchange among U.S. exchange point participants, Internet service providers, and end users.

Network Access Points

Where ISPs agree to drop down their lines and establish peering arrangements and let their customers communicate.

Digital communication at the 64 Kbps or lower rate. Also known as "baseband."

Network Access Server

Cisco platform (or collection of platforms such as an AccessPath system which interfaces between the packet world (e.g. the Internet) and the circuit world (e.g. the PSTN).

Network Address Translation

Mechanism for reducing the need for globally unique IP addresses. NAT allows an organization with addresses that are not globally unique to connect to the Internet by translating those addresses into globally routable address space. (2) The translation of an Internet Protocol address (IP address) used within one network to a different IP address known within another network. One network is designated the internal network and the other is the external. The internal network then appears as one entity to the outside world. In the case of wireless LANs with an outside Internet connection, the NAT capability of Internet sharing software allows the sharing of one Internet connection among all the wireless PCs connected.

Network Addressable Unit

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

Nearest Active Upstream Meighbor

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 multi-access 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).

New Common Carriers

Those companies competing with NTT in Japan's domestic long distance market.

Network Code Of Practice

Specifications designed to ensure the quality of private networks connected to public switched telephone networks.

Network Control Protocol

Series of protocols for establishing and configuring different network layer protocols, such as for AppleTalk over PPP.

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.

National Centre for Supercomputing Applications

National Computer Security Centre. 

Network Driver Interface Specification.

NetWare Directory Services

Network Element

In OSS, a single piece of telecommunications equipment used to perform a function or service integral to the underlying network.

Network Element Management Server

NetBIOS Extended User Interface

Enhanced version of the NetBIOS protocol used by network operating systems such as LAN Manager, LAN Server, Windows for Workgroups, and Windows NT. NetBEUI formalizes the transport frame and adds additional functions. NetBEUI implements the OSI LLC2 protocol.

Network Basic Input/Output System

A transport protocol connecting network hardware with the network operating system. There are a variety of NetBIOS implementations, many of which do not work together.

NetView is IBM's host-based network management product. NetView/PC is an IBM product that runs on personal computers and provides limited network management functions.

Novell's network operating system.

Medium used to connect one system element to another; could be wire, cable, fibre optic, infrared, radio frequency, etc.

Determines the type of call that is being placed: 0 = international, 1 = reserved, 2= national, and 3 = national spare.

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.

Takes place once a service order is generated including assignment of bandwidth, IP address, trunking facilities, hub routing, site survey, workforce management, etc.

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, and others. These protocols are part of a larger architecture that Sun refers to as 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.

Next Hop Server

Server defined by the NHRP protocol that maintains next-hop resolution cache tables containing the IP-to-ATM address mappings of associated nodes and nodes that are reachable through routers served by the NHS.

Network Interface Card

PC board that provides network communication capabilities to and from a computer system.

Network Information Centre

Internet authority responsible for assigning Internet-related numbers, such as IP addresses and autonomous system numbers. See also IANA.

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.

National Institute of Standards and Technology.

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 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.

Network-to-Network Interface

The interface between two networks. This could be two different carriers (for example between an LEC and an IEC), or between a customer network and an IEC network.

Nature of Address

Network Operations Centre

Organization responsible for maintaining a network.

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) H.323 entity that uses RAS to communicate with the gatekeeper (for example, an endpoint such as a terminal, proxy, or gateway). (3) In SNA, the basic component of a network and the point at which one or more functional units connect channels or data circuits.

Network Operating System

An operating system for networks or the software that runs on local area networks. It manages the continual conversation between all computers on a network.

Number Plan Identification

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

Signals that maintain constant voltage levels with no signal transitions (no return to a zero-voltage level) during a bit interval.

Nonreturn to Zero Inverted

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.

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.

Network Service Provider

An NSP is a company that provides Internet connectivity to Internet Service Providers (ISPs) and other organizations requiring high-speed access to the Internet.

Network Termination 1

In ISDN, a device that provides the interface between customer premises equipment and central office switching equipment.

Network Time Protocol

Protocol built on top of TCP that assures accurate local time-keeping with reference to radio and atomic clocks located on the Internet. This protocol is capable of synchronizing distributed clocks within milliseconds over long time periods.

Number Translation Services

National Television Standards Committee

The TV standard used primarily in North America and Japan with 525 lines transmitted at 60 interlaced half-frames per second

NonVolatile RAM

RAM that retains its contents when a unit is powered off.

Network Virtual Terminal ASCII Nailed Line

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