Glossary of Terms
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• LAN (Local Area Network) A communications system that links computers into a network, usually via a wiring-based cabling scheme. LANs connect PCs, workstations and servers together to allow users to communicate and share resources like hard disk storage and printers. Devices linked by a LAN may be on the same floor or within a building or campus. It is user-owned and does not run over leased lines, though a LAN may have gateways to the PSTN or other, private, networks.
• LAN Manager for Unix Systems An implementation of LAN Manager for use with Unix. Known colloquially as LM/X.
• LAN Manager LAN Network Operating System developed by Microsoft which runs or top of OS/2 and recently Windows NT.
• LAN Network Manager IBM's network management software for Token Ring networks.
• LAN Segment A part of a LAN that is separated from the rest by one or more bridges.
• LAN Server IBM version of IBM LAN Manager.
• LAP (Link Access Protocol) The Data Link or OSI Layer Two protocol specified by the ITU-TS for the X.25 interface standard.
• LAP-B: A link set-up routine to establish and maintain links between DCE and DTE. Lap-D: The Layer Two protocol for an ISDN D-channel specified in the ITU-TS recommendation Q.921. It is a framed, bit-oriented protocol similar to Lap and Lap-B protocols specified for X.25 circuits. Lap-M: A variation of Lap-B used in the V.42 modem error control standard.
• LAT (Local Area Transport protocol) A DecNet specific protocol for the exchange of small packets of data between typically Dec Vax host computers and terminal servers in a LAN.
• Layer Description of divisions in specifications Such as OSI and SNA communications protocols. Functions are grouped together that comprise one step in the hierarchy necessary for successful data communications.
• Line conditioning A collection of techniques for keeping the quality of transmissions within specified parameters.
• Line driver A signal converter that conditions the digital signal transmitted by an RS232 interface to extend reliable communication beyond the 50ft RS232 limit up to several miles. It is a baseband transmission device.
• Line turnaround The interval on a transmission link between the time one block of data was sent and received and the time the next one can be sent.
• Line signal standards In the US: T1 carries data at 1.544Mbit/s and has 24 voice circuits; T1C 3.152 Mbit/s with 48 voice circuits; T2 6.312Mit/s with 96 voice circuits, and T3, 44.736Mbit/s. In Europe, the standards are of the form En. E1 line speed is 2.048Mbit/s with 3C voice circuits; E2 is 8.448Mit/s with 120 voice channels. E3 is 34.368Mbit/s with 480 voice circuits. In the UK, E1 is often referred to as MegaStream, a BT label for its 2Mbit/s leased circuits.
• Link state algorithm A routing algorithm such as OSPF which takes into account lowest delay when choosing a route: link speed and congestion as well as hop count.
• LLC (Logical Link Control) A data link protocol based or HDLC, developed for LANs by the IEEE 802 Committee and consequently common to all LAN standards for Data Link OSI Layer Two transmission.
• Local bridge Bridge that links two local LANs: in the same building, for example.
• Local security A security method available for 386 and 486 servers running HPFS386. This method extends LAN Manager security measures to protect the files on a server by restricting access of the users working at the server. With local security, a user must be assigned permissions to access any file or directory in an HPFS386 partition, whether or not the resource is shared as part of a LAN Manager resource.
• LocalTalk An Apple cabling scheme underlying its low-cost LANs. A 230Kbit/s baseband network primarily for Mac computers and LaserWriter printers, it uses the CSMA/CA media access method. The current Phase II allows theoretically unlimited networks.
• Lobe The cable between a Token Ring station and the Trunk Coupling Unit to which it is connected. Lobe length comprises a patch cable from the TCU to the main wiring panel, the length of the main wiring to the user station's location, then a patch cable from a floor/desk socket to the station.
• Logon script A batch program containing LAN Manager, NetWare and other operating system commands used to configure workstations. Logon scripts can be written for one or more users.
• Logon server For a domain, a logon server is the primary domain controller and the backup domain controllers. For a user, the server that processes the user's logon request.
• Loopback A diagnostic test that returns the transmitted signal back to the sending device after it has passed through a network or across a particular link. The returned signal can then be compared to the transmitted one. The discrepancy between the two help to trace the fault. When trying to locate a faulty piece of equipment, loopbacks will be repeated, eliminating satisfactory machines until the problem is found.
• LU (Logical Unit) An IBM SNA network function defined in layers four, five and six (Transmission Control, Data Flow Control and Presentation Services) of the SNA architecture. In the SNA network, corresponding LUs are able to exchange information. Originally, particular types of LU has specific functions: LU1 for printers, LU2 for displays and so on. As SNA has developed, new types of LU have been introduced that support a broader range of communications facilities. LUs are normally associated with particular Physical Units (PUs), or network devices. LUs provide the services required by Applications (APs) in the IBM SNA environment, sitting between the APs and the PUs. A Dependent LU relies on the host for activation, physically and logically, while an Independent LU can initiate a session without host involvement.
• LU 6.2 An IBM SNA Logical Unit that provides general communications functions, including the communications functions necessary for peer-to-peer networking. Underlying LU 6.2 is a type of node: node type 2.1, which facilitates peer-to-peer networking. Two SNA units which implement rode type 2.1 can set up a full peer-to-peer session without invoking SSCP capabilities in a host processor. This is defined as SNA Low-Entry Networking.

  M

• MAC (Media Access Control) layer A sub-layer of the Data Link Layer (Level Two) of the ISO OSI Model responsible for media control.
• MAN (Metropolitan Area Network) A high speed network designed to link together sites in a metropolitan or campus area. The IEEE has defined its 802.6 standard for MANs based on the Distributed Queue Dual Bus technology.
• MAP (Manufacturing Automation Protocol) An ISO OSI protocol stack that is defined as a functional profile. Originally developed by General Motors for use in factory floor manufacturing environments it is based around the IEEE 802.4 Token Bus LAN technology.
• MAPI (Messaging Application Programming Interface) Microsoft's standard for the applications interface to e-mail. See also VIM.
• Master station A device that controls/polls the nodes in multipoint circuits or, in point-to-point circuits, the unit that controls the slave station. In LAN terms, the device on a token passing ring that enables recovery from error conditions, such as lost, busy or duplicate tokens, usually by generating a new token. Servers are sometimes called master stations.
• Matrix switching A form of data switching at the heart of ATM, enabling the appropriate of bandwidth to be available end-to-end for the duration of the session without contention.
• MAU (Medium Attachment Unit) A transceiver (transmitter/receiver) comprising hardware circuitry that provides the correct electrical or optical connection between the computer and IEEE 802.3 LAN media. Since MAUs typically support only one type of network medium, a choice of MAUs is available to support different media. It detects carrier and collision activity, passing the information to the Computer. It can be a standalone unit or incorporated in a circuit board inside the computer,
• Media Access Control driver A LAN device driver that works directly with the network adapter cards, acting as an intermediary between the transport driver and the hardware.
• Medium The physical method or equipment used for transmission, from a tangible fiber optic or copper cable to a satellite link. Alternatively, a little old lady in a shawl used as a last resort to retrieve lost data.
• Medium Interface Controller (MIC) An hermaphrodite connector on IBM patch parels specified in 802.5.
• Member server A server in a domain that keeps and uses a copy of the domain's user accounts database but does rot validate logon requests.
• Monolithic driver A network device driver that acts as network adapter card driver and transport protocol driver combined.
• MMS (Message Handling System) The engine underlying an electronic messaging system. Also a proprietary e-mail integration scheme developed by Action Technologies.
• MIB (Management Information Base) The set of variables or database that a gateway running CMOT, SNMP, or CMIP network management protocols maintains. It defines variables needed by the SNMP protocol to monitor and control components in a network. Managers fetch or store into these variables. MIB-II refers to an extended SNMP management database that contains variables not shared by both CMOT and SNMP. The CMIP and SNMP MIB formats differ in structure and complexity.
• Microchannel A proprietary bus developed by IBM for its PS/2 computer family's internal expansion cards. It offers improved performance over ISA-based machines like the IBM PC/AT.
• Microwave Wireless transmission at very high frequency to deliver telecommunications services, including TV distribution, between two points. It is dependent on line of sight.
• MTBF (Mean Time Between Failures) A term describing the reliability of equipment established by testing kit to its limits and promoting the MTBF as a selling point. As most users know, however, laboratory and operational environments have little in common.
• MNP (Microcom Networking Protocol) A series of protocols designed by Microcom to support error control and data compression for asynchronous modem transmission.
• Milnet (Military Network) Originally part of Arpanet, Milnet was partitioned in 1984 to make it possible for military installations to have a reliable network service while the Arpanet continued to be used for research. Under normal circumstances, Milnet is part of the Internet.
• Modem A device named from an amalgam of the words modulator and demodulator. A modem will modulate an outgoing binary bit stream or to an analog carrier, and demodulate an incoming binary bit stream from an analog carrier.
• Modem Approvals Group Established in January 1993 to raise awareness of the UK law against connecting unapproved devices to the PSTN, this group demands a level playing field in the modem market with better law enforcement or more open standards.
• Modem eliminator A device that can replace a modem in some instances when the distance to be covered is short. It takes the power it needs to operate from the transmission line.
• MSAU (Multi-Station Access Unit) A wiring concentrator on a Token Ring network that allows devices, typically eight to 12 Token Ring stations, to be connected to the ring. Relays in the MAU ensure the integrity of the network when devices are attached or removed. A Managed Multi-Port/Multi-Station Access Unit has built-in network management support.
• MS-Net Microsoft DOS-based networking system software product (Microsoft Network).
• Multi-drop A transmission circuit with multiple terminals and peripherals. Could also be described as branches off a bus.
• Multi-point A link that connects more than two points. Interchangeable with multi-drop.
• Multi-point connection A single channel or circuit interconnecting devices in different locations. This usually means using polling techniques with each terminal[terminal a unique address. Also know as a multi-drop line.
• Multi-cast bit A bit found in the Ethernet addressing scheme that indicates that the message is to be sent to all stations.
• Multi-cast message A message that is intended for a set of stations on a network.
• Multimedia Generic description of the generation and transfer of voice/data/video traffic between users. Applications to exploit multimedia to the full are emerging in the wake of advanced switching techniques and develop merits in desktop and server processing architectures. It may be essential to a physically separated group that communicates as if it was physically networked.
• Multi-Port Repeater An Ethernet wiring center that allows multiple devices to be attached at one point on an Ethernet. A Managed Multi-Port Repeater has network management capabilities.
• Multiplexer A device that can send several signals over a single line. They are then separated by a similar device at the other end of the link. This can be done in a variety of ways: time division multiplexing, frequency division multiplexing and statistical multiplexing. Multiplexers are also becoming increasingly efficient in terms of data compression, error correction, transmission speed and multi-drop capabilities.
• Multi-tasking The concurrent execution of two or more tasks or the concurrent use of a single program that can carry out many functions.

  N

• Named pipe A connection used to transfer data between separate processes, usually on separate computers. Named pipes are the foundation of interprocess communications and underpin Microsoft's LAN Manager Nos.
• Narrowcasting CATV term distinguishing cable from broadcasting, it describes the function of distributing a range of TV channels or programs designed for minority interests rather than mass appeal.
• NCoP (Network Code of Practice) A voluntary code of practice for the design of networks covering transmission quality, safety and technical standards.
• NetBEUI (NetBios Extended User Interface) A network device driver or transport protocol that is the transport driver supplied with LAN Manager, It can bind with as many as eight media access control drivers.
• NetBios (Network Basic Input/Output System) Software developed by IBM that provides the interface between the PC operating system, the i/o bus, and the network. Since its design, NetBIOS has become a de facto standard.
• NETBLT (Network Block Transfer) A Transport Level, flow controlled, bulk data transfer protocol used with TCP/IP internets. NETBLT controls the rate at which data is sent to allow a steady, high speed flow,
• Netlogon service A LAN Manager service that implements logon security. This service verifies the usernarne and password supplied by each user logging on to the local area network. See also LAN Manager.
• NDIS (Network Driver Interface Specification) A de facto standard interface specification developed by Microsoft to separate communications protocols from PC networking hardware. The driver can also run multiple stacks concurrently.
• Network interface card/controller Circuitry connecting a node to a network, usually in the form of a card in a PC expansion slot. In conjunction with the nos and PC operating system it helps transmit and receive messages on the network.
• NetView IBM's network management system. A text message-based system that monitors, manages and controls SNA networks. It is an implementation of IBM's Open Network Management Architecture. The term NetView is normally associated with the focal point of the architecture.
• NetView/PC An implementation of IBM's NetView running on an OS/2 PC-based platform that allows non-IBM networks and equipment to be managed via an SNA network management station. NetView/PC is a service point in IBM's Open Network Management Architecture.
• NetWare LAN Network Operating System and related products developed by Novell. There are three main product lines - NetWare 2.X (latest version 2.2) designed to run on a Intel 80286 platform and above, and NetWare 3.X (latest version NetWare 3.11), designed to run on an Intel 80386 platform and NetWare 4.0. NetWare is currently installed on more than 70 per cent of LANs worldwide.
• Network adapter card A printed circuit board, installed in a computer, enabling the computer to join the LAN.
• Network adapter card driver A network device driver that controls the physical function of a network adapter card.
• Network address A group of characters that uniquely identify the location of a node on a network.
• Network architecture The communication equipment, protocols and transmission links that constitute a network, and the methods by which they are arranged.
• Network computing A term analogous to client/server computing.
• Network device A computer, peripheral or other related communications equipment attached to a network.
• Network device driver A program that enables the operating system software to communicate the network adapter cards. Also a software module running on a host or workstation that is responsible for the communications between the computer and the network or a device attached to the network.
• Network topology The different configurations that can be adopted in building networks, such as a ring, bus, star or meshed.
• NETS (Normes Europenne de Telecommunications) The Net program will produce a range of mandatory standards for type approval of telecommunications equipment in all EC states. Once a piece of equipment has passed its Net compliance tests, which could be undertaken in any member state, that piece of equipment can be sold in all EC countries for connection to the public network. Key Nets include: Net 1 - X.21 Access; Net 2 - X.25 Access; Net 3 - ISDN Basic Access; - Net 4 - Public Switched Telephone Network Access; and Net 5 - Primary Rate ISDN Access. Net 3 can be further subdivided into Net 3 Part 1 which corresponds to the ITU-TS Q.921 standard, and Net 3 Part 2 which is functionally equivalent to ITU-TS Q.931, but Net 3 Part is still incompletely defined.
• Network element A piece of network equipment that can be managed through an element manager as part of a network management system.
• Network interface The point of interconnection between a telephone network operator's communications facilities and terminal equipment, protective apparatus or wiring at a subscriber's premises. This demarcation point is on the subscriber's side of the phone company's protector or its equivalent.
• Network Layer Level Three in the OSI stack responsible for the necessary routing and relaying through one or more networks in multiple link or wide area environments.
• Network management The process and techniques of remotely or locally monitoring and configuring networks. Under the OSI model network management takes account of five key areas: configuration management, fault management, performance management, accounting management, and security management. A major challenge and often a headache to users because there are no complete answers today, only a patchwork of systems covering different parts of the subject. Vendors either concentrate on the physical (hardware) elements or logical (control and management of interprocess communications) sides. The ITU-TS is slowly considering standards for public networks.
• Network management integration The highest level of network management system that brings together information from a number of Element Management Systems.
• Network management protocol The protocol used to transfer network management NetView, and HP OpenView.
• Nodes Devices on a network that demand or supply services or where transmission paths are connected. Node is often used instead of workstation.
• NOS (Network Operating System) The software that connects all the devices on a network so that resources can be shared efficiently and files can be transferred. It handles administration of all network functions, Network operating systems are usually in two parts; server and client/requester. The requester puts the workstation on the server machine and makes disks, software, ports and other facilities available to a node on request. Each device's services requested by a PC are accessed via the requester software.
• NOTA (Novell Open Technology Association) A group of companies that have adopted a suggested software platform suggested by Novell that will lead to the development of a new range of CTI applications.
• NREN (National Education and Research Network) The planned successor in the US to the connected Internet that will provide high speed access to scientific and educational institutions primarily within the US.
• NSF (National Science Foundation) A US government agency that has funded the development of a cross country backbone network as well as regional networks designed to connect scientists to the Internet. It operates a US network, the National Science Foundation Network (NSFNET).
• NSI (NASA Science Internet) A computer networking project started by NASA's Office of Space Science and Applications. It contains two major networks, Span and NSN. Also see NSN, Span
• NSN (NASA Science Network) Using TCP/IP, NSN is part of the connected Internet.
• Null modem cable An RS232 cable that has pins 2 and 3 reversed so that the two connected computers are under the impression they are linked using modems. It is a device that connects two DTE devices directly by emulating the Physical connections of a DCE unit.

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