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,
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
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
Line conditioning A
collection of techniques for keeping the quality of transmissions within specified
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
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
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
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
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
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
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.
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
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
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
Multi-cast message A message
that is intended for a set of stations on a network.
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
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
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.
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
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
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
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
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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