ProFlow Instrumentation Systems Inc.
Instrumentation and process control specialists.

30 Titan Road, Unit # 6
Toronto, ON M8Z 5Y2
Phone: (416) 477-7669
Fax: (416) 239-1263
E-mail: sales@proflow.ca
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Glossaries

Standards Glossary | Control System Glossary | Network Glossary

Standards Glossary

Terms	Definition
BS	British Standards Institution Standards
BS/CP	British Standards Institution Codes of Practice
SFA/TRNS/BASEEFA	Health and Safety Executive
EN	Cen/Cenelec European Standards
ISO/IEC	International Standards Organization/International Electrotechnical Commission
NAMAS	EEC Listed Certification Bodies/Accreditation Service
IGE	Institution of Gas Engineers
IEE	Institution of Electrical Engineers
IP	Institute of Petroleum
INST.M.C.	Institute of Measurement And Control
E.I.C.	Energy Industries Council
IEEE	IEEE Standards
EEMUA	Engineering Equipment and Material Users Association
RoSPA	Royal Society for the Prevention of Accidents
BSI/ILI ANSI	Standards Discs (Perinorm and Infodisk) American National Standards Institute
AGA	American Gas Association
API	American Petroleum Institute
ASME	American Society of Mechanical Engineers
ASTM	American Society for Testing and Materials
ISA	Instrument Society of America
OIML/IOLM.	Organisation Internationale de Metrologie Legale (Oiml).(The International Organisation of Legal Metrology)
S.I.	Statutory Instruments for Offshore Work
DEn	Department of Energy Guidance Notes
D.T.I.	Department of Trade And Industry
B.T.I.	British Telecom International
C.C.I.R.	International Radio Consultative Committee
C.I.T.T.	International Telegraph and Telephone Consultative Committee
C.A.A.	Civil Aviation Authority

Control Systems Glossary

Terms	Definition
ADC	Analogue to Digital Convertor
AI	Artificial Intelligence
Algorithms	Algorithms are routines to deal with particular situations; for example, a controller formula to correct an element in a continuous process.
Analogue	Analogue devices are those which communicate via a small electric current. For example, food industry flow meters send a current of between 4mA to 20mA. The lowest value would represent no flow at all; the largest would indicate maximum flow.
ANN	An abbreviation sometimes used for artificial neural networks.
ANSI	American National Standards Institute.
APC	Advanced Process Control. This includes continuous applications such as cracking towers and advanced batch control involving activities like blend ratio control or bleaching.
BMS	Building Management System
CAD	Computer Aided Design. This may allow designers to manipulate parts drawings and simulate processes.
CAM	Computer Aided Manufacturing is a generic term for systems help manufacturing. They include CNC and process control.
CIM	Computer Integrated Manufacturing is a term used to describe an operation which makes all or most of its information available through a fully integrated data management network. The object is to increase efficiency by integrating all the facility's data management systems.
Closed Systems	See open systems. Closed systems are the opposite to open systems. In other words, they are proprietary.
CNC	Computer Numerical Control allows machines to be operated from PLCs by means of a numerical code.
Console	A console is the term for the actual screen and keyboard used in the work stations.
Controller	A device which controls another machine in the process directly, usually being wired to it directly.
DAC	Digital to Analogue Convertor
DCS	A Distributed Control System is designed to have a series of decentralised control centres which have some degree of autonomy, but are still integrated into a whole system (except in an emergency shutdown). The centre has hierarchical control over the rest, but most control takes place away from the centre.
DDE	Direct Digital Embedding.
Digital	Digital devices transmit in bits, i.e. a series of binary numbers, to other parts of the system.
Discrete Process	A process handling distinct, separate products. The usual example is an automotive factory product line, where each car is a distinct artefact. Discrete processes are in contradistinction to continuous processes handling liquids.
ERP	Enterprise Resource Planning.
ESD	Emergency Shut Down.
EWS	Engineering Work Station
Expert Systems	See Knowledge Based Systems (KBS).
Fault Tolerant	Fault tolerant architecture allows the system to continue working even when part of the system fails. This is usually done by having multiple components running in parallel; when one part fails the redundant devices can take over, allowing engineers to repair the system without disrupting the process.
FCU	Field Control Unit.
FDDI	A Fibre Distributed Data Interface is a type of LAN.
FF	Fieldbus Foundation.
Fieldbus	Fieldbus is a generic term used to describe a common communications protocol for control systems and/or field instruments. Although some standard forms have been agreed for instruments, the DCS industry as a whole have so far no agreed fieldbus. Often, the Foundation Fieldbus is referred to simply as the Fieldbus.
Function Block	Smart devices on a fieldbus are capable of operating independently. The microprocessors which store control software are the function blocks. They are particular to an application.
Fuzzy Logic	Fuzzy logic is designed for situations where information is inexact and traditional digital on/off decisions are not possible. It divides data into vague categories such as "hot", "medium" and "cold".
Gas Chromatagraphs	Gas chromatagraphs are used to analyse the make up of a gas at various points in the process. It has been suggested that neural networks might be used to replace their functions in some circumstances at much lower cost.
Genetic Algorithms (Gas)	These are routines which are capable of self adaption. As with neural networks, they are based on an analogy with nature; in this case the best algorithms breed with each other to provide new variants in a "survival of the fittest". As yet this cutting edge technology is not widely used in process control.
GOT	Graphic Operator Terminal. A kind of HMI.
Granule	An information granule is a term used by some fuzzy logic experts to describe a fuzzy set of objects which can be seen as a unit in fuzzy logic calculations.
GUI	The standard abbreviation for Graphic User Interface; this is an interface which uses graphics rather than characters to communicate.
GUS	Global User Station
HMI	Human Machine Interface. Sometimes these are calledMan Machine Interface. See MMI.
HVAC	Heating, Ventilation and Air Conditioning.
ICS	An Information and Command Station is used by operators to control and monitor the plant's processes.
IEC	International Electrotechnical Commission.
IFC	International Fieldbus Consortium. An hybrid body formed from the IFG and the OFC in 1990. It voted to stop work after the FF was created in 1994.
IFG	International Fieldbus Group
ILD	Instrument Loop Diagram. A drawing showing the connections from the field device all the way through to the system terminations.
IMC	Institute of Measurement and Control. InstMC.
Interchangeability	Interchangeability is the ability, in an open system, to swap instruments on a network without losing functionality.
Interoperability	Interoperability is the ability to plug instruments or other elements produced by more than one manufacturer into a fieldbus network and still have them able to communicate with each other and the control system(s). They may, however, have different levels of functionality.
I/O Module	An Input/Output module, which usually contains several I/O points.
I/O point	An Input/Output point, used as a connection point.
ISA	Instrument Society of America.
ISP	This is the standard abbreviation for the Interoperable Systems Project, which a number of companies are hoping will produce an international fieldbus. The main industry backers are Fisher-Rosemount, Yokogawa and Siemens.
JIT	Just In Time. A manufacturing process that produces products just in time to meet orders, not for stock.
KBS	A Knowledge Based System is a system which attempts to use a database to solve problems by inference. These are sometimes called expert systems.
LAN	Local Area Networks are used to link up computers. The best known protocol for LANs is Ethernet.
LonWorks	Local Operating Networks is another fieldbus, used by about 2,000 companies. The chips are made by Toshiba and Motorola for the German Echelon. They are then sold onto to various manufacturers.
Loop	Each DCS controls a number of loops. These consist of a measurement device, a controller and a valve. Each loop is composed of devices to control the flow of liquid at a particular point.
Master Modules	The master is set over the "slave" module, i.e. is able to control it. These are sometimes called "parent" modules.
MCS	Management Command System. A kind of HMI.
MES	Management Execution System. By monitoring labour resources, process history and machine usage and failures, a MES will help various features such as preventive maintenance, employee time and attendance, quantity maintenance and operator data.
MIS	Management Information System
MMI	Man-Machine Interface. Also known as Human Machine Interface (HMI).
Migration	When manufacturers produce new products they usually provide a migration path whereby their existing clients can upgrade their systems without total replacement. Rival manufacturers also provide migration paths away from the systems of others' in order to gain market share.
MRPII	Manufacturing Resource Planning 2.
Multitasking	The ability of a computer to handle more than two programs at the same time.
MTU	Master Telemetry Unit
NC	Numerical Controller
Neural Network	A neural network is a computer network designed to function in a similar way to natural neural structures such as a human brain.
OCS	Open Control System. This term is sometimes used to emphasize the lack of proprietary architecture. ABB include the term in their DCS brandname, Advant OCS.
OEM	Original Equipment Manufacturer.
OFC	Open Fieldbus Consortium.
OIS	Operator Interface Station. A kind of HMI.
OLE	Object Linking and Embedding, Microsoft's greatest contribution to industrial control, allows operators to link the same object in several different applications.
OPC	OLE for process control.
Open Systems	Open systems are customarily defined as those systems that can be supplied by hardware components from multiple vendors, and whose software can be operated from different platforms. They are opposite to closed or proprietary systems.
OS	An OS is an abbreviation for an Operating System which is the basic computer system which makes all computers function.
PC	Personal Computer
PFD	Process Flow Diagram
PID	PID stands for proportional, integral, derivative. Proportional means changing a variable in proportion to its difference from the set-point. Integral rectifies any small difference in the variable and the set-point. Derivative reduces the other oscillations.
P & ID	Process and Instrumentation Diagram
PIMS	Process Information Management System
PLC	A Programmable Logic Controller is a controller which stores instructions to command a device, such as a valve, to which it is connected to start up, operate and shut down.
PNET	The Danish fieldbus. The Profibus organization is seeking to integrate this in the common Profibus PA protocol.
Process Variable	An aspect of the processed product which changes during processing, e.g. temperature. Some variables can be measured, but in some processes some variables can only be judged by dead reckoning.
Profibus	The German fieldbus, not to be confused with the common European fieldbus Profibus PA.
Profibus PA	This is the name agreed on a common European Fieldbus for process automation, still disputed by mainly American companies. Its main pusher in the industry is Siemens.
Protocol	A set of rules to govern system-to-system use. For example, a protocol might specify communication method, transmission rate, data format or error check method.
Redundancy	This is the capacity to switch from primary equipment to standby equipment automatically without affecting the process under control.
RIO Bus	Remote Input/Output bus. This is a communication bus used to connect a field control unit with remote I/O points or nodes.
RTU	Remote Terminal Unit
Safety PLC	A PLC specifically designed to be reliable through the device of redundancy. It could be used either for safety reasons or to minimize the commercial impact of a serious failure.
SCADA	Supervisory Control And Data Acquisition software.
Set-point	A desired level for a process variable. The systems seeks to correct the variable when it deviates from this standard.
SFC	Sequence Function Chart. An IEC1131-1 programming/configuration language.
Single Window	Single window refers to the ability to provide multiple displays via a single terminal.
Slave Modules	Slave modules are distributed modules that report back to a central Master. Despite the name, they have their own processing ability. Another name for them is "child" modules.
SLC	Soft Logic Control.
Smart Device	A device with intelligence, i.e. capable of monitoring itself.
Soft Logic	A PC operating system used for soft control. It allows a PC to replace a PLC.
SPC	Statistical Process Control.
Structured Text	An IEC1131-1 programming/configuration language.
Tag	This is a number given to individual DCS control units so that the system can identify them.
TMR	In safety PLCs, Triple Modular Redundancy is the provision of three micro processors instead of one in situations where continuing functioning has to be ensured.
Trunkwire	A trunkwire will be possible for a series of digital devices. Such a series will be able to use a single wire, rather than the multiplicity of wires used on analogue devices which all require separate wiring.
Web Inspection	In the paper industry cameras are inserted to monitor the sheet for visual defects.
World FIP	The fieldbus adopted in France. FIP stands for factory instrument protocol. The Profibus organization is seeking to integrate this with the common European Profibus PA protocol

Network Glossary

Terms	Definition
10BASE2	IEEE 802.3 specification thin coaxial cable that can support 10 Mbps and has a maximum distance of 185 meters (607 feet) per segment. Also called thinwire and cheapernet.
10BASE5	IEEE 802.3 specification thick coaxial cable that can support 10 Mbps and has a maximum distance of 500 meters (1604 feet) per segment. Also called thickwire.
10BASE-FL	IEEE 802.3 specification fibre optic cable that can support 10 Mbps and has a maximum distance of 2000 meters (6561 feet).
10BASE-T	IEEE 802.3 specification unshielded twisted pair cable that can support 10 Mbps and has a maximum distance of 100 meters (328 feet). This cable meets EINTIA category 3 wire specifications.
100BASE-FX	IEEE 802.3 specification fibre optic cable that can support 100 Mbps and has a maximum distance of 412 meters (1352 feet)
100BASE-T	IEEE 802.3 specification unshielded twisted pair cable that can support 100 Mbps and has a maximum distance of 100 meters (328 feet). This cable meets EIA/TIA category 5 wire specifications.
Adapter	A circuit board that provides communication capabilities between a computer or computer system and a communication network. Also called network interface card (NIC).
Address	Data structure used to identify a unique entity (process, network location, etc.).
Agent	Software that processes queries and returns replies on behalf of an application. In network managed systems, agents reside in all managed devices and report the values of specified variables to management work stations.
API	Application programming interface. A specification of function call conventions that defines an interface to a service.
AppleTalk	A series of related communications protocols introduced and maintained by Apple Computer. Two phases currently exist: Phase I and Phase II. Phase II, which includes support for internetworks, is the most recent version.
Application layer	Layer seven of the OSI reference model. This layer is implemented by various network applications including electronic mail, file transfer, and terminal emulation.
ARCnet	Attached resource computer network. A 2.5 Mbps token bus LAN network developed in the late 1970s and early 1980s by Datapoint Corporation. Primary characteristics include simplicity, ease of use, and relative low cost.
ARP	Address resolution protocol. An Internet protocol used to bind an IP address to Ethernet /IEEE 802.3 addresses. Defined in RFC 826.
ARPANET	A packet switching network developed in the early 1970s by BBN (Bolt, Beranek, and Newman Inc.) and funded by ARPA (advanced research projects agency). The ARPANET evolved into the Internet, and the term ARPANET was officially retired in 1990.
ASCII	American standard code for information interchange. An eight bit (seven bits plus parity) code for character representation.
ASN.1	Abstract syntax notation one. An OS1 language for describing data types in a manner independent of particular computer structures and representation techniques.
Asynchronous transmission	Operation of a network system wherein events occur without precise clocking. In such systems, individual characters are usually encapsulated in control bits called start and stop bits, which designate the beginning and ending ofcharacters.
ATM	Asynchronous transfer mode. The CCITT standard for cell relay wherein information for multiple types of services (voice, video, data) is conveyed in small, fixed size cells. Also, a BISDN transfer mode wherein an accelerated version of asynchronous time division multiplexing (ATDM) is used to move multiple streams of information across a communication channel.
Attenuation	Loss of communication signal energy.
AUI	Attachment unit interface. An IEEE 802.3 cable connecting the MAU (mediaaccess unit) to the networked device. The term AUI also can be used to refer to the host back panel connector to which an AUI cable (transceiver cable) attaches,
Backbone network	A network acting as a primary conduit for traffic that is often both sourced from, and destined for, other networks.
Balun	Balanced, unbalanced. Device used for matching impedance between a balanced and unbalanced line (usually twisted pair and coaxial cable).
Bandwidth	The difference between the highest and lowest frequencies available for network signals. The term is also used to describe the rated throughput capacity.
Baseband	Characteristic of a network technology where only one carrier frequency is used. Baseband is the opposite of broadband. Ethernet is an example of a baseband network.
Baud	A unit of signalling speed equal to the number of discrete conditions or signal events per second. Baud is synonymous with bits per second if each signal event represents exactly one bit.
BISDN	Broadband ISON. Communication standards being developed by the CCITT to handle high bandwidth applications such as video. BISDN will use ATM technology over SONET-based transmission circuits to provide data rates of 155 Mbps to 622 Mbps and beyond.
Bit	Smallest unit of information recognised by a computer and its associated equipment.
BNC connector	Standard connector used to connect IEEE 802.3 1 OBASE2 coaxial cable to a transceiver.
BootP	A protocol used by a network node to determine the IP address of its Ethernet interfaces, in order to effect network booting.
Boot PROM	Boot programmable read-only memory. A chip mounted on a printed circuit board used to provide executable boot instructions to a computer device.
Bridge	A device that connects and passes packets between two network segments. Bridges operate at layer two (data link) of the 031 reference model and are insensitive to upper layer protocols.
Broadband	A transmission system that multiplexes multiple independent signals onto one cable, Broadband is the opposite of baseband.
Broadcast	A message sent to all network destinations.
Broadcast storm	Undesirable network event in which many broadcasts are sent all at the same time, using substantial network bandwidth and, typically, causing network time-outs.
Bus topology	Linear LAN architecture in which transmissions from network stations propagate thewhole length of the medium and are received by all other stations.
Byte	A series of consecutive binary digits that are operated upon as a unit (for example, an eight bit byte).
Carrier	A signal suitable for modulation by another signal containing information to be transmitted.
CCITT	Consultative committee for international telegraph and telephone. An international organisation that develops communication standards.
Cell	The basic unit for ATM switching and multiplexing. Each cell consists of a five byte header and 48 bytes of payload.
Cell relay	Network technology based on the use of small, fixed-size packets, or cells. Cells contain identifiers that specify the data stream to which they belong. Because the cells are ixed length, they can be processed and switched in hardware at very high speeds.
Cheapernet	IEEE 802.3 1 OBASE2 standard or the cable specified in that standard. Thinnet, also used to describe this standard, specifies a less expensive, thinner version of Ethernet cable.
Client	A node or software program (front end device) that requests services from aserver.
Client-server computing	Distributed processing (computing) network systems in which transaction responsibilities are divided into the client (front end) part and the server (back end) part. Both client and server can be applied to both software programs or actual computing devices.
Coaxial cable	A cable consisting of a hollow outer cylindrical conductor that surrounds a single inner wire conductor.
Concentrator	A device that serves as the hub of a star-topology network. Also, sometimes used to refer to a device that contains multiple modules of network and internetwork equipment.
Connectionless	Data transfer without the existence of a virtual circuit.
CRC	Cyclic redundancy check. An error checking technique in which the frame recipient calculates a remainder by dividing frame contents by a prime binary divisor and compares the calculated remainder (which itself is often called a CRC) to a value stored in the frame by the sending node.
CSMA/CD	Carrier sense multiple access with collision detection. A channel access mechanism wherein devices wishing to transmit first check the channel for a carrier. If no carrier is sensed for some period of time, devices can transmit. If two devices transmit at once, a collision occurs and is detected by all colliding devices, which subsequently delay their retransmission for some random length of time.
Datagram	A logical grouping of information sent as a network-layer unit over a transmission medium without prior establishment of a virtual circuit. The terms packet, frame, segment, and message are also used to describe logical information groupings at various layers of the OSI reference model and in various technologies. IP datagrams are the primary information units in the Internet.
Data link layer	Layer two of the OSI reference model. This layer takes a raw transmission facility and transforms it into a channel that appears, to the network layer, to be free of transmission errors. Its main services are addressing, error detection, and flow control.
DCS	Distributed control system.
DECnet	A group of communications products (including a protocol suite) developed and supported by Digital Equipment Corporation. The most recent iteration is DECnet Phase V, which is largely based upon the OSI protocols.
DNS	Domain name system. Distributed name system used in the Internet.
DTE	Data terminal equipment. The part of a data station that serves as a data source, destination, or both, and that provides for the data communications control function according to protocols. DTE includes computers, protocol translators, and multiplexers.
Emulation mode	Function of a network control program that enables it to perform activities equivalent to those performed by a transmission control unit.
Encryption	The application of a specific algorithm to data so as to alter the appearance of the data to make it incomprehensible to those who might attempt to misuse the information.
Enterprise network	A network (usually large, diverse) connecting most major points in a company. Differs from WAN network in that it is typically private and contained within a single organisation.
Ethernet	A baseband LAN specification invented by Xerox Corporation and developed jointly by Xerox, Intel, and Digital Equipment Corporation.
FDDI	Fibre distributed data interface. An ANSI defined standard specifying a 100 Mbps token passing network using fibre optic cable.
Fibre optic cable	Thin, flexible, medium capable of conducting modulated light transmission.
File server	A networked computer system that stores files for network users and provides network access to the files.
Flash EPROM	A EPROM (electronically programmable read-only memory) technology developed by Intel and licensed to other semiconductor companies, Flash EPROM is non-volatile storage that can be electrically erased in the circuit and reprogrammed.
Fragment	A piece of a larger packet that has been broken down to smaller units.
Fragmentation	The process of breaking a packet into smaller units when transmitting over a network medium that cannot support the original size of the packet.
Frame	A logical grouping of information sent as a link layer unit over a transmission medium.
Frame relay	A protocol used across the interface between user devices (hosts and routers) and network equipment (switching nodes).
FTP	File transfer protocol. An IP application protocol for transferring files between network nodes.
Full duplex	A capability for simultaneous transmission of data in both directions.
GAN	Global area network. A network that spans the globe.
Gateway	In the past, this referred to a routing device. Today, this refers to a special purpose device that performs a layer seven conversion of information from one protocol stack to another.
Hardware address	A data link layer address associated with a particular network device. Also called physical address or MAC layer address.
Header	Control information added (before data) when encapsulating the data for network transmission.
Hop	The passage of a packet through one router.
Hop count	A routing metric used to measure the distance between a source and a destination.
Host	Computer system on a network. Similar to the terms device or node except that host usually implies a computer system, whereas device and node generally apply to any networked system, including communication servers and routers.
Hub	A device that serves as the centre of a star topology network. In Ethernet/IEEE 802.3 terminology, a hub is an Ethernet multiple port repeater (sometimes called concentrator). Hub is also used to refer to a hardware/software device that contains multiple independent but connected modules of network and internetwork equipment.
Hybrid network	An internetwork made up of more than one type of network technology, including LAN and WAN networks.
ICMP	Internet control message protocol. A network layer Internet protocol that provides message packets to report errors and other information relevant to Internet protocol packet processing.
Interface	A connection between two systems or devices.
International standards organisation	Expansion of the acronym ISO.
Internet	The world's largest internetwork, connecting thousands of networks world-wide and having a "culture" based upon simplicity, research, and standardization based on real-life use.
Internet address	A 32 bit address assigned to hosts using TCP/IP. The address is written as four octets separated with periods (dotted decimal format) that are made up of a network section, an optional subnet section, and a host section. Also called IP address.
Internetwork	A collection of networks interconnected by routers that functions (generally) as a single network. Sometimes called an internet, which is not to be confused with the Internet.
Internetworking	The industry that has arisen around the problem of connecting networks together.
Interoperability	The ability of computing equipment manufactured by different vendors to communicate successfully over a network,
IP	Internet protocol. A layer three (network layer) protocol that contains addressing information and some control information that allows packets to be routed.
IP address	Refer to Internet address.
IPX	Internetwork packet exchange. Novell layer three protocol similar to XNS and IP that is used in NetWare networks.
ISDN	Integrated services digital.network Communication protocols proposed by telephone companies to permit telephone networks to carry data, voice, and other source material.
ISO	International organisation for standardization. Often incorrectly referred to as the international standards organisation. An international organisation that is responsible for a wide range of standards, including those relevant to networking.
lsochronous transmission	Asynchronous (start-stop) transmission over a synchronous data link.
LAN	Local area network. A network covering a relatively small geographic area (usually not larger than a floor or small building).
LAT	Local area transport. A network virtual terminal protocol developed by Digital Equipment Corporation.
Latency	The amount of time between when a device requests access to a network and when it is granted permission to transmit.
Leased line	A transmission line reserved by a communications carrier for the private use of a customer.
Line driver	Inexpensive amplifier/signal converter that conditions digital signals to insure reliable transmissions over extended distances.
MAC layer address	Refer to hardware address or physical address.
MAC sublayer	Media access control sublayer. The lower portion of the OSI reference model data link layer that Is concerned with media access issues, such as whether token passing or contention will be used.
MAN	Metropolitan area network. A network that spans a metropolitan area.
MAU	Medium attachment unit (IEEE 802.3) or multi-station access unit (IEEE 802.5). In IEEE 802.3, a device that performs IEEE 802.3 onto the network. A MAU is referred to as a transceiver in the Ethernet specification.
Mbps	Megabits per second.
Media	The physical environment through which transmission signals pass. Common network media include twisted pair, coaxial, fibre optic cable, and the atmosphere.
MMF	Multi-mode fibre optic cable.
Modem	Modulator-demodulator. A device that converts digital signals into a form suitable for transmission over analogue communication facilities and vice versa.
MTU	Maximum transmission unit. The maximum packet size, in bytes, that a particular interface will handle.
Multi-mode fibre	Optical fibre supporting propagation of multiple frequencies of light.
Multiplexing	Putting multiple signals on a single channel.
Name server	A server provided on the network that resolves network names into network locations or addresses..
Netbios	Network basic input/output system. A session layer interface for work stations networks from IBM and Microsoft =Symbol> .
NetView	IBM network management architecture and related applications.
NetWare	The world's most popular distributed file system that provides transparent remote file access and numerous other distributed network services.
Network	A collection of computers and other devices that are able to communicate with each other over some network medium.
Network address	A network layer address referring to a logical, rather than a physical, network device. Also called protocol address.
Network layer	Layer three of the OSI reference model. Layer three is the layer at which routing occurs.
Network management	Systems or actions that help maintain, characterize, or troubleshoot a network.
NIC	Network interface card. A circuit board that provides communication capabilities between a computer or computer system and a communication network. Also called adapter.
Node	An entity that can access a network. Also called device.
NOS	Network operating system. Distributed file systems such as NetWare, Banyan, VINES, NFS, LAN Manager, etc.
Null modem	Small box or cable used to join computing devices directly, rather than over a network.
NVRAM	Non-volatile RAM. Random access memory that retains its contents when a Unit is powered oft.
Open architecture	An architecture according to which third-party developers can legally develop products and for which public domain specifications exist.
OSI	Open system interconnection. An international standardization program created by ISO and CCITT to develop standards for data networking, that facilitates multiple vendor equipment interoperability.
OSI reference model	A network architectural model developed by ISO and CCITT, The model consists of seven layers, each of which specifies particular network functions such as addressing, flow control, error control, encapsulation, and reliable message transfer. The highest layer (the application layer) is closest to the user. The lowest layer (the physical layer) is closest to the media technology. The OSI reference model is used universally as a method for teaching and understanding network functionality.
Packet	A logical grouping of information that includes a header and (usually) user data.
Packet buffer	Storage area to hold incoming data until the receiving device can process the data.
Packet switching	Network on which nodes share bandwidth with each other by intermittently sending logical information units (packets).
Parity check	A process for checking the integrity of a character. A parity check involves appending a bit that makes the total number of binary 1 digits in a character or work (excludingthe parity bit) either odd (for 'odd parity") or even (for "even parity"),
PDU	Protocol data unit, Another work for packet as defined by the OSI.
Peer to peer computing	Distributed processing network systems in which each network device runs both client and server portions of an application,
Physical address	The link layer address of a network device. Also called hardware address.
Physical layer	Layer one of the OSI reference model. The physical layer defines the electrical, mechanical, and physical interfaces to the network and aspects of the network medium.
Ping	Packet internet grouper. Refers to the IOMP echo message and its reply. Often used to test the reachablility of a network device.
Port	An interface on an internetworking device.
PPP	Point-to-Point Protocol. A successor to SLIP protocol that provides router-to-router and host-to-network connections over synchronous and asynchronous circuits.
Presentation layer	Layer six of the OSI reference model. This layer is concerned with the syntax of the data exchanged between two application-layer entities.
Print server	A networked computer system that fields, manages, and executes print requests from other network devices.
Propagation delay	The time required for data to travel over a network from source to final destination.
Protocol	A formal description of a set of rules and conventions that govern how devices on a network exchange information.
Protocol converter	Enables equipment with different data formats to communicate by translating the data transmission code of one device to the data transmission code of another device.
Protocol stack	Related layers of protocol software that function together to implement a particular communications architecture.
Proxy	An entity that, in the interest of efficiency, essentially stands in for another entity.
Query	Message used to inquire about the value of some variable or set of variables.
Queue	An ordered list of elements waiting to be processed,
Repeater	A device that regenerates and propagates electrical signals between two network segments.
RFC	Request for comments. Documents used as the primary means for communicating information about the Internet. Some RFC's are designated as Internet standards.
RG-58	Coaxial cable with 50-ohm impedance.
RG-62	Coaxial cable with 93-ohm impedance (used by ARCnet).
Ring topology	Topology in which the network consists of a series of repeaters connected to one another by unidirectional transmission lines to form a single closed loop. Each station on the network connects to the network at a repeater.
RIP	Routing information protocol. An interior gateway protocol (IGP) supplied with Berkeley UNIX systems. RIP is the most common IGP in the Internet and uses hop count as a routing metric.
RJ-1 1	Standard four conductor connectors for phone lines.
RJ-45	Standard eight conductor connectors for IEEE 802.3 networks that also can be used as phone lines.
Route	A path through an internetwork.
Router	An OSI layer three device that can decide which of several paths network traffic will follow based upon some metric. Also called a gateway, routers forward packets from one network to another, based on network layer information.
Routing	The process of finding a path to the destination host. Routing is very complex in large networks because of the many potential intermediate destinations a packet might traverse before reaching its destination host.
Routing table	A table stored in a router or some other internetworking device that keeps track of routes to particular network destinations.
APO	Remote procedure call. The technological foundation of distributed (client-server) computing. Remote procedure calls are procedure calls that are built or specified by clients and executed on servers, with the results returned over the network to the clients.
RS-232-C	Popular physical layer interface.
Segment	TCP specification for a single transport layer unit of information.
Serial transmission	A method of data transmission in which the bits of a data character are transmitted sequentially over a single channel.
Sewer	A node or software program that provides services to a client.
Session layer	Layer five of the OSI reference model. Co-ordinates session activity between applications, Including application level error control, dialog control, and remote procedure calls.
Simplex transmission	Data transmission in only one direction.
Single mode fibre	Optical fibre with a relatively narrow diameter through which only one mode will. propagate. Such fibre is higher bandwidth than multiple mode fibre, but requires a light source with a narrow spectral width.
SLIP	Serial line internet protocol. Used to run IP over serial lines such as telephone circuits.
SMTP	Simple mail transfer protocol. An Internet protocol providing electronic mail services.
SNMP	Simple network management protocol. The Internet network management protocol. SNMP provides a means to monitor and set network configuration and runtime parameters.
Socket	Software structure operating as a communications end point within a network device.
SONET	Synchronous optical network. High speed (up to 2.5 Gbps) synchronous network approved as an international standard in 1988.
Source address	Address of a sending network device.
Spanning tree	A loop-free subset of a networks topology.
Spanning tree algorithm	An algorithm, the original version of which was invented by Digital Equipment Corporation, used to prevent bridging loops by creating a spanning tree.
Star topology	LAN topology in which end points on a network are connected to a common central switch by point-to-point links.
Store and forward	Message-switching technique where messages are temporarily stored at intermediate points between the source and destination until such time as network resources are available for message forwarding.
Subnet mask	A 32 bit address mask used in IP to specify a particular subnet.
Switch	Multiple port Ethernet device designed to increase network performance by allowing only essential traffic on the attached individual Ethernet cable segments. Packets are filtered or forwarded based upon their source and destination addresses.
Synchronous transmission	Operation of a network system wherein events occur with precise clocking.
T1	Bell system terminology referring to a digital carrier facility used for transmission of data through the telephone hierarchy. The rate of transmission is 1.544 Mbps.
T3	A digital WAN service that operates at 45 Mbps.
T connector	T shaped device with two female and one male BNC connectors.
TCP/IP	Transmission control protocol/internet protocol. The two best known Internet protocols, often erroneously thought of as one protocol. TCP corresponds to layer four (transport layer) of the OSI reference model. It provides reliable transmission of data. IP corresponds to layer three (network layer) of the OSI reference model and provides connectionless datagram service. TCP/IP was developed by the U.S. Department of Defense in the 1970s to support the construction of worldwide intemetworks.
TDR	Time domain reflectometer. Device capable of sending signals through a network medium to check cable continuity and other attributes. TDRs are used to find physical layer network problems.
Terminal emulation	A very popular network application in which a computer runs software that makes it appear to a host across the network as a directly attached dumb terminal.
TFTP	Trivial file transfer protocol. A simplified version of FTP allowing the transfer of files from one computer to another over a network.
Thinnet	IEEE 802.3 l0Base2 standard.
Thinwire	IEEE 802.3 specification coaxial cable that can support 10 Mbps and has a maximum distance of 185 meters (607 feet) per segment. Also called 10BASE2 or cheapemet.
Thickwire	IEEE 802.3 specification coaxial cable that can support 10 Mbps and has a maximum distance limit of 500 meters (1604 feet) per segment. Also called 10BASE5.
Time-out	An event that occurs when one network device expects to hear from, but does not hear from, another network device within a specified period of time. The resulting time-out usually results in a retransmission of information or the outright dissolving of the virtual circuit between the two devices.
Token ring	A token passing LAN network developed and supported by IBM.
Topology	The physical arrangement of network nodes and media within an enterprise networking structure.
Transceiver	Refer to MAU.
Transceiver cable	Refer to AUI cable.
Transport layer	Layer four of the OSI reference model. The transport layer is responsible for reliable network communication between end nodes.
Traps	Unsolicited messages sent by an SNMP agent to a network management system that indicate the occurrence of a significant event.
Twisted pair	Relatively low speed transmission medium consisting of two insulated wires arranged in a regular spiral pattern. The wires may be shielded or unshielded.
USENET	Initiated in 1979, one of the oldest and largest co-operative networks, with over 10,000 hosts and a quarter of a million users. Its primary service is news and a distributed conferencing service.
VINES	Virtual network system. A NOS developed and marketed by Banyan Systems.
Virtual network	The ability to create separate work groups within a network topology without having to after physical cabling.
WAN	Wide area network. A network spanning a wide geographic area.
Wiring closet	Specially designed room used for wiring data and voice networks. Wiring closets serve as a central junction point for wiring and wiring equipment that is used for interconnecting devices.
X.25	A CCITT standard that defines the packet format for data transfers in a public data network. Many establishments have X.25 networks in place that provide remote terminal access. These networks can be used for other types of data, including IP, DECnet,and XNS.
X.500	A CCITT recommendation specifying a standard for distributed maintenance of files and directories.
X windows	Distributed, network-transparent, device-independent, multitasking windowing and graphics system originally developed by MIT for communication between X terminals and UNIX workstations.