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.
IEEE 802.3 specification fibre optic cable that can support 10 Mbps and has a maximum distance of 2000 meters (6561 feet).
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.
IEEE 802.3 specification fibre optic cable that can support 100 Mbps and has a maximum distance of 412 meters (1352 feet)
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.
Application programming interface. A specification of function call conventions that defines an interface to a service.
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.
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.
Address resolution protocol. An Internet protocol used to bind an IP address to Ethernet /IEEE 802.3 addresses. Defined in RFC 826.
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.
American standard code for information interchange. An eight bit (seven bits plus parity) code for character representation.
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 of characters.
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.
Loss of communication signal energy.
Attachment unit interface. An IEEE 802.3 cable connecting the MAU (media access 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.
Balanced, unbalanced. Device used for matching impedance between a balanced and unbalanced line (usually twisted pair and coaxial cable).
The difference between the highest and lowest frequencies available for network signals. The term is also used to describe the rated throughput capacity.
Characteristic of a network technology where only one carrier frequency is used. Baseband is the opposite of broadband. Ethernetis an example of a baseband network.
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.
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.
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.
A protocol used by a network node to determine the IP address of its Ethernet interfaces, in order to effect network booting.
Boot programmable read-only memory. A chip mounted on a printed circuit board used to provide executable boot instructions to a computer device.
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.
A transmission system that multiplexes multiple independent signals onto one cable, Broadband is the opposite of baseband.
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 the whole length of the medium and are received by all other stations.
A series of consecutive binary digits that are operated upon as a unit (for example, an eight bit byte).
A signal suitable for modulation by another signal containing information to be transmitted.
Consultative committee for international telegraph and telephone. An international organisation that develops communication standards.
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 fixed length, they can be processed and switched in hardware at very high speeds.
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.
A node or software program (front end device) that requests services from a server.
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.
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.
Data transfer without the existence of a virtual circuit.
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.
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.
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.
Distributed control system.
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.
Domain name system. Distributed name system used in the Internet.
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.
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.
A baseband LAN specification invented by Xerox Corporation and developed jointly by Xerox®, Intel®, and Digital Equipment Corporation.
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.
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.
A piece of a larger packet that has been broken down to smaller units.
The process of breaking a packet into smaller units when transmitting over a network medium that cannot support the original size of the packet.
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).
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.
Global area network. A network that spans the globe.
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.
Control information added (before data) when encapsulating the data for network transmission.
The passage of a packet through one router.
Hop count A routing metric used to measure the distance between a source and a destination.
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.
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.
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.
A connection between two systems or devices.
International standards organisation
Expansion of the acronym ISO.
The world's largest internetwork, connecting thousands of networks world-wide and having a "culture" based upon simplicity, research, and standardisation 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.
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.
The industry that has arisen around the problem of connecting networks together.
The ability of computing equipment manufactured by different vendors to communicate successfully over a network,
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.
Internetwork packet exchange. Novell layer three protocol similar to XNS and IP that is used in NetWare® networks.
Integrated services digital.network Communication protocols proposed by telephone companies to permit telephone networks to carry data, voice, and other source material.
International organisation for standardisation. 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.
Local area network. A network covering a relatively small geographic area (usually not larger than a floor or small building).
Local area transport. A network virtual terminal protocol developed by Digital Equipment Corporation.
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.
Metropolitan area network. A network that spans a metropolitan area.
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.
Megabits per second.
The physical environment through which transmission signals pass. Common network media include twisted pair, coaxial, fibre optic cable, and the atmosphere.
Multi-mode fibre optic cable.
Modulator-demodulator. A device that converts digital signals into a form suitable for transmission over analogue communication facilities and vice versa.
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.
Putting multiple signals on a single channel.
Name server
A server provided on the network that resolves network names into network locations or addresses..
Network basic input/output system. A session layer interface for work stations networks from IBMand Microsoft
IBM network management architecture and related applications.
The world's most popular distributed file system that provides transparent remote file access and numerous other distributed network services.
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, characterise, or troubleshoot a network.
Network interface card. A circuit board that provides communication capabilities between a computer or computer system and a communication network. Also called adapter.
An entity that can access a network. Also called device.
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.
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.
Open system interconnection. An international standardisation 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.
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 (excluding the parity bit) either odd (for 'odd parity") or even (for "even parity").
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.
Packet internet grouper. Refers to the IOMP echo message and its reply. Often used to test the reachablility of a network device.
An interface on an internetworking device.
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.
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.
An entity that, in the interest of efficiency, essentially stands in for another entity.
Message used to inquire about the value of some variable or set of variables.
An ordered list of elements waiting to be processed,
A device that regenerates and propagates electrical signals between two network segments.
Request for comments. Documents used as the primary means for communicating information about the Internet. Some RFC's are designated as Internet standards.
Coaxial cable with 50-ohm impedance.
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.
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.
Standard eight conductor connectors for IEEE 802.3 networks that also can be used as phone lines.
A path through an internetwork.
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.
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.
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.
Popular physical layer interface.
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.
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.
Serial line internet protocol. Used to run IP over serial lines such as telephone circuits.
Simple mail transfer protocol. An Internet protocol providing electronic mail services.
Simple network management protocol. The Internet network management protocol. SNMP provides a means to monitor and set network configuration and runtime parameters.
Software structure operating as a communications end point within a network device.
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.
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.
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.
A digital WAN service that operates at 45 Mbps.
T connector
T shaped device with two female and one male BNC connectors.
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 internetworks.
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.
Trivial file transfer protocol. A simplified version of FTP allowing the transfer of files from one computer to another over a network.
IEEE 802.3 l0Base2 standard.
IEEE 802.3 specification coaxial cable that can support 10 Mbps and has a maximumdistance of 185 meters (607 feet) per segment. Also called 10BASE2 or cheapemet.
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.
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.
The physical arrangement of network nodes and media within an enterprise networking structure.
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.
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.
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.
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