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Subnetting Calc.
IEEE 802.11b




CNDS Glossary


IEEE-defined standard for 100Mbps Ethernet using multimode fiber-optic cable.

100Base-TX (802.3u)

IEEE-defined standard for 100Mbps Ethernet using two pairs of Cat-5 twisted-pair cable.


HP-derived network architecture based on the IEEE 802.12 standard that uses 100Mbps transmission rates. It uses a centrally controlled access method referred to as the Demand Priority Protocol (DPP), where the end node requests permission to transmit and the hub determines which node may do so, depending on the priority of the traffic.


IEEE-defined standard for 10Mbps Ethernet using twisted-pair cables.


IEEE-defined standard for LAN security. It is sometimes used by network switches as a VLAN protocol and uses a technique where frames on any LAN carry a virtual LAN identification. For large networks this can be modified to provided security over the Internet.

802.12 Demand Priority Protocol

IEEE-defined standard of transmitting 100Mbps over voice grade (telephone) twisted-pair cabling. See 100VG-AnyLAN.


IEEE-defined bridging standard for Spanning Tree protocol that is used to determine factors on how bridges (or switches) forward packets and avoid networking loops. Networks which use redundant loops (for alternative routes) need to implement the IEEE 802.1d standard to stop packets from looping forever.


A set of IEEE-defined specifications for Logical Link Control (LLC) layer. It provides some network functions and interfaces the IEEE 802.5, or IEEE 802.3, standards to the transport layer.


IEEE-defined standard for CSMA/CD networks. IEEE 802.3 is the most popular implementation of Ethernet.


IEEE-defined standard for 100Mbps Fast Ethernet. It also covers a technique called auto sensing which allows 100Mbps devices to connecting to 10Mbps devices.


IEEE-defined token bus specifications.


IEEE-defined standard for token ring networks.


ATM adaptation layer. A service-dependent sublayer of the data link layer, which accepts data from different applications and presents it to the ATM layer as a 48-byte ATM payload segment. AALs have two sublayers: CS and SAR. There are four types of AAL, recommended by the ITU-T, these are: AAL1, AAL2, AAL3/4, and AAL5.


ATM adaptation layer 1. Connection-oriented, delay-sensitive services requiring constant bit rates, such as uncompressed video and other isochronous traffic.


ATM adaptation layer 2. Connection-oriented services that support a variable bit rate, such as some isochronous video and voice traffic.


ATM adaptation layer 3/4. Connectionless and connection-oriented links, but is primarily used for the transmission of SMDS packets over ATM networks.


ATM adaptation layer 5. Connection-oriented, VBR services, and is used predominantly for the transfer of classical IP over ATM and LANE traffic.


AppleTalk Address Resolution Protocol. An AppleTalk protocol which maps the data-link address to a network address.


AppleTalk probe packets. Data packets which determine if a node ID is being used by another node in a AppleTalk network. If the node determines that the node ID is not being used, the node will use it. If not, it will send out more AARP packets.


Asynchronous Balanced Mode. An HDLC communication mode supporting peer-oriented, point-to-point communications between two nodes, where either station can initiate transmission.


Available bit rate. A QoS class defined by the ATM Forum for ATM networks. ABR is used for connections that do not require a timing relationships between source and destination. It also provides no guarantees in terms of cell loss or delay, providing only best-effort service.

Access list

A list which is kept by Cisco routers which define the control access for the router.

Access method

The method that network devices use to access the network medium.

Access server

A communications device that allows the connection of asynchronous devices, such as serial port terminals, to a LAN. It thus converts an asynchronous protocol to a synchronous one.


Notification sent from one network device to another to acknowledge an event.


Allowed cell rate. This is used in ATM and is used for traffic management.


Association control service element. This has been defined by the OSI and is used to establish, maintain, or terminate a connection between two applications.

Active hub

Multiported device that amplifies LAN transmission signals.

Active monitor

A device which is responsible for managing a Token Ring. A node becomes the active monitor if it has the highest MAC address on the ring, and is responsible for such management tasks, such as ensuring that tokens are not lost, or that frames do not circulate indefinitely.


Device which usually connects a node onto a network, normally called a network interface adapter (NIC).

Adaptive cut-through switching

A forwarding technique on a switch which determines when the error count on frames received has exceeded the pre-configured limits. When this count is exceeded, it modifies its own operating state so that it no longer performs cut-through switching and goes into a store-and-forward mode. The cut-through method is extremely fast but suffers from the inability to check the CRC field. Thus if incorrect frames are transmitted they could have severe effects on the network segment. This is overcome with an adaptive cut-through switch by checking the CRC as the frame moves through the switch. When errors become too great the switch implements a store-and-forward method.


Adaptive delta modulation PCM

Similar to delta modulation PCM, but uses a number of bits to code the slope of the signal.

Adaptive Huffman coding

Uses a variable Huffman coding technique which responds to local changes in probabilities.


Advanced Data Communications Control Protocol. An ANSI-defined standard for a bit-oriented data link control protocol.

Address aging

The time that a dynamic address stays in the address routing table of a bridge or switch.

Addressed call mode

A mode that uses control signals and commands to establish and terminate calls in V.25bis.

Address resolution

Resolves the data link layer address from the network layer address.

Address tables

These are used by routers, switches and hubs to store either physical (such as MAC addresses) or higher-level addresses (such as IP addresses). The tables map node addresses to network addresses or physical domains. These address tables are dynamic and change due to nodes moving around the network.


A unique label for the location of data or the identity of a communications device. This address can either be numeric or alphanumeric.

Administrative distance

Rating of the trustworthiness of a routing information source (typically between 0 and 255). The higher the value, the lower the trustworthiness rating.

Address mask

A combination of bits which define the address part and the host part.

Address resolution

A method which resolves differences in addressing schemes, typically between data link and network addresses.

Administrative distance

Used on Cisco routers to define the trustworthiness of a routing information source. It varies between 0 and 255, where 255 gives the lowest trustworthiness rating.


Method used by routers where routing or service updates are sent at specified intervals so that other routers on the network can maintain lists of usable routes.


AppleTalk Echo Protocol. This is used to test the connectivity between two AppleTalk nodes.


A program which allows users to configure or fault-find nodes on a network, and also a program that processes queries and returns replies on behalf of an application.


The removal of an address from the address table of a router or switch that is no longer referenced to forward a packet.


The ITU-T companding standard used in the conversion between analog and digital signals in PCM systems. Used mainly in European telephone networks.

Alignment error

In Ethernet, an error that occurs when the total number of bits of a received frame is not divisible by eight.


Amplitude modulation. Modulation technique which represents the data as the amplitude of a carrier signal.


American National Standards Institute. ANSI is a non-profit making organization which is made up of expert committees that publish standards for national industries.


American Standard Code for Information Interchange. An ANSI-defined character alphabet which has since been adopted as a standard international alphabet for the interchange of characters.


Amplitude modulation. Information is contained in the amplitude of a carrier.


Amplitude-Shift Keying. Uses two, or more, amplitudes to represent binary digits. Typically used to transmit binary over speech-limited channels.


Series of communications protocols designed by Apple Computer.

Application layer

The highest layer of the OSI model.


Address Resolution Protocol. Internet protocol used to map an IP address to a MAC address.


Advanced Research Projects Agency. Research and development organization that is part of DoD. ARPA evolved into DARPA, but have since changed back to ARPA.


Advanced Research Projects Agency Network, which was developed in the 1970s (funded by ARPA, then DARPA).


Abstract Syntax Notation One. OSI language for describing data types independent of particular computer structures and representation techniques.

Asynchronous transmission

Transmission where individual characters are sent one-by-one. Normally each character is delimited by a start and a stop bit. With asynchronous communications the transmitter and receiver only have to be roughly synchronized.


Communication which does not depend on a clock.


Asynchronous Transfer Mode. Networking technology which involves sending 53-byte fast packets (ATM cell), as specified by the ANSI T1S1 subcommittee. The first 5 bytes are the header and the remaining bytes are the information field which can hold 48 bytes of data. Optionally the data can contain a 4-byte ATM adaptation layer and 44 bytes of actual data. The ATM adaptation layer field allows for fragmentation and reassembly of cells into larger packets at the source and destination respectively. The control field also contains bits which specify whether this is a flow control cell or an ordinary data cell, a bit to indicate whether this packet can be deleted in a congested network, and so on.

ATM Forum

Promotes standards-based implementation agreements for ATM technology.

ATM layer

Service-independent sublayer of the data link layer in an ATM network. The ATM layer receives the 48-byte payload segments from the AAL and attaches a 5-byte header to each, producing standard 53-byte ATM cells.


Loss of communication signal energy.


Attachment unit interface. In Ethernet, it is the interface between an MAU and a NIC (network interface card).

Automatic broadcast control

Technique which minimizes broadcast and multicast traffic flooding through a switch. A switch acts as a proxy server and screens previously resolved ARP. This eliminates broadcasts associated with them.


Technique used by an IEEE 802.3u node which determines whether a device that it is receiving or transmitting data in one of a number of Ethernet modes (100Base-TX, 100Base-TX Full Duplex, 10Base-T, 10Base-T Full Duplex or 100Base-T4). When the mode is learned, the device then adjusts to the required transmission speed.

Autonomous system

A collection of networks which have a common administration and share a common routing strategy. Each autonomous system is assigned a unique 16-bit number by the IANA.


Used by a 100Base-TX device to determine if the incoming data is transmitted at 10Mbps or 100Mbps.

Back pressure

Technique which slows the incoming data rate into the buffer of a 802.3 port preventing it from receiving too much data. Switches which implement back pressure will transmit a jam signal to stop data input.

Backbone cabling

Cabling interconnects wiring closets, wiring closets, and between buildings.


The primary path for networked traffic.


The retransmission delay enforced when a collision occurs.


Bandwidth allocation control protocol. Protocol which monitors network traffic and allows or disallows access to users, depending on their needs. It is awaiting approval by the IETF.


In an analogue system it is defined as the range of frequencies contained in a signal. As an approximation it is the difference between the highest and lowest frequency in the signal. In a digital transmission system it is normally quoted as bits per second.


Data transmission using unmodulated signals.


Basic rate interface. Connection between ISDN and the user. It has three separate channels, one D-channel (which carries control information) and two B channels (which carry data).

Baud rate

The number of signaling elements sent per second with RS-232, or modem, communications. In RS-232 the baud rate is equal to the bit-rate. With modems, two or more bits can be encoded as a single signaling element, such as 2 bits being represented by four different phase shifts (or one signaling element). The signaling element could change its amplitude, frequency or phase-shift to increase the bit-rate. Thus the bit-rate is a better measure of information transfer.


Bit error rate. The ratio of received bits that contain errors.


Border Gateway Protocol. Interdomain routing protocol that replaces EGP.


Method of storing or transmitting data in which the most significant bit or byte is presented first.

Bit stuffing

The insertion of extra bits to prevent the appearance of a defined sequence. In HDLC the bit sequence 01111110 delimits the start and end of a frame. Bit stuffing stops this bit sequence from occurring anywhere in the frame by the receiver inserting a 0 whenever there are five consecutive 1?s transmitted. At the receiver if five consecutive 1?s are followed by a 0 then the 0 is deleted.


A commonly used connector for coaxial cable.


A standard TCP/IP protocol which allows nodes to be dynamically allocated an IP address from an Ethernet MAC address.

Border gateway

Router that communicates with routers in other autonomous systems.


A device which physically links two or more networks using the same communications protocols, such as Ethernet/Ethernet or token ring/token ring. It allows for the filtering of data between network segments.


Data transmission using multiplexed data using an analogue signal or high-frequency electromagnetic waves.

Broadcast address

Special address reserved for sending a message to all stations. Generally, a broadcast address is a MAC destination address of all ones.

Broadcast domain

Network where broadcasts can be reported to all nodes on the network bounded by routers. Broadcast packets cannot traverse a router.

Broadcast storm

Flood of broadcast packets generated by a broadcast transmission where high numbers of receivers are targeted for a long period of time.


Data packet that will be sent to all nodes on a network. Broadcasts are identified by a broadcast address.


Berkeley Standard Distribution. Term used to describe any of a variety of UNIX-type operating systems.


A temporary-storage space in memory.


A network topology where all nodes share a common transmission medium.


A group of eight bits.


The maximum data rate in Mbps.

Cat-1 cable

Used for telephone communications and is not suitable for transmitting data.

Cat-2 cable

Used for transmitting data at speeds up to 4 Mbps.

Cat-3 cable

An EIA/TIA-568 wiring standard for unshielded or shielded twisted pair cables. Up to 10Mbps.

Cat-4 cable

Used in Token Ring networks and can transmit data at speeds up to 16 Mbps.

Cat-5 cable

An EIA/TIA-568 wiring standard for unshielded or shielded twisted-pair cables for the transmission of over 100Mbps.


Constant bit rate. QOS class defined by the ATM Forum for ATM networks and is used for connections that depend on precise clocking to ensure undistorted delivery.


Consultative Committee for International Telegraph and Telephone. International organization responsible for the development of communications standards. Now named ITU-T.


Cisco Discovery Protocol. Used in Cisco routers, bridges and switches to pass information on the connected networks.

Cell relay

Networking technology based on the use of small, fixed-size packets, or cells.


The basic unit for ATM switching and multiplexing. Cells contain identifiers that specify the data stream to which they belong. Each cell consists of a 5-byte header and 48 bytes of payload.


Conf,rence Europ,enne des Postes et des T,l,communications. Association


Challenge-handshake authentication protocol. Identification method used by PPP to determine the originator of a connection.


IEEE 802.3 10Base2 standard.


An error-detection scheme in which bits are grouped to form integer values which are then summated. Normally, the negative of this value is then added as a checksum. At the receiver, all the grouped values and the checksum are summated and, in the absence of errors, the result should be zero.

Circuit switching

Switching system in which a dedicated physical circuit path must exist between sender and receiver for the call duration

Cisco IOS software

Cisco Internetwork Operating System software. Provides an operating system for a Cisco router.


Node or program that connects to a server node or program.


Cell loss priority. Field in the ATM cell header that determines the probability of a cell being dropped if the network becomes congested.

Coaxial cable

A transmission medium consisting of one or more central wire conductors surrounded by an insulating layer and encased in either a wire mesh or extruded metal sheathing. It supports RF frequencies from 50 to about 500 MHz. It comes in either a 10-mm diameter (thick coax) or a 5-mm diameter (thin coax).

Collapsed backbone

Non-distributed backbone in which all network segments are interconnected by way of an internetworking device.

Collision domain

The network area within which frames that have collided are propagated. Repeaters and hubs propagate collisions, but switches, bridges and routers do not.


Occurs when one or more devices try to transmit over an Ethernet network simultaneously.


Describes data transfer without the existence of a virtual circuit.


Describes data transfer that requires the establishment of a virtual circuit. See also connectionless.


Access method in which network devices compete to get access the physical medium.


The speed and ability of a group of internetworking devices running a specific routing protocol to agree on the topology of an internetwork after a change in that topology.


Copper distributed data interface. FDDI over copper.


An arbitrary value used by routers to compare different routes. Typically it is measured by hop counts, typical time delays or bandwidth.

Count to infinity

Occurs in routing algorithms that are slow to converge, where routers continuously increment the hop count to particular networks. It is typically overcome by setting an arbitrary hop-count limit.


Cyclic Redundancy Check. An error-detection scheme.


Interference noise caused by conductors radiating electromagnetic radiation to couple into other conductors.


Carrier sense multiple access collision detect. Media-access method in which nodes contend to get access to the common bus. If the bus is free of traffic (Carrier Sense) any of the nodes can transmit (Multiple Access). If two nodes gain access at the same time then a collision occurs (Collision Detection). A collision then occurs, and the nodes causing the collision then wait for a random period of time before they retransmit. CSMA/CD access is used by Ethernet and IEEE 802.3.

Cut sheet

Rough diagram indicating where cable runs are located and the numbers of rooms they lead to.

Cut-through switching

Technique where a switching device directs a packet to the destination port(s) as soon as it receives the destination and source address scanned from the packet header.


Defense Advanced Research Projects Agency. US government agency that funded research for and experimentation with the Internet.

Data link layer

Second layer of the OSI model which is responsible for link, error and flow control. It normally covers the framing of data packets, error control and physical addressing. Typical data link layers includes Ethernet and FDDI.

Data stream

All data transmitted through a communications line in a single read or write operation.


Logical grouping of information sent as a network layer unit over a transmission medium without prior establishment of a virtual circuit. IP datagrams are the primary information units in the Internet.


Data communications equipment. These are devices and connections of a communications network that comprise the network end of the user-to-network interface, such as modems and cables.

Decorative raceway

Wall-mounted channel with removable cover used to support horizontal cabling.

Delta modulation PCM

Uses a single-bit code to represent the analogue signal. A 1 is transmission when the current sample increases its level, else a 0 is transmitted. Delta modulation PCM requires a higher sampling rate that the Nyquist rate, but the actual bit rate is normally lower.

Destination MAC address

A 6-byte data unique of the destination MAC address. It is normally quoted as a 12-digit hexadecimal number (such as A5:B2:10:64:01:44).

Destination network address

A unique Internet Protocol (IP) or Internet Packet Exchange (IPX) address of the destination node.

Differential encoding

Source coding method which is used to code the difference between two samples. Typically used in real-time signals where there is limited change between one sample and the next, such as in audio and speech.

Distance vector routing algorithm

Routing algorithms which use the number of hops in a route to find a shortest-path spanning tree. With distance vector routing algorithms, each router to send its entire routing table in each update, but only to its neighbors. They be prone to routing loops, but are relatively simple as compared with link state routing algorithms.


Domain Naming System. Used on the Internet to translated domain names into IP addresses.

Dot address

Notation for IP addresses in the form where each number represents, in decimal, 1 byte of the 4-byte IP address.


Distributed Queue Dual Bus. Data link layer communication protocol, specified in the IEEE 802.6 standard, designed for use in MANs.


Data terminal equipment. Device at the user end of a user-network interface that is a data source, destination, or both.

Dual homing

Topology where devices connect to the network by two independent access points (points of attachment). One gives the primary connection, and the other is the standby connection that is activated in the event of a failure of the primary connection.

Dynamic address resolution

Use of an address resolution protocol to determine and store address information on demand.


Dynamic host control protocol. It manages a pool of IP addresses for computers without a known IP address. This allows a finite number of IP addresses to be reused quickly and efficiently by many clients.

Dynamic routing

Routing that adjusts automatically to network topology or traffic changes.


Wide-area digital transmission scheme that is used in Europe to carry data at a rate of 2.048 Mbps.

Early token release

Used in Token Ring networks that allows stations to release the token onto the ring immediately after transmitting, instead of waiting for the first frame to return.


Exterior Gateway Protocol. Internet protocol for exchanging routing information between autonomous systems (RFC904). Replaced by BGP.


Electronic Industries Association. Specifies electrical transmission standards.


Physical layer interface standard that supports unbalanced circuits at signal speeds of up to 64 kbps.


Physical layer interface for rates up to 2 Mbps.


Characteristics and applications for UTP cabling.


Standard for the telecommunications infrastructure of commercial buildings, such as terminations, media, pathways, spaces and grounding.


Wrapping of data in a particular protocol header.

End system

An end-user device on a network.


An individual, manageable network device.

Entropy coding

Coding scheme which does not take into account the characteristics of the data and treats all the bits in the same way. It produces lossless coding. Typical methods used are statistical encoding and suppressing repetitive sequences.


Used to compensate for communications channel distortions.

Ethernet address

48-bit number that identifies a node on an Ethernet network. Ethernet addresses are assigned by the Xerox Corporation.


A local area network which uses coaxial, twisted-pair or fiber-optic cable as a communication medium. It transmits at a rate of 10Mbps and was developed by DEC, Intel and Xerox Corporation. The IEEE 802.3 network standard is based upon Ethernet.


European Telecommunication Standards Institute. Created by the European PTTs and the European Community (EC) for telecommunications standards in Europe.

Even parity

An error-detection scheme where defined bit-groupings have an even number of 1?s.


Extended Binary Coded Decimal Interchange Code. An 8-bit code alphabet developed by IBM allowing 256 different bit patterns for character definitions.

Exterior gateway protocol

Any internetwork protocol that exchanges routing information between autonomous systems.

Fast Ethernet

See IEEE 802.3u standard.

Fat pipe

Term used to indicate a high level of bandwidth the defined port.


Fiber Distributed Data Interface. A standard network technology that uses a dual counter-rotating token-passing fiber ring. It operates at 100Mbps and provides for reliable backbone connections.

File server

Computer that allows the sharing of files over a network.


File transfer protocol. A protocol for transmitting files between host computers using the TCP/IP protocol.


Device which filters incoming and outgoing traffic.

Flow control

Procedure to regulate the flow of data between two nodes.

Forward adaptive bit allocation

This technique is used in audio compression and makes bit allocation decisions adaptively, depending on signal content.

Fragment free cut-through switching

A modified cut-through switching technique where a switch or switch module waits until it has received a large enough packet to determine if it is error free.


Frame check sequence. Standard error detection scheme.


Normally associated with a packet which has layer 2 information added to it. Packets are thus contained within frames. Frames and packets have variable lengths as opposed to cells which have fixed lengths.


Frequency-shift Keying. Uses two, or more, frequencies to represent binary digits. Typically used to transmit binary data over speech-limited channels.

Full duplex

Simultaneous, two-way communications.


A device that connects networks using different communications protocols, such as between Ethernet and FDDI. It provides protocol translation, in contrast to a bridge which connects two networks that are of the same protocol.


Standard image compression technique which is copyrighted by CompuServe Incorporated. It uses LZW compression and supports a palette of 256 24-bit colors (16.7M colors). GIF support local and global color tables and animated images.

Half-duplex (HDX)

Two-way communications, one at a time.


Messages or signals exchanged between two or more network devices to ensure transmission synchronization.


A reliable method for two devices to pass data.


Horizontal cross-connect. Wiring closet where the horizontal cabling connects to a patch panel which is connected by backbone cabling to the main distribution facility.


ISO standard for the data link layer.

Hello packet

Message transmitted from a root bridge to all other bridges in the network to constantly verify the Spanning Tree setup.

Heterogeneous network

Network consisting of dissimilar devices that run dissimilar protocols.

Hierarchical routing

Routing based on a hierarchical addressing system. IP has a hierarchical structure as they use network numbers, subnet numbers, and host numbers.


A router state where they will not advertise information on a specific route, nor accept advertisements about the route for a specific length of time (the hold-down period). This time is used to flush bad information about a route from all routers in the network, or when a fault occurs on a route.

Hop count

Used by the RIP routing protocol to measure the distance between a source and a destination.


The number of gateways and routers in a transmission path.

Host number

Part of an IP address which identifies the node on a subnetwork.


A computer that communicates over a network. A host can both initiate communications and respond to communicaštions that are addressed to it.


A hub is a concentration point for data and repeats data from one node to all other connected nodes. Hubs can be active (where they repeat signals sent through them) or passive (where they do not repeat, but merely split, signals sent through them).

Huffman coding

Uses a variable length code for each of the elements within the data. It normally analyses the probability of the element in the data and codes the most probable with fewer bits than the least probable.

Hybrid network

Internetwork made up of more than one type of network technology.


Hypertext markup language. Standard language that allows the integration of text and images over a distributed network.


Internet Architecture Board. A group that discusses important matters relating to the Internet.


Internet Assigned Numbers Authority. Organization which delegates authority for IP address-space allocation and domain-name assignment to the NIC and other organizations.


Internet Control Message Protocol. Used to report errors and provides other information relevant to IP packet processing.


Internet Engineering Task Force. Consists of a number of working groups which are responsible for developing Internet standards.


Interior Gateway Protocol. Used to exchange routing information within an autonomous system.


Interior Gateway Routing Protocol. Developed by Cisco for large and heterogeneous networks.


Integrated systems digital network. Communication technology that contains two data channels (2B) and a control channel (H). It supports two 64kbps data channels and sets up a circuit-switched connection.


International Telegraph Union Telecommunications Standards Sector. Organization which has replaced the CCITT.

Internet address

An address that conforms to the DARPA-defined Internet protocol. A unique, four byte number identifies a host or gateway on the Internet. This consists of a network number followed by a host number. The host number can be further divided into a subnet number.


Internet Engineering Task Force. A committee that reviews and supports Internet protocol proposals.


Connection of nodes on a global network which use a DARPA-defined Internet address.


Two or more connected networks that may, or may not, use the same communication protocol.


A company specific network which has additional security against external users.

Inverse ARP

Inverse Address Resolution Protocol. This is a method of building dynamic routes in a network, and allows an access server to discover the network address of a device associated with a virtual circuit.

IP (Internet Protocol)

Part of the TCP/IP which provides for node addressing.

IP address

An address which is used to identify a node on the Internet.

IP multicast

Addressing technique that allows IP traffic to be propagated from one source to a group of destinations.


Internet Packet Exchange. Novell NetWare communications protocol which is similar to the IP protocol. The packets include network addresses and can be routed from one network to another.

IPX address

Station address on a Novell NetWare network. It consists of two fields: a network number field and a node number field. The node number is the station address of the device and the network number is assigned to the network when the network is started up. It is written in the form: NNNNNNNN:XXXXXX-XXXXXX, where N?s represent the network number and X?s represent the station address. An example of an IPX address is: DC105333:542C10-FF1432.


International Standards Organization.

Isochronous transmission

Asynchronous transmission over a synchronous data link. Isochronous signals require a constant bit rate for reliable transport.


The Consultative Committee for International Telephone and Telegraph (now known at the ITU-TSS) is an advisory committee established by the United Nations. It attempts to establish standards for inter-country data transmission on a worldwide basis.


Occurs when the transmission of network signals exceeds the maximum allowable transmission time (20 ms to 150 ms). The medium becomes overrun with data packets. This is caused by a faulty node or wiring connection.


Movement of the edges of pulse over time, that may introduce error and loss of synchronization.


Image compression technique defined by the Joint Photographic Expert Group (JPEG), a subcommittee of the ISO/IEC. It uses a DCT, quantization, run-length and Huffman coding.

Keep alive interval

Time period between each keep alive message.


Defines the amount of time between a device receiving data and it being forwarded on. Hubs have the lowest latency (less than 10ms), switches the next lowest (between 40ms and 60ms), then bridges (200ms to 300ms) and routers have the highest latency (around 1000ms).

Learning bridge

Bridge which learns the connected nodes to it. It uses this information to forward or drop frames.

Leased line

A permanent telephone line connection reserved exclusively by the leased customer. There is no need for any connection and disconnection procedures.

Lempel-Ziv coding

Coding method which takes into account repetition in phases, words or parts of words. It uses pointers to refer to previously defined sequences.

LZW coding

Lempel-Ziv Welsh coding. Coding method which takes into account repetition in phases, words or parts of words. It builds up a dictionary of previously sent (or stored) sequences.

Line driver

A device which converts an electrical signal to a form that is transmit-table over a transmission line. Typically, it provides the required power, current and timing characteristics.

Link layer

Layer 2 of the OSI model.

Link segment

A point-to-point link terminated on either side by a repeater. Nodes cannot be attached to a link segment.

Link state routing algorithm

Routing algorithm where each router broadcasts or multicasts information regarding the cost of reaching each of its neighbors to all nodes in the internetwork. These algorithms create a consistent view of the network but are much more complete that distance vector routing algorithms).


Storage method in which the least byte is stored first.


Logical Link Control. Higher of the two data link layer sublayers defined by the IEEE, which provides error control, flow control, framing, and MAC-sublayer addressing (IEEE 802.2).

Lossless compression

Where information, once uncompressed, is identical to the original uncompressed data.

Lossy compression

Where information, once uncompressed, cannot be fully recovered.


Link-state advertisement. Used by link-state protocols to advertise information about neighbors and path costs.

MAC address

A 6-byte data unique data-link layer address. It is normally quoted as a 12-digit hexadecimal number (such as A5:B2:10:64:01:44).

Masking effect

Where noise is only heard by a person when there are no other sounds to mask it.


Medium Dependent Interface. The IEEE standard for the twisted-pair interface to 10Base-T (or 100Base-TX).


Media Access Control. Media-specific access-control for Token Ring and Ethernet.


Media Interface Controller. Media-specific access-control for Token Ring and Ethernet.


Medium Attachment Unit. Method of converting digital data into a form which can be transmitted over a band-limited channel. Methods use either ASK, FSK, PSK or a mixture of ASK, FSK and PSK.


Division of a network into smaller segments. This helps to increase aggregate bandwidth to network devices.


Modulator-Demodulator. A device which converts binary digits into a form which can be transmitted over a speech-limited transmission channel.


Maximum Transmission Unit. The largest packet that the IP protocol will send through the selected interface or segment.


Packets which are sent to all nodes on a subnet of a group within a network. This differs from a broadcast which forwards packet to all users on the network.

Multimode fiber

Fiber-optic cable that has the ability to carry more than one frequency (mode) of light at a time.


Network driver interface specification. Software specification for network adapter drivers. It supports multiple protocols and multiple adapters, and is used in many operating systems, such as Windows.

Network layer

Third layer of the OSI model, which is responsible for ensuring that data passed to it from the transport layer is routed and delivered through the network. It provides end-to-end addressing and routing. It provides support for a number of protocols, including IP, IPX, CLNP, X.25, or DDP.


Network termination. Network termination for ISDN.


Network File System. Standard defined by Sun Microsystems for accessing remote file systems over a network.


Network Information Service. Standard defined by Sun Microsystems for the administration of network-wide databases.


NetWare Loadable Module. Program that can be loaded into the NetWare NOS.


Any point in a network which provides communications services or where devices interconnect.

N-series connectors

Connector used with thick coaxial cable.


Same as a byte, a group of eight bits (typically used in communications terminology).

Odd parity

An error-detection scheme where a defined bit-grouping has an odd number of 1?s.


Open Data-Link Interface. Software specification for network adapter drivers used in NetWare and Apple networks. It supports multiple protocols and multiple adapters.

Optical repeater

A device that receives, restores, and re-times signals from one optical-fiber segment to another.

Packet switching

Network switching in which data is processed in units of whole packets rather than attempting to process data by dividing packets into fixed-length cells.


A sequence of binary digits that is transmitted as a unit in a computer network. A packet usually contains control information and data. They normally are contained with data link frames.


Password authentication protocol. Protocol which checks a user?s password.

Patch panel

An assembly of pin locations and ports which are typically mounted on a rack or wall bracket in the wiring closet.


Phase-Locked Loop. Tunes into a small range of frequencies in a signal and follows any variations in them.


Phase-Shift Keying. Uses two, or more, phase-shifts to represent binary digits. Typically used to transmit binary data over speech-limited channels.

Physical layer

Lowest layer of the OSI model which is responsible for the electrical, mechanical, and handshaking procedures over the interface that connects a device to a transmission medium


Standard protocol used to determine if TCP/IP nodes are alive. Initially a node sends an ICMP (Internet Control Message Protocol) echo request packet to the remote node with the specified IP address and waits for echo response packets to return.


Point of presence. Physical access point to a long distance carrier interchange.


Point-to-point protocol. Standard protocol to transfer data over the Internet asynchronously or synchronously.


Physical connection on a bridge or hub that connects to a network, node or other device.


Power-on self test. Hardware diagnostics that runs on a hardware device when that device is powered up.


Specification for coding of messages exchanged between two communications processes.


Involves converting an analogue level into a discrete quantized level. The number of bits used in the quantization process determines the number of quantization levels.

Quartet signaling

Signaling technique used in 100VG-AnyLAN networks that allows data transmission at 100Mbps over frame pairs of UTP cabling.


A device that receives, restores, and re-times signals from one segment of a network and passes them on to another. Both segments must have the same type of transmission medium and share the same set of protocols. A repeater cannot translate protocols.


Reverse address resolution protocol. The opposite of ARP which maps an IP address to a MAC address.


Connector used with US telephones and with twisted-pair cables. It is also used in ISDN networks, hubs and switches.


An SNMP MIB that specifies the types of information listed in a number of special MIB groups that are commonly used for traffic management. Some of the popular groups used are Statistics, History, Alarms, Hosts, Hosts Top N, Matrix, Filters, Events, and Packet Capture.

Routing node

A node that transmits packets between similar networks. A node that transmits packets between dissimilar networks is called a gateway.


EIA-defined standard for serial communications.

RS-422, 423

EIA-defined standard which uses higher transmission rates and cable lengths than RS-232.


EIA-defined standard for the interface between a DTE and DCE for 9- and 37-way D-type connectors.


EIA-defined standard which is similar to RS-422 but uses a balanced connection.


Run-length encoding. Coding technique which represents long runs of a certain bit sequence with a special character.


Service Access Point. Field defined by the IEEE 802.2 specification that is part of the address specification.


Service Advertisement Protocol. Used by the IPX protocol to provide a means of informing network clients, via routers and servers of available network resources and services.


A segment is any length of LAN cable terminated at both ends. In a bus network, segments are electrically continuous pieces of the bus, connected by repeaters. It can also be bounded by bridges and routers.


Serial line internet protocol. A standard used for the point-to-point serial connections running TCP/IP.


One-way communication.


Simple Network Management Protocol. Standard protocol for managing network devices, such as hubs, bridges, and switches.

Source encoding

Coding method which takes into account the characteristics of the information. Typically used in motion video and still image compression.

Statistical encoding

Where the coding analyses the statistical pattern of the data. Commonly occurring data is coded with a few bits and uncommon data by a large number of bits.

Suppressing repetitive sequences

Compression technique where long sequences of the same data is compressed with a short code.


A very fast, low-latency, multiport bridge that is used to segment local area networks.


Data which is synchronized by a clock.


Digital WAN carrier facility for 1.544 Mbps transmission.


Part of the TCP/IP protocol which provides an error-free connection between two cooperating programs.

TCP/IP Internet

An Internet is made up of networks of nodes that can communicate with each other using TCP/IP protocols.


Standard program which allows remote users to log into a station using the TCP/IP protocol.


Graphics format that supports many different types of images in a number of modes. It is supported by most packages and, in one mode, provides for enhanced high-resolution images with 48-bit color.

Time to live

A field in the IP header which defines the number of routers that a packet is allowed to traverse before being discarded.


A token transmits data around a token ring network.


The physical and logical geometry governing placement of nodes on a network.


A device that transmits and receives signals.

Transform encoding

Source-encoding scheme where the data is transformed by a mathematical transform in order to reduce the transmitted (or stored) data. A typical technique is the discrete cosine transform (DCT) and the fast Fourier transform (FFT).

Transport layer

Fourth layer of the OSI model. It allows end-to-end control of transmitted data and the optimized use of network resources.


Universal asynchronous receiver transmitter. Device which converts parallel data into a serial form, which can be transmitted over a serial line, and vice-versa.


ITU-T-defined specification, similar to RS-232C.


ITU-T specification describing procedures for call set-up and disconnection over the DTE-DCE interface in a PSDN.


ITU-T standard serial communication for bi-directional data transmissions at speeds of 4.8 or 9.6Kbps, or 14.4 Kbps for V.32bis.


Improved v.32 specification with higher transmission rates (28.8Kbps) and enhanced data compression.


ITU-T standard describing a synchronous, physical layer protocol used for communications between a network access device and a packet network.


ITU-T standard protocol for error correction.

VLC-LZW code

Variable-length-code LZW code. Uses a variation of LZW coding where variable-length codes are used to replace patterns detected in the original data.

Vertical cabling

Backbone cabling.

Virtual circuit

Logical circuit which connects two networked devices together.


Collection of nodes on a LAN which exchange data with each other.


ITU-T standard for an addressing scheme used in X.25 networks.


ITU-T-defined specification for the interconnection of DTEs and DCEs for synchronous communications.


ITU-T standard for the physical layer protocol for communication between DCE and DTE in an X.25 network.


ITU-T-defined for packet-switched network connections.


ITU-T recommendation for terminal-to-PAD interface in X.25 networks.


ITU-T recommendation for control information in the terminal-to-PAD interface used in X.25 networks.


ITU-T recommendation for PAD parameters used in X.25 networks.


ITU-T recommendation for electronic mail transfer.


ITU-T recommendation for distributed maintenance of files and directories.


ANSI Task Group definition of FDDI.


The Transmitter On/ Transmitter Off characters are used to control the flow of information between two nodes.




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