Glossary of Common Terms

address resolution protocol (ARP)
a routing (network-layer) protocol to convert an IP number on a local machine to its MAC address; the reverse conversion is RARP
digital exchange out of time sequence; sends isolated bursts of data, and delimits characters using start and stop bits, e.g. RS232C, V.24, a modem, X.21
asynchronous transfer mode (ATM)
A method for the dynamic allocation of bandwidth by switching small 53-byte fixed-size packets called cells.
The top level in a hierarchical network, or a part of the network that interconnects other parts of the network. In a wide area network (WAN), such as the Internet, a high-speed, high-capacity medium that transfers data over hundreds or thousands of miles. A variety of physical media are used for backbone services, including microwave relay, satellites, and dedicated telephone lines
amount of data that can be transferred over a communication channel in a given time, or range of frequencies
a single communications channel occupies the entire bandwidth
baud rate
signalling speed in signals per second
bit rate
data transfer rate in bits per second; may be a multiple of the baud rate
a device that connects two network segments at the media access layer
division of a signal into multiple frequencies (frequency division multiplexing) to carry multiple communications channels simultaneously
a message (e.g. packet or frame) sent to all devices on the network
carrier sense multiple access with collision detection (CSMA/CD)
The method by which nodes on an Ethernet/IEEE 802.3 LAN gain access to the network, i.e. one of several techniques that have been built into different LAN technologies to allow multiple nodes to share the same wires/electronics to send their data. Nodes can sense whether information is being sent, and detect whether a collision of signals has occurred.
A computed value which depends on the contents of a block of data and which is transmitted or stored along with the data in order to detect corruption of the data. The receiving system recomputes the checksum based upon the received data and compares this value with the one sent with the data. If the two values are the same, the receiver has some confidence that the data was received correctly.
circuit switching
opening a fixed route/path for data transmission
coaxial cable
any of a number of kinds of electrical communications cable designed so one conductor is in the center and the second conductor forms a ring around it; used for Ethernet networks and cable TV
common gateway interface (CGI)
a standard mechanism for a web server to communicate with a script or program running on the same server in order to pass data between them
no connection or route needs to be established before data transmission
circuit switching
a virtual connection is created and the message is sent as a stream of bytes
a program or machine that requests and receives services from a server
client-server network
a centrally administered LAN with one or more dedicated servers
running a data through an algorithm that reduces the space required to store it or the bandwidth required to transmit it
a multiplexing device such as a hub or switch which allows a number of stations to be connected to a LAN. It combines the data streams from many simultaneously active inputs into one shared channel in such a way that the streams can be separated after transmission
cracking program
a program that attempts to guess a password or gain access to a system by trying many combinations
cyclical redundancy check (CRC)
a method to detect data transmission errors by creating extra bits of information to be sent with the data bits, often by using polynomial division
data communications (or circuit-terminating) equipment (DCE)
device to attach a DTE to a telecommunications network, e. g. a modem
data encryption standard (DES)
a one-way encryption algorithm that combines a secret key with a password to create a publicly readable code
data terminal equipment (DTE)
user device connected to a network, e.g. a computer
a data packet in a network that uses packet switching
In telecommunications, the process of receiving and transforming an analog signal into its digital equivalent so that a computer can use the information
denial of service
a type of security attack which makes a system becomes so overloaded that it cannot provide its usual level of service
domain name system (DNS)
a protocol to translate between domain names and IP numbers
dynamic host configuration protocol (DHCP)
a Microsoft protocol based on BOOTP that allows a server to automatically assign IP numbers to newly connected clients; useful for administering networks where computers are frequently added and removed
encoding data so that it cannot be read without a decoding system or key
a very common local area network data transmission standard based on IEEE 803.2
extensible markup language (XML)
a meta-language derived from SGML and used for defining other languages; developers can create new tags and rules (document type definitions)
fibre data distribution interface (FDDI)
LAN data-link protocol for multi-mode fibre. "Raw" rate of data transmission is 100 megabits/second. Developed by the American National Standards Institute
file transfer protocol (FTP)
an Internet protocol for uploading and downloading files
software and hardware between an organisation's network and the Internet for security access control
flow control
Hardware and software techniques used in serial asynchronous communications to stop the sender sending data until the receiver can accept it, often by using a buffer.
breaking a message into smaller units for ease of transmission
a unit of data sent at the OSI data link layer
full duplex
a communications channel that sends information in both directions at once
any device acting above the data link layer that allows the interconnection of two networks
half duplex
a communications channel that sends information in both directions but only one direction at a time
software technology that allows users to browse and retrieve information by following hyperlinks rather than following a linear structure
hypertext link (hyperlink)
text with information pointing to another document, used to link documents
hypertext meta language (HTML)
a set of tags and related rules used to create web pages
hypertext transfer protocol (HTTP)
Internet standard that supports the exchange of information on the Web. HTTP defines the process by which a Web client, called a browser, originates a request for information and sends it to a Web server, a program that responds to HTTP requests and provides the desired information.
Institute of Electrical and Electronic Engineers (IEEE)
a group that has made widely accepted standards for local area networks
a boundary across which two devices communicate, possibly a hardware connection or a convention
international organization for standardization (ISO)
a group which creates international standards for many areas including computers and communications
an international network of computer networks which uses protocols like TCP/IP, permits public access to information on many subjects and allows users to send and receive messages and obtain products and services
Internet protocol (IP)
the connectionless standard that describes how an Internet-connected computer should break data down into packets for transmission across the network, and how those packets should be addressed so that they arrive at their destination. An IP number uniquely identifies a computer on the Internet.
Internet service provider (ISP)
an organisation that charges a fee to enable individuals and organisations to connect to the Internet
a private network that uses Internet protocols like TCP/IP and tools like web servers and browsers but operates within an organisation 
a programming language used as a software development tool for the Internet
local area network (LAN)
A computer network that connects computers in a limited geographical area (typically less than one mile) so that users can exchange information and share hardware, software, and data resources
a pseudo network device in the UNIX operating system which, rather than sending data out onto a physical network, sends packets straight back into the system. The protocols for talking to the loopback device are the same as those for the physical network, so programs employing interprocess communication have only to hold to a single standard, regardless of whether the processes are on the same machine, or on different machines
Manchester encoding
a method of signalling digital data with an embedded clock
metropolitan area network (MAN)
A high-speed regional network typically used to connect universities with other research facilities in a large metropolitan area
electronic device for converting between serial data from a computer and an audio signal suitable for transmission over telephone lines
changing a digital signal into an analog signal
a message (e.g. packet or frame) sent to more than one device on the network
to switch between several activities or devices
a system of connected computers and other electronic devices and software for communication and resource sharing
network basic input output system (NetBIOS)
a Windows API for small LANs that is still the basis of current Microsoft protocol suites
network file system (NFS)
an IP-based protocol originally developed by Sun Microsystems which provides file services, allowing a computer to access files over a network as if they were on its local disks
network interface card (NIC) or network adapter
a card inserted into a PC that allows it to be attached to a LAN
open shortest path first (OSPF)
a link state routing protocol used by routers to exchange information about costs or metrics to reach other networks
open systems interconnect (OSI) reference model
A standard put forth by the ISO for communication between computer equipment and networks, which includes seven layers of protocols
OSI physical layer
defines connections, electrical and wiring specifications
OSI data link layer
provides hardware addressing and error detection/correction
OSI network layer
provides addressing, routing between networks, network control and congestion control
OSI transport layer
provides reliable end-to-end transfer, including error detection and correction, packet segmentation and sequencing, flow control, addressing and security
OSI session layer
establishes sessions between services; synchronizes and performs translations for naming services
OSI presentation layer
performs data format conversion; provides compression, encoding and encryption of data
OSI application layer
provides standard services to applications and end-user interfaces
a unit of data transfer at the OSI network layer. In a packet-switching unit, a unit of data of a fixed size--not exceeding the network's maximum transmission unit (MTU) size--that has been prepared for network transmission. Each packet contains a header that indicates its origin and its destination
packet switching
parts of messages are individually routed and later reassembled
parity bit
an extra bit of information sent with a byte of data and used for detecting transmission errors
peer to peer network
a small LAN consisting of "equal" peer workstations that share resources; each workstation acts as both client and server and there is no dedicated server
a programming language designed for processing text and used for writing CGI scripts
a freely available server-side screipting language derived from Perl and embedded in HTML for dynamic generation of web page content and database access
an endpoint (source or destination) of communication that represents a process address on a computer in a TCP/IP network
private (automatic) branch exchange (PBX or PABX)
A telephone exchange local to a particular organisation used for switching calls between internal lines and between internal and PSTN lines. In contrast to a PMBX, a PABX can route calls without manual intervention, based entirely on the number dialed
the rules by which two network elements trade information in order to communicate; standard specifying the format of data and the rules to be followed
public key encryption
a system of asymmetric cryptography with a public and private key used to encrypt and decrypt messages and digital signatures
public switched telephone network (PSTN)
the collection of interconnected systems operated by the various telephone companies and administrations (telcos and PTTs) around the world
a device that interconnects LANs, e.g. repeater, bridge, router, gateway
remote procedure call (RPC)
a protocol which allows a program running on one host to cause code to be executed on another host without the programmer needing to explicitly code for this; an easy and popular paradigm for implementing the client-server model of distributed computing
a relay that regenerates and cleans up signals, but does no buffering of data packets. It can extend an Ethernet by strengthening signals. It acts at the OSI physical layer.
A network "relay" that uses a protocol beyond the data-link protocol (usually the network layer) to route traffic between LANs and other network links; electronic device that examines each packet of data it receives, and then decides which way to send it toward its destination
routing information protocol (RIP)
a distance vector routing protocol that only uses the number of hops and in which routers regularly exchanges routing table information with all other routers
a host program or machine that provides services to clients
shielded twisted pair (STP)
Ethernet cabling with pairs of wires surrounded by a shielding for protection against interference and for faster speeds.
simple mail transfer protocol (SMTP)
a protocol used to transfer electronic mail between computers
simple network management protocol (SNMP)
A protocol originally developed to manage IP based network equipment like routers and bridges, now extended to wiring hubs, workstations, toasters, jukeboxes, etc.
a communications channel that sends information only in one direction
a Unix mechanism for creating a virtual connection between processes; an  interface between standard I/O and network communication facilities. Also a library function which creates a communications end-point in the OSI transport layer and returns a file descriptor with which to access it. It has an address, consisting of a port number and the local host's network address.
a humorous imitation, hoax or trick; pretending to be someone or something you are not; taking on a false identity for purposes of a security attack
coordinates sender and receiver communication using a clock or timing signal, e.g. baseband LANs like Ethernet and Token Ring, fibre optic networks like FDDI
occurs when a time limit for receiving a response to a request has been exceeded
a protocol for remote login using a terminal interface
a data structure containing control information used in token ring/bus networks
a physical layout of a network and its wiring (e.g. star, bus, ring, mesh, hierarchy, hybrid)
transport control protocol (TCP)
a connection-oriented Internet protocol acting at the OSI transport layer
uniform resource locator (URL)
a string of characters that precisely identifies/specifies the type and location of an Internet object/resource such as a web page
unshielded twisted pair (UTP)
Inexpensive Ethernet cabling consisting of twisted pairs of wires without shielding
user datagram protocol (UDP)
a connectionless TCP/IP transport-level protocol used instead of TCP for higher performance when reliable transmission is not needed such as local area networks and higher-level protocols that handle reliability
virtual circuit
a temporary data path that provides sequenced, error free delivery between two nodes
virtual private network (VPN)
use of a public network such as the Internet to transmit private data
web browser
A client application program that runs on an Internet-connected computer, displays hypertext documents and multimedia, and allows the user to navigate and access information on the World Wide Web
web page
a formatted hypertext document on the World Wide Web
web server
a program to run programs and send web documents in response to client requests
wide area network (WAN)
A commercial data network that provides data communications services for businesses and government agencies, usually constructed with serial lines or X.25, extending over distances greater than one kilometre
world wide web (WWW)
A global hypertext system that uses the Internet as its transport mechanism
an international standard for connecting devices to a packet switching network