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
- asynchronous
- 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.
- backbone
- 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
- bandwidth
- amount of data that can be transferred over a
communication channel in a given time, or range of frequencies
- baseband
- 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
- bridge
- a device that connects two network segments at the media access layer
- broadband
- division of a signal into multiple frequencies (frequency
division multiplexing) to carry multiple communications channels simultaneously
- broadcast
- 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.
- checksum
- 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
- connectionless
- 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
- client
- 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
- compression
- running a data through an algorithm that reduces the space required to store
it or the bandwidth required to transmit it
- concentrator
- 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
- datagram
- a data packet in a network that uses packet switching
- demodulation
- 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
- encryption
- encoding data so that it cannot be read without a
decoding system or key
- Ethernet
- 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
- firewall
- 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.
- fragmentation
- breaking a message into smaller units for ease of
transmission
- frame
- a unit of data sent at the OSI data link layer
- full duplex
- a communications channel that sends information in both directions at once
- gateway
- 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
- hypertext
- 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
- interface
- 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
- Internet
- 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
- intranet
- a private network that uses Internet protocols like TCP/IP and tools like
web servers and browsers but operates within an organisation
- Java
- 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
- loopback
- 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
- modem
- electronic device for converting between serial data from a
computer and an audio signal suitable for transmission over telephone lines
- modulation
- changing a digital signal into an analog signal
- multicast
- a message (e.g. packet or frame) sent to more than one device on the network
- multiplex
- to switch between several activities or devices
- network
- 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
- packet
- 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
- Perl
- a programming language designed for processing text and used for writing CGI
scripts
- PHP
- a freely available server-side screipting language derived from Perl and
embedded in HTML for dynamic generation of web page content and database
access
- port
- 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
- protocol
- 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
- relay
- 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
- repeater
- 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.
- router
- 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
- server
- 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.
- simplex
- a communications channel that sends information only in one direction
- socket
- 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.
- spoofing
- 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
- synchronous
- 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
- timeout
- occurs when a time limit for receiving a response to a request has been exceeded
- telnet
- a protocol for remote login using a terminal interface
- token
- a data structure containing control information used in token
ring/bus networks
- topology
- 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
- X.25
- an international standard for connecting devices to a packet
switching network