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A selection of networking terms
This document was written, and licensed for publication by MDA.
Introduction
You need know nothing whatsoever of telephone network technology to make a successful phone call, to order a new service, or to get a problem fixed by the phone company.
Unfortunately, if you use a computer network it is much harder to avoid some of the technicalities. You may need advice from specialists to set up the system or do problem determination. Familiarity with some of their technical jargon can help you get your requirements understood and met.
The aim of this fact sheet is to explain some of the more common networking terms. If you glance through the following paragraphs you will find a number of them. They are all included in the list below.
When you use a telephone, your voice is carried down a twisted pair of copper wires as an analogue signal to the local exchange where it is converted to a digital format consisting of a stream of 0s and 1s, at a speed of 64 Kbits/second. It is then multiplexed with other digital streams across the network, probably on optical fibre, at aggregate speeds of up to 1200 Mbps.
Many large organisations connect their offices together with a Wide Area Network (WAN) using leased or private lines provided by the telephone companies. Their computers and terminals communicate across this WAN. The network topology or design may incorporate a high-speed backbone consisting of digital links at 2 Mbits/sec.
Within an office location, computers, printers, and sometimes fax machines can be connected by locally installed wiring to form a Local Area Network (LAN) and allow sharing of resources and data. Larger LANs tend to have one or more server machines dedicated to tasks such as printer and file sharing, fax handling, communicating with external systems, or accessing data bases on behalf of smaller computers (clients) attached to the LAN.
Nowadays some people work from home, using a computer connected to a network by a dial up line with a modem. This allows them to use e-mail, access central files, transmit information etc.
Network specifications often require compliance with OSI standards, although many organisations now prefer TCP/IP, used for many years in engineering, academic and scientific networks, including the Internet.
All universities and most other academic institutions in the UK are connected to the Joint Academic Network (JANET) - a packet switched network. JANET is connected by gateways to networks in other countries, and to the Internet.
Terms
10BaseT
A wiring standard for Ethernet using telephone twisted pairs.
Analogue
A varying electrical signal representing a continuous range of values. When you use a phone, the variations in your voice are transformed by a microphone into similar (analogous) variations in an electrical signal and carried down the line to the exchange.
AppleTalk
Network software found on Macintosh systems.
ATM
A very high-speed digital standard for voice, data, image and video transmission across public networks using cell relay. Speeds of up to 1200 Mbits/sec are being implemented. Super JANET will move to this standard.
Backbone
Usually refers to a higher speed or quality network (LAN or WAN) to which subsidiary networks are connected.
Bandwidth
The total capacity of a circuit.
Baud
A unit of signalling speed. Very commonly, but incorrectly, used to mean line speed.
Bits
The 0s and 1s of a digital signal. Short for BInary digiTS.
Bits per second
The units in which data transmission speeds are given. Usually abbreviated to: bits/sec or bps. Typical WAN line speeds using modems are 2400, 9600 and 14400 bits/sec. Higher speed digital links are often at 64 Kbits/sec or 2Mbits/sec (pronounced '2 megabits per second'). LANs use speeds such as 4,10,16 or even 100 Mbps.
K is an abbreviation for Kilo (a thousand), but here means 1024.
M is an abbreviation for Mega (a million), but here means 1024 x 1024 (somewhat over a million).
There are usually 8 bits per character, but compression techniques can increase the theoretical data rate.
Bridge
A device on a LAN allowing connection to another LAN of similar characteristics. Bridges can connect locally, or across a WAN.
Broadband
Refers to high capacity circuits along which many individual transmissions are multiplexed.
Buffer
A temporary store for data being received or transmitted.
CCITT
Comité Consultatif International Téléphonique et Télégraphique. An organisation that sets telecommunications standards.
Their parent body is the ITU (International Telecommunications Union). When you see V.32, V.42bis, or X.25 you are looking at a CCITT standard. (These are for modems at 9600 Kbps, data compression, and packet switching). They have recently changed name to ITLU-TS to show their parentage (TS means Telecommunications Standardisation), but the old name is still well known.
Cell relay
Very fast packet switching, with small fixed length packets.
Client/Server
Worksharing for computers. The client is typically a computer on a network. It provides the user interface and does some of the processing. The server, which can be a different type of computer, does the remaining processing and performs activities such as database lookup for all of its clients.
Co-axial cable
A cable similar to UK domestic TV aerial wiring, used by Ethernet. The original Ethernet required a thick co-axial cable with special connectors. Current systems allow thinner, cheaper co-axial cable with 'T-piece' connectors - as well as twisted pair wiring.
Compression
Modern modems can compress data files before transmission and reconstitute them at the other end. A compressed file is sent more quickly. The amount of compression depends on the contents of the file. One with a lot of blanks is a good subject.
Dial up line
An ordinary telephone line, used for data. Connection is made by dialing, often automatically from a computer, and a modem is required at each end.
Digital
A varying electrical signal representing a series of 0s and 1s. Modern telephone exchanges, and networks connecting them, use digital technology.
Dumb terminal
Equipment, consisting of screen and keyboard, used for communicating with another computer, often across a network. Unlike a computer it has no local processing capabilities. The availability of cheap computers has made it obsolescent.
Duplex
Information is sent both ways simultaneously.
E-mail
Electronic mail. One of the justifications for introducing a network.
Ethernet
The most widespread type of LAN. It has a nominal speed of 10 Mbits/second. It conforms to international standards and is supported by all major network software suppliers.
Fax modem
A modem that allows fax as well as data transmission.
FDDI
Fibre Distributed Data Interface. A high speed (100 Mbps) standard for optical fibre LANs.
Firewall
A piece of security software that protects a network. It does this by putting a barrier between the network and the outside world, e.g. the Internet.
Frame relay
An international standard for fast packet switching. It supports speeds of up to 2 Mbps.
FTP
File Transfer Protocol. The TCP/IP standard for transferring files from one machine to another.
Gateway
A non-technical term, often meaning a device on a LAN providing a connection point to an outside system such as a computer at another location. A computer on the LAN would use the gateway to access the other computer.
Half duplex
Information is sent one way at a time. Old-fashioned radio, where the operators had to say 'Over' whenever they stopped sending and wished to receive, is an example.
Hub
A central point containing LAN circuitry and logic, to which devices on the LAN are connected.
IEEE
Institute of Electrical & Electronic Engineers. An international body that sets LAN standards.
Internet
A worldwide network of computer networks, communicating using the same 'language' - TCP/IP.
ISDN
Integrated Services Digital Network. An international standard for high-speed lines for data and telephony using digital technology in all parts of the circuit. One version provides two 64 Kbits/sec circuits down an ordinary telephone line.
JANET
Joint Academic NETwork. Connects UK universities and academic institutions. It runs as a packet switched network, with gateways to other systems.
LAN
Local Area Network. A communication system that links computers and printers together in a network, over privately owned wiring.
Modem
The name comes from 'MOdulator DEModulator'. The interface between a computer or terminal and a telephone line. It converts the computer's digital signals of 1's and 0's into analogue signals that can be sent down a telephone line.
Multiplexing
Mixing several transmission paths along the same physical circuit. Telephone companies multiplex your phone calls with thousands of others when they send them across their trunk networks.
NetBIOS
Network Basic Input/Output System. A low level, widely used network software interface.
NetWare
LAN software supplied by Novell. Widely used.
Network interface card
Every computer needs one of these to connect to a LAN.
Network management
Essential for any network of more than a few dumb terminals or computers. Effective management requires careful planning, suitable software tools, and sensible operational procedures.
Packet switching
A data transmission technique in which data is separated into small 'packets', each with its own routing information and then sent through a shared, often public, network. At the other end the packets are reassembled into the original data format.
PAD
Packet Assembler Disassembler. A device that allows computers, or dumb terminals, to communicate across an X.25 network without having to install X.25 software. The computers normally dial the PAD, which handles the special X.25 protocols on their behalf.
Peer-to-peer
Used to describe a LAN in which printers and files on any computer can be shared by other computers on the LAN. There is no need to have a dedicated server machine on a peer-to-peer network.
Private line
A telephone line leased permanently from a phone company, often used for data. Also called a leased line.
PSTN
Public Switched Telephone Network.
Segmentation
When data is sent across a network it is frequently broken into smaller pieces for transmission. These pieces are variously called frames, packets or cells depending on the network.
Server
A device on a LAN providing common services such as printing, disk sharing, file sharing, database management, fax handling. Gateways, bridges and routers are really special forms of servers, although not usually so called. A server is often a large dedicated computer, not used for other work.
Shielded twisted pair
A high grade twisted pair with a metallic sheath to eliminate signal interference. Abbreviated to STP.
Star wired
A LAN wiring arrangement, usually using twisted pairs, in which the connections for each device are brought back to a central point where they can be joined up appropriately
Super JANET
A very high-speed version of JANET. It offers speeds of 155 and 600 Mbps.
TCP/IP
Transmission Control Program/Internet Protocol. A de facto worldwide networking standard. Used by the Internet.
TELNET
A TCP/IP standard for remote terminal connection to another machine.
Token ring
A LAN architecture with transmission speeds of 4 or 16 Mbits/sec. Though less popular than Ethernet, it performs better under heavy load. It conforms to international standards and is supported by all major network software suppliers.
Topology
The shape of a network.
Twisted pair
A pair of thin, insulated wires, twisted together to reduce signal interference. Originally used for telephones, now also used for LAN wiring. Supported by both Ethernet and token ring. Sometimes called Unshielded Twisted Pair (UTP) to distinguish it from shielded twisted pair. Not all grades of UTP are suitable for LAN use.
WAN
Wide Area Network. This is a network carried over telephone company wires, often privately leased, and often over quite long distances. Modems or their equivalents are used for lower speed connections (up to 64 Kbps). Special equipment is used for higher speeds, which require digital techniques.
Windows NT
Microsoft's, business oriented, network operating system.
X.25
The international standard for packet switching at speeds of up to 64 Kbps.
X.Windows
A graphical interface allowing one terminal to display simultaneously information from several machines running UNIX operating systems.
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