Glossary
ADSL: A type of high-speed digital telephone connection which supports very high data rates (6mbps in one direction and 640kbps in the other direction). ADSL is an open line onto the Internet which means that unlike modem connections you don't dial a number to get onto the Net. As you are effectively on the Internet all the time the services will be introduced using unmetered pricing structures.
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Analogue: The term used to describe the continuously variable wave-form nature of voices and other signals.
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ARPANET: Acronym for Advanced Research Projects Agency Network. The early US military network that forms the basis of what we know now as the Internet.
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BPS: Acronym for Bits Per Second. A commonly used measure of the speed of data transmission usually in association with modems.
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Browser: A browser is a program you use to view webpages and 'browse' websites. Netscape Navigator and Internet Explorer are the main competitors, and are considered the industry standards, but there are many others out there, some of which offer features and cool functions that may come in handy. The 'version number' tells you the range of HTML features it understands. For example, you'll need a browser numbered 3.0 or higher to view a site which contains tables, a feature introduced in HTML version 3. With an older browser, the page will look different and may not include all the features that its author intended.
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Broadband: Broadband provides high speed Internet access by delivering multiple channels of data over a single communications medium. It is able to carry much larger amounts of information than narrowband.
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Digitization: the conversion of a signal's usual analogue representation, into a stream of binary numbers.
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DLE:(Digital local exchange): The main telephone exchange in an area
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Domain Name System (DNS): Name resolution software that lets users locate computers on a UNIX network or the Internet (TCP/IP network) by domain name. The DNS server maintains a database of domain names (host names) and their corresponding IP addresses.
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DTMF: (Dual Tone Multi-Frequency) a direct algebraic summation, in real time, of the amplitudes of two sine (cosine) waves of different frequencies. e.g.. pressing '1' will send a tone made by adding the frequencies of 1209 Hz and 697 Hz to the other end of the line.
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Edison transmitter: the carbon-button microphone invented by Thomas Edison in 1877. (The transmitters used by A.G.Bell at that time used acid instead of carbon and produced an unexpectedly week signal.)
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Electret microphone:In modern electret transmitters, developed in the 1970s, the carbon layer is replaced by a thin plastic sheet that has been given a conductive metallic coating on one side.
When the diaphragm vibrates due to sound, variations in an electric field across a tiny air gap between the diaphragm and an electrode produce a small voltage. The voltage must be amplified before transmission over the telephone line.Back
Electromagnet: The magnetism that results from an electric current passing through a wire wrapped around a metal core such as iron.
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Email: Email consists of simple text files sent from one person to another. The basics are the same regardless of whether the email is sent within the same office network or across the Internet - messages are stored in electronic mailboxes and may be opened by the intended recipient wherever they are in the world. As well as being a rapid (and cheap) messaging service, the most recent email software allows you to send and receive other kinds of files as attachments to simple text messages.
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Fiber-optic: Cable incorporating a number of very thin strand of glass on which information is conveyed in the form of pulses of light.
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File Transfer Protocol (FTP): The transmission of a file from one machine to another machine. Both the machines are usually physically apart by a great distance but are linked by the telephone lines and modems and an appropriate communication software. This is normally used in quick transportation of large files. It is a set of commands used to govern gateways and file sharing. FTP is normally used to upload files on distant servers or the Internet.
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ISDN: An agreed standard for digital communication over telephone lines. ISDN is based on the fact that modern telephone networks turn analogue sound waves into a digital format at the telephone exchange, send them to the destination telephone exchange as a digital signal (at 64kbps) and then turn them back into analogue sound waves again. An ISDN line eliminates the analogue portion and simply gives you a digital connection direct to the exchange. Most ISDN users are offered two lines at once - one for the Internet and the other for your telephone. However, you can use both lines for the Internet at the same time to offer speeds of 128Kbps.
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Internet: A global computer network connecting governments, companies, universities and many other networks. Services offered over the Internet include the WWW, Email and Video conferencing. The users are increasing daily with some estimates suggesting that these are into billions.
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Line concentrator: Reduces the number of lines that need to be run to an exchange. (E.g. on average, an RCU has one connection to a DLE for every 4 customer lines, so an RCU serving 6000 customers will have about 1500 lines connecting it to the DLE)
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Local Loop: (Also known as the 'last mile') The wired connection from a telephone company's exchange in a locality, to its customers' telephones at homes and businesses.
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Message Transfer Agent (MTA): This is associated with the electronic mail system and are agents responsible for relaying messages.
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Microwave: A high frequency form of radio transmission, transmitted with the use of microwave dishes
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Multiplexing: A technique enabling transmission of multiple signals or voice channels simultaneously along a single transmission medium.
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Open System Interconnection (OSI): An ISO standard for world-wide communications is that which defines a framework for implementing protocols in seven layers. Control is passed from one layer to the next, starting at the application layer in one station, proceeding to the bottom layer, over the channel to the next station and back up the hierarchy.
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Piezoelectric Transducer A material which naturally converts the mechanical stress of a sound wave upon it into a varying electrical signal.
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Post Office Protocol (POP): This is a protocol responsible for storing or fetching electronic mails at the users request once the user domain has been identified.
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PSTN: The switched telephone telecommunications network to which public customers are connected.
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Pulses: Regular abrupt changes in a voltage or waveform.
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RCU: (Remote Concentator Unit) An RCU is a simple switch that runs under the control of a DLE - each RCU belongs to exactly one DLE (see Line concentrator)
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Simple Mail Transfer Protocol (SMTP): This is a protocol responsible for routing the Message Transfer Agents (MTA).
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Tandem Network Also known as the Trunk Network - The transmission, switching and signalling systems within the PSTN which enable calls to be routed from one local exchange to another.
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Tandem Switching centres Previously known as Trunk Exchanges - Transit exchanges through which a long distance call may pass on its route between 2 local exchanges.
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TELNET: A terminal emulation protocol commonly used on the Internet and TCP/IP-based networks. It allows a user at a terminal or computer to log onto a remote device and run a program. Telnet was originally developed for ARPAnet and is an inherent part of the TCP/IP communications protocol.
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Transmission Control Protocol / Internet Protocol (TCP/IP): A widely used network protocol. TCP deals with the process of sending 'packets' of information from one computer to another. IP deals with the process of passing these packets from one computer to the next until they reach their final destination.
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