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One way of understanding how telecommunications systems work and how they are changing is to consider a number of essential concepts.

A basic item that appears throughout any communications description is the prefix used in metric units for designating parameters such as length, speed, power level, and information transfer rate. As a handy reference, the table in Fig. 1 lists standard prefixes, their symbols, and their magnitudes, which range in size from 10²⁴ to 10^-24. As an example, a distance of 2 X 10^-9 m (meters) (two times ten to the minus ninth power) = 2nm (nanometers). The three highest and lowest designations are not especially common in communication systems (yet!), but are included in the table for completeness.

Some terms and concepts that are used in communications include: information (the content, such as spoken words, an image, the measurement of a physical unit, or values of bank accounts), a message (the physical manifestation of the information produced by the source, ranging from a single number or symbol to a long string of sentences), data (facts, concepts, or instructions presented as some type of encoded entities used to convey the information – these include arrays of

Fig.1. Metric prefixes, their symbols and their magnitudes

Prefix	Symbol	Decimal	Magnitude	Multiple
yotta zetta exa peta tera giga mega kilo deci centi milli micro nano pico femto atto zepto yocto	Y Z E P T G M k d c m μ n p f a z y	1,000,000,000,000,000,000,000,000 1,000,000,000,000,000,000,000 1,000,000,000,000,000,000 1,000,000,000,000,000 1,000,000,000,000 1,000,000,000 1,000,000 1,000 0.1 0.01 0.001 0.000001 0.000000001 0.000000000001 0.000000000000001 0.000000000000000001 0.000000000000000000001 0.000000000000000000000001	Septillion Sextillion Quintillion Quadrillion Trillion Billion Million Thousand Tenth Hundredth Thousandth Millionth Billionth Trillionth Quadrillionth Quintillionth Sextillionth Septillionth	1024 1021 1018 1015 1012 109 106 103 10-1 10-2 10-3 10-6 10-9 10-12 10-15 10-18 10-21 10-24

integers, lines of text, video frames, digital images, etc.), signals (understood as electromagnetic waves (in encoded electrical or optical formats) used to transport the data over a physical medium).

The word 'telecommunication' was adapted from the French word télécommunication, coined in 1904 by the French engineer and novelist Éd. Estaunié. It is a compound of the Greek prefix tele-, meaning "far off", and the Latin communicare, meaning "to share". Thus, telecommunication means literally sharing (sending and receiving) information over distances.

A simple telecommunication system consists of three units that are always present in some form: a) a transmitter that takes information and converts it to a signal; b) a transmission medium, also called the “physical channel” that carries the signal; c) a receiver that takes the signal from the channel and converts it back into usable information.

Every human being is equipped with a basic communication system. The mouth (and vocal cords) is the transmitter, ears are the receivers, and air is the transmission medium over which sound travels between mouth and ear. Between the speaker and the listener (the receiver), there might be other devices that do or do not introduce their own distortions of the original vocal signal (e.g. telephone, ham radio, IP phone, etc.) Modern telecommunications include the use of such devices as telegraphs, telephones, and teletypes, the exploitation of radio and microwave communications, as well as fiber optics and their associated electronics, plus the use of the orbiting satellites and the Internet.

Telecommunication over telephone lines is called point-to-point communication because it is between one transmitter and one receiver. Telecommunication through radio broadcasts is called broadcast communication because it is between one powerful transmitter and numerous low-power but sensitive radio receivers.