Telecommunication

Telecommunication

From Wikipedia, the free encyclopedia

[pic]

Copy of Alexander Graham Bell's original telephone, at the Musée des Arts et Métiers in Paris

Telecommunication is the assisted transmission of signals over a distance for the purpose of communication. In earlier times, this may have involved the use of smoke signals, drums, semaphore, flags, or heliograph. In modern times, telecommunication typically involves the use of electronic transmitters such as the telephone, television, radio or computer. Early inventors in the field of telecommunication include Alexander Graham Bell, Guglielmo Marconi and John Logie Baird. Telecommunication is an important part of the world economy and the telecommunication industry's was estimated to be $1.2 trillion dollars in 2006.

|Contents |

|[hide] |

|1 Key concepts |

|1.1 Basic elements |

|1.1.1 Analogue or digital |

|1.1.2 Networks |

|1.1.3 Channels |

|1.1.4 Modulation |

|2 Society and telecommunication |

|3 History |

|3.1 Early telecommunications |

|3.2 Telegraph and telephone |

|3.3 Radio and television |

|3.4 Computer networks and the Internet |

|4 Modern operation |

|4.1 Telephone |

|4.2 Radio and television |

|4.3 The Internet |

|4.4 Local area networks |

|5 Telecommunications by region |

|6 See also |

|7 References |

|8 External links |

[pic][edit] Key concepts

|Etymology |

|The word telecommunication was adapted from the French word télécommunication. It is a |

|compound of the Greek prefix tele- (τηλε-), meaning 'far off', and the Latin |

|communicare, meaning 'to share'.[1] The French word télécommunication was coined in 1904|

|by French engineer and novelist Édouard Estaunié.[2] |

[edit] Basic elements

A telecommunication system consists of three basic elements:

* a transmitter that takes information and converts it to a signal;

* a transmission medium that carries the signal; and,

* a receiver that receives the signal and converts it back into usable information.

For example, in a radio broadcast the broadcast tower is the transmitter, free space is the transmission medium and the radio is the receiver. Often telecommunication systems are two-way with a single device acting as both a transmitter and receiver or transceiver. For example, a mobile phone is a transceiver.[3]

Telecommunication over a phone line 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 receivers.[3]

[edit] Analogue or digital

Signals can be either analogue or digital. In an analogue signal, the signal is varied continuously with respect to the information. In a digital signal, the information is encoded as a set of discrete values (for example ones and zeros). During transmission the information contained in analogue signals will be degraded by noise. Conversely, unless the noise exceeds a certain threshold, the information contained in digital signals will remain intact. This noise resistance represents a key advantage of digital signals over analogue signals.[4]

[edit] Networks

A collection of transmitters, receivers or transceivers that communicate with each other is known as a network. Digital networks may consist of one or more routers that route information to the correct user. An analogue network may consist of one or more switches that establish a connection between two or more users. For both types of network, repeaters may be necessary to amplify or recreate the signal when it is being transmitted over long distances. This is to combat attenuation that can render the signal indistinguishable from noise.[5]

[edit] Channels

A channel is a division in a transmission medium so that it can be used