August 6, 2003

Today's technologies

Although telecommunications technologies have come a long way since the early years, messages are still carried in the same way, using cables and electromagnetic waves. Copper wire, fibre-optic cable and radio waves form complementary networks. Satellites are also used to relay messages between thousands of ground stations worldwide.

How a telephone call gets from A to B

When you ring someone, an electrical signal travels from your phone to your local telephone exchange along two copper wires. The signal is then directed through other exchanges to the person you are calling. Depending on the type of call, the electric signal travels from one exchange to another via fibre-optic cable or radio relay. In the latter case, 30 percent of calls are transmitted via satellite.

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Telecommunications have also benefited from the development of information technology, which makes it possible to store, exchange, process and retrieve all types of information automatically. Such change has been facilitated by the use of digital signals, which were previously analogue. 
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Analogue or digital?
Until recently, all telephones worked by sending analogue signals, i.e. an electric current that varies in amplitude continuously and proportionally in response to your voice. Today, most telephone systems are digital. Your voice is sampled at a rate of 8,000 samples per second, then binary coded (i.e. converted into a series of 0s and 1s). The signal is neither proportional nor continuous. Analogue signals are, however, still used for certain applications.
The first communications networks, which paved the way for the Internet, were developed in the 1970s for military purposes. Used by scientists and businesses, these networks expanded and merged over the period of 10 years to form a global network called the Interconnecting Network, better known as the Internet.

Based on a common communications protocol called Internet Protocol (IP), the Internet connects local networks across the globe. By early 2000, the number ran into hundreds of thousands. The Internet's architecture evolved to meet increasing demand and offer different services such as e-mail, e-commerce, discussion forums, file transfer and, of course, browsing web pages for information.
These technology networks are constantly evolving and merging to provide access to a wide range of services, from mobile telephony, multimedia applications and television to geographic positioning, data collection and rescue systems.

Information carriers

Type of carrier Description Typical use
Copper wire Metallic wire Fixed telephones (emission and final distribution)
Fibre-optic cable Filament of dielectric material such as glass or silica, capable of transmitting light Transmission of digital information across high-speed networks, final distribution of television services
Radio waves Electromagnetic radiation with a lower frequency than optical waves (i.e. with wavelengths over 1 mm). Each signal is also characterized by a bandwidth (or frequency range):
L band: 1.5/1.6 GHz Radionavigation, satellite-based mobile services
S band: 1.8/2.5 GHz Satellite-based mobile services for aviation, terrestrial and maritime applications
C band: 4/6 GHz Fixed telephones and radio broadcasting
X band: 7/8 GHz Encrypted government and military communications
Ku band: 11/14 GHz High-data-rate communications such as television broadcasting and multimedia applications (videoconferencing, file transfer, etc.)
Ka band: 20/30 GHz High-speed civil communications
EHF band 20/40 GHz Military communications
V band: 60 GHz Intersatellite links

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