Before transmitting information on a transmission medium, it must be encoded of adequately. Networks must allow very high speeds over distances more or shorter. In this context, three approaches are possible for coding bits from applications:
• Information is conveyed directly to baseband, which allows obtaining Cash flow rates in gigabits per second. The distances without regeneration are rather short and depend on the speed. One can reach several kilometers.
• The speeds reached are much smaller, but the distances larger. To increase the speed, you have to be able to transport a large number of bits per time interval.
• Digital signals are modulated on a carrier, and each type of information is allocated a bandwidth according to their needs. This is the approach known broadband.
The baseband transmission is the simplest, since no modulation is necessary. The bit string representing the information is transmitted directly to the support by the changes introduced in representing the information signals in the form of voltage transitions, or light pulses if the fiber is used Optical.
The baseband signals are subject to attenuation, whose importance depends on employee support. They must be regenerated periodically over a long distance. This regeneration is carried out using repeaters which receive the signals and memorize a split second before retransmitting them in the outgoing line.
This method uses the frequency division multiplexing. Different channels are created, resulting from the division of the bandwidth of support in several sub-bands frequencies. This technique has the advantage of allowing simultaneous transmissions independent.
Each device on the cable is equipped with a particular modem. This allows choosing the mode of transmission, digital or analog, the most suitable and most effective for the type of information to be transmitted. For example, computer data is output on a digital tape and the voice and image on analog tape. Transmission However broadband connection increases the cost compared to a strip network base, easier to install and generally less expensive.