Saturday, September 15, 2012

What is a Modem

What is a Modem?

A modem (a modulator/demodulator) lets you connect your computer to a standard telephone line so you can transmit and receive electronically transmitted data. It is the key that unlocks the world of the Internet and its World Wide Web, commercial online services, electronic mail (E-mail), and bulletin board systems (BBSes).

How Modems Work?

When a modem first makes a connection, you will hear screeching sounds coming from the modem. These are digital signals coming from the computer to which you are connecting being modulated into audible sounds. The modem sends a higher-pitched tone to represent the digit I and a lower-pitched tone to represent the digit 0.

At the other end of your modem connection, the computer attached to its modem reverses this process. The receiving modem demodulates the various tones into digital signals and sends them to the receiving computer. Actually, the process is a bit more complicated than sending and receiving signals in one direction and then another. Modems simultaneously send and receive signals in small chunks. The modems can tell incoming from outgoing data signals by the type of standard tones they use.

Another part of the translation process involves transmission integrity. The modems exchange an added mathematical code along the way. This special code, called a checksum, lets both computers know if the data segments are coming through properly. If the mathematical sums do not match, the modems communicate with each other by resending the missing segments of data. Modems also have special circuitry that allows them to compress digital signals before modulating them and then decompressing them after demoduating the signals. The compression/decompression process compacts the data so that it can travel along telephone lines more efficiently.

Modems convert analog data transmitted over phone lines into digital data computers can read; they also convert digital data into analog data so it can be transmitted. This process involves modulating and demodulating the computer’s digital signals into analog signals that travel over the telephone lines. In other words, the modem translates computer data into the language used by telephones and then reverses the process to translate the responding data back into computer language.

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