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Chapter 17. How a Modem (Really) Works

Chapter 17. How a Modem (Really) Works

Modems have become an integral part of everyday life. They are taken for granted. We use them daily perhaps without even thinking about it. We use them to connect to the Internet to surf the Web, read an email message, or send a fax. Modems are everywhere: in the malls and gas stations where we use our credit cards; ATMs for instant cash; vending machines even have modems to monitor product inventory; and in many other devices we come into contact with every day. Few of us are probably aware how big a role modems play in our modern lives.

A hint as to what a modem does can be found in the word itself. Modem is actually a contraction of two words: modulate and demodulate. In its simplest form, the modem modulates (or converts) your computer's digital signal because computers “speak” in binary 0s and 1s, represented by different voltage levels into an analog (tonal) signal that can be carried by standard copper twisted-pair telephone line to another modem. The analog signal is then demodulated back into its original digital form (Figure 17.1) for the benefit of the receiving computer. Your modem also handles the dialing/answering functions and controls data transmission.


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