What Phones Do for Voice, Modems Do for Data

What Phones Do for Voice, Modems Do for Data

When you make a phone call and say something, the telco transmits the sounds you make to the telephone on the other end of the circuit. You and the other person, being humans, can speak to generate sound waves and listen to hear sound waves. The telephone converts what the human can do (sound waves) to what the telco network can do (analog electrical signals).

To use those same telephone lines to send data, you need a device that has some similarities to a phone. Like a phone, this device needs to know how to generate and receive the analog electrical signals. However, instead of converting sound waves to and from those analog electrical signals, the device needs to convert binary 0s and 1s on behalf of a computer. Figure 16-3 shows the general idea.