An analog modem converts the digital signals of the sending computer to analog signals
that can be transmitted through telephone lines. When the signal reaches its destination, another modem reconstructs the original digital signal, which is processed by the receiving computer. A standard analog modem has a maximum speed of 33.6 Kbps.
The word modem is an acronym formed from the two basic functions of an analog modem: modulation and demodulation. To convert a digital signal to an analog one, the modem generates a carrier wave and modulates, or adjusts, it according to the digital signal. The kind of modulation used depends on the application and the speed of operation for which the modem is designed. For example, many high-speed modems use a combination of amplitude modulation, in which the amplitude (see Wave Motion) of the carrier wave is changed to encode the digital information, and phase modulation, in which the phase of the carrier wave is changed to encode the digital information. The process of receiving the analog signal and converting it back to a digital signal is called demodulation.
