To support the immediate delivery of the millions of messages being exchanged between people all over the world, we rely on a web of interconnected networks. The standardization of the various elements of the network enables equipment and devices created by different companies to work together. It is important that IT technicians understand the purpose and function of different network equipment used to support personal and business operations.

A modem is an electronic device that connects to the Internet via an ISP. The modem converts digital data to analog signals for transmission over a phone line. Because the analog signals change gradually and continuously, they can be drawn as waves. In this system, the digital signals are represented as binary bits. The digital signals must be converted to a waveform to travel across telephone lines. They are converted back to bits by the receiving modem so that the receiving computer can process the data.

The modem at the receiving end reconverts the analog signals back to digital data to be interpreted by the computer. The process of converting analog signals to digital and back again is called modulation/demodulation. The accuracy of modem-based transmission has increased with the development of error detection and correction protocols, which has reduced or eliminated noise and interference on telephone lines.

An internal modem plugs into an expansion slot on the motherboard. External modems connect to a computer through the serial and USB ports. Software drivers must be installed and connection ports configured for the modem to work properly.

When computers use the public telephone system to communicate, it is called Dialup Networking (DUN). Modems communicate with each other using audio tone signals. This means that modems are able to duplicate the dialing characteristics of a telephone. DUN creates a Point-to-Point Protocol (PPP). A PPP is simply a connection between two computers over a phone line.