ABSTRACT
This chapter outlines the development of basic communication technologies, and explains how networks evolved. It introduces terminology, and explains how modems work. Since the discovery of electricity, inventors, scientists, and engineers have worked on ways to use electrical signals for communication. The principles discovered have resulted in fast, reliable communication systems. People's knowledge of digital communication can be divided into roughly three historical stages. The first stage focused on the properties of signals. The second stage focused on how to use signals to send bits and how to organize the bits into characters. The third stage focused on how to detect and correct errors that occur during transmission. Modulation technology is used throughout the Internet — when computerized devices communicate across a long cable, they need a modulator at one end and a demodulator at the other. Modulation technology is also used for wireless Internet communication. Inside a digital device, all values are stored in bits.
