6 - Digital Transmission Techniques

Abstract

This chapter explains the principles of using digital techniques to transmit telephone signals. It describes pulse code modulation (PCM) and time division multiplexing (TDM) systems, and compares them with analog systems. Digital transmission techniques deal with information all in digital form. Because the early telephone systems were completely analog and a large portion of the system today is still analog, there is a need for conversion from analog signals to digital signals so they may be transmitted using digital techniques. The first digital transmission system was installed by the Bell System in Chicago. Instead, the advantages of digital transmission techniques applied to speech signals have proved to be so numerous as to make the continued installation of analog facilities a poor business choice. The telephone transmission network and switching equipment for digital systems can use the same types of integrated circuit logic used in digital computers.