The telephone system is the largest and most complex electronic communication system in the world. It uses just about every type of electronic communication technique available including virtually all the ones described in this book. The telephone communication system is so large and widely used that no text on electronic communication would be complete without a discussion of it.

Although the primary purpose of the telephone system is to provide voice communication, it is also widely used for many other purposes including facsimile transmission and computer data transmission. Data transmission via modems and DSL was discussed in Chap. 11, so it will not be repeated here. The chapter concludes with coverage of the newest telephone technology called Voice over Internet Protocol (VoIP).