An introduction to telephony

In this opening chapter we introduced the basics of telephony, in which economies are gained by the use of a single pair of wires to convey a two-way telephone call over the link to the serving exchange. We also examined the role of local, trunk and international exchanges, noting that they can be manual or automatic. This led to an understanding of the basic structure of a PSTN. A simple example of a call across the country has been examined to illustrate the sequence of events involved in progressing a telephone call. This highlighted the roles of numbering and addressing, call control, and the need for signalling between the control systems of exchanges involved in the call. We also introduced the concept of the two forms of wave forms used in telecommunications networks. Subsequent chapters develop these basic concepts.