TABLE OF CONTENTS In Chapter 1 we considered how a PSTN establishes telephone call connections between subscribers on its network. However, this is only part of the story. First, there are usually several PSTNs in any one country, each owned by different operators, although some may have a limited geographical coverage or serve only certain (typically corporate business) customers. Many countries also have Cable TV operators who provide telephone service, in addition to broadcasting TV distribution. Then, of course, nearly all countries now have one or more mobile telephone networks, which are separate from the, so-called, fixed PSTNs. All these networks need to interconnect so that their subscribers can call subscribers on any of the other networks. This chapter, therefore, briefly describes the various telephone networks and how they all interconnect.
Although the fixed PSTN and mobile networks are primarily designed for voice communications, they do also enable subscribers to connect their computers to the Internet (a network primarily designed for data service). Thus, to complete the interconnect story, this chapter briefly introduces the concept of the Internet and how access to it is provided by the telephone networks.
The second aspect of the story is the need for a set of specialist networks which enables a typical national telephone operator to provide a wide range of services beyond simple telephone calls. This chapter briefly reviews these specialised networks and uses a simple model to help explain how they link and support each other.
So, clearly there are many networks in...
