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.

The first two chapters have considered the way that a telephone call is set up and how the various networks providing telephone service are interconnected. Also, Chapter 2 introduced the roles of the other types of network: specialised voice networks and data networks. This chapter considers the basic components that go together to make up these networks. In fact these components can be treated as part of a set of building bricks, each of a different shape and size; all of the telecommunications networks described in this book are made up using a suitable mix of these bricks. Subsequent chapters describe the networks and systems in more detail, assuming the reader has an understanding of the basic components described in this chapter.

Chapter 4 introduces the concept of modulating the information (voice, data, video, etc.) onto a variety of transmission systems. We now need to consider how these systems are used in telecommunication networks. As discussed in Chapter 1, all telecommunication networks, and indeed most other sorts of networks, comprise an access portion which connects the population of users to a serving network node, and a core portion which interconnects the set of serving network nodes. These portions are transmission networks in their own right, containing links and nodes, and are usually known as the Access Network and the Core Transmission Network (or similar), respectively. (Of course, the core portion also contains switches or exchanges, data routers, control nodes, etc., which are contained in separate core switching, data routeing, control networks, etc.) The Access Network may be provided over fixed transmission links (using wires, optical fibre cable or radio systems) or over mobile radio links (using a mobile handset), while the core is always provided over a fixed link. This chapter describes the structure and characteristics of the fixed Access and Core Transmission Networks; Chapter 9 covers the mobile access.

This chapter is focussed on examining how the control of telephone call routeings across the networks (PSTN and others) is achieved. To this end, this chapter first considers the mechanism of signalling between nodes across the networks, and then the principal features of call switching control are introduced.

Mobile phones are now such an everyday feature of life throughout the World that in total they outnumber the population of fixed telephone lines. For many, the mobile phone is the preferred means of communication. This chapter explains how a mobile phone system works and the relationship between mobile and fixed networks. We begin by considering the nature of a mobile system. After a simple review of how a telephone call can be carried over a radio link, we examine the various cellular mobile network systems, and conclude by looking at how the mobile and fixed networks in the future may begin to merge.

In the first ten chapters of this book we considered various aspects of telecommunications networks: their components, how they are constructed, and the way that voice and data is carried. Now, in this final chapter we take a holistic view of how all the pieces are put together, how the end-to-end service provided to the users is managed, and how the networks are progressively enhanced and developed to take advantage of new technology. Specifically, the so-called NGN concept is examined. It is hoped that by the end of this chapter readers will have gained an insight into the intriguing question raised in the Foreword to the book, i.e. whether it is right to assume that all communications will eventually move onto the Internet.

This appendix contains the list of ITU-T recommendation E.164 assigned country codes.