This book provides a broad introduction to all aspects of modern telecommunications networks, covering the principles of operation of the technology and the way that networks using this technology are structured. The main focus is on those technologies in use today in the majority of the public telecommunications networks. Discussion of new technology, in particular the move to the so-called next generation networks (NGN) is also included.
Inspec keywords: mobile communication; circuit switching; next generation networks; cable television; telecommunication signalling; Internet telephony
Other keywords: signalling; Internet; mobile telecommunications networks; next generation networks; PSTN; telephony; cable television; IP; circuit switching
Subjects: Communication switching; CATV and wired systems; Telephony; Mobile radio systems
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.
This chapter introduced the concept of the many telecommunications networks that exist today and how they all interlink. First, we looked briefly at the two other types of network, in addition to the PSTN, that carry telephone calls, namely: mobile networks and Cable TV networks. It is noted that all three networks use essentially the same type of switching system, but the mobile networks use radio links and mobility management in place of the fixed-wire access of the PSTN and Cable TV networks. The necessary interconnection of all these types of networks within a country and to networks in other countries was described. We also introduced the concept of the Internet and how subscribers gain access to it via the PSTN, cable modems over Cable TV networks, ADSL broadband or over private circuits using optical fibre.
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.
This chapter describes the wide variety of transmission systems used in telecommunications networks today. In doing this, we will be drawing upon the concepts of multiplexing and analogue to digital conversion introduced in the previous chapter. Earlier chapters have also introduced the important distinction between the access network, which serves the subscribers, and the core transmission network, which provides links between network nodes only. In general, the transmission systems described in this chapter may be deployed in both the access and the core transmission networks although they are usually more appropriate to one or the other, and this will be indicated. Chapter 2 introduced the model of the networks associated with the PSTN (Fig. 2.11), in which the access and core transmission networks act as a common utility for providing circuits to the various specialised networks as well as the PSTN. However, we will leave the description of how the various transmission systems are deployed in the access and core transmission networks until Chapter 5.
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.
Having considered in Chapters 1 and 2 how a call is conveyed across one or more networks, this chapter is all about how the exchanges or more precisely, the switching units within the exchanges in a PSTN actually work. Section 6.2 considers the basic components of circuit-switching systems, often referred to as 'Voice switches'. For clarity, this chapter describes the arrangement for the fixed-network exchanges (also called 'wireline exchanges'); consideration is given to the additional elements that are included in a mobile network exchange in Chapter 9.
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.
Previous chapters have concentrated on the communication of voice, primarily in the form of the telephony service as carried over the PSTN. We are now in a position to consider the various non-voice services, generally referred to as data, and the networks that carry them. At the end of this chapter we will investigate the way that these data networks can also convey voice, and that leads us to consider the new generation of communication networks.
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.
However, this chapter confines itself to considering how numbering and addressing is defined and applied to the various types of networks (both fixed and mobile). After considering the two different approaches made in telephone and data networks, particularly IP networks, we examine the newly introduced integrated system that allows full interworking between telephone numbers and Internet addresses. It should be appreciated that this is a surprisingly fast moving area of national regulation and there may be changes made to the established principles of numbering and addressing,particularly as new implementation of voice services, such as VOIP (see Chapters 8 and 11) are implemented.
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.
By its very nature, telecommunications depends on successful interaction between distant systems and for this to be successful some degree of commonality is required in specification of the equipment interfaces and protocols used. There are several organisations addressing the areas of standards for telecommunications networks. These are organised on a global, regional or national basis. In addition, there are a range of other organisations, often consortium or forums of interested parties in the industry that set ad hoc standards, many of which become adopted later by the more formal regional and global organisations. The key organisations referred to throughout this book are summarised below.
This appendix contains the list of ITU-T recommendation E.164 assigned country codes.
