OVERVIEW

The packet-switched networks that we studied in Chapters 3 and 4 are well suited for message traffic. Virtual circuit-switched networks, designed for variable bit rate traffic, are discussed in Chapter 6. Constant bit rate traffic is better transported by circuit-switched networks, which we study in this chapter. The most important circuit-switched networks are the telephone, cable TV or CATV, and some cellular telephone and satellite networks. We discuss only the telephone and CATV networks.

This chapter presents the underlying concepts and the technologies deployed in the 1980s and 1990s that changed the telephone system from a voice-only network to one that supports all types of traffic. You will become familiar with the most important technologies: SONET, DWDM, optical local loop, digital subscriber line solutions including ISDN and xDSL, and INA. You will also learn how CATV systems are changing from a one-way video distribution system into a network that also offers communication in the upstream direction. The telephone and CATV networks, which until 1990 served separate markets, have since begun to compete and collaborate. It is still too early to assess the full impact of the 1996 Telecommunications Bill. A notable example of that impact is AT&T's $37 billion acquisition of the cable TV company TCI and the $58 billion acquisition of MediaOne, with the objective of developing a two-way system that can handle voice, data, and video services. This chapter explains the technological basis underlying this change.

Today's telephone network consists of a high-speed digital backbone network. Most...