REFERENCES 1. IEEE Standard Dictionary of Electrical and Electronic Terms, 6th ed., IEEE Std 100-1996, IEEE, New York, 1996. 2. R. L. Freeman, Telecommunication Transmission Handbook, 4th ed., Wiley, New York, 1998. 3. National Networks for the Automatic Service, CCITT-ITU Geneva, 1968. 4. Specifications of Signaling Systems 4 and 5, CCITT Recommendations, Fascicle VI.4, IXth Plenary Assembly, Melbourne, 1988. 5. "Signaling" from Telecommunications Planning Documents, ITT Laboratories, Madrid, Novem- ber, 1974. 6. Specifications for Signaling Systems R1 and R2, CCITT Recommendations, Fascicle VI.4, IXth Plenary Assembly, Melbourne, 1988. 7. BOC Notes on the LEC Networks-1994, Special Report SR-TSV-002275 Issue 2, Bellcore, Piscataway, NJ, 1994. 8. W. D. Reeve, Subscriber Loop Signaling and Transmission Handbook-Analog, IEEE Press, New York, 1992. LOCAL AND LONG-DISTANCE NETWORKS 8.1 CHAPTER OBJECTIVE This chapter concentrates on the network design of the PSTN, how it is structured and why. Routing techniques have a strong influence on how a network is structured. Thus we also discuss routing and, in particular, dynamic routing. The third topic deals with transmission, namely, assigning losses in the network to eliminate any possibility of singing and to keep echo inside some tolerable limits. 8.2 MAKEUP OF THE PSTN As we discussed in Section 1.3, the PSTN consists of a group of local networks connected by a long-distance network. In countries where competition is permitted, there may be two or many long-distance networks. Some of these may cover the nation, whereas others are regional long-distance networks. The heart of a local network is the subscriber plant. This consists of customer premise equipment (CPE), a copper wire distribution network made up of subscriber loops that con- nect to a local serving switch via the main distribution frame (MDF). The concept of the subscriber plant feeding the local network, which, in turn, feeds the long-distance network to a distant local network and associated subscriber 