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20INTRODUCTION TO PACKETNETWORKS AND VoIPMost of the previous chapters deal with circuit-switched telecommunication networks(such as the public switched circuit network—SCN), where an end-to-endconnection is set up at the start of a call and released when the call ends (see beginningof Chapter 1). This chapter introduces signaling for voice connections andtransmission of speech in a different type of network, namely, digital data networksthat use packet communication. While circuit-switched networks were developedand optimized for voice communication, packet networks were developed and optimizedfor data communication, that is, communication between computers or hosts(in the rest of the chapter we will use the two terms interchangeably). Packet networksare a relatively recent development, and they are growing more rapidlythan circuit-switched networks because of the large number of new computer applicationsin the business, government, and academic worlds that rely on host-to-hostcommunication.20.1 PACKET-BASED COMMUNICATIONThis section presents a brief introduction to familiarize the reader with basic conceptsthat will be helpful later in the chapter. Readers who are interested in amore detailed description of this topic are referred to [1,2].20.1.1 Data versus VoiceData communication covers a range of applications (e.g., file transfer, e-mailservice, message service, time-sharing, and interactive computer sessions) withcharacteristics that differentiate it from voice communication, namely,Signaling in Telecommunication Networks, Second Edition, by John G. van Bosse and Fabrizio U. DevetakCopyright # 2007 John Wiley & Sons, Inc.631