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There are two types of communication networks: circuit-switched networks and packed-switched networks. In circuit-switched networks, a dedicated physical circuit between the calling and called party is set up at the start of a call, and released when the call has ended. Telephone networks are circuit-switched networks. Today, these networks are used for speech and other purposes, such as facsimile, and are usually referred to as telecommunication networks. | Signaling in Telecommunication Networks. John G. van Bosse Copyright 1998 John Wiley Sons Inc. ISBNs 0-471-57377-9 Hardback 0-471-22415-4 Electronic INTRODUCTION TO TELECOMMUNICATIONS There are two types of communication networks circuit-switched networks and packed-switched networks. In circuit-switched networks a dedicated physical circuit between the calling and called party is set up at the start of a call and released when the call has ended. Telephone networks are circuit-switched networks. Today these networks are used for speech and other purposes such as facsimile and are usually referred to as telecommunication networks. Initially all communication networks were circuit-switched networks. Data communication networks made their appearance around 1970. In these networks a call consists of short data bursts packets followed by relatively long silent intervals and does not require a dedicated physical circuit. Internet is an example of a data communication network. Today the terms telecommunication network and data communication network usually imply circuit-mode and packet-mode networks respectively. This book is about signaling in telecommunication networks. To understand signaling it is necessary to be familiar with some basic telecommunication concepts and terms. This chapter presents an overview of telecommunication networks. It is intended as an introduction and sets the stage for the later chapters. TELECOMMUNICATION NETWORKS Introduction Figure shows a small part of a telecommunication network. It consists of exchanges trunks and subscriber lines. Trunks are circuits between exchanges 1 2 INTRODUCTION TO TELECOMMUNICATIONS Figure Partial view of a telecommunication network. and the group of trunks between a pair of exchanges is known as a trunk group TG . Subscriber lines SL are circuits between a subscriber S and his local exchange A B C . Exchanges D and E do not have subscriber lines and are known as intermediate tandem toll .