f signals or detailed knowledge of the operation and functions of mobile networks, is left to dedicated courses. I have tried not to cover too many aspects of modern telecommunica- tions in this book SO as to keep its structure clear. The goal is to lay the basis for later studies of telecommunications for which many good sources are available. Some of them are listed at the end of each chapter. Preface Objectives Like the first edition of this book, this second edition is designed to provide answers to the fundamental questions concerning telecommunications net- works and services, telecommunications as a business area, and the general trends of technical development. These questions include the following: What is the structure and what are the main components of a modern telecommunications network? What is the importance of standardization and what are the main standardization bodies for telecommunications? How are analog signals processed for transmission over digital circuits? What are the basic techniques used in a primary pulse code modula- tion system that transmits analog speech through the digital tele- communication network? How does the Integrated Services Digital Network (ISDN) differ from the ordinary telephone network? What are the fundamental limiting factors of the rate of information transmission through a transmission channel? How do cellular mobile networks operate and what are their main components? What are the fundamental differences between circuit and packet switching techniques? What technical alternatives are available for provision of wideband access to the Internet? What are local area networks (LANs) and how are connections arranged over LANs? How does the Internet carry its traffic? What are its protocols and how do they operate? What happens when I click a mouse on a Web page? Second Edition In this second edition, the data communication sections, especially those dealing with local-area networks and the Internet, have been greatly expanded. The Internet has become a very important 