y and to acquire an organized view of the wider telecommunication environment. Finally, a comment on the organization of the bibliography. We have chosen not to mention who has discovered a certain technique or which research group has first intro- duced a certain type of analysis. Frequently, the first work in which a concept appears is neither the most complete nor the most useful from a didactical point of view. We have decided to mention only those papers that have helped us in gaining more insight into a topic or in explaining it. Where possible, we have cited complete works, or even books if available. Acknowledgments This book would not have been possible without the continuous support and encourage- ment of my wife Flavia and of my three children Emanuele, Maria Grazia, and Gabriele. I enjoyed the rare advantage of finding in my wife dedication, understanding, support, and technical help, and I took full advantage from them. My friends and colleagues have provided a great number of suggestions and discus- sions that have been invaluable. Among them, I would like to thank, in particular, Stefano Santoni, Massimo Gentili, Marco Romagnoli, and Roberto Sabella for their help in review- ing a few key points of the book. I would also like to remember Filippo Bentivoglio. At the very beginning of optical net- working, Filippo and I worked together in the exciting mission of defining a complete new network layer. A few still valid concepts regarding optical protection (and a few schemes relating to that) derive from our common work. Drivers for Telecommunication Network Evolution 2.1 Market of Telecom Carriers The telecommunication market has been, for a long time, characterized by a set of very specific features that distinguished it from all other markets. Up to the early 1990s, there was almost no competition due to the legal monopoly exist- ing in the main western European countries and the practical monopoly existing in the United States. As a matter of fact, in all the western European countries, telecommun