This book is about networks. It is one of the few network-oriented books, that is, books that approach telecommunications through the “eyes” of networks. This networking view is important because of the = Growth in the importance of networks as service has become more complex = Need to understand modern networking issues and techniques = Need to understand how services are affected by network capabilities and network evolution = Need to address the next stage of network evolution The evolution of existing networks draws them into seamless networks, networks that hide any service-related differences from the user. In this book we will look at different aspects of networking that must be appreciated in order to understand what is involved in the making of a seamless network. We will also get a glimpse of the future that a seamless network promises.