Organization of this book 7 that meet their performance requirements. The input to these systems is network traffic that is consistent with the protocols stated in the system specification. This book follows a systematic approach to network systems based on the pro- tocols they implement. Considering the large number of existing and emerging protocols defined for different purposes, we use the OSI reference model for our presentation. The OSI reference model has well-defined and well-understood layers, which match the popular Transmission Control Protocol (TCP)/Internet Protocol (IP) protocol stack as a special case, and enables us to easily identify the functionality and requirements of specific network systems. It must be stressed that adoption and use of the OSI reference model in the book does not promote or limit the presented architectures and systems to specific protocols. Rather, this approach provides a basis for a systematic classification of network systems and avoids the complexity of considering the wide landscape of protocols standardized by several bodies and groups. The book is organized in the following three parts: · The first part of the book, constituted by Chapters 2 and 3, addresses the types and general structure of network systems, as well as evaluation techniques for the resulting architectures and designs. Chapter 2 presents and classifies net-