Preface WHY WRITE THIS BOOK? Data communication networks are widely used today and are an integral part of our daily life. The Internet is a medium for business, personal, and government com- munication, and it is difficult to envision today's society without this essential infrastructure. The continued success of the Internet is dependent on our ability to maintain and improve the functionality, performance, and scalability of these networks. As a basis for obtaining the necessary knowledge about networks, there is a clear need for textbooks that provide an introduction to the foundations of this topic as well as a detailed understanding of more advanced issues. While many available books cover the design of network protocols and their operation, there has been preciously little focus on the systems that implement networks. Early data communication networks struggled with the scarcity of trans- mission bandwidth, which led to significant efforts to improve management and efficient use of this resource. Over the last three decades, advances in transmission technology have led to the availability of vast amounts of bandwidth, thus shifting the main bottleneck of networks from the transmission medium to the switching and processing of transmitted data. As a result, modern networks and the Internet