This book is a revised version of the author's PhD thesis, which was selected as the winning thesis of the 2001 ACM Doctoral Dissertation Competition. Ion Stoica did his PhD work at Carnegie Mellon University with Hui Zhang as thesis adviser. The author addresses the most pressing and difficult problem facing the Internet community today: how to enhance the Internet to support rich functionalities, such as QoS and traffic management, while still maintaining the scalability and robustness properties embodied in the original Internet architecture. The monograph presents complete solutions including architectures, algorithms, and implementations dealing with fundamental problems of today's Internet: providing guaranteed services, differentiated services, and flow protection. Compared to existing solutions, Ion Stoica's solution eliminates the complex operations on both data and control paths in the network core. All in all, the research results presented in this monograph constitute one of the most important contributions to networking research in the past ten years.