This book introduces the reader to the principles used in a broad selection of modern data communication protocols and basic algorithms for use in distributed applications, including not only simple point-to-point data transfer protocols but also multi-party protocols and protocols for ensuring data security. The presentation uses CSP notation to give a concise description of the protocols considered and to provide a basis for analysis of their properties. Relating theory to practice, with a strong focus on currently important Internet protocols, the book clearly explains how the principles are exploited in real-life protocol designs. Principles of Protocol Design is aimed at third-year students and graduates who are studying computer networks/distributed systems or data communications, as well as professional system designers who are looking for the broad view of the area.