This book presents the range of analytical tools and techniques that ensure traffic performance and quality of service in telecommunication systems and networks. To that end, it provides a methodology that may be applied to all phases of development, from conception to practical exploitation. Architectures and functions from the point of view of performance are described, and the basic concepts of teletraffic are introduced. This is then followed by definitions of quality of service and normalisation, and then the appropriate tools (probability theory, probability laws, and statistics), and techniques of evaluation (reliability, dependability, and queueing theory). These tools and techniques are also given a practical standpoint through the use of models and simulation techniques. They are placed in an industrial environment, providing a methodology to attain maximum effectiveness when dealing with the constraints of industrial application as well as the market.