This book contains a selection of papers presented at a symposium organized under the aegis of COST Telecommunications Action 285. The main objective of the Action is to enhance existing tools and develop new modeling and simulation tools for research in emerging multi-service telecommunication networks in the areas of model performance improvements, multilayer traffic modeling, and the important issue of evaluation and validation of the new modeling tools. The studies related to the activities above are carried out by members of the Action Group with contributions from invited experts/scientists from non-COST country academia and industry (within and outside Europe) when deemed necessary. The book in your hands is the collection of some important aspects of study results achieved by this mixed group of experts/scientists from Europe and the United States of America. The symposium presentations were made in four sessions as follows: 1. Multilayer Traffic and Mulimedia Behavior, 2. Quality of Simulations, 3. Accelerated Simulation Methods, 4. Verification, Validation and Credibility of Simulations, and covered nearly all of the important aspects of the subjects and issues above. It is hoped and expected that this book will be useful as a reference work for practicing engineers as well as academic researchers.