The IP Multimedia Subsystem (commonly called IMS) seems to be the perfect fit for new cellular networks which have known a revolutionary transition towards an IP-based architecture. However, this new architecture requires a massive work in order to enhance its reliability aspect. In this book, Ed-daoui, Mazri and Hmina represent technical challenges, internal issues and external threats facing IMS-based systems. They provide a thorough and comprehensive classification of these issues and threats. They also explain the role of reliability in the pursuit of a complete transition. And they give the syntax and semantics of their model for reliability monitoring. The need of such a book is evident, it provides a source for practitioners, researchers and students. For practitioners, this book explains best practices, guiding selection for IMS-based systems reliability monitoring. For researchers, this book provides a foundation for the development of more effective methods. For students, it explains the tremendous evolution of cellular networks, IMS, the reliability concept and the proposed model for monitoring.