We have telephony to talk to each other, messaging to dispatch mail or instant messages, browsing to read published content and search engines to locate content sites. However, current mobile networks do not provide the possibility for one application rich terminal to communicate with another in a peer-to-peer session beyond voice calls. Mobile telephony with the current technology has been hugely successful and shows that there is immense value in communicating with peers while being mobile, and with increasingly available smarter multimedia terminals the communication experience will be something more than just exchanging voice. Those multimedia terminals need IP multimedia networks. Hence, the Third Generation Partnership Project (3GPP) has developed a standard for SIP based IP multimedia service machinery known as 'The IMS (IP Multimedia Subsystem)' and this informative book explains everything you need to know about it . Presents the architecture and functionality of logical elements of IMS and their interfaces providing detailed description of how elements are connected, what protocols are used and how they are used Explains how the optimisation and security of the mobile communication environment has been designed in the form of user authentication and authorisation based on mobile identities Illustrates how optimisation at the radio interface is achieved using specific rules at the user to network interface. This includes signalling compression mechanisms as well as security and policy control mechanisms, allowing radio loss and recovery detection Addresses important aspects from an operator's point of view while developing architecture such as charging framework, policy and service control Describes many services on top of IMS in detail, including voice, presence, messaging and conferencing. Written in a manner that allows readers to choose the level of knowledge and understanding they need to gain about the IMS, this volume will have instant appeal to a wide audience ranging from marketing managers, research and development engineers, network engineers, developers, test engineers to university students.