Third edition of this best-selling guide to IMS: fully revised, and updated with brand new material The IMS (IP Multimedia Subsystem) is the technology that merges the Internet with the cellular world. It makes Internet technologies such as the web, email, instant messaging, presence, and videoconferencing available nearly everywhere at any time. The third edition of this bestselling book is fully updated and provides comprehensively expanded content, including new chapters on emergency calls and on Voice Call Continuity (VCC). As well as this, The 3G IP Multimedia Subsystem (IMS) presents updated material including a comprehensive picture of Session Initiation Protocol (SIP) as well as its applicability to IMS. As most of the protocols have been designed in the IETF, this book explains how the IETF developed these protocols and describes how these protocols are used in the IMS architecture. This is an indispensable guide for engineers, programmers, business managers, marketing representatives and technically aware users who want to understand how the IMS works and explore the business model behind it. New chapters on emergency calls, Voice Call Continuity (VCC), service configuration (XCAP, XDM), and conferencing Fully updated throughout, including Policy and Charging Control (PCC), QoS, Presence, Instant Messaging, Multimedia Telephony Services, and Push-to-talk over Cellular (PoC) Describes the IP Multimedia Subsystem from two different perspectives: from the IETF perspective, and from the 3GPP perspective. Provides details on the latest policy technology and security architecture Written by experienced professionals in the field.