VoLTE and the IP Multimedia Subsystem
Christopher Cox · 2014
This chapter discusses the likely long-term solution for LTE voice calls, namely the delivery of voice over IP streams that are controlled by the IP multimedia subsystem (IMS). The IMS is not part of LTE: instead it is a separate network whose relationship with LTE is the same as that of the Internet. The chapter reviews the history of the IMS and Voice over LTE (VoLTE), and discusses the architecture and protocols of the IMS and the procedures for registration and call setup. It then covers three aspects of interoperation between the IMS and the 2G/3G circuit switched domain, namely access domain selection, single radio voice call continuity (SRVCC) and IMS centralized services (ICS), and concludes by discussing IMS emergency calls and SMS.