 8.1.2. Roaming applied to the IMS network 8.2. Procedures 8.2.1. Session establishment for nominal routeing 8.2.2. Session establishment for optimal routeing Chapter 9. Service Centralization and Continuity 9.1. ICS function 9.1.1. Functional architecture 9.1.2. Procedures 9.2. e-SRVCC function 9.2.1. Functional architecture 9.2.2. Procedures Chapter 10. Short Message Service 10.1. Message structure 10.1.1. SM-TL layer 10.1.2. SM-RL layer 10.1.3. SM-CL layer 10.2. SMS over SGsAP 10.2.1. Functional architecture 10.2.2. Procedures 10.3. SMS over SIP 10.3.1. Functional architecture 10.3.2. Procedures Bibliography Index Preface This book presents the mechanisms used in the 4G evolved packet system (EPS) mobile network and in the IP Multimedia sub-system (IMS) for the supply of voice over long term evolution (VoLTE) and video over long term evolution (ViLTE) service (Figure 1). Bearer IP packet IP packet Bearer Operator A Operator B Figure 1. Implementation of VoLTE or ViLTE services The EPS network does not provide telephone service because it does not deal with telephone signaling. VoLTE and ViLTE The EPS network operates in packet-switched (PS) mode and acts as the transport of internet protocol (IP) packets through bearers. The EPS network, therefore, transfers the IP packets containing voice or video real-time transport protocol (RTP) streams or telephone signaling session initiation protocol (SIP). Telephone or videophone service is provided by the IMS network which provides the functions as follows: - routing the call; - supplementary telephone and videophone services; - interconnection to the third-party networks. Chapter 1 presents the architecture of EPS and IMS networks and these networks environment: databases, charging, policy and charging control (PCC), DIAMETER routing, ENUM system and internet protocol exchange (IPX). Chapter 2 presents various signaling protocols: - signaling of the EPS network, allowing the mobile to attach, to update its location, to establish sessions for the transport of IP packe