Voice over LTE (Long Term Evolution) presents the mechanisms put in place in 4G mobile networks for the transportation of IP packets containing voice data and telephone signaling, as well as the technologies used to provide a telephone service in the IMS (IP Multimedia Sub-system) network. Despite the difficulty connected to the handover of the 4G network to the 2G/3G network, a telephone communication will not be established on the 4G network. This book analyzes the technologies that have been put in place, such as CSFB (Circuit Service FallBack), an interim solution that enables a mobile connected to the 4G network to receive an alert transmitted by the 2G/3G network. The book also goes on to develop the SIP (Session Information Protocol) on which the telephone signaling transferred by the 4G network is based, the IMS network that provides the service and defines the routing, the SRVCC (Single Radio Voice Call Continuity) mechanism that maintains communication and the TAS (Telephony Application Server) that supplies supplementary services. Contents 1. The EPS Network. 2. The LTE Interface. 3. The CSFB Function. 4. SIP and SDP Protocols. 5. The IMS Network. 6. Telephone Services. 7. The SRVCC Function. About the Authors André Perez is a consultant and teacher in networks and telecommunications. He works with industrialists and operators regarding architecture studies and leads training on the 4G and IMS networks for NEXCOM.