V-PCRF Visited PCRF Wide Band XML Configuration Access Protocol eXtensible Markup Language Network Architecture 1.1. EPS network 1.1.1. Functional architecture The functional architecture of the evolved packet system (EPS) network is illustrated in Figure 1.1. E-UTRAN Figure 1.1. Functional architecture of EPS network VoLTE and ViLTE: Voice and Conversational Video Services over the 4G Mobile Network, First Edition. André Perez. ISTE Ltd 2016. Published by ISTE Ltd and John Wiley & Sons, Inc. VoLTE and ViLTE The EPS mobile network consists of an evolved packet core (EPC) network and an evolved universal terrestrial radio access network (E-UTRAN). The E-UTRAN access network ensures the connection of the User Equipment (UE). The EPC core network interconnects the access networks, provides the interface to the packet data network (PDN) and ensures the attachment of mobile phones and the establishment of bearers. 1.1.1.1. eNB entity The E-UTRAN access network includes a single type of entity, the evolved Node Base station (eNB) that connects to the mobiles. The eNB entity is responsible for the management of radio resources, for the control of the establishment of the data radio dearer (DRB), in which the mobile traffic is transmitted and for its mobility management during the session (handover). The eNB entity transfers the traffic data from the mobile (respectively from the Serving Gateway (SGW)) to the SGW entity (to the mobile phones concerned, accordingly). When the eNB entity receives data from the mobile or the SGW entity, it refers to the QoS class identifier (QCI) in accordance with the data scheduling mechanism. The eNB entity can perform the marking of the DiffServ code point (DSCP) field of IP header, based on the assigned QCI identifier, for the outgoing data to the SGW entity. The eNB entity performs compression and encryption of traffic data on the radio interface. The eNB entity performs encryption and integrity control of signaling data exchanged with the mobile. It also undertakes the selection of t