QCI identifier. During attachment, the PGW entity grants an IPv4 or IPv6 address to the mobile. The PGW entity constitutes the anchor point for inter-SGW mobility when the mobile changes groups. The PGW entity hosts the policy and charging enforcement function (PCEF) which applies the rules relating to mobile traffic data on packet filtering, on charging and on quality of service (QoS) to be applied to the bearer to build. The policy charging and rules function (PCRF) entity, outside the EPS network, provides the PCEF function of the PGW entity with the rules to apply when establishing bearers. The PGW entity generates data for use by charging entities to develop the record tickets processed through the billing system. The PGW entity performs replication of the mobile traffic data within the framework of lawful interception. 1.1.2. Protocol architecture The protocol architecture of the EPS network is illustrated in Figure 1.2 for the control plane and in Figure 1.3 for the traffic plane. VoLTE and ViLTE S1-MME S1-AP S1-AP GTP-C GTP-C GTP-C GTP-C LTE L1 LTE-L1 eNode B Figure 1.2. Protocol architecture: control plane The LTE-Uu interface is the reference point between the mobile and the eNB entity. This interface supports radio resource control (RRC) signaling exchanged between the mobile and the eNB entity, transmitted in the signaling radio bearer (SRB) and the mobile traffic data transmitted in the data radio bearer (DRB). The RRC signaling also provides transport of the non-access stratum (NAS) protocol exchanged between the mobile and the MME entity. GTP-U GTP-U GTP-U GTP-U Bearer Bearer LTE-L1 LTE-L1 eNode B Figure 1.3. Protocol architecture: traffic plane The S1-MME interface is the reference point between the MME and eNB entities for signaling, via the S1-AP (Application Part) protocol. Network Architecture The S1-AP protocol also provides transport of the NAS protocol exchanged between the mobile and the MME entity. The S11 interface is the reference point between the MME and SGW entities for signaling via