n reference points as defined between SGSN and GGSN. S5a: It provides the user plane with related control and mobility support between MME/UPE and 3GPP anchor. S5b: It provides the user plane with related control and mobility support between 3GPP anchor and SAE anchor. S6: It enables transfer of subscription and authentication data for authenticating/authorizing user access to the evolved system (between HSS and MME). S7 It provides transfer of (QoS) policy and charging rules from PCRF to Policy and Charging Enforcement Point (PCEP). SGi: It is a reference point between the PDN GW and the packet data network. The node that performs control-plane functionality MME (Mobility Management Entity) is separated from the node that performs bearer-plane functionality (GW), with a well-defined open interface between them (S11), and by using an optional interface (S5) the Gateway (GW) can be split into two separate nodes (Serving Gateway and the PDN Gateway). This allows for independent scaling and growth of throughput traffic and control signal processing and operators can also choose optimized topological locations of nodes within the network in order to optimize the network in different aspects. The basic EPC architecture is shown in Figure 8.7, where support nodes such as AAA and policy control nodes have been excluded for clarity [12-14]. 8.2.1.6.4 E-UTRAN and EPC Split 3GPP has defined the functional split between radio access and core network as shown in Figure 8.8. E-UTRAN consists of eNB (enhanced Node B) which is described in Chapter 3. EPC consists of three elements, namely MME in the control plane, Serving GW and PDN Gateway in the user plane: MME: The MME main function is to manage UE mobility and UE identity. It also per- forms authentication and authorization; idle-mode UE tracking and reach-ability; security negotiations; and NAS (Non Access Stratum) signaling. It is connected to EUTRAN via S1-MME interface. Core Networks and Operations Support Systems Internet node 8 Figure 8.7 3GPP Release 8 EPS architectu