 is separated from the node that performs bearer-plane functionality (GW), with a well-defined open interface between them (S11). The GW is also split into two separate nodes namely Serving Gateway (S-GW) and Packet Data Network Gateway (PDN-GW). The overall EPS architecture is divided into two parts that is, E-UTRAN and EPC (Enhanced Packet Core) as shown in Figure 3.23. E-UTRAN consists of eNodeB whereas MME and GW fall into the category of EPC. The eNodeBs are interconnected with each other by means of the X2 interface and are connected to EPC via S1 interface. eNodeBs are connected to MME via S1-MME and to the Serving Gateway (S-GW) by means of the S1-U. The S5 interface provides user plane tunneling and tunnel man- agement between S-GW and PDN-GW. The PDN-GW connects the EPS user to the Internet and to other packet data services via SGi interface. The LTE devices connect to the eNodeBs via LTE-Uu interface. 3.8.1 E-UTRAN and EPC Functional Split 3GPP has defined a functional split for the EPS between radio access (E-UTRAN) and core network (EPC) as shown in Figure 3.24. All radio-related signaling and all layers of retransmission are located LTE-Uu S1-MME eNodeB S1-MME INTERNET LTE-Uu PDN-GW eNodeB Figure 3.23 EPS architecture Next Generation Mobile Communications Ecosystem Inter Cell RRM RB Control Connection Mobility Cont. Radio Admission Control NAS Security eNB Measurement Configuration & Provision Idle State Mobility Dynamic Resource Handling Allocation (Scheduler) EPS Bearer Control Mobility UE IP address Anchoring allocation Packet Filtering Internet E-UTRAN Figure 3.24 Functional split between E-UTRAN and EPC. Reproduced with permission from © 2009 3GPP [14]¹3 in eNodeB, which is the only remaining element of the radio access network. Similar to HSPA the MAC layer functionality remains in the eNodeB. The new functionalities in base stations compared to HSPA are the Radio Link Control Layer (RLC) and Radio Resource Control (RRC). Also ciphering and header compression as functions of Packet Data Conver