gence Protocol (PDCP) are now located in eNodeB [11,14]. 3.8.2 eNodeB The key functions of eNodeB are as follows [14]: Functions for Radio Resource Management: Radio Bearer (RB) Control, Radio Admission Control, Connection Mobility Control, Dynamic allocation of resources to UEs in both uplink and downlink (scheduling) are performed by eNodeB. IP header compression and encryption of user data stream. Selection of an MME at UE attachment when no routing to an MME can be determined from the information provided by the UE. Routing of User Plane data towards Serving Gateway. Scheduling and transmission of paging messages (originated from the MME). Scheduling and transmission of broadcast information (originated from the MME or O&M). Measurement and measurement reporting configuration for mobility and scheduling. Scheduling and transmission of ETWS (Earthquake and Tsunami Warning System) messages (origi- nated from the MME). Some functions of EPC are provided in this figure; the details are provided in Chapter 8. 3GPP Evolved Packet System (EPS) Figure 3.25 User plane protocol stack. Reproduced with permission from C 2009 3GPP [14] 3.8.3 Radio Protocol Architecture The radio protocol architecture of the EUTRAN consists of user plane and control plane. In the user plane, eNodeB hosts the layer 1 (PHY) and sublayers of layer 2. The sublayers MAC, RLC, and PDCP are terminated in eNodeB on the network side as shown in Figure 3.25. The control plane protocol stack as shown in Figure 3.26 also includes the RRC layer in the eNodeB and UE. PDCP, RLC, MAC, and RRC are terminated in eNodeB on the network side. Additionally, MME and UE host the NAS (Non Access Stratum) 14 plane in EPS. The NAS control protocol is terminated in MME on the network side. 3.8.4 EPS Home eNodeBs 3GPP has included the support of HeNBs or Femtocells in EPS networks. Figure 3.27 shows a logical architecture for E-UTRAN HeNB that has a set of S1 interfaces to connect the HeNB to the EPC. In this architecture Home eNB Gateway (HeNB GW) can connect multipl