llows the UEs to be either in RRC_CONNECTED state when an RRC connection is established or in RRC_IDLE stated in when no RRC connection is established. The RRC states can further be characterized as follows [14,2 20]: RRC_IDLE: A UE specific DRX may be configured by upper layers. UE controlled mobility. The UE: Monitors a paging channel to detect incoming calls, system information change, and for sending ETWS (Earthquake and Tsunami Warning System) notification to EWTS capable UEs. Performs neighboring cell measurements and cell (re-)selection. Acquires system information. RRC_CONNECTED: Transfer of unicast data to/from UE. At lower layers, the UE may be configured with a UE specific DRX. Network controlled mobility, that is, handover and cell change order with optional network assistance (NACC) to GERAN. The UE: Monitors a Paging channel to detect system information change, and for ETWS capable UEs, ETWS notification. Monitors control channels associated with the shared data channel to determine if data is scheduled for it. Provides channel quality and feedback information. Performs neighboring cell measurements and measurement reporting. Acquires system information. PDCP header PDCP SDU PDCP PDU Figure 3.21 PDCP PDU structure (user plane). Reproduced with permission from © 2009 3GPP [14] Next Generation Mobile Communications Ecosystem GSM_Connected CELL_DCH Handover E-UTRA Handover RRC CONNECTED GPRS Packet transfer mode CELL_FACH CCO with optional CELL PCH Reselection URA_PCH Reselection Connection Connection establishment/release establishment/release Connection establishment/release Reselection UTRA_Idle E-UTRA Reselection GSM_Idle/GPRS RRC IDLE Packet_Idle CCO, Reselection Figure 3.22 E-UTRA states and inter RAT mobility procedures. Reproduced with permission from © 2009 3GPP Figure 3.22 provides an overview of the RRC states in E-UTRA and it also illustrates the mobility support between E-UTRAN, UTRAN and GERAN. 3.7.1 Services and Functions The RRC protocol offers the following services to upper layers: Br