between the eNB and the MME. Next Generation Mobile Communications Ecosystem 11.6.1.4 E-UTRAN to HRPD Cell Re-selection The pre-condition for cell re-selection from E-UTRAN to HRPD is that the UE has previously established a presence in the target HRPD network, either through the pre-registration procedure or previous HRPD attachment. The UE performs Cell re-selection to HRPD while in RRC_IDLE. Cell reselection from E-UTRAN to HRPD should be aligned with 3GPP inter RAT cell reselection mechanism. 11.6.1.5 E-UTRAN to HRPD Handover The pre-condition for the E-UTRAN to HRPD handover procedure is that the UE is attached in the E- UTRAN network in E-UTRAN_ACTIVE state and has pre-registered with the HRPD network. Based on measurement reports received from the UE the eNB initiates a handover by sending an RRC HANDOVER FROM E-UTRA PREPARATION REQUEST message to the UE to indicate to the UE that it should begin the handover procedure. The MME will, based on indications provided by the HRPD network, get information about whether the handover succeeded or failed making it possible for the MME to set the handover status in the S1 CDMA2000 tunneling messages (e.g., handover success, handover failure). The UE can continue to send and receive data on the E-UTRAN radio until it receives the RRC MOBILITY FROM E-UTRA message including a tunneled "CDMA2000 handover command." After this message is received by the UE, the UE leaves the E-UTRAN radio and starts to acquire the HRPD traffic channel. The HRPD handover signaling is tunneled between the UE and HRPD network. 11.6.1.6 E-UTRAN and eHRPD Interworking Architecture Figure 11.8 is an example of E-UTRAN and eHRPD4 interworking architecture. An eHRPD system consists of HRPD BTS, Evolved Access Network (eAN) and Evolved Packet Control Function (ePCF) that supports evolved mode operation in addition to legacy mode and operation. An eHRPD system may be standalone or may support interworking with E-UTRAN. The introduction of eHRPD requires introduction of a HRPD Serving Gateway (HSGW)