ropped. 7.2. Handover based on X2 7.2.1. Handover based on X2 without relocation The functional architecture of the handover based on X2 without relocation of the SGW entity is described in Figure 7.1. VoLTE and ViLTE E-UTRAN Source S1-MME LTE-Uu S1-U S1-MME LTE-Uu Target Figure 7.1. Handover based on X2 without relocation functional architecture The X2-based handover procedure without relocation of the SGW entity is described in Figure 7.2: - the preparation phase includes messages 1 and 2; - the implementation phase includes messages 3 to 5; - the completion phase includes messages 6 to 15. 1) On receipt of the RRC MeasurementReport message, the source eNB entity decides to perform a cell change and transmits to the target eNB entity the message X2-AP HANDOVER REQUEST containing the context of the mobile, particularly the tunnel endpoint identifier (TEID) of the S1 bearer provided by the SGW entity. 2) The target eNB entity responds with the message X2-AP HANDOVER REQUEST ACK, containing the technical characteristics of the radio interface in the information element. Handover command and the TEID identifier of the unidirectional X2 temporary bearer built between source and target eNB entities. 3) The source eNB entity eNB starts the execution phase by sending to the mobile the message RRC ConnectionReconfiguration containing information element handover. Handover 4) The source eNB entity sends to the target eNB the sequence numbers of the packet data convergence protocol (PDCP) in the message X2-AP SN STATUS TRANSFER and incoming data that have not been acknowledged by the mobile and that the target eNB entity will store until the mobile is able to receive them. 5) When the RRC connection is established between the mobile and the target eNB entity, the mobile transmits the message RRC ConnectionReconfigurationComplete, which will trigger the transfer of incoming data stored by the target eNB entity to the mobile. Source Target Traffic Radio Bearer S1 Bearer S5 Bearer Incoming data Outgoing data X2-AP HANDOVER R