o the UE as an RRC message to perform the handover. This completes the handover preparation stage. The AMF sends the Handover Command to the source gNB. The message carries the list of PDU sessions to handover, the list of PDU sessions to release, the target-to-source RRC transparent container received in step 6, and some other information. 8. The source gNB triggers the handover by sending the Handover Command to the UE containing the information required to access the target cell. 9. The UE synchronizes to the target cell. 10. If Packet Data Convergence Protocol (PDCP) status preservation is required, the source gNB sends the Uplink RAN Status Transfer message to the AMF. The message car- ries the list of DRBs with their associated information about missing PDCP sequence numbers. The AMF sends the information received in step 10 to the target gNB in the Downlink RAN Status Transfer message. 12. After the UE has successfully synchronized to the target cell, it sends the Handover Confirm message to the target gNB. 13. The target gNB sends the Handover Notify message to inform the AMF that the UE has been identified in the target cell and the handover has been completed. 14. The AMF sends the UE Context Release Command message to the source gNB to request the release of the UE-associated logical NG connection. 15. The source gNB sends the UE Context Release Complete message to the AMF to con- firm the release of the UE-associated logical NG connection. Note that in the present section we describe the handover via 5GC procedure, while the Xn handover is described in Section 3.3.3. 3.3.3.2 NG-U Interface The NG-U interface between an NG-RAN node and a UPF uses the same GTP-U-based protocol stack as the rest of the NG-RAN interfaces, with NG-specific user-plane protocol on top of GTP-U (i.e. in the NG-specific GTP-U container), as shown in Figure 3.3.6. This user-plane protocol is referred to as a PDU Session User-Plane protocol (3GPP TS 38.415). Connectivity for a UE over the NG interface is provided over one or mor