Section: 8.2.1.6 LTM with gNB-CU-UP change
Content: Figure 8.2.1.6-1 shows the procedure used for LTM with the change of gNB-CU-UP within a gNB. Figure 8.2.1.6-1 LTM with the change of gNB-CU-UP 0. The source gNB-DU forwards the Measurement Report to the gNB-CU-CP. 1. The gNB-CU-CP decides to initiate LTM configuration. 2. The gNB-CU-CP sends a BEARER CONTEXT SETUP REQUEST message containing UL TNL address information for NG-U to setup the bearer context in the target gNB-CU-UP. 3. The target gNB-CU-UP responds with a BEARER CONTEXT SETUP RESPONSE message containing the UL TNL address information for F1-U, DL TNL address information for NG-U, and the TNL address information for data forwarding to the target gNB-CU-UP. 4. LTM configuration procedures are performed between gNB-CU and candidate gNB-DUs, and between gNB-CU and source gNB-DU as specified from step 3 to step 8 in section 8.2.1.5. 5 - 6. The gNB-CU-CP sends the RRC Reconfiguration message to the UE. 7. The UE sends the lower layer measurement result to the source gNB-DU, and the source gNB-DU decides to execute LTM to a candidate target cell. 8. The source gNB-DU sends the DU-CU CELL SWITCH NOTIFICATION message to the gNB-CU-CP with the selected target cell ID. 9-10. The gNB-CU-CP performs the Bearer Context Modification procedure to retrieve the PDCP UL/DL status and to exchange the TNL address information for data forwarding for the bearers. 11-12. The gNB-CU-CP performs the Bearer Context Modification procedure to send the DL TNL address information for F1-U and the PDCP UP/DL status to the target gNB-CU-UP. 13. Data Forwarding may be performed from the source gNB-CU-UP to the target gNB-CU-UP. 14. The target gNB-DU detects the UE in the target cell. 15. The target gNB-DU sends an ACCESS SUCCESS message to the gNB-CU-CP. 16-18. Path Switch procedure is performed to update the DL TNL address information for the NG-U towards the core network. 19-20. Bearer Context Release procedure may be performed to release the UE context in the source gNB-DU.