Section: 8.2.2.3 Inter-gNB-DU Conditional PSCell Change using MCG SRB without MN negotiation
Content: This procedure is used for the case where the UE moves from one gNB-DU to another gNB-DU within the same gNB-CU when only MCG SRB is available and the MN’s configuration is not changed during EN-DC operation for conditional PSCell change. Figure 8.2.2.3-1 shows the inter-gNB-DU conditional PSCell change procedure using MCG SRB in EN-DC. Figure 8.2.2.3-1: Inter-gNB-DU Conditional PSCell Change using MCG SRB without MN negotiation in EN-DC 1-4. The steps 1-4 are as defined in clause 8.2.2.1. 5. The gNB-CU sends an UE CONTEXT SETUP REQUEST message to the candidate gNB-DU to create an UE context and setup one or more data bearers. The UE CONTEXT SETUP REQUEST message is sent for each candidate cell and includes a CG-ConfigInfo. 6. The candidate gNB-DU responds the gNB-CU with an UE CONTEXT SETUP RESPONSE message including the target cell ID that was requested from the gNB-CU. The response message is sent for each requested candidate cell. 7. The gNB-CU sends an SGNB MODIFICATION REQUIRED message to the MeNB, which includes a generated RRCReconfiguration message. 8. The MeNB and the UE perform RRC Connection Reconfiguration/Complete procedure. 9. The MeNB sends an SGNB MODIFICATION CONFIRM message to the gNB-CU, to convey the received RRCReconfigurationComplete message at step 8. 10. An execution condition to trigger initiation of conditional PSCell change is fulfilled. 11. Random Access procedure is performed at the candidate gNB-DU, which becomes the target gNB-DU if successful. The target gNB-DU sends a Downlink Data Delivery Status frame to inform the gNB-CU. The target gNB-DU also sends an ACCESS SUCCESS message to inform the gNB-CU of which cell the UE has successfully accessed. 12-13. The UE responds with an RRCReconfigurationComplete message (embedded in an ULInformationTransferMRDC message), which the MeNB forwards to the gNB-CU via an RRC TRANSFER message. 14. The gNB-CU sends a UE CONTEXT MODIFICATION REQUEST message to the source gNB-DU and indicates to stop the data transmission for the UE. The source gNB-DU sends a Downlink Data Delivery Status frame to inform the gNB-CU about the unsuccessfully transmitted downlink data to the UE. Downlink packets, which may include PDCP PDUs not successfully transmitted in the source gNB-DU, are sent from the gNB-CU to the target gNB-DU. Downlink packets are sent to the UE. Also, uplink packets are sent from the UE, which are forwarded to the gNB-CU through the target gNB-DU. NOTE: The step 14 may happen before step 13, as soon as the gNB-CU knows which cell the UE has successfully accessed. NOTE: The gNB-CU may initiate UE Context Release procedure toward the other signalling connections or other candidate target gNB-DUs, if any, to cancel conditional PSCell change for the UE. 15. The source gNB-DU responds to the gNB-CU with the UE CONTEXT MODIFICATION RESPONSE message. 16-17. The steps 16-17 are as defined in steps 11-12 in clause 8.2.1.1.