The purpose of the UE Context Release procedure is to enable the gNB-CU to order the release of the UE-associated logical connection or candidate cells in conditional handover or conditional PSCell change. The procedure uses UE-associated signalling.
The gNB-CU initiates the procedure by sending the UE CONTEXT RELEASE COMMAND message to the gNB-DU.
Upon reception of the UE CONTEXT RELEASE COMMAND message, the gNB-DU shall release all related signalling and user data transport resources and reply with the UE CONTEXT RELEASE COMPLETE message.
If the old gNB-DU UE F1AP ID IE is included in the UE CONTEXT RELEASE COMMAND message, the gNB-DU shall additionally release the UE context associated with the old gNB-DU UE F1AP ID.
If the UE CONTEXT RELEASE COMMAND message contains the RRC-Container IE, the gNB-DU shall send the RRC container to the UE via the SRB indicated by the SRB ID IE.
If the UE CONTEXT RELEASE COMMAND message includes the Execute Duplication IE, the gNB-DU shall perform CA based duplication, if configured, for the SRB for the included RRC-Container IE.
If the Candidate Cells To Be Cancelled List IE is included in the UE CONTEXT RELEASE COMMAND message, the gNB-DU shall consider that the gNB-CU is cancelling only the conditional handover or conditional PSCell change associated to the cells identified by the included NR CGIs and associated to the UE-associated signaling identified by the gNB-CU UE F1AP ID IE and the gNB-DU UE F1AP ID IE.
Interactions with UE Context Setup procedure:
The UE Context Release procedure may be performed before the UE Context Setup procedure to release an existing UE-associated logical F1-connection and related resources in the gNB-DU, e.g. when gNB-CU rejects UE access it shall trigger UE Context Release procedure with the cause value of UE rejection.
If one or more candidate cells in the Candidate Cells To Be Cancelled List IE included in the UE CONTEXT RELEASE COMMAND message were not prepared using the same UE-associated signalling connection, the gNB-DU shall ignore those non-associated candidate cells.