Section: 6.7.3.4 Transitions from RRC_INACTIVE to RRC_CONNECTED states
Content: At state transition from RRC_INACTIVE to RRC_CONNECTED, the source gNB/ng-eNB shall include the UE 5G security capabilities and the ciphering and integrity algorithms the UE was using with the source cell in the Xn-AP Retrieve UE Context Response message. The target gNB/ng-eNB shall check if it supports the received algorithms, if the target gNB/ng-eNB supports the received ciphering and integrity algorithms, the target gNB/ng-eNB shall check the received algorithms to its locally configured list of algorithms (this applies for both integrity and ciphering algorithms). If the target gNB/ng-eNB selects the same security algorithms, the target gNB/ng-eNB shall use the selected algorithms to derive RRC integrity and RRC encryption keys to protect the RRCResume message and send to the UE on SRB1. If the target gNB/ng-eNB does not support the received algorithms or if the target gNB/ng-eNB prefers to use different algorithms, the target gNB/ng-eNB shall send an RRCSetup message on SRB0 in order to proceed with RRC connection establishment as if the UE was in RRC_IDLE (fallback procedure) to the UE. Then the UE performs NAS based RRC recovery and negotiates a suitable algorithm with target gNB/ng-eNB via AS SMC procedure.