UE will initiate this request to re-establish RRC COnncetion.
A UE in RRC_CONNECTED with AS security has been activated with SRB2 and at-least one DRB has been setup may initiate this procedure.
Initiation
The UE initiates the procedure when one of the following conditions is met:
-> upon detecting radio link failure of the MCG
-> upon re-configuration with sync failure of the MCG
-> upon mobility from NR failure
Reception of the RRCReestablishment by the UE
On reception, UE shall:
-> stop timer T301;
-> consider the current cell to be the PCell;
-> update the KgNB key based on the current KgNB key
-> derive the KRRCenc and KUPenc keys associated with the previously configured cipheringAlgorithm
-> derive the KRRCint and KUPint keys associated with the previously configured integrityProtAlgorithm
TS 38.331