Question: Upon receiving an RRCConnectionReconfiguration message, if a User Equipment (UE) is unable to comply with part of the new configuration and security has already been activated, what procedure does the UE initiate?
Option 1: Continue using the previous configuration without any further action.
Option 2: Initiate the connection re-establishment procedure as specified in the RRC protocol.
Option 3: Perform actions upon leaving RRC_CONNECTED with a release cause 'other'.
Option 4: Apply partial configuration changes that were successfully validated.
Explanation: According to the failure handling rules for RRCConnectionReconfiguration, if the UE is unable to comply with part of the new configuration and security has already been activated, it initiates the connection re-establishment procedure. This ensures the UE attempts to recover and maintain connectivity while addressing the configuration issue, highlighting the importance of robust connection management in wireless communications.