A user terminal transmits and/or receives downlink traffic through cellular/WLAN aggregation by using a first communication and a second communication. The downlink traffic is divided into traffic for cellular communication network and traffic for WLAN. The user terminal further transmits an uplink control signal through the cellular/WLAN aggregation by using the first communication and without using the second communication. The user terminal further notifies the base station of a report regarding the second communication by the first communication. The report indicates a radio link failure in the second communication and includes a reason for the radio link failure. The reason includes a first reason and a second reason. The first reason relates to a radio environment in the second communication. The second reason does not relate to the radio environment.