In a communication system according to an embodiment, a base station transmits first information for establishing a second data bearer, to a user terminal in a state where a predetermined data bearer is established. The predetermined data bearer is a first data bearer passes through the base station without passing through an access point. The second data bearer: passes through the base station and the access point; and is for aggregation in which the cellular communication and the WLAN communication are used to communicate data of the user terminal. The first information includes a bearer identifier indicating the predetermined data bearer and type information associated with the bearer identifier. The user terminal starts control to change the predetermined data bearer from the first data bearer to the second data bearer if the type information indicates a change from the first data bearer to the second data bearer.