A method of offloading data is provided by a UE. The UE receives data from a macro cell base station over an MC-RB while an E-RAB between the macro cell base station and a gateway is established. The UE receives a first connection reconfiguration message from the macro cell base station after the E-RAB between a small cell base station and the gateway is established, and establishes an SC-RB according to the first connection reconfiguration message. Next, the UE receives a second connection reconfiguration message from the macro cell base station after a path between the macro cell base station and the gateway is switched to a path between the small cell base station and the gateway, and data for the MC-RB are exhausted on the macro cell base station. Then, the UE releases the MC-RB and switches to the SC-RB.