A multi-RAT UE having capability to access two or more radio access technologies (RATs) can be present. To access a specific RAT, connection to the specific RAT is established on the basis of a request of the UE and transmission and reception of data are performed.
However, the multi-RAT UE cannot simultaneously access multiple RATs even though the multi-RAT UE has capability to access two or more RAT. That is, current UEs cannot simultaneously transmit and receive data through different RATs even if the UEs have multi-RAT capability.
Conventional multi-RAT has a problem of low system efficiency since the conventional multi-RAT does not require interworking between a wireless LAN and a cellular network. Furthermore, the problem has not been studied.