A disclosure of the present specification provides a method for transmitting a radio resource control (RRC) message by a wireless device. The method may comprise the steps of: acquiring, by an access stratum (AS) layer of a wireless device, at least one of the value and indication of an RRC establishment cause field from a non-access stratum (NAS) layer which requests transmission of an NAS signaling request message; transmitting, to a base station, an RRC connection request message including the at least one of the value and indication of the RRC establishment cause field; and when the at least one of the value and indication of the RRC establishment cause field is set to a value, which indicates that the NAS signaling request message includes user data, according to an optimization scheme through a control plane (CP), if a network is in an overload state, receiving an RRC connection rejection message or an RRC connection release request message from the base station.