1. A communication method, comprising:receiving, by a user equipment from a base station included in a Radio Access Network (RAN), a first RRC message for suspending an RRC connection between the user equipment and the RAN, the first RRC message including a resumption identifier;
entering, by the user equipment, an RRC idle state in response to reception of the first RRC message;
when the user equipment is in the RRC idle state, transmitting, by the user equipment to the base station, uplink user data together with an RRC Resume Request message including the resumption identifier without entering an RRC connected state, the uplink user data being user data to be transmitted from the user equipment to a core network via the base station,
transmitting, by the base station, the uplink user data received from the user equipment to the core network; and
when the user equipment is in the RRC idle state, receiving, by the user equipment from the base station, a second RRC message for keeping the user equipment in the RRC idle state, after the uplink user data is transmitted by the base station to the core network.