User equipment having a dual connectivity function to communicate with multiple base stations simultaneously, comprising: a transmission buffer configured to store uplink data for transmission; a buffer status management unit configured to manage a data amount stored in the transmission buffer ; and a transmission control unit configured to: receive splitting trigger information indicative of a threshold for the data amount stored in the transmission buffer and indicative of a first base station when bearer splitting is configured in an RRC, Radio Resource Control; and select a base station to which to transmit the uplink data stored in the transmission buffer from the multiple base stations , wherein the first base station is selected when the data amount stored in the transmission buffer is smaller than or equal to the threshold, characterised in that the transmission control unit is configured to receive the splitting trigger information including an index value corresponding to the threshold; wherein when the data amount stored in the transmission buffer is smaller than or equal to the threshold, the transmission control unit is configured to transmit the uplink data stored in the transmission buffer to the first base station ; and wherein when the data amount stored in the transmission buffer is exceeding the threshold, the transmission control unit is configured to start to transmit the uplink data stored in the transmission buffer to a second base station ; the transmission control unit being configured to receive the splitting trigger information from a master base station for dual connectivity. a transmission buffer configured to store uplink data for transmission; a buffer status management unit configured to manage a data amount stored in the transmission buffer ; and a transmission control unit configured to: receive splitting trigger information indicative of a threshold for the data amount stored in the transmission buffer and indicative of a first base station when bearer splitting is configured in an RRC, Radio Resource Control; and select a base station to which to transmit the uplink data stored in the transmission buffer from the multiple base stations , wherein the first base station is selected when the data amount stored in the transmission buffer is smaller than or equal to the threshold, characterised in that the transmission control unit is configured to receive the splitting trigger information including an index value corresponding to the threshold; receive splitting trigger information indicative of a threshold for the data amount stored in the transmission buffer and indicative of a first base station when bearer splitting is configured in an RRC, Radio Resource Control; and select a base station to which to transmit the uplink data stored in the transmission buffer from the multiple base stations , wherein the first base station is selected when the data amount stored in the transmission buffer is smaller than or equal to the threshold, characterised in that the transmission control unit is configured to receive the splitting trigger information including an index value corresponding to the threshold; wherein when the data amount stored in the transmission buffer is smaller than or equal to the threshold, the transmission control unit is configured to transmit the uplink data stored in the transmission buffer to the first base station ; and wherein when the data amount stored in the transmission buffer is exceeding the threshold, the transmission control unit is configured to start to transmit the uplink data stored in the transmission buffer to a second base station ; the transmission control unit being configured to receive the splitting trigger information from a master base station for dual connectivity. <EOS>