A radio communication system comprising: a radio terminal; a first radio station configured to operate a first cell and establish a radio resource control, RRC, connection with the radio terminal; and a second radio station configured to operate a second cell and establish a radio bearer, RB, associated with the radio terminal; where the radio terminal is configured to use the first cell and the second cell simultaneously for transmitting or receiving signals; and a core network comprising a network apparatus adapted to perform signal transmission or reception to or from the radio terminal via the first and second radio stations (1, 2), wherein the network apparatus comprised in the core network is configured to set up a control bearer for sending or receiving on the first cell at least a control signal related to the radio terminal between the core network and the first radio station via the first radio station, and is configured to set up a second bearer for sending or receiving on the second cell user data related to the radio terminal on the second cell between the core network and the second radio station via the second radio station, in response to receiving by the core network a setup request from the second radio station, the sending of which by the second radio station is triggered by receiving at the second radio station from the first radio station a bearer setup request, the first radio station is configured to set up a control bearer for sending or receiving at least a control signal related to the radio terminal between the core network and the first radio station, and to send the bearer setup request to the second radio station to trigger the second radio station to send, to the core network, the setup request for the second bearer for sending or receiving user data related to the radio terminal between the core network and the second radio station, the first radio station being further configured to send to the radio terminal an instruction of use initiation of the second cell, and the second radio station is configured to send, in response to the bearer setup request received from the first radio station, the setup request for the second bearer to the core network. a radio terminal; a first radio station configured to operate a first cell and establish a radio resource control, RRC, connection with the radio terminal; and a second radio station configured to operate a second cell and establish a radio bearer, RB, associated with the radio terminal; where the radio terminal is configured to use the first cell and the second cell simultaneously for transmitting or receiving signals; and a core network comprising a network apparatus adapted to perform signal transmission or reception to or from the radio terminal via the first and second radio stations (1, 2), wherein the network apparatus comprised in the core network is configured to set up a control bearer for sending or receiving on the first cell at least a control signal related to the radio terminal between the core network and the first radio station via the first radio station, and is configured to set up a second bearer for sending or receiving on the second cell user data related to the radio terminal on the second cell between the core network and the second radio station via the second radio station, in response to receiving by the core network a setup request from the second radio station, the sending of which by the second radio station is triggered by receiving at the second radio station from the first radio station a bearer setup request, the first radio station is configured to set up a control bearer for sending or receiving at least a control signal related to the radio terminal between the core network and the first radio station, and to send the bearer setup request to the second radio station to trigger the second radio station to send, to the core network, the setup request for the second bearer for sending or receiving user data related to the radio terminal between the core network and the second radio station, the first radio station being further configured to send to the radio terminal an instruction of use initiation of the second cell, and the second radio station is configured to send, in response to the bearer setup request received from the first radio station, the setup request for the second bearer to the core network.