A master base station for discarding data packets destined for a mobile station, the mobile station being connected to both the master base station and a secondary base station having no PDCP, Packet Data Convergence Protocol, layer for a split bearer, the master base station comprising: a transmitter which is configured to forward data packets as PDCP PDUs, Protocol Data Units to an RLC, Radio Link Control, layer of the secondary base station; a receiver which is configured to receive an indication from the secondary base station, the indication including first information on the PDCP PDUs forwarded by the master base station and successfully delivered by the secondary base station to the mobile station and second information on the PDCP PDUs forwarded by the master base station and unsuccessfully delivered by the secondary base station to the mobile station; and a controller which is configured to discard, based on the first information, the PDCP PDUs forwarded by the master base station and successfully delivered by the secondary base station to the mobile station and to hold, based on the second information, the PDCP PDUs forwarded by the master base station and unsuccessfully delivered by the secondary base station to the mobile station, wherein the master base station is configured to: determine a value to which a discard timer for a discarding function of the master base station is set; and adjust said value based on third information related to a backhaul delay on an X2 interface between the master base station and the secondary base station and based on a buffer capacity of the secondary base station; and send a configuration message to the secondary base station, wherein said configuration message includes said adjusted value to which the secondary base station is to set a discard timer for a discarding function of the secondary base station. a transmitter which is configured to forward data packets as PDCP PDUs, Protocol Data Units to an RLC, Radio Link Control, layer of the secondary base station; a receiver which is configured to receive an indication from the secondary base station, the indication including first information on the PDCP PDUs forwarded by the master base station and successfully delivered by the secondary base station to the mobile station and second information on the PDCP PDUs forwarded by the master base station and unsuccessfully delivered by the secondary base station to the mobile station; and a controller which is configured to discard, based on the first information, the PDCP PDUs forwarded by the master base station and successfully delivered by the secondary base station to the mobile station and to hold, based on the second information, the PDCP PDUs forwarded by the master base station and unsuccessfully delivered by the secondary base station to the mobile station, wherein the master base station is configured to: determine a value to which a discard timer for a discarding function of the master base station is set; and adjust said value based on third information related to a backhaul delay on an X2 interface between the master base station and the secondary base station and based on a buffer capacity of the secondary base station; and send a configuration message to the secondary base station, wherein said configuration message includes said adjusted value to which the secondary base station is to set a discard timer for a discarding function of the secondary base station. determine a value to which a discard timer for a discarding function of the master base station is set; and adjust said value based on third information related to a backhaul delay on an X2 interface between the master base station and the secondary base station and based on a buffer capacity of the secondary base station; and send a configuration message to the secondary base station, wherein said configuration message includes said adjusted value to which the secondary base station is to set a discard timer for a discarding function of the secondary base station.