A master base station configured to discard data packets destined for a mobile station, connected to both the master base station and a secondary base station having no PDCP, Packet Data Convergence Protocol, layer for a split bearer, wherein the data packets are forwarded from the master base station, via the secondary base station, to the mobile station, 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; said master base station being characterized by : 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 holds, 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 configures the secondary base station to control a discard timer of a discarding function at the secondary base station based on a discard timer of a PDCP discard function in the master base station and on third information related to a backhaul delay on an X2 interface between the master base station and the secondary base station and to a buffer capacity 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; said master base station being characterized by : 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 holds, 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 configures the secondary base station to control a discard timer of a discarding function at the secondary base station based on a discard timer of a PDCP discard function in the master base station and on third information related to a backhaul delay on an X2 interface between the master base station and the secondary base station and to a buffer capacity of the secondary base station. <EOS>