A master base station comprising: a memory for keeping E-UTRAN Radio Access Bearer, E-RAB, configuration information for an E-RAB between a user equipment, UE, and a data transfer apparatus through the source base station, after establishment of the E-RAB and a signaling radio bearer between the UE and the master base station; a first reception means (11, 14) for receiving (S204, S205), from the source base station or the UE, a trigger notification for determining to transfer the E-RAB; a first control means for determining, based on the trigger notification, to transfer the E-RAB from the source base station to a target base station; a first transmission means for transmitting, to the target base station, a first message comprising at least a part of the E-RAB configuration information kept in the memory, whereby the target base station configures a data radio bearer, DRB, between the UE and the target base station and an endpoint of a data bearer between the target base station and the data transfer apparatus; a second reception means for receiving, from the target base station, a first response to the first message, the first response including a Tunnel Endpoint Identifier, TEID, of the data bearer of the target base station, the TEID corresponding to the E-RAB; a second control means for updating the E-RAB configuration information kept in the memory based on the first response; a second transmission means for transmitting, to the UE, a second message including DRB, configuration information, based on the updated E-RAB configuration information, for configuring the DRB between the UE and the target base station; a third reception means for receiving, from the UE, a second response to the second message; a third transmission means for transmitting, to a mobility management apparatus, a third message requesting the mobility management apparatus to switch the E-RAB from the source base station to the target base station, wherein the third message includes the TEID, an identifier of the E-RAB, and an address of the target base station; and a fourth reception means for receiving, from the mobility management apparatus, a third response indicating completion of the switching the E-RAB after the transmission of the third message. a memory for keeping E-UTRAN Radio Access Bearer, E-RAB, configuration information for an E-RAB between a user equipment, UE, and a data transfer apparatus through the source base station, after establishment of the E-RAB and a signaling radio bearer between the UE and the master base station; a first reception means (11, 14) for receiving (S204, S205), from the source base station or the UE, a trigger notification for determining to transfer the E-RAB; a first control means for determining, based on the trigger notification, to transfer the E-RAB from the source base station to a target base station; a first transmission means for transmitting, to the target base station, a first message comprising at least a part of the E-RAB configuration information kept in the memory, whereby the target base station configures a data radio bearer, DRB, between the UE and the target base station and an endpoint of a data bearer between the target base station and the data transfer apparatus; a second reception means for receiving, from the target base station, a first response to the first message, the first response including a Tunnel Endpoint Identifier, TEID, of the data bearer of the target base station, the TEID corresponding to the E-RAB; a second control means for updating the E-RAB configuration information kept in the memory based on the first response; a second transmission means for transmitting, to the UE, a second message including DRB, configuration information, based on the updated E-RAB configuration information, for configuring the DRB between the UE and the target base station; a third reception means for receiving, from the UE, a second response to the second message; a third transmission means for transmitting, to a mobility management apparatus, a third message requesting the mobility management apparatus to switch the E-RAB from the source base station to the target base station, wherein the third message includes the TEID, an identifier of the E-RAB, and an address of the target base station; and a fourth reception means for receiving, from the mobility management apparatus, a third response indicating completion of the switching the E-RAB after the transmission of the third message.