Secondary base station, mobile station, communication control method, and master base station

A mobile communication system in which a master base station and a secondary base station are configured to connect each other via an X2 interface and performing a dual connectivity communication, which is to transmit downlink data from the master base station through a split bearer to a user equipment, the mobile communication system comprising:

• the secondary base station includes:
• a receiver configured to receive the downlink data transferred from the master base station;
• a transmitter configured to transmit the downlink data received by the receiver to the user equipment;
• and
• a controller configured to determine a release of the split bearer;
• wherein
• the transmitter configured to transmit a release request message for requesting the release of the split bearer to the master base station in response to determining the release of the split bearer.

A mobile communication method in which a master base station and a secondary base station are configured to connect each other via an X2 interface and performing a dual connectivity communication, which is to transmit downlink data from the master base station through a split bearer to a user equipment, the mobile communication method comprising steps of:

• receiving, at the secondary base station, the downlink data transferred from the master base station;
• transmitting, from the secondary base station, the downlink data received by the receiver to the user equipment;
• determining, at the secondary base station, a release of the split bearer;
• transmitting, from the secondary base station, a release request message for requesting the release of the split bearer to the master base station in response to determining the release of the split bearer.