A method for a user equipment, UE, operating in a wireless communication system comprising a first base station, BS, and a second BS, the method comprising: configuring a Packet Data Convergence Protocol, PDCP, entity for a radio bearer by receiving ratio information and threshold information, wherein the PDCP entity is connected with a first Medium Access Control, MAC, entity through a first Radio Link Control, RLC, entity and a second MAC entity through a second RLC entity, and wherein the first MAC entity and the first RLC entity are configured for the first BS and the second MAC entity and the second RLC entity are configured for the second BS for the radio bearer; calculating an amount of uplink data available for transmission in the PDCP entity; calculating an amount of uplink data available for transmission in the first RLC entity; calculating an amount of uplink data available for transmission in the second RLC entity; wherein when the calculated amount of the uplink data available for transmission in the PDCP entity being less than the threshold information: indicating, by the PDCP entity, the calculated amount of the uplink data available for transmission in the PDCP entity to the first MAC entity for the first BS; indicating, by the PDCP entity, the calculated amount of the uplink data available for transmission in the PDCP entity as '0' to the second MAC entity for the second BS; indicating, by the first RLC entity, the calculated amount of the uplink data available for transmission in the first RLC entity to the first MAC entity for the first BS; indicating, by the second RLC entity, the calculated amount of the uplink data available for transmission in the second RLC entity to the second MAC entity for the second BS; calculating an amount of uplink data available for transmission for the first BS by adding the indicated amount of the uplink data available for transmission in the PDCP entity and the indicated amount of the uplink data available for transmission in the first RLC entity; and calculating an amount of uplink data available for transmission for the second BS by adding the indicated amount of the uplink data available for transmission in the PDCP entity and the indicated amount of the uplink data available for transmission in the second RLC entity. configuring a Packet Data Convergence Protocol, PDCP, entity for a radio bearer by receiving ratio information and threshold information, wherein the PDCP entity is connected with a first Medium Access Control, MAC, entity through a first Radio Link Control, RLC, entity and a second MAC entity through a second RLC entity, and wherein the first MAC entity and the first RLC entity are configured for the first BS and the second MAC entity and the second RLC entity are configured for the second BS for the radio bearer; calculating an amount of uplink data available for transmission in the PDCP entity; calculating an amount of uplink data available for transmission in the first RLC entity; calculating an amount of uplink data available for transmission in the second RLC entity; wherein when the calculated amount of the uplink data available for transmission in the PDCP entity being less than the threshold information: indicating, by the PDCP entity, the calculated amount of the uplink data available for transmission in the PDCP entity to the first MAC entity for the first BS; indicating, by the PDCP entity, the calculated amount of the uplink data available for transmission in the PDCP entity as '0' to the second MAC entity for the second BS; indicating, by the first RLC entity, the calculated amount of the uplink data available for transmission in the first RLC entity to the first MAC entity for the first BS; indicating, by the second RLC entity, the calculated amount of the uplink data available for transmission in the second RLC entity to the second MAC entity for the second BS; calculating an amount of uplink data available for transmission for the first BS by adding the indicated amount of the uplink data available for transmission in the PDCP entity and the indicated amount of the uplink data available for transmission in the first RLC entity; and calculating an amount of uplink data available for transmission for the second BS by adding the indicated amount of the uplink data available for transmission in the PDCP entity and the indicated amount of the uplink data available for transmission in the second RLC entity. indicating, by the PDCP entity, the calculated amount of the uplink data available for transmission in the PDCP entity to the first MAC entity for the first BS; indicating, by the PDCP entity, the calculated amount of the uplink data available for transmission in the PDCP entity as '0' to the second MAC entity for the second BS; indicating, by the first RLC entity, the calculated amount of the uplink data available for transmission in the first RLC entity to the first MAC entity for the first BS; indicating, by the second RLC entity, the calculated amount of the uplink data available for transmission in the second RLC entity to the second MAC entity for the second BS; calculating an amount of uplink data available for transmission for the first BS by adding the indicated amount of the uplink data available for transmission in the PDCP entity and the indicated amount of the uplink data available for transmission in the first RLC entity; and calculating an amount of uplink data available for transmission for the second BS by adding the indicated amount of the uplink data available for transmission in the PDCP entity and the indicated amount of the uplink data available for transmission in the second RLC entity.