Method for triggering a buffer status reporting in dual connectivity and a device therefor

1. A method for a user equipment (UE) operating in a wireless communication system, the UE including a processor having a packet data convergence protocol (PDCP) entity, a first Medium Access Control (MAC) entity and a second MAC entity, the method comprising:

based on a first total amount of uplink data available for transmission being less than a threshold value, the first total amount based on first PDCP data:

indicating, by the PDCP entity to the first MAC entity, a volume of the first PDCP data that is available for transmission by the first MAC entity, thereby triggering transmission of a first buffer status report (BSR) by the first MAC entity; and

indicating, by the PDCP entity to the second MAC entity, that a volume of the first PDCP data that is available for transmission by the second MAC entity is ‘0’ so that no BSR is generated by the second MAC entity;

based on a second total amount of uplink data available for transmission being greater than the threshold value, the second total amount based on second PDCP data:

indicating, by the PDCP entity to the second MAC entity, a volume of the second PDCP data that is available for transmission by the second MAC entity, thereby triggering transmission of a second BSR by the second MAC entity.

2. The method according to claim 1 , wherein the threshold value is configured for the PDCP entity, the PDCP entity being simultaneously associated with the first MAC entity and the second MAC entity for a radio bearer.

3. The method according to claim 2 , further comprising:

receiving a Radio Resource Control (RRC) message for configuring the UE so that uplink data available for transmission is transmitted to a second base station corresponding to the second MAC entity even if an amount of the uplink data available for transmission in the upper entity is less than the threshold value.

4. The method according to claim 1 , wherein the threshold value is a positive non-zero value.

5. The method according to claim 1 , wherein the first BSR is transmitted by the first MAC entity when a corresponding buffer is empty.

6. The method according to claim 1 , wherein the first BSR is transmitted by the first MAC entity when the first MAC entity has no previous data to transmit.

7. The method according to claim 1 , further comprising:

based on the second total amount of uplink data available for transmission being greater than the threshold value: indicating, by the PDCP entity to the first MAC entity, a volume of the second PDCP data that is available for transmission by the first MAC entity, thereby triggering transmission of a third BSR by the first MAC entity.

8. A User Equipment (UE) operating in a wireless communication system, the UE comprising:

a Radio Frequency (RF) module including a transceiver; and

a processor operably coupled with the RF module, the processor including a packet data convergence protocol (PDCP) entity, a first Medium Access Control (MAC) entity and a second MAC entity and configured to:

based on a first total amount of uplink data available for transmission being less than a threshold value, the first total amount based on first PDCP data:

indicate, by the PDCP entity to the first MAC entity, a volume of the first PDCP data that is available for transmission by the first MAC entity, thereby triggering transmission of a first buffer status report (BSR) by the first MAC entity; and

indicate, by the PDCP entity to the second MAC entity, that a volume of the first PDCP data that is available for transmission by the second MAC entity is ‘0’ so that no BSR is generated by the second MAC entity;

based on a second total amount of uplink data available for transmission being greater than the threshold value, the second total amount based on second PDCP data:

indicate, by the PDCP entity to the second MAC entity, a volume of the second PDCP data that is available for transmission by the second MAC entity, thereby triggering transmission of a second BSR by the second MAC entity.

9. The UE according to claim 8 , wherein the threshold value is configured for the PDCP entity, the PDCP entity being simultaneously associated with the first MAC entity and the second MAC entity for a radio bearer.

10. The UE according to claim 9 , wherein the processor is further configured to receive a Radio Resource Control (RRC) message for configuring the UE so that uplink data available for transmission is transmitted to a second base station corresponding to the second MAC entity even if an amount of the uplink data available for transmission in the upper entity is less than the threshold value.

11. The UE according to claim 8 , wherein the threshold value is a positive non-zero value.

12. The UE according to claim 8 , wherein the first BSR is transmitted by the first MAC entity when a corresponding buffer is empty.

13. The UE according to claim 8 , wherein the first BSR is transmitted by the first MAC entity when the first MAC entity has no previous data to transmit.

14. The UE according to claim 8 , wherein, based on the second total amount of uplink data available for transmission being greater than the threshold value, the processor is further configured to indicate, by the PDCP entity to the first MAC entity, a volume of the second PDCP data that is available for transmission by the first MAC entity, thereby triggering transmission of a third BSR by the first MAC entity.