Method for transmitting uplink data in a dual connectivity and a device therefor

A user equipment (UE) operating in a dual connectivity mode in a wireless communication system, the UE comprising:

• a radio frequency (RF) module including a transceiver;
• and
• a processor configured to:
• configure a split bearer associated with both a base station (BS) of master cell group (MCG) and a BS of secondary cell group (SCG),
• wherein the configuring the split bearer comprises configuring:
• a packet data convergence protocol (PDCP) entity of the UE,
• a first radio link control (RLC) entity and a first medium access control (MAC) entity of the UE, and
• a second RLC entity and a second MAC entity of the UE,
• wherein the PDCP entity is connected with both of the first RLC entity and the second RLC entity, the first RLC entity is connected with the first MAC entity, and the second RLC entity is connected with the second MAC entity, and
• wherein the first RLC entity and the first MAC entity are used to communicate with the BS of the MCG and the second RLC entity and the second MAC entity are used to communicate with the BS of the SCG;
• while in the dual connectivity mode, receive a Radio Resource Control (RRC) signal including an indication related to a transmission path;
• and
• based on the indication and while in the dual connectivity mode, transmitting, by the PDCP entity, the data of the PDCP entity of the UE only to the first RLC entity without duplication to the second RLC entity or only to the second RLC entity without duplication to the first RLC entity.