Method for establishing/releasing a mac (medium access control) entity in a wireless communication system and a device therefor

A method for a user equipment (UE) operating in a wireless communication system comprising a master base station (BS) and a secondary BS, the UE configured with a first MAC entity for a master cell group (MCG) associated with the master BS, the method comprising:

• receiving, from the master BS, a first Radio Resource Control (RRC) message via a serving cell of the MCG for configuration of a new secondary cell group (SCG) associated with the secondary BS,
• configuring, by the UE, a second MAC entity for the new SCG, according to the first RRC message, in addition to the previously configured first MAC entity, when a second MAC entity is not already configured for the UE,
• receiving, from the master BS, a second RRC message for addition of a new SCG cell to the SCG;
• and
• adding, by the UE, the new SCG cell to the SCG according to the second RRC message,
• wherein the second MAC entity is commonly configured for one or more secondary cells, including the new SCG cell, belonging to the SCG.

A user equipment (UE) in a wireless communication system comprising a master base station (BS) and a secondary BS, the UE configured with a first MAC entity for a master cell group (MCG) associated with the master BS, the UE comprising:

• a transmitter and a receiver;
• and
• a processor, operatively coupled to the transmitter and the receiver, configured to:
• control the receiver to receive, from the master BS, a first Radio Resource Control (RRC) message via a serving cell of the MCG,
• configure a new secondary cell group (SCG), associated with the secondary BS, according to the RRC message,
• configure a second MAC entity for the new SCG, according to the first RRC message, in addition to the previously established first MAC entity, when a second MAC entity is not already configured for the UE,
• control the receiver to receive, from the master BS, a second RRC message for addition of a new SCG cell to the SCG;
• and
• add the new SCG cell to the SCG according to the second RRC message,
• wherein the second MAC entity is commonly configured for one or more secondary cells, including the new SCG cell, belonging to the SCG.