Method for switching data between plurality of communications systems and apparatus therefor

A user equipment for performing data switching between a plurality of communication systems, the user equipment comprising:

• a receiver configured to receive a message for commanding data switching to a second communication system from a base station of a first communication system, at least one data radio bearers (DRB) being configured between the base station of the first communication system and the user equipment;
• and
• a processor configured to:
• perform an operation of the data switching to the second communication system based on the message;
• and
• when the message instructs the user equipment to maintain a specific DRB of the at least one DRB after entering RRC idle mode, perform data communication with a base station of the second communication system while maintaining the specific DRB after entering RRC idle mode;
• and,
• when the message instructs the user equipment to release the specific DRB after entering RRC idle mode, perform data communication with the base station of the second communication system after releasing the specific DRB,
• wherein the specific DRB comprises a default DRB or a dedicated DRB, and
• wherein the first communication system corresponds to a cellular communication system and wherein the second communication system corresponds to a wireless LAN communication system.