Method and apparatus for secondary base station change in mobile wireless communication system

A Master Node (MN) in a wireless communication system, the MN comprising:

• a transceiver configured to transmit and receive a signal;
• and
• a controller configured to control the transceiver to:
• transmit to a target Secondary Node (SN) a first base station control message requesting resource allocation;
• receive from the target SN a second base station control message accepting request,
• determine to perform a 1st reconfiguration procedure or a 2nd reconfiguration procedure;
• perform the 1st reconfiguration procedure in response to MN receiving a 2nd information;
• perform the 2nd reconfiguration procedure in response to MN not receiving the 2nd information;
• transmit, in response to MN determining to perform the 1st reconfiguration procedure, to a terminal a first Downlink (DL) message, wherein the first DL message includes a first identifier and one or more CondReconfigToAddMod, wherein each of the one or more CondReconfigToAddMod includes an execution condition, a second identifier, and a reconfiguration message, wherein the first identifier is a transaction identifier and the second identifier is a conditional reconfiguration identifier;
• receive from the terminal a first Uplink (UL) message, wherein the first UL message includes the first identifier;
• and
• transmit to a source SN a third base station control message after a second UL message is received from the terminal, wherein the second UL message includes the second identifier, wherein the second identifier corresponds to the reconfiguration message in the CondReconfigToAddMod, wherein the second UL message is received after the first UL message is received, and wherein the third base station control message requests release of the source SN,
• wherein 1st information is comprised in the first base station control message in case that the 1 st reconfiguration procedure is requested,
• wherein the 2nd information comprises a specific cell's global identity.