Device and method for handling always-on PDU session in wireless communication system

A method performed by a session management function (SMF) in a wireless communication system, the method comprising:

• receiving, from an access and mobility management function (AMF), a second message including information for requesting user plane activation of at least one always-on protocol data unit (PDU) session, which is omitted from a list of PDU sessions to be activated of a user equipment (UE) included in a first message transmitted from the UE to the AMF;
• receiving, from the AMF, information on a connection management-connected (CM-connected) state notification of the UE;
• and
• identifying whether the at least one always-on PDU session has been omitted from the list of PDU sessions to be activated.

An access and mobility management function (AMF) in a wireless communication system, the AMF comprising:

• a transceiver;
• and
• at least one processor coupled with the transceiver,
• wherein the at least one processor is configured to:
• receive, from a user equipment (UE), a first message including a list of protocol data unit (PDU) sessions to be activated;
• identify, based on UE context information of the UE, whether identifiers (IDs) of all of always-on protocol data unit (PDU) sessions are included in the list of PDU sessions to be activated;
• and
• in case that at least one always-on PDU session omitted from the list of the PDU sessions to be activated is identified, transmit, to a session management function (SMF), a second message including information for requesting user plane activation of the at least one always-on PDU session.