Handover method in wireless communication system and apparatus therefor

A Target-Access and Mobility Management Function (T-AMF) for supporting a User Equipment (UE) handover in a wireless communication system, comprising:

• a transceiver for transmission and receiving a signal;
• and
• a processor for controlling the transceiver,
• wherein the processor is configured to:
• receive, from a Source-AMF (S-AMF), a create UE context request message, wherein the create UE context request message includes Packet Data Unit (PDU) session Identifiers (IDs) which are related to a target of handover and Single-Network Slice Selection Assistance Information (S-NSSAI) corresponding to each of the PDU session IDs;
• and
• determine whether the S-NSSAI corresponding to each of the PDU session IDs is available in the T-AMF;
• and
• transmit a PDU session update Session Management (SM) context request message to a Session Management Function (SMF), only for the PDU session ID corresponding to the S-NSSAI determined to be available in the T-AMF among the PDU session IDs;
• receive a PDU session update SM context response message in response to the PDU session update SM context request message, wherein the PDU session update SM context response message includes a PDU session ID of which handover is accepted by the SMF, and
• generate a non-accepted PDU session list including (i) a PDU session ID for which handover is not accepted by the T-AMF and/or the SMF, (ii) and a cause of non-acceptance for the PDU session ID for which handover is not accepted,
• wherein the SMF is a network node that determines whether handover for the PDU session ID corresponding to the S-NSSAI determined to be available is accepted,
• wherein the cause of non-acceptance of handover includes information representing that the handover is not accepted by the T-AMF because the PDU session is related to an S-NSSAI which is determined to be not available in the T-AMF, and
• wherein the non-accepted PDU session list is transmitted to a Source-Radio Access Network (S-RAN).