Method for selecting network node in wireless communication system and device therefor

A network node configured to select a serving Access and Mobility Management Function (AMF) in a wireless communication system, the network node comprising:

• a transceiver;
• at least one processor;
• and
• at least one computer memory operably connectable to the at least one processor and storing instructions that, when executed by the at least one processor, perform operations comprising:
• receiving a registration request message of a user equipment (UE), the registration request message including (i) a network slice selection assistance information (NSSAI) for a slice requested by the UE and iii) priority information of the NSSAI, wherein the priority information indicates at least one of (i) whether the NSSAI or at least one S(single)-NSSAI included in the NSSAI is ‘required’ for the UE or (ii) whether the NSSAI or the at least one S-NSSAI is ‘preferred’ by the UE;
• determining whether the NSSAI is valid for the UE;
• based on the NSSAI being valid for the UE and based on the priority information:
• searching a first AMF which is able to support the NSSAI;
• and
• based on the first AMF being not searched or the NSSAI being not valid for the UE, transmitting, to the UE a registration reject message as a response to the registration request message, wherein the registration reject message includes a registration reject cause;
• and
• based on the registration reject cause indicating that the NSSAI is not valid for the UE, receiving, from the UE, a retransmission of the registration request message, wherein the priority information of the NSSAI or the at least one S-NSSAI in the registration request message is updated to the ‘preferred’ by the UE.