The disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. Disclosed is a method performed by a UE, the method comprising: having at least one existing PDU session associated with an S-NSSAI; requesting, from an upper layer, a new PDU session; determining a condition; performing checking operations comprising: (i) checking whether allowed NSSAI includes only one S-NSSAI, and (ii) checking whether any of the at least one existing PDU sessions have an attribute which matches a corresponding attribute in the requested new PDU session; and when both checking operations (i) and (ii) are true: selecting a PDU session from the at least one existing PDU sessions which matches at least one attribute, determining that the selected PDU session can be used or associated with the request from the upper layer, and forwarding details of the selected PDU session to the upper layer.