Method and apparatus for selecting network slice admission control function

A communication device being a first session management function (SMF), comprising:

• a transceiver;
• a memory;
• and
• a processor, connected to the transceiver and the memory and configured, by executing computer-executable instructions on the memory, to control wireless signal transmission and reception of the transceiver and to:
• select a network slice admission control function NSACF for a network slice based on service area information of the NSACF after receiving a protocol data unit (PDU) session creation request or a PDU session update request from a user equipment (UE), wherein the NSACF selected is used to monitor a number of created PDU sessions of the network slice;
• send a session number availability check and update request to the NSACF selected, wherein the session number availability check and update request comprises single-network slice selection assistance information (S-NSSAI) and a first update flag, and the first update flag indicates to increase the number of the created PDU sessions;
• receive a session number availability check and update response message from the NSACF selected;
• and
• perform a PDU session creation procedure or a PDU session update procedure, and return a session creation acceptance message or a session update acceptance message to the UE in case the session number availability check and update response message indicates that availability check is successful;
• or, return a session creation rejection message or a session update rejection message to the UE in case the session number availability check and update response message indicates that availability check is failed.