4.6.3.2 Support of network slice admission control and interworking with EPC

If EPS counting is required for a network slice, the network performs network slice admission control for the S-NSSAI(s) subject to NSAC to monitor and control the number of UEs per network slice and number of PDU sessions per network slice during the PDN connection establishment procedure. If the maximum number of UEs on a network slice associated with an S-NSSAI or the maximum number of PDU sessions on a network slice associated with an S-NSSAI have already been reached, the network rejects the PDN connectivity request using ESM cause #26 "insufficient resources" as specifed in 3GPP TS 24.301 [15].

NOTE: If there are more than one S-NSSAI associated with the APN used in the PDN connectivity request and some of but not all associated S-NSSAIs are not available due to either maximum number of UEs reached or maximum number of PDU sessions reached, the network can use the associated S-NSSAI for which maximum number of UEs and maximum number of PDU sessions have not reached to avoid PDN connectivity request rejection.