Section: 4.2.11.4a Hierarchical NSACF-based Number of PDU Sessions per network slice availability check and update procedure
Content: Figure 4.2.11.4a-1: Hierarchical NSAC-based number of PDU Sessions per network slice availability check and update procedure For an S-NSSAI subject to counting of the number of PDU sessions, if hierarchical NSACF architecture is deployed in the network the enforcement of maximum number of PDU Session established for an S-NSSAI is performed as follow: 1-2. Same as for steps 1-2 defined in clause 4.2.11.4. 3. The NSACF performs NSAC for the indicated S-NSSAI. If the PDU session ID entry update at the NSACF is possible, e.g. create a new entry associated with the received NSAC request for increase case, the same action as for step 3 defined in clause 4.2.11.4 is executed. Steps 4-8 are skipped. If the PDU session ID entry at the NSACF is not possible, i.e. by admitting the PDU session the local maximum PDU session number is exceeded, the NSACF delegates the request to the Primary NSACF for an updated local maximum PDU sessions from the Primary NSACF. 4. If the Primary NSACF has not been discovered before, the NSACF discovers and selects the Primary NSACF, which manages the global NSAC service area as for clause 6.3.22 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. 5. The NSACF invokes Nnsacf_NSAC_NumOfPDUsUpdate request to the Primary NSACF. The request message includes the S-NSSAI. 6. The Primary NSACF checks the global maximum PDU session number and determines whether to accept or reject the request to update local maximum PDU session number from NSACF. NOTE: When NSACF sends a delegation request to the Primary NSACF, the Primary NSACF either increases local maximum number at NSACF or rejects the NSAC request. 7. The Primary NSACF returns the Nnsacf_NSAC_NumOfPDUsUpdate response. The response includes a new allocated local maximum PDU sessions number or an indication to reject the request to update local maximum PDU session number. 8. If the primary NSACF provides an updated local maximum number, the NSACF replaces the local maximum PDU session number with the received local maximum PDU sessions number value. The same action is executed as for step 3 in clause 4.2.11.4 based on the updated configured value. 9. Same as for step 4 of clause 4.2.11.4.