Section: 4.2.11.5.2 Network Slice Admission Control Support for Roaming by HPLMN
Content: 4.2.11.5.2.1 General For maximum number of UEs in roaming case, there are two types of NSAC admission modes requiring interaction with HPLMN for inbound roamers; VPLMN with HPLMN assistance NSAC admission mode or HPLMN NSAC admission mode. For PDU sessions in the home-routed roaming case, the SMF in HPLMN performs NSAC for the S-NSSAI(s) subject to NSAC. For LBO PDU sessions, there are two types of NSAC admission mode requiring interaction with HPLMN for LBO PDU sessions; VPLMN with HPLMN assistance NSAC admission mode or HPLMN NSAC admission mode. 4.2.11.5.2.2 VPLMN with HPLMN assistance NSAC admission mode For inbound roamers, depending on the NSAC architecture deployed in the VPLMN, enforcement for the maximum number of registered UEs with an S-NSSAI is done in the VPLMN by an NSACF in the VPLMN per the procedure described in clause 4.2.11.2 or 4.2.11.2a with the following differences: - The AMF verifies the applicable NSAC admission mode for the inbound roamer based on the subscription data from UDM. - When the AMF invokes the Nnsacf_NSAC_NumOfUEsUpdate_Request service operation with the NSACF in the VPLMN, the AMF provides in the Request the additional NSAC admission mode parameter, i.e. VPLMN with HPLMN assistance NSAC admission mode. - If the maximum number of UEs is not available or the maximum number of UEs has been reached at the Primary (or Central) NSACF of the VPLMN and the type of NSAC admission mode is VPLMN with HPLMN assistance NSAC admission mode, the following is performed: - The Primary (or Central) NSACF in the VPLMN invokes Nnsacf_NSAC_NumOfUEsUpdate_Request to the Primary (or central) NSACF in the HPLMN for NSAC delegation and to receive an initial or a new allocated maximum number of UEs for the mapped S-NSSAI in HPLMN for inbound roamers. The request includes mapped S-NSSAI in HPLMN, PLMN ID and NSAC admission mode. - The Primary (or central) NSACF in HPLMN provides Nnsacf_NSAC_NumOfUEsUpdate_Response message to the Primary (or Central) NSACF of VPLMN. The response message includes mapped S-NSSAI in HPLMN, the new allocated maximum number of UEs for the mapped S-NSSAI in HPLMN for inbound roamers. Alternatively, the Primary (or central) NSACF rejects the request for the NSAC delegation. - The Primary (or central) NSACF in VPLMN updates the previous stored maximum number of UEs based on the new received allocated maximum UEs number. - At any time, the Primary (or central) NSACF in HPLMN may trigger Nnsacf_NSAC_LocalNumberUpdate Request message to the Primary (or central) NSAC in VPLMN to provide an updated maximum number of registered UEs for the mapped S-NSSAI in HPLMN for inbound roamers. Based on the updated maximum UEs number of the S-NSSAI, where applicable, the Primary NSACF in VPLMN may further perform distribution of local maximum UEs number to the NSACFs it interacts with. For more detail refer to clause 4.2.11.6. The complete procedure of the VPLMN with HPLMN assistance NSAC admission mode for number of registered UEs is described in clause 4.2.11.5.2.3. For LBO PDU sessions, depending on the NSAC architecture deployed in the VPLMN, enforcement for the maximum number of LBO PDU sessions established for an S-NSSAI is performed by the NSACF in the VPLMN per the procedure described in clause 4.2.11.4 or 4.2.11.4a with the following differences: - The SMF verifies the applicable NSAC admission mode for the S-NSSAI PDU session associated with the inbound roamer based on the subscription data from UDM. - When the SMF invokes the Nnsacf_NSAC_NumOfPDUsUpdate_Request service operation to the NSACF in the VPLMN, the SMF provides in the Request the additional NSAC admission mode parameter, i.e. VPLMN with HPLMN assistance NSAC admission mode. - If the maximum number of PDU Session is not available or the maximum number of PDU Sessions has been reached at the Primary (or Central) NSACF of the VPLMN and the type of NSAC admission mode is VPLMN with HPLMN assistance NSAC admission mode, the following is performed: - The Primary (or Central) NSACF in the VPLMN invokes Nnsacf_NSAC_NumOfPDUsUpdate_Request to the Primary (or central) NSACF in the HPLMN for the NSAC delegation and to receive an initial or a new allocated maximum number of LBO PDU Sessions for the mapped S-NSSAI in HPLMN for inbound roamers. The request includes mapped S-NSSAI in HPLMN, PLMN ID and NSAC admission mode. - The Primary (or central) NSACF in HPLMN provides the Nnsacf_NSAC_NumOfPDUsUpdate_Response message to the Primary NSACF of VPLMN. The response message includes mapped S-NSSAI in HPLMN, the allocated maximum number of LBO PDU Sessions for the mapped S-NSSAI in HPLMN for inbound roamers. Alternatively, the Primary (or central) NSACF rejects the request for the NSAC delegation. - The Primary (or central) NSACF in VPLMN updates the previous stored maximum number of PDU Sessions based on the new received allocated maximum number of LBO PDU Sessions. - At any time, the Primary (or central) NSACF in HPLMN may trigger Nnsacf_NSAC_LocalNumberUpdate Request message to the Primary (or central) NSAC in VPLMN to provide an updated new allocated maximum number of LBO PDU Sessions for the mapped S-NSSAI in HPLMN for the roaming UEs. Based on the updated maximum number of LBO PDU Sessions number of the S-NSSAI, where applicable, the Primary NSACF in VPLMN may further perform distribution of local maximum PDU Sessions number to the NSACFs it contacts. For more detail refer to clause 4.2.11.6. The complete procedure for the VPLMN with HPLMN assistance NSAC Admission mode for number of registered UEs and number of LBO PDU Sessions is described in Clause 4.2.11.5.2.4. NSACF nodes to be contacted in all the above are either configured or discovered. 4.2.11.5.2.3 VPLMN with HPLMN assistance NSAC Admission mode for number of Registered UEs Figure 4.2.11.5.2.3-1: HPLMN Delegated NSAC admission for UE number Procedure The procedure of NSAC for maximum number of UEs for a roaming UE registration is performed as follows: 1. Same as step 1 defined in clause 4.2.11.2. For the inbound roaming UE, the AMF checks the NSAC admission mode of the registered S-NSSAI based on the subscription data from UDM. If the Hierarchical NSAC architecture is deployed in the VPLMN, steps 2a-3a are executed and step 2b is skipped. 2a. The AMF invokes Nnsacf_NSAC_NumOfUEsUpdate request to the NSACF in VPLMN same as step 2 of clause 4.2.11.2a with the additional parameter NSAC admission mode, i.e. VPLMN with HPLMN assistance NSAC admission mode. 3a. Same procedure of steps 3-5 in clause 4.2.11.2a is executed. If the centralized NSAC architecture is deployed in the VPLMN, step 2b is executed and steps 2a-3a are skipped. 2b. The AMF invokes Nnsacf_NSAC_NumOfUEsUpdate request to the central NSACF in VPLMN same as step 2 of clause 4.2.11.2 with the additional parameter NSAC admission mode, i.e. VPLMN with HPLMN assistance NSAC admission mode. 4. If there is no allocated maximum number of UEs from HPLMN or the allocated maximum number of registered UEs has been reached and the type of NSAC admission mode is VPLMN with HPLMN assistance NSAC admission mode, the Primary (or central) NSACF in VPLMN interacts with HPLMN. In this case, steps 5-7 are executed. Otherwise, steps 5-7 are skipped. The Primary (or central) NSACF in VPLMN discovers the Primary (or central) NSACF in HPLMN. NOTE 1: The Primary (or central) NSACF in HPLMN can be configured or be discovered via NRF. 5. The Primary (or central) NSACF in the VPLMN invokes Nnsacf_NSAC_NumOfUEsUpdate Request to the Primary (or central) NSACF in the HPLMN for NSAC delegation and to receive an initial or an updated maximum number of registered UEs for the mapped S-NSSAI in HPLMN for the inbound roamers. The request includes mapped S-NSSAI in HPLMN, PLMN ID and NSAC admission mode. 6. The Primary (or central) NSACF in HPLMN invokes Nnsacf_NSAC_NumOfUEsUpdate Response message to the Primary (or central) NSACF of VPLMN. The response message includes mapped S-NSSAI in HPLMN, the allocated maximum number of registered UEs for the mapped S-NSSAI in HPLMN for inbound roamers. Alternatively, the Primary (or central) NSACF in HPLMN rejects the request for the NSAC delegation. 7. The Primary (or central) NSACF in VPLMN updates the previous stored maximum number of UE based on the received allocated maximum number of UEs. If the Hierarchical NSAC architecture is deployed in the VPLMN, steps 8a-9a are executed and steps 8b-9b are skipped. 8a. This step is executed only if the NSACF in VPLMN has interacted with Primary NSACF in VPLMN at step 3a before. The NSACF with the assistance of Primary NSACF in VPLMN perform NSAC according to the steps 6-8 in clause 4.2.11.2a. 9a. Based on the response from Primary NSACF in VPLMN, the NSACF in VPLMN returns the response (i.e. acceptance or rejection) message to the AMF. The AMF provides the corresponding response to the inbound roaming UE. If the centralized NSAC architecture is deployed in the VPLMN, steps 8b-9b are executed and steps 8a-9a are skipped. 8b. Same as the step 3 in clause 4.2.11.2 with the replacement of NSACF with Central NSACF. 9b. The Central NSACF in VPLMN returns the response (i.e. acceptance or rejection) message to the AMF. The AMF provides the corresponding response to the inbound roaming UE. 4.2.11.5.2.4 VPLMN with HPLMN assistance NSAC Admission mode for number of LBO PDU Sessions Figure 4.2.11.5.2.4-1: HPLMN Delegated NSAC admission for PDU Session number procedure The NSAC procedure for maximum number of LBO PDU Sessions for inbound roamers, is performed as follow: 1. Same as steps 1 defined in clause 4.2.11.4. For the inbound roaming UE, the SMF checks the NSAC admission mode of the S-NSSAI for the LBO PDU session based on the subscription data from UDM. If the Hierarchical NSAC architecture is deployed in the VPLMN, steps 2a-3a are executed and step 2b is skipped. 2a. The SMF invokes Nnsacf_NSAC_NumOfsPDUsUpdate request to the NSACF in VPLMN same as step 2 of clause 4.2.11.4 with the additional parameter NSAC admission mode, i.e. VPLMN with HPLMN assistance NSAC admission mode. 3a. Same procedure of steps 3-5 in clause 4.2.11.4a is executed. If the centralized NSAC architecture is deployed in the VPLMN, step 2b is executed and steps 2a-3a are skipped. 2b. The SMF invokes Nnsacf_NSAC_NumOfsPDUsUpdate request to the central NSACF in VPLMN same as step 2 of clause 4.2.11.4 with the additional parameter NSAC admission mode, i.e. VPLMN with HPLMN assistance NSAC admission mode. 4-7. The same procedure as step 4-7 of Figure 4.2.11.5.2.3-1 is applied with the difference that the maximum number of registered UE parameter is replaced with the maximum number of LBO PDU Sessions number. Nnsacf_NSAC_NumOfUEsUpdate service operation is replaced with Nnsacf_NSAC_NumOfPDUsUpdate service operation. If the Hierarchical NSAC architecture is deployed in the VPLMN, steps 8a-9a are executed and steps 8b are skipped. 8a. This step is executed only if the NSACF in VPLMN has interacted with Primary NSACF in VPLMN at step 3a before. The NSACF with the assistance of Primary NSACF in VPLMN performs NSAC according to the steps 6-8 in clause 4.2.11.4a. 9a. Based on the response from Primary NSACF in VPLMN, the NSACF in VPLMN returns the response (i.e. acceptance or rejection) message to the SMF. The SMF provides the corresponding response to the inbound roaming UE. If the centralized NSAC architecture is deployed in the VPLMN, steps 8b-9b are executed and steps 8a-9a are skipped. 8b. Same as the step 3 in clause 4.2.11.4 with the replacement of NSACF with Central NSACF. 9b. The Central NSACF in VPLMN returns the response (i.e. acceptance or rejection) message to the SMF. The SMF provides the corresponding response to the inbound roaming UE. 4.2.11.5.2.5 HPLMN NSAC Admission Monitoring and enforcement for the maximum number of UEs registered with a network slice monitoring is done by the NSACF in the HPLMN per the procedure described in clause 4.2.11.2 with the following differences: - Step 1, the AMF verifies the applicable NSAC admission mode for the registered S-NSSAI for the UE based on the subscription data from UDM. The S-NSSAI is the mapped S-NSSAI in HPLMN. - Step 2, in the Nnsacf_NSAC_NumOfUEsUpdate_Request service operation the V-AMF provides both the S-NSSAI in VPLMN and the corresponding mapped S-NSSAI in HPLMN to the NSACF in the HPLMN. - Step 3, the NSCAF in the HPLMN performs NSAC for the corresponding mapped S-NSSAI in HPLMN. Enforcement of the maximum number of LBO PDU Sessions established for an S-NSSAI is performed by the NSACF in the HPLMN as per the procedure described in clause 4.2.11.4 with the following differences: - Step 1, the SMF verifies the applicable NSAC admission mode for the S-NSSAI used for the established PDU session based on the subscription data from UDM. The S-NSSAI is the mapped S-NSSAI in HPLMN. - Step 2, in the Nnsacf_NSAC_NumOfPDUsUpdate_Request service operation the V-SMF provides both the S-NSSAI in VPLMN and the corresponding mapped S-NSSAI in HPLMN to the NSACF in the VPLMN. - Step 3, the NSACF in the HPLMN performs NSAC for the corresponding mapped S-NSSAI in HPLMN. NSACF nodes to be contacted in all the above are either configured or discovered as defined in clause 6.3.22 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2].