Section: 16.6.3 Subscription/unsubscription procedure of NSACF notification service
Content: Figure 16.6.3-1: Subscription/unsubscription of NSACF notification procedure 0. Authentication of the AF: the AF is authenticated based on the description in clause 13 or clause 12. The AF authorization is based on clause 13 or clause 12 or local configuration at the NEF. If a token based authorization mechanism is used, a token is generated for the AF after authentication and authorization. 1. To subscribe or unsubscribe for the number of UEs or the number of PDU Sessions per network slice notification with the NSACF, the AF sends Nnef_EventExposure_Subscribe/Unsubscribe Request (Event ID, Event Filter, Event Reporting information) message to the NEF as described in TS 23.502[ Procedures for the 5G System (5GS) ]  [8]. The Event Filter parameter shall be AF-Service-Identifier for an AF deployed outside the 3GPP operator domain. Other parameters are specified in TS 23.502[ Procedures for the 5G System (5GS) ]  [8]. 2. The NEF confirms with Nnef_ SliceStatusEventExposure _Subscribe/Unsubscribe Response message to the AF. The Event Filter parameter is the mapped AF-Service-Identifier for the AF deployed outside the 3GPP operator domain. 3. The NEF checks whether the AF is authorised for the requested subscription based on the AF token. It needs to check whether the token claims match the AF’s identity and the Event Filter parameter. If authorised, the NEF may query the NRF to find the NSACF responsible for the requested S-NSSAI (NEF needs to map to S-NSSAI based on AF-Service-Identifier for the AF deployed outside the 3GPP operator domain). 4. The NEF forwards the request to the NSACF with Nnsacf_SliceEventExposure_Subscribe/Unsubscribe Request (Event ID, Event Filter, Event Reporting information). The Event Filter parameter shall be the mapped S-NSSAI for the AF deployed outside the 3GPP operator domain. 5. The NSACF confirms with Nnsacf_SliceEventExposure_Subscribe/Usubscribe Response message to the NEF as in TS 23.502[ Procedures for the 5G System (5GS) ]  [8]. 6-7a. The NSACF triggers a notification towards the AF and sends the Nnsacf_SliceEvent Exposure_Notify (Event ID, Event Filter, Event Reporting information) message to the NEF as described in TS 23.502[ Procedures for the 5G System (5GS) ]  [8]. 7b-9. The NEF forwards the message to the AF for single NSACF or aggregates reporting information for multiple NSACFs in the Nnef_EventExposure_Notify (Event ID, Event Filter, Event Reporting information) message as described in TS 23.502[ Procedures for the 5G System (5GS) ]  [8]. The Event Filter parameter shall be the mapped AF-Service-Identifier from the S-NSSAI for the AF deployed outside the 3GPP operator domain.