5.2.21 NSACF services
23.5023GPPProcedures for the 5G System (5GS)Release 18TS
5.2.21.1 General
The following table illustrates the NSACF services.
Table 5.2.21.1-1: List of NSACF services
|
Service Name |
Service Operations |
Operation Semantics |
Example Consumer(s) |
|
Nnsacf_NSAC |
NumOfUEsUpdate |
Request/Response |
AMF, SMF (NOTE 1) |
|
NumOfPDUsUpdate |
SMF |
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|
EACNotify |
AMF |
||
|
Nnsacf_SliceEventExposure |
Subscribe |
Subscribe/Notify |
NEF, NWDAF, AF (NOTE 2) |
|
Unsubscribe |
NEF, NWDAF, AF |
||
|
Notify |
NEF, NWDAF, AF |
||
|
NOTE 1: If EPS counting is required for the S-NSSAI, the SMF+PGW-C uses the Nnsacf_NumberOfUEs Update services operation and Nnsacf_NumberOfPDUsUpdate at PDN connection establishment procedure. NOTE 2: The AF can access NSACF services either via NEF to NSACF in case of untrusted AF or directly in case of trusted AF. |
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5.2.21.2 Nnsacf_NSAC services
5.2.21.2.1 General
Service Description: The Nnsacf_NSAC services control the number of UEs registered with a network slice and the number of PDU Sessions associated with a network slice for the network slices subject to NSAC. The consumer NF (e.g. AMF) can request the NSACF to check whether the number of UEs registered with a network slice has reached the maximum number of UEs per network slice and the consumer NF can also request the NSACF to update the number of UEs registered with a network slice. The SMF can request the NSACF to check whether the number of PDU Sessions established on a network slice has reached the maximum number of PDU Sessions per network slice and the SMF can also request the NSACF to update the number of PDU Sessions established on a network slice.
5.2.21.2.2 Nnsacf_NSAC_NumOfUEsUpdate service operation
Service Operation name: Nnsacf_NSAC_NumOfUEsUpdate
Description: Updates the number of UEs registered with a network slice (e.g. increase or decrease) when the UE registration status for a network slice subject to NSAC has changed. Also, if the number of the UEs registered with the network slice is to be increased and the Early Admission Control (EAC) mode in the NSACF is activated for that network slice (see Nnsacf_NSAC_EACNotify service operation), the NSACF first checks whether the number of UEs registered with the network slice has reached the maximum number of UEs per network slice threshold. If the maximum number of UEs registered with the network slice has already been reached, the UE registration for that network slice via the same Access Type configured in the NSACF is rejected. If the EAC is not activated, the NSACF increases or decreases the number of UEs per network slice as per the input parameters below.
Inputs, Required: S-NSSAI(s), UE ID (SUPI), NF ID, Access Type, update flag.
Inputs, Conditional: Notification endpoint for EAC Notification for the S-NSSAI.
The S-NSSAI(s) parameter is a list of one or more network slices for which the number of UEs registered with a network slice is to be updated and checked if the maximum number of UEs per network slice threshold has already been reached.
The UE ID parameter is used by the NSACF to maintain a list of UE IDs registered with the network slice. The NSACF also takes Access Type into account for increasing and decreasing the number of UEs per network slice as described in clause 5.15.11.1 of TS 23.501 [2].
The NF ID parameter is the NF instance ID of the NF (e.g. AMF or SMF + PGW-C) sending the request to the NSACF.
The update flag input parameter indicates whether the number of UEs registered with a network slice is to be:
– increased when the UE registers to a new network slice subject to NSAC. If the UE ID is already in the list of UEs registered with the network slice, the number of UEs registered with the network slice is not increased as the UE has already been counted as registered with the network slice. If the UE ID is not in the list of UE IDs registered with the network slice and the maximum number of UEs registered with the network slice has not been reached yet, the NSACF adds the UE ID in the list of UEs registered with the network slice and increases the number of the UEs registered with the network slice. If the UE_ID is not in the list of UEs registered with that S-NSSAI and the maximum number of UEs per network slice for that S-NSSAI has already been reached, then the NSACF returns maximum number of UEs per network slice reached result;
– decreased when the UE deregisters for a network slice that is subject to NSAC. The NSACF decreases the number of the UEs registered with the network slice and removes the UE ID from the list of UEs registered with the network slice.
The NSACF may optionally return the current status of the network slice availability (e.g. a percentage out of the maximum number of UEs registered with a network slice) in the availability status parameter. This information may be used for NSACF signalling and load balancing in case multiple NSACFs are serving the same network slice.
Outputs, Required: Result indication.
The Result indication parameter contains the outcome of the update and check operation in the NSACF and may indicate one of the values ‘maximum number of UEs for the S-NSSAI not reached’ or ‘maximum number of UEs for the S-NSSAI reached’.
Outputs, Optional: None.
5.2.21.2.3 Nnsacf_NSAC_EACNotify service operation
Service Operation name: Nnsacf_NSAC_EACNotify
Description: The NSACF is configured with the information about which network slices are subject to NSAC. The NSACF may trigger notification to the consumer NF (e.g. AMF) to indicate the activation of the Early Admission Control (EAC) mode for a certain network slice which is subject to NSAC when the number of the UEs registered with the network slice is above certain operator defined threshold (e.g. a percentage of the maximum number of UEs allowed to register with the network slice) and the deactivation of the EAC mode when the number of the UEs registered with the network slice is below certain operator defined threshold which may be same or different from the activation threshold.
Inputs, Required: S-NSSAI(s), EAC flag(s).
The S-NSSAI input parameter is the network slice for which the NSACF activates or deactivates the EAC mode.
The EAC flag input parameter indicates whether the Slice EAC mode is activated or deactivated.
Inputs, Optional: None.
Output, Required: None.
Output, Optional: None.
5.2.21.2.4 Nnsacf_NSAC_NumOfPDUsUpdate service operation
Service Operation name: Nnsacf_NSAC_NumOfPDUsUpdate
Description: Updates the number of PDU Sessions established on a network slice (e.g. increase or decrease). Also, if the number of PDU Sessions on the network slice is to be increased, the NSACF first checks whether the number of the PDU Sessions on that network slice has reached the maximum number of PDU Sessions per network slice. If the maximum number of PDU Sessions on the network slice has already been reached, the PDU Session Establishment procedure is rejected.
Inputs, Required: S-NSSAI, UE ID, PDU Session ID, Access Type, update flag.
The S-NSSAI parameter is the network slice for which the number of PDU Sessions established on a network slice is to be updated.
The UE ID parameter is used by the NSACF to maintain a list of UE IDs that has established PDU sessions with the network slice.
PDU Session ID parameter is used by the NSACF to maintain for each UE ID, the PDU Session ID(s) for established PDU Sessions.
The Access Type parameter indicates over which access network type the PDU Session is established. In the case of MA PDU Session, one or multiple Access Types may be included for a PDU Session ID.
The update flag input parameter indicates ‘increase’, ‘decrease’ or ‘update’ as specified in clause 4.2.11.4.
Inputs, Optional: None.
Outputs, Required: Result indication, Access Type.
The Result indication parameter contains the outcome of the update and check operation in the NSACF and may indicate one of the values ‘maximum number of PDU Sessions for the S-NSSAI not reached’ or ‘maximum number of PDU Sessions for the S-NSSAI reached’.
The Access Type parameter is associated with the Result indication parameter.
Outputs, Optional: None.
5.2.21.3 Void
5.2.21.4 Nnsacf_SliceEventExposure services
5.2.21.4.1 General
Service Description: The Nnsacf_SliceEventExposure services provide event based notifications to the consumer NF related to the current number of UEs registered for a network slice or/and the current number of PDU Sessions established on a network slice.
5.2.21.4.2 Nnsacf_SliceEventExposure_Subscribe service operation
Service operation name: Nnsacf_SliceEventExposureSubscribe
Description: This service operation is used by the consumer NF to subscribe or modify a subscription with the NSACF for event based notifications of the current number of UEs registered for a network slice or the current number of PDU Sessions established on a network slice.
Inputs, Required: Event ID, Event Filter, Event Reporting information.
The Event ID parameter defines whether to notify the number of UEs registered with a network slice or the number of PDU Sessions established on a network slice.
The Event Filter parameter is the S-NSSAI for which the current number of UEs registered for a network slice or the current number of PDU Sessions established on a network slice or both are to be notified to the consumer NF.
The Event Reporting information parameter defines whether the notification is threshold based (e.g. the notification is triggered when the current number of UEs or PDU Sessions with a network slice reaches a defined threshold value) or the notification is periodical (e.g. the notification is triggered at expiry of a periodic timer) and optionally the Immediate reporting flag.
Inputs, Optional: Notification threshold, Notification periodicity.
The Notification threshold parameter is optional. It is provided when the Notification is threshold base. The notification threshold parameter may be a numeric value or a percentage of the maximum number of the UEs or PDU Sessions per network slice.
The Notification periodicity parameter is optional. It is provided when the Notification is periodical. The Notification periodicity parameter defines the time between the notification periodicity.
Outputs, Required: Operation execution result response, Subscription Correlation Id.
5.2.21.4.3 Nnsacf_SliceEventExposure_Unsubscribe service operation
Service operation name: Nnsacf_SliceEventExposure_Unsubscribe
Description: This service operation is used by the consumer NF to unsubscribe from the event notification.
Inputs, Required: Subscription Correlation Id.
Outputs, Required: Operation execution result response.
5.2.21.4.4 Nnsacf_SliceEventExposure_Notify service operation
Service operation name: Nnsacf_SliceEventExposure_Notify
Description: This service operation is used by the NSACF to report the current number of UEs registered with a network slice or the current number of PDU Sessions established on a network slice in numbers or in percentage from the maximum allowed numbers, based on threshold or at expiry of periodic timer.
Inputs, Required: Event ID, Event Filter, Event Reporting information, Notification Correlation Information.
The Event ID parameter defines the type of the reported information, i.e. the number of UEs registered with a network slice or the number of PDUs Sessions established on a network slice.
The Event Filter parameter is the S-NSSAI for which the Notification applies.
The Event Reporting information parameter provides the network slice status information in terms of the current number of UEs registered with a network slice or the current number of PDU Sessions established on a network slice. If the Notification is threshold based where the threshold is a certain number of UEs registered with a network slice or PDU Sessions established on a network slice or the threshold is a percentage of the maximum number of UEs registered with a network slice or the maximum number of PDU Sessions established on a network slice, the Event Reporting information parameter contains confirmation for reaching this threshold value. If the Notification is periodical, the Event Reporting information parameter provides information for the current number of UEs registered with a network slice (e.g. represented in percentage of the maximum number of the UEs registered with the network slice) or information for the current number of PDU Sessions established on a network slice (e.g. represented in percentage of the maximum number of the PDU Sessions established on the network slice) with periodicity provided during the subscription.
Outputs, Required: None.