4.6.2.9 Mobility management based network slice usage control

If the network supports network slice usage control, the AMF monitors network slice usage by running a slice deregistration inactivity timer per S-NSSAI and access type. If the UE supports network slice usage control, the AMF may also provide on-demand NSSAI to the UE in the REGISTRATION ACCEPT message or in the CONFIGURATION UPDATE COMMAND message. The on-demand NSSAI consists of one or more on-demand S-NSSAIs and, optionally, the slice deregistration inactivity timer per on-demand S-NSSAI.

The slice deregistration inactivity timer is started using the stored slice deregistration inactivity timer value as follows:

• for a PDU session which is released using 5GSM signalling, after a PDU session is released and there is no established PDU session, including any MA PDU session, associated with the S-NSSAI over the corresponding access type;
• for a PDU session which is released locally:
• when the UE or AMF indicates via the PDU session status IE that a PDU session is now in 5GSM state PDU SESSION INACTIVE and there is no established PDU session, including any MA PDU session, associated with the S-NSSAI over the corresponding access type; or
• when the UE or AMF receives the the PDU session status IE for which a PDU session that was previously in 5GSM state PDU SESSION ACTIVE is now indicated as being in 5GSM state PDU SESSION INACTIVE and there is no established PDU session, including any MA PDU session, associated with the S-NSSAI over the corresponding access type;
• successful completion of handover of PDU session to other access and there is no established PDU session, including any MA PDU session, associated with the S-NSSAI over the corresponding access type; or
• when there is no established PDU session, including any MA PDU session, associated with the S-NSSAI included in the allowed NSSAI or in the partially allowed NSSAI over the corresponding access type.

The slice deregistration inactivity timer is stopped and reset:

• when at least a PDU session, including any MA PDU session, associated with the S-NSSAI is successfully established over the corresponding access type(s) or the S-NSSAI is removed from the allowed NSSAI or partially allowed NSSAI; or
• when the UE enters the state 5GMM-DEREGISTERED.

NOTE 0A: If the PDU session is established with an alternative S-NSSAI, then this PDU session is considered as associated with both the S-NSSAI to be replaced and with the alternative S-NSSAI.

If the slice deregistration inactivity timer included in the REGISTRATION ACCEPT message or in the CONFIGURATION UPDATE COMMAND message is set to zero, then the AMF shall stop the timer for the associated S-NSSAI if running.

If the UE receives the slice deregistration inactivity timer value associated with an S-NSSAI and the timer value indicates zero, the UE shall stop running the slice deregistration inactivity timer for the associated S-NSSAI, if any.

If the slice deregistration inactivity timer value is updated, the AMF updates the stored timer value and may provide the updated timer value to the UE in the REGISTRATION ACCEPT message, in a current or the next registration procedure for mobility and periodic registration update, or the CONFIGURATION UPDATE COMMAND message.

When the UE receives an updated slice deregistration inactivity timer value in the REGISTRATION ACCEPT message or the CONFIGURATION UPDATE COMMAND message from the AMF, the UE shall update the stored timer value.

Upon expiry of the slice deregistration inactivity timer, the AMF:

• for UE supporting network slice usage control, shall locally remove the S-NSSAI from the allowed NSSAI over the corresponding access type. In addition, the AMF may send the CONFIGURATION UPDATE COMMAND message to the UE with the new allowed NSSAI; and
• for UE not supporting network slice usage control, shall provide the updated allowed NSSAI excluding the S-NSSAI in the CONFIGURATION UPDATE COMMAND message to the UE.

If the AMF locally removes either the replaced S-NSSAI or the alternative S-NSSAI in the allowed NSSAI upon expiry of the associated slice deregistration inactivity timer, the AMF shall delete the entry including the replaced S-NSSAI or the alternative S-NSSAI stored in the alternative NSSAI.

The UE includes the on-demand S-NSSAI which the UE requests in the requested NSSAI during the registration procedure. Upon expiry of the slice deregistration inactivity timer, the UE shall locally remove the S-NSSAI from the allowed NSSAI over the corresponding access type. If the locally removed on-demand S-NSSAI is included in the entry of the stored alternative NSSAI, the UE shall delete the entry as specified in clause 4.6.2.2.

NOTE 0: If the UE determines the on-demand S-NSSAI for a PDU session establishment as specified in clause 4.2.2 of 3GPP TS 24.526 [19], the UE includes the on-demand S-NSSAI in the requested NSSAI during the registration procedure.

On-demand NSSAI is associated with the configured NSSAI. The on-demand S-NSSAI(s) is deleted by the UE from the stored on-demand NSSAI, when the associated configured S-NSSAI(s) is deleted by the UE from the stored configured NSSAI.

NOTE 1: Based on regulatory requirements and operator policy, the AMF ensures that the network slice usage control does not apply for the S-NSSAI used for emergency services.

NOTE 2: In this version of the specification, the network slice usage control feature is not supported in roaming scenarios.