5.4.12a.2 Core Network Assistance for LP-WUSPS

To support the LP-WUSPS, the LP-WUS Paging Subgrouping Support Indication and the LP-WUSPS Assistance Information are used by the AMF and NG-RAN to help determine whether LP-WUSPS applies to the UE and which paging subgroup is used when paging the UE (see TS 38.300 [27]).

In the Registration Request message, the UE includes the LP-WUS Paging Subgrouping Support Indication if the UE supports AMF LP-WUSPS Assistance Information for LP-WUS Paging Subgrouping. If the UE includes the LP-WUS Paging Subgrouping Support Indication, the UE may also include the paging probability information to assist the AMF. An AMF supporting LP-WUSPS stores the UE provided LP-WUS Paging Subgrouping Support Indication and the AMF determined AMF LP-WUSPS Assistance Information in the UE context. The AMF may use local configuration, the UE's paging probability information if provided, information provided by the RAN (e.g. any of the Information On Recommended Cells And RAN nodes For Paging), and/or previous statistical information for the UE to determine AMF LP-WUSPS Assistance Information. The AMF LP-WUSPS Assistance Information includes the Paging Subgroup ID.

NOTE 1: To minimise MT voice call setup latency, the AMF could allocate Paging Subgroup IDs for LP-WUS taking into account whether or not the UE is likely to receive IMS voice over PS session calls.

NOTE 2: To avoid MT traffic for more mobile UEs causing more stationary UEs to be woken up, the AMF could allocate Paging Subgroup IDs for LP-WUS taking into account the UE's mobility pattern.

If the AMF has determined AMF LP-WUSPS Assistance Information for the UE and has not disabled LP-WUS for the UE, the AMF stores it in the UE context in AMF and provides it to the UE in every Registration Accept message.

If the AMF has determined AMF LP-WUSPS Assistance Information and has not disabled LP-WUS for the UE, the AMF shall provide it to NG RAN when paging the UE. In addition, in order to support LP-WUSPS for UEs in RRC_INACTIVE mode, the AMF shall provide the AMF LP-WUSPS Assistance Information to NG-RAN as part of the RRC Inactive Assistance Information.

When the NG-RAN is using AMF allocated subgroups for LP-WUSPS, both the UE and NG-RAN use the AMF LP-WUSPS Assistance Information to determine the paging subgroup to apply as defined in TS 38.300 [27].

The AMF may use the Registration procedure (as described in clause 4.2.2 of TS 23.502 [3]) or UE Configuration Update procedure (as described in clause 4.2.4 of TS 23.502 [3]) and the N2 UE Context Modification procedure (as described in clause 8.3.4 of TS 38.413 [34]) to update or remove the AMF LP-WUSPS Assistance Information in the UE and NG-RAN.