Section: 5.4.12.2 Core Network Assistance for PEIPS
Content: To support the Paging Early Indication with Paging Subgrouping (PEIPS), Paging Subgrouping Support Indication and the PEIPS Assistance Information is used by the AMF and NG-RAN to help determine whether PEIPS applies to the UE and which paging subgroup used when paging the UE (see TS 38.300[ NR; NR and NG-RAN Overall description; Stage-2 ]  [27]). In the Registration Request message, the Paging Subgrouping Support Indication indicates whether the UE supports PEIPS with AMF PEIPS Assistance Information. If the UE includes Paging Subgrouping Support Indication, the UE may also include the paging probability information to assist the AMF. If the AMF supports PEIPS assistance and if the UE provided Paging Subgrouping Support Indication, the AMF stores the indication in the UE context in AMF. 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 the AMF PEIPS Assistance Information. The AMF PEIPS Assistance Information includes the Paging Subgroup ID. NOTE 1: To minimise MT voice call setup latency, the AMF could allocate Paging Subgroup IDs 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 taking into account the UE's mobility pattern. If the AMF has determined AMF PEIPS Assistance Information 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 PEIPS Assistance Information, the AMF shall provide it to NG RAN when paging the UE. In addition, in order to support PEIPS for UEs in RRC_INACTIVE mode, the AMF shall provide the AMF PEIPS Assistance Information to NG-RAN as part of the RRC Inactive Assistance Information. The NG-RAN chooses on a per-cell basis whether to use PEIPS and which paging subgrouping mechanism to use. When using AMF allocated subgroups, both the UE and NG-RAN use the AMF PEIPS Assistance Information to determine the paging subgroup to apply as defined in TS 38.300[ NR; NR and NG-RAN Overall description; Stage-2 ]  [27]. The AMF may use the UE Configuration Update procedure (as described in clause 4.2.4 of TS 23.502[ Procedures for the 5G System (5GS) ]  [3]) and N2 UE Context Modification procedure (as described in clause 8.3.4 of TS 38.413[ NG-RAN; NG Application Protocol (NGAP) ]  [34]) to update the AMF PEIPS Assistance Information in the UE and NG-RAN. When the UE has an active emergency PDU Session: - The UE shall not signal Paging Subgrouping Support Indication in the Registration Request message.