5.4.4.3 Paging assistance information

The paging assistance information contains UE radio related information that assists the RAN for efficient paging. The Paging assistance information contains:

• UE radio capability for paging information:
• The UE Radio Capability for Paging contains information derived by the NG-RAN node (e.g. band support information) from the UE Radio Capability information. The NG-RAN provides a single UE Radio Capability for Paging (including different NG-RAN RATs) to the AMF as specified in TS 38.413 [34] and the AMF stores this information without needing to understand its contents.

NB-IoT specific UE Radio Capability information, including paging relation information, is stored separately in AMF and only communicated to NG-RAN when UE is camping on NB-IoT as described in clause 5.4.4.1.

As the AMF only infrequently (e.g. at Initial Registration) prompts the NG-RAN to retrieve and upload the UE radio capabilities i.e. UE Radio Capability information to the AMF and the AMF may be connected to more than one wideband NG-RAN RAT, it is the responsibility of the NG-RAN to ensure that UE Radio Capability for Paging (which is derived by the NG-RAN node) contains information on NG-RAN RATs and relevant functionality that the UE support as specified in TS 38.413 [34]. To assist the NG-RAN in this task, the AMF provides its stored UE Radio Capability for Paging in every NG-AP INITIAL CONTEXT SETUP REQUEST message sent to the NG-RAN. If the NG-RAN detects an omission, then the NG-RAN should ensure that an update of the UE Radio Capability for Paging is sent to the AMF.

NOTE: For functions (e.g. LP-WUS) relying on UE Radio Capability for Paging to work properly, it is expected that NG-RAN nodes provide UE Radio Capability for Paging specific to these functions when supported by NG-RAN as specified in TS 38.413 [34].

• The UE Radio Capability for Paging is maintained in the core network, even during AMF reselection and is stored in the UCMF alongside the UE Radio Capability information associated to a UE Radio Capability ID.
• Information On Recommended Cells and RAN nodes For Paging:
• Information sent by the NG-RAN and used by the AMF when paging the UE to help determining the NG RAN nodes to be paged as well as to provide the information on recommended cells to each of these RAN nodes, in order to optimize the probability of successful paging while minimizing the signalling load on the radio path.
• The RAN provides this information during N2 release.