5.31.7.2.4 Paging for extended DRX for RRC_INACTIVE in NR connected to 5GC

For NR, the NG-RAN may request the CN to handle mobile terminated (MT) communication for the UE configured with eDRX for RRC_INACTIVE state by means of the Connection Inactive procedure with CN based MT communication handling Procedure (see clause 4.8.1.1a of TS 23.502 [3]). This allows the CN to apply high latency communication functions as specified in clause 5.31.8. The NG-RAN provides the determined eDRX values (i.e. the eDRX cycle length and the Paging Time Window length) for RRC_INACTIVE to AMF (i.e. >10.24s). Based on the request from NG-RAN, the AMF responds to NG-RAN and informs other NFs (e.g. SMF and UPF) involved in downlink data or signalling handling and trigger the data buffering as specified in clause 4.8.1.1a of TS 23.502 [3]. Based on local policy and/or an indication from the AMF, e.g. the RAT type of REDCAP or the CN based MT handling indication, the SMF may trigger the UPF to provide the DL data size in case of DL data arrival when data buffering is executed in the UPF.

When MT data or signalling arrives for a UE in RRC_INACTIVE state, the other NFs communicate with the AMF for delivery of MT data or signalling. The AMF calculates the UE reachability based on the eDRX values for RRC_INACTIVE state provided by NG-RAN and triggers NG-RAN paging via an N2 RAN Paging Request message if the UE is considered reachable as specified in clause 4.8.2.2b of TS 23.502 [3]. Otherwise, the AMF stores the information received in the NF request and replies to the requesting NF to apply high latency communication functions as specified in clause 5.31.8 based on eDRX values for RRC_INACTIVE (e.g. an Estimated Maximum Wait Time is calculated based on eDRX values for RRC_INACTIVE). When the AMF determines that the UE has become reachable for paging, the AMF uses the stored information to send an N2 RAN Paging Request message. If UPF/SMF provides the downlink data size information, the AMF provides the information to NG-RAN as described in clause 4.8.2.2b of TS 23.502 [3].

When the UE resumes the RRC connection as specified in TS 38.300 [27] (e.g. including mobile originated small data transmission procedure), if the NG-RAN had sent the indication for the CN to handle mobile terminated (MT) communication, NG-RAN proceeds as specified in clause 4.8.2.2 of TS 23.502 [3], which indicates to the AMF that the UE is now reachable for downlink data and/or signalling. The AMF then informs other NFs that the UE is now reachable using the high latency communication functions as specified in clause 5.31.8 and MT data and signalling can be delivered to the UE.