Section: 5.38.3 Paging Cause Indication for Voice Service
Content: A Multi-USIM UE and the network may support Paging Cause Indication for Voice Service feature. The network that supports Paging Cause Indication for Voice Service feature shall provide a Voice Service Indication for IMS voice service in the Paging message, only if the UE indicates the Paging Cause Indication for Voice Service feature is supported to the network. The network determines the IMS voice service based on the Paging Policy Indicator as specified in clause 5.4.3.2. Upon reception of the Voice Service Indication in NGAP Paging Message from AMF, the NG-RAN supporting Paging Cause Indication for Voice Service should include the Voice Service Indication in the Uu Paging message to the UE. When the UE context in the AMF indicates Paging Cause Indication for Voice Service feature is supported, in order to require NG RAN to deliver the Voice Service Indication in RAN paging for the UE in RRC_INACTIVE state, the AMF provides an indication indicating the Paging Cause Indication for Voice Service feature is supported to the NG-RAN. Upon reception of the indication, the NG-RAN that supports the feature stores a Paging Cause Indication for Voice Service indication in its the UE context. For a UE in RRC_INACTIVE, the NG-RAN should provide the Voice Service Indication in the RAN Paging message only when there is Paging Cause Indication for Voice Service indication in the UE context and detects the downlink data which triggers the RAN Paging message is related to voice service based on the Paging Policy Indicator, in the header of the received downlink data, as specified in clause 5.4.3.2. UE that supports the Paging Cause Indication for Voice Service feature is capable of differentiation between Paging from a network that does not support the Paging Cause Indication for Voice Service feature and Paging without the Voice Service Indication. How the UE distinguishes the Paging from a RAN that does not support the Paging Cause Indication for Voice Service feature and Paging without the Voice Service Indication is defined in TS 38.331[ NR; Radio Resource Control (RRC); Protocol specification ]  [28]. The UE determines whether the Paging Cause Indication for Voice Service feature is supported in the current Registration Area by 5GC based on the MUSIM capability exchange with the AMF, see clause 5.38.1. The UE determines that the Paging Cause Indication for Voice Service feature is supported if it is supported by both the RAN, as indicated in the received Uu Paging message, and by 5GC, as indicated in the MUSIM capability exchange with the AMF. The UE uses the Paging Cause Indication for Voice Service as described in TS 24.501[ Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3 ]  [47] and TS 38.331[ NR; Radio Resource Control (RRC); Protocol specification ]  [28].