Section: 4.3.33.3 Paging Cause Indication for Voice Service
Content: A Multi-USIM UE and the network may support the Paging Cause Indication for Voice Service feature. The MME that supports Paging Cause Indication for Voice Service feature should provide a Voice Service Indication in the S1AP Paging message for the MMTel voice service, only if the UE indicates the Paging Cause Indication for Voice Service feature is supported. The MME determines the downlink data triggering the paging is related to a MMTel voice service based on the Paging Policy Indicator as specified in clause 4.9 for MMTel voice. NOTE: The indication of CS voice in the CN domain indication in S1AP paging message and Uu paging message is not modified by the Paging Cause Indication for Voice Service feature. Upon reception of the Voice Service Indication in S1AP Paging Message, an eNodeB that supports the Paging Cause Indication for Voice Service should include the Voice Service Indication the Uu Paging message to the UE. A 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 Uu 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 36.331[ Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification ]  [37]. The UE determines whether the Paging Cause Indication for Voice Service feature is supported in the current Tracking Area by EPC based on the MUSIM capability exchange with the MME, see clause 4.3.33.1. 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 EPC, as indicated in the MUSIM capability exchange with the MME. The UE uses the Paging Cause Indication for Voice Service as described in TS 24.301[ Non-Access-Stratum (NAS) protocol for Evolved Packet System (EPS); Stage 3 ]  [46] and TS 36.331[ Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification ]  [37].