VoWifi Mobile-Terminated (MT) Call Creation Call Flow

This section describes the Mobile-Terminated (MT) call flow.

VoWifi MT Call Creation Call Flow
VoWifi MT Call Creation Call Flow Description
StepDescription
1UE requests for establishment of the IMS default bearer, PDU session, through PCF. After establishing the session, the UE receives the P-CSCF addresses from PCF.
2The UE-initiates the SIP signaling towards the P-CSCF (AF).
3The P-CSCF (AF) sends the NPCF Policy Authorization Update message to the PCF.
4The PCF sends the NPCF SM Policy Control Update Notify Request to the SMF+PGW-C.
5The SMF+PGW-C sends the NPCF SM Policy Control Update Notify Response back to the PCF.
6SMF sends ChargingDataUpdateReq by including Multi-Unit-Usage with Rating-Group-Id that are received as part of Charging_Description of Sm_PolicyControl_UpdateNotify_Request to install PCC Rules.
7CHF provides ChargingDataUpdateResp with Multi-Unit-Information for received Rating-Group values in requested message. CHF also provides params changes for Session-Level and Rating-Group values.
8SMF sends N4 Session Modification Request to the UPF by including Create ULPDRs and Create ULFARs. Create ULPDRs include SDFs and QER Info which are received as part of PCC Rule Installation.
9UPF responds back with N4 Session Modification Response to SMF by including Created ULPDR and Created ULFAR. Create ULFAR contains UL Tunnel Information of UPF for the dedicated bearer creation.
10The SMF+PGW-C sends the GTPv2 Create Bearer Request to the S-GW.
11The S-GW sends the GTPv2 Create Bearer Request to the ePDG.
12IKE_CHILD_SA exchange happens between the UE and ePDG.
13The ePDG sends the GTPv2 Create Bearer Response back to the SMF+PGW-C.
14The established N4 session is modified between SMF+PGW-C and UPF+PGW-C.
15The SMF+PGW-C sends the NPCF SM Policy Control Update Request to the PCF.
16The PCF sends the NPCF SM Policy Control Update Response back to the SMF+PGW-C.
17PCF sends the NPCF policy authorization notify request to P-CSCF (AF).
18Establishes SIP-signaling and voice call between end-users through UE and P-CSCF (AF).