VoLTE Mobile-Originated (MO) Call Creation Call Flow

This section describes the VoLTE MO call creation call flow.

VoLTE MO Call Creation Call Flow
VoLTE MO 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.
2UE sends the requested bearer resource modification information to MME.
2aMME sends the bearer resource command to S-GW.
2bS-GW sends the bearer resource command to SMF+PGW-C.
3SMF+PGW-C sends the NPCF SM policy control update request to PCF.
4PCF sends the NPCF SM Policy control update response back to SMF+PGW-C.
5UE initiates SIP signaling toward P-CSCF (AF).
5aP-CSCF sends NPCF Policy Authorization Update message to PCF through CHF.
6PCF sends the NPCF SM policy control update notify request to SMF+PGW-C.
6aSMF+PGW-C sends the NPCF SM Policy control update notify response back to PCF.
7SMF 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.
8CHF 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.
9SMF 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.
10UPF 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.
11SMF+PGW-C sends the GTPv2 create bearer request to S-GW.
12S-GW sends the GTPv2 create bearer request to MME.
13MME sends the bearer setup request and session management request to eNodeB.
14RRC connection reconfiguration starts between UE and eNodeB.
15The eNodeB sends the bearer setup response to MME.
16UE initiates a direct transfer toward eNodeB.
17eNodeB sends the session management response to MME.
18MME sends the GTPv2 create bearer response to S-GW.
19S-GW sends the GTPv2 create bearer response to SMF+PGW-C.
20SMF+PGW-C sends the N4 session modification request or response to UPF+PGW-U.
21SMF+PGW-C sends the NPCF SM policy control update request to PCF.
22PCF sends the NPCF SM policy control update response back to SMF+PGW-C.
23PCF sends the NPCF policy authorization notify request to P-CSCF (AF).
24Establishes SIP-signaling and voice call between end-users through UE and P-CSCF (AF).
Note
  • The PCC rules that the PCF provides are mapped to TFTs for the new dedicated bearer. The associated QoS is mapped to 4G QoS.

  • The NCHF Converged Charging Update service procedures replace all the Gy and Gz interface messages.

  • The User Plane resources for dedicated bearers are added through the N4 Session Modification procedure towards the UPF. PDRs, QERs, and FARs are added for the SDF filters for the new dedicated bearer.

  • SMF+PGW-C saves the EBI for the dedicated bearer that is received in the create bearer response.