How it Works
The serving PLMN AMF sends an indication toward the UE during the registration procedure to indicate whether an IMS voice over PS session is supported in the 3GPP access network. A UE with "IMS voice over PS" voice capability over 3GPP access takes this indication into account when performing voice domain selection. The UE includes extended Protocol Configuration Options (ePCO) IE in "PDU Session Establishment Request" by setting P-CSCF container options in the AMF. Further, the AMF forwards these ePCO IE options in smContextCreate Request towards the SMF. The SMF fetches the P-CSCF addresses based on DNN profile, which maintains IMS-related data. The SMF includes P-CSCF IPv4 and IPv6 address in N1N2Message Transfer towards the AMF as per PDN-Types and requested P-CSCF container values.
Important | The SMF does not include the P-CSCF address if the UE does not set the P-CSCF container options in the ePCO IE. |