Initial or Mobility Registration—IMS VoNR Support Procedure Call Flow
This section describes the Initial or Mobility Registration—IMS VoNR Support Procedure call flow.

Step |
Description |
---|---|
1 |
The UE or gNB sends a Registration Request message to the new AMF instance. During the UE registration (initial, mobility update, and AMF change or EPC to 5GC handover) procedure, after the operator policy and Call Control Profiles are associated with the subscriber context, the AMF checks the following:
|
2 |
The UE or the gNB and the AMF completes the authentication procedure. |
3 |
The new AMF and the old AMF process the inter-AMF Context Transfer procedure. |
4 |
The new AMF and the old AMF complete the N26 identification procedure. If the UE Radio Capability matching is required and the AMF has not received or discovered it yet, the AMF starts the UE Radio Capability check procedure towards gNB. The gNB provides the IMS VoPS capability information to AMF and confirms if it is supported or matching. The AMF considers the UE to provide the IMS VoPS services indicator as supported. AMF checks if the IMS VoPS service is configured to be supported or enabled under the current TA of the subscriber and its support in TAI's list object under TAI DB. If the criteria is matched, AMF considers the IMS VoPS support for the subscriber to be supported for current TA. The AMF informs UDM about the IMS VoPS support for the subscriber in all the TAs that AMF serves or in the 3GPP Access Registration procedure to UDM. Based on CCP configuration, if the subscriber is eligible or capable of the IMS VoPS support, AMF provides the imsVoPS parameter to UDM in 3GPP Access Registration message as HOMOGENEOUS_SUPPORT. This parameter indicates the subscriber about the AMF level support of IMS VoPS service and the TA level support. After UDM receives this information, if the IMS service sent to the subscriber (For example, local configuration change) is modified, the AMF updates UDM using the 3GPP Access Registration Modification procedure. |
5 |
The AMF indicates IMS VoPS service support for the subscriber for current registration area (TA) in Registration Accept message in IMSVoPS-3GPP indicator under 5GS network feature support information element. The UE or the gNB and new AMF processes the Initial Context Setup Downlink NAS TPT. |
6 |
The gNB sends the Initial Context Setup Response to the new AMF. |
7 |
The UE or gNB sends the Registration Complete Uplink NAS TPT to the new AMF. |
8 |
The new AMF sends the UE Context Release Command to the gNB. |
9 |
The gNB sends the UE Context Release Complete to the new AMF. |