UE initiates an IMS voice call, it will be released to 4G RAN by gNB with RRC Release with Redirection or with Inter System Handover. When the UE attaches the 4G RAN, the IMS voice call setup procedure for VoLTE continues. In this case, both RATs are utilizing the same 5GC. Wi-Fi calling In many VoLTE networks, Wi-Fi calling is already available. This is also called Voice over Wi-Fi (VoWi-Fi). Therefore, there is no reason for the service providers to deploy Wi-Fi calling together with their VoNR services by utilizing the common IMS. All traffic is anchored in the UPF regardless of the RAN that the UE is using. This RAN can be 5G NR or Wi-Fi. In the VoNR case, the UE utilizes the PDU session and the appropriate QoS flows for the transmission of SIP signaling and RTP-based voice packets toward the UPF. However, the Wi-Fi network, which includes the Access Point (AP), must connect to a Non-3GPP Interworking Function (N3IWF) for security purposes. N3IWF provides direct connectivity to the UPF. Therefore, even though the UE is on a Wi-Fi network, it can still set up VoWi-Fi call connectivity to the common IMS. Similar to VoNR, bearers can carry out SIP signaling and voice packets as appropriate. Voice over New Radio (VoNR) VoWi-Fi N3IWF ((1p) Access Point Figure 8.15 - VoNR and VoWi-Fi In this section, we have analyzed the necessity of interworking between VoNR-capable networks and other legacy networks. We've seen that the necessity of this interworking is due to legacy subscribers, coverage gaps, and utilization of other radio technologies. Summary In summary, we have looked at some of the key concepts and drivers behind VoNR. Circuit-switched networks are slowly being phased out and replaced with voice networks supported by IMS call control. The voice requirements for the 5G system have been defined, SO the standard bodies, specifically the 3GPP, have already been looking at what the 5G system needs to support with respect to voice. There is already a great deal of interest in ultra-high-definition voice services.