Ralf Kreher explained EPS Fallback mechanism in his post earlier, which is still quite popular. This post contains couple of videos that also explain this procedure.
The first is a very short and simple tutorial from Mpirical, embedded below:
The second is a slightly technical presentation explaining how 5G system can redirect the 5G VoNR capable device to the 4G system to continue for IMS based VoLTE voice call.
Related Posts:
- The 3G4G Blog: EPS Fallback in 5G Standalone Deployments
- The 3G4G Blog: IP Multimedia Subsystem (IMS) Support for Service Based Architecture (SBA)
- The 3G4G Blog: Two Types of SMS in 5G
- The 3G4G Blog: 5G User Plane Redundancy
- The 3G4G Blog: Network Slicing using User Equipment Route Selection Policy (URSP)
- The 3G4G Blog: Voice over New Radio (VoNR) Establishment and Release between NG RAN and 5G Core
- The 3G4G Blog: A quick starter on 4G voice (for beginners)