CSFB

Hello, ADD_Li.
CSFB is when the UE initiates the CS service, and the MME (Mobility Management Entity) instructs the UE to fall back to the target system CS network and then initiate the CS service. The CSFB feature is essentially a session establishment process, that is, the UE has entered the CS network before the CS session is established. During the entire CS call, the UE is always located in the CS network. The CS service includes services such as voice, short message, location, and emergency call. After receiving the CSFB instruction, the eNodeB handles various CS services in a unified manner.
Thanks!