VoNR call setup — Mobile Terminated (MT)

MT Call — The Paging Challenge

A Mobile Terminated VoNR call must handle the case where the UE may be idle in CM-IDLE state. The incoming SIP INVITE arrives at the S-CSCF via the I-CSCF. The S-CSCF evaluates iFC and invokes TAS to check call forwarding on busy or no reply conditions. It then sends the INVITE to the P-CSCF. If the UE is in idle mode, the P-CSCF cannot reach it directly. The AMF must initiate Paging via the N1/N2 interface, and the gNB broadcasts a paging message. The UE wakes up and performs a Service Request to re-establish the signaling connection.