Patent attributes
A network-based solution of supporting IP multimedia subsystem (IMS) call setup in a next generation system (5GS) is proposed. During an attach or registration area update procedure, a serving base station sends an indication to a UE indicating whether IMS voice over PS session is supported or not. Upon receipt of the indication that IMS VoPS is supported, the UE triggers an IMS registration procedure. However, when an MO/MT call happens, the network determines that the UE may be in conditions where voice service is not supported because the network is not able to provide a successful IMS VoPS over the current serving cell connected to 5G core network. The network then triggers a RAT change or a EPS fallback procedure such that the UE is handover to a target cell that supports IMS VoPS.
