Patent ID: 8811936

Claim:
A method of handling call origination for a mobile device in a wireless communication system, the mobile device camping on a first cell, the method comprising the steps of: originating a service; establishing a radio resource control (RRC) connection corresponding to the service; receiving a non-access stratum (NAS) message via the RRC connection or a broadcast message from a first network; determining whether the first network supports the service of an IP multimedia subsystem (IMS) domain, according to the NAS message or the broadcast message; performing the service in a circuit switched (CS) domain when the first network does not support the service of the IMS domain; receiving a CS fallback command; transferring the RRC connection from the first network to a second network which provides the service in the CS domain, according to the CS fallback command; and selecting a second cell which provides the service in the CS domain; wherein transferring the RRC connection from the first network to the second network which provides the service in the CS domain, according to the CS fallback command, comprises: transferring the RRC connection through a handover procedure, redirection procedure or a cell changed order procedure, wherein the second network uses other radio access technology (RAT) than the one used in the first network and the handover procedure or the cell changed order procedure is triggered by a “MobilityFromEUTRA” message sent by the first network.