System and method for circuit switched fallback in IMS centralized services

摘要

A method of performing CSFB in an IMS comprises receiving, at a TAS, an incoming voice call for a UE attached to an EPS; paging the UE by the first ICS GW; receiving, by a second ICS GW associated with a second CS RAN currently connected to the UE, a Location Update message from the UE, the Location Update message containing a first CSFB indicator; transmitting, by the second ICS GW, a Registration message to the TAS, the Registration message containing a second CSFB indicator in response to the first CSFB indicator in the Location Update message; transmitting, by the TAS, a Cancel message to the first ICS GW; and transmitting, by the TAS, an Invite message to the second ICS GW to complete the voice call with the UE.