A user agent (UA), core network (CN) device, and method for a circuit switched (CS) fallback service in an evolved packet system (EPS). In one embodiment, the UA or CN includes a protocol layer having a non-access stratum (NAS). A processor of the UA or CN is configured to promote the NAS to process an EXTENDED SERVICE REQUEST having a service type with a decode value. The decode value identifies an EPS-defined radio resource control (RRC) establishment cause (EC).