Patent ID: 9749905
Date: 2017-08-29
CPC Classifications: H04W

Claim:
1. An improved circuit switched fallback (CSFB) method to be performed in a user equipment (UE) operating in a multi-mode network comprising a non-access stratum (NAS), a universal mobile telecommunications system (UMTS) access stratum (AS), a global system for mobile communication (GSM) AS, and an evolved universal terrestrial radio access network (E-UTRAN) AS, the improved CSFB method comprising: determining that the UE is camped in the E-UTRAN AS and is either initiating or receiving a voice call; noting a CSFB call start indication between the NAS and the E-UTRAN AS, wherein the CSFB call start indication triggers an extended service request (ESR) by the UE to all AS in the multi-mode network; determining that a radio resource control (RRC) connection release following the ESR provides no redirection information; and before a timer, initiated at the CSFB call start indication, expires, forcing redirection of the UE from E-UTRAN AS to a second radio access technology (RAT) such that the UE camps at the second RAT and is able to successfully complete the voice call; wherein an inter-RAT redirection fail indication is not transmitted from the UE to the NAS.