A method by a terminal configured to use a circuit switched fall back, CSFB, in a mobile communication system, comprising: initiating a call based on an IMS voice over PS, IMS VoPS; transmitting a tracking area update, TAU, request message in a tracking area, wherein the TAU request message includes network update information of combined tracking area and location area updating; receiving a TAU accept message including network support information indicating on whether a network supports the IMS VoPS and network update result information on whether tracking area updating for evolved packet system, EPS, service and location area updating for non-EPS service are successful; maintaining, until an established bearer associated with the call is released, a context of the bearer associated with the call based on the network support information; identifying that the bearer associated with the call is released; and attempting to select a GSM edge radio access network, GERAN, or a UMTS terrestrial radio access network, UTRAN, and disabling an evolved UMTS terrestrial radio access network, E-UTRAN, function, based on the network support information and the network update result information, in case that a number of TAU attempt is equal to a predetermined value, wherein the number of the TAU attempt is a number of the transmission of TAU request message, wherein the transmission of the TAU request message is triggered again, in case that the TAU accept message is received in response to the TAU request message and includes the network support information indicating that the IMS VoPS is not supported by the network and the network update result information indicating TA updated that the tracking area updating is successful and the location area updating is not successful. initiating a call based on an IMS voice over PS, IMS VoPS; transmitting a tracking area update, TAU, request message in a tracking area, wherein the TAU request message includes network update information of combined tracking area and location area updating; receiving a TAU accept message including network support information indicating on whether a network supports the IMS VoPS and network update result information on whether tracking area updating for evolved packet system, EPS, service and location area updating for non-EPS service are successful; maintaining, until an established bearer associated with the call is released, a context of the bearer associated with the call based on the network support information; identifying that the bearer associated with the call is released; and attempting to select a GSM edge radio access network, GERAN, or a UMTS terrestrial radio access network, UTRAN, and disabling an evolved UMTS terrestrial radio access network, E-UTRAN, function, based on the network support information and the network update result information, in case that a number of TAU attempt is equal to a predetermined value, wherein the number of the TAU attempt is a number of the transmission of TAU request message, wherein the transmission of the TAU request message is triggered again, in case that the TAU accept message is received in response to the TAU request message and includes the network support information indicating that the IMS VoPS is not supported by the network and the network update result information indicating TA updated that the tracking area updating is successful and the location area updating is not successful. <EOS>