A method of moving from a Next Generation System, NGS, to an Evolved Packet System, EPS, by a User Equipment, UE, in a wireless communication system, the method comprising: determining, by the UE, to move to the EPS based on at least one of the UE being out of coverage of the NGS and an instruction of the NGS; and transmitting a Radio Resource Control, RRC, Connection Request and an Attach Request to the EPS, wherein, based on the UE determining to move to the EPS and the UE having an ongoing voice call, the UE maintains the ongoing voice call by performing at least one of: executing Access Class Barring, ACB, using 'ongoing voice call' call type information; or transmitting information related to the ongoing voice call, wherein, a) based on the UE executing ACB, the executing ACB comprises: obtaining a first barring factor for the 'ongoing voice call' call type information; generating a random number and comparing the random number with the first barring factor; and performing a random access based on the random number is greater than the first barring factor, wherein the first barring factor is configured to be smaller than a second barring factor for an 'originating signaling' call type, wherein, b) based on the UE transmitting information related to the ongoing voice call, the method further comprises: receiving an acceptation message in response to the RRC Connection Request based on a highest priority of the UE than other UEs not transmitting the information, wherein the information is for informing that the ongoing voice call is present. determining, by the UE, to move to the EPS based on at least one of the UE being out of coverage of the NGS and an instruction of the NGS; and transmitting a Radio Resource Control, RRC, Connection Request and an Attach Request to the EPS, wherein, based on the UE determining to move to the EPS and the UE having an ongoing voice call, the UE maintains the ongoing voice call by performing at least one of: executing Access Class Barring, ACB, using 'ongoing voice call' call type information; or transmitting information related to the ongoing voice call, wherein, a) based on the UE executing ACB, the executing ACB comprises: obtaining a first barring factor for the 'ongoing voice call' call type information; generating a random number and comparing the random number with the first barring factor; and performing a random access based on the random number is greater than the first barring factor, wherein the first barring factor is configured to be smaller than a second barring factor for an 'originating signaling' call type, obtaining a first barring factor for the 'ongoing voice call' call type information; generating a random number and comparing the random number with the first barring factor; and performing a random access based on the random number is greater than the first barring factor, wherein the first barring factor is configured to be smaller than a second barring factor for an 'originating signaling' call type, wherein, b) based on the UE transmitting information related to the ongoing voice call, the method further comprises: receiving an acceptation message in response to the RRC Connection Request based on a highest priority of the UE than other UEs not transmitting the information, wherein the information is for informing that the ongoing voice call is present. <EOS>