A gateway configured to relay traffic between a core network and a base station, the gateway comprising: first communication means for communicating with the base station through a public network; second communication means for communicating with a server capable of communicating with the core network; and control means for controlling the first and second communication means (111, 112), wherein the control means is configured to: acquire, when first identification information temporarily assigned to one user equipment requesting to camp on the base station is received from the base station, second identification information permanently assigned to the one user equipment and associated with the first identification information from the core network through the server; and identify the one user equipment by using the second identification information, characterized in that the control means is configured to: start a timer that is set to a time period that is shorter than a cycle for the one user equipment to transmit a location updating request, after transmitting an instruction to the base station for releasing the connection between the base station and the gateway; acquire, when the time period has elapsed, from the server third identification information of a different gateway accommodating a base station on which the one user equipment camps; and determine, when the third identification information does not match identification information assigned to the gateway, that the one user equipment camps on a different base station. first communication means for communicating with the base station through a public network; second communication means for communicating with a server capable of communicating with the core network; and control means for controlling the first and second communication means (111, 112), wherein the control means is configured to: acquire, when first identification information temporarily assigned to one user equipment requesting to camp on the base station is received from the base station, second identification information permanently assigned to the one user equipment and associated with the first identification information from the core network through the server; and identify the one user equipment by using the second identification information, characterized in that the control means is configured to: start a timer that is set to a time period that is shorter than a cycle for the one user equipment to transmit a location updating request, after transmitting an instruction to the base station for releasing the connection between the base station and the gateway; acquire, when the time period has elapsed, from the server third identification information of a different gateway accommodating a base station on which the one user equipment camps; and determine, when the third identification information does not match identification information assigned to the gateway, that the one user equipment camps on a different base station. acquire, when first identification information temporarily assigned to one user equipment requesting to camp on the base station is received from the base station, second identification information permanently assigned to the one user equipment and associated with the first identification information from the core network through the server; and identify the one user equipment by using the second identification information, characterized in that the control means is configured to: start a timer that is set to a time period that is shorter than a cycle for the one user equipment to transmit a location updating request, after transmitting an instruction to the base station for releasing the connection between the base station and the gateway; acquire, when the time period has elapsed, from the server third identification information of a different gateway accommodating a base station on which the one user equipment camps; and determine, when the third identification information does not match identification information assigned to the gateway, that the one user equipment camps on a different base station. start a timer that is set to a time period that is shorter than a cycle for the one user equipment to transmit a location updating request, after transmitting an instruction to the base station for releasing the connection between the base station and the gateway; acquire, when the time period has elapsed, from the server third identification information of a different gateway accommodating a base station on which the one user equipment camps; and determine, when the third identification information does not match identification information assigned to the gateway, that the one user equipment camps on a different base station.