Routing rule updating method and user device for moving specific ip flow to specific access

One disclosure of the present specification provides a routing rule updating method for moving a specific IP flow to a specific access. The updating method can include a step of receiving a routing rule updating request message for network based IP flow mobility (NBIFOM) initiated by a network, wherein the routing rule updating request message can include: a routing rule for moving a specific IP flow of a user device from a first access to a second access; and a timer value calculated by the network. The timer value can be calculated by the network on the basis of at least one of subscriber information, load information and statistical information. The updating method can include the steps of: transmitting an acceptance message to the network in response to the routing rule updating request; and operating a timer according to the timer value.