Optimization of the handover can not be trusted to non-3gpp network

The present invention, in executing IP session of the mobile node via the packet data network gateway, to a method of ensuring the continuity of the IP session during handover of the mobile node to the non-3GPP network. For non-3GPP network, discovers the security gateway, then the tunnel corresponding to the ePDG for forming a new data path, i.e. the security tunnel between the mobile node and the security gateway, a packet data network gateway and the security gateway it is necessary to establish the IP tunnel between. To prepare a handover to non-3GPP access may be implemented, although establishes two tunnels in advance, until their use is actually required to maintain in an inactive state. Therefore, when handover to non-3GPP network, by the active state of the tunnel that is already established, it is possible to continue the IP session without significant interruption.