To ensure smooth, continuous communication sessions even in transit in a packet-switched data communications network.

Each of a plurality of lower interfaces, when its associated access mechanism is in an active state, can obtain connection to a packet-switched data communications network 150 using its home address HoA.1 or its care-of-address CoA.BS1. When the lower interface 101-a loses its connection obtained using the care-of-address CoA.BS1, a multiple access decision unit instructs a mobility support unit to set up the home-address HoA.1 and either of the home-address HoA.2 or the care-of-address CoA.BS2 of the other lower interface 101-b.