A relay unit includes a main-system switch and a sub-system switch that are connected to each other via an inter-system line, that are connected to a main-system line and a sub-system line, and that relays a frame; and control sections that control a relay operation of the main-system switch and the sub-system switch. The float preferably has a cylindrical-shaped through-bore. The programming strategy provides for the setting of the phase change material once for each time a multiple of a potential factor is present in the number to be factored. Upon receiving this multicast message, the client starts sending data to and receiving data from the receiver within the server.