The present invention connects a ring topology Ethernet network to other networks of various shapes. To that end, a first ring topology network configured in a ring shape has three or more expandable nodes (each have three or more Ethernet ports), and is connected to other networks through Ethernet ports that are not used for the formation of the first ring topology network among Ethernet ports of the expandable node. Thus, it is possible to add equipment without changing a ring topology network previously built and it is possible to integrate and manage networks of various shapes into a single network.