Communication system, communication method, node, and node program

In an RPR network (20), when a terminal under an RPR node (240) not belonging to an interlink connection node group transmits an Ethernet frame to a terminal under an RPR node belonging to another RPR network (10), the RPR node (240) transmits an RPR frame storing the Ethernet frame to one of interlink connection nodes (200, 230, 270) belonging to the same network. The interlink connection node receiving the RPR frame then extracts the Ethernet frame from the RPR frame and transfers it to the another RPR network (10).