A server creates a communication path table indicating a communication path for packet data, based on connection information reported by a parent device and a relay device, and distributes the created communication path table to the parent device, the relay device and a child device. The child device transmits the packet data to a relay device indicated in the communication path table, based on the distributed communication path table. The relay device transfers the packet data transmitted from the child device, to a relay device or a parent device indicated in the communication path table, based on the distributed communication path table.