Communication device and communication method for communication to a root device

A communication method comprising:

• receiving a first hello packet broadcast from one or more transmitting devices, each first hello packet including, as information, at least an identifier of its respective transmitting device and a hierarchical number indicating a number of hops necessary for the transmitting device to communicate with a root device located at a highest level of a hierarchical structure;
• setting an own-device hierarchical number being a hierarchical number of an own device, to a value obtained by adding one to a smallest hierarchical number in the one or more transmitting devices;
• registering and storing, as a parent device, each transmitting device having a hierarchical number smaller than the own-device hierarchical number by one, out of the one or more transmitting devices;
• registering and storing, as a sibling device, each transmitting device having a same hierarchical number as the own-device hierarchical number, out of the one or more transmitting devices;
• registering and storing, as a child device, each transmitting device having a hierarchical number larger than the own-device hierarchical number by one or more, out of the one or more transmitting devices;
• transmitting first other-device registration information so as to make the first other-device registration information reach the parent device, the first other-device registration information being information including an indication of having been retained as the parent device;
• transmitting second other-device registration information so as to make the second other-device registration information reach the sibling device, the second other-device registration information being information including an indication of having been retained as the sibling device;
• transmitting third other-device registration information so as to make the third other-device registration information reach the child device, the third other-device registration information being information including an indication of having been retained as the child device;
• when the first other-device registration information, the second other-device registration information, and the third other-device registration information are transmitted from other devices so as to reach the own device, receiving the first other-device registration information, the second other-device registration information, and the third other-device registration information respectively as first own-device registration information, second own-device registration information, and third own-device registration information;
• registering and storing each transmitting device being a source device of the first own-device registration information, as the child device;
• registering and storing each transmitting device being a source device of the second own-device registration information, as the sibling, device;
• registering and storing:
• each transmitting device being a source device of the third own-device registration information, as the parent device;
• broadcasting a second hello packet being a hello packet including, as information, at least an identifier of the own device and the own-device hierarchical number.