Relay device, display device, connection information transmission method, and network configuration display method

A connection information transmission method for a relay device connected to two networks of a plurality of layered networks and connected to a first communication device directly under a first lower layer network that is on a lower level of the two networks,

• the relay device comprising
• a memory to store connection information including model identification information associated with each of a second communication device and the first communication device and information on the number of connected second communication devices or on a memory area assigned to each of the first communication device and the second communication device, the second communication device being connected to a lower side through a second lower layer network that is situated lower than the first lower layer network, the connection information being arranged in a format capable of specifying a network layer to which each communication device is connected,
• the method comprising:
• an acquisition step of connection information acquisition circuitry, in a case where the first communication device is another relay device, acquiring first connection information from the other relay device, the first connection information being connection information stored in the other relay device;
• a generation step of connection information generation circuitry, in a case where second connection information that is the connection information storable in the memory is not stored in the memory and the memory stores, for the first communication device, network information including the model identification information and the information on the memory area, generating the second connection information using the network information and the first connection information, and storing the generated second connection information in the memory;
• and
• a response step of connection information response circuitry, in response to a request of reading the second connection information from a third communication device connected to an upper side through an upper layer network that is situated higher than the second lower layer network, transmitting the second connection information stored in the memory to the third communication device.