Patent ID: 8024625

Claim:
A network system comprising: a network; and a plurality of nodes connected to the network to transmit/receive data frames, wherein each of the plurality of nodes comprises: a start-up signal transmitting unit which transmits a start-up signal on the basis of an initial data frame after a respective node is reset and restored; a reception error count unit which counts, from every communication partner node, a reception error frequency, which is measurement indicating periods during which data frames could not be received from respective communication partner nodes; a monitoring result returning unit which, when a start-up signal is received from another node, returns a count result to said respective node indicating the reception error frequency of said respective node; and a self-diagnosing unit which makes a self-diagnosis based on the count result which is returned from other nodes, and wherein the self-diagnosing unit of the respective node judges that the respective node is abnormal by comparing the count result obtained from the other nodes to a threshold.