Patent ID: 7864688

Claim:
A communication system for a plurality of devices performing communications through a network, comprising: a transmitter/receiver included in each of the plurality of devices and configured to alternately transmit a data packet to another device and receive the data packet from the device periodically; a reception status detector included in each of the plurality of devices and configured to detect whether the data packet is periodically received and prepare failure information in the case an interruption occurred in the reception of the data packet; and a failed location detector configured to identify which of a first device and second device, caused a communication failure, wherein the identifying includes: (1) a request for information from the first device and the second device on a respective last time a first data packet was received from the other device, (2) when the respective last times of receiving the particular data packet are approximately the same, a request for information from the first device and the second device on the last time each received a second data packet from a third device and a request for information from the third device on the last time a third data packet was received from each of the first device and the second device, and (3) based upon the last times of receiving the second data packets and the last times of receiving the third data packet, determining which of the first device and second device caused the communication failure.