A communication system for a plurality of devices performing communications through a network is provided. The communication system includes a transmitter/receiver, a reception status detector, and a recorder. The transmitter/receiver is included in each of the plurality of devices and configured to alternately transmit a data packet with ID information indicating time to another device and receive the data packet from the device periodically in the plurality of devices. The reception status detector is included in each of the plurality of devices and configured to detect whether the data packet is periodically received based on the ID information added to the data packet received from another device. The recorder is configured to record a result detected by the reception status detector in each of the plurality of devices.