| 摘要 |
A first unit 2A and a second unit 2B manage a plurality of devices (a first device 8a, 8b), respectively. In addition, the first and second units 2A, 2B repeat to transmit a keep-alive packet and to confirm a response each other, and thus detect each other's malfunction. When the second unit 2B malfunctions, the first unit 2A detects the malfunction of the second unit 2B and transmits a connection command to the connection unit 5. The connection unit 5 connects a lower net Nia and a lower net Nib when receiving the connection command. Then, the first unit 2A communicates with the first device 8a as heretofore, and further communicates with a second device 8b via the connection unit 5. Thus, even if a master unit malfunctions, the device management system can maintain to manage without stopping a management of a slave unit which had been managed by the master unit until then.
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