| 摘要 |
PROBLEM TO BE SOLVED: To easily and surely detect restoration from a broken line state of a network in a network system where loopback is conducted. SOLUTION: In the case of detecting a broken line in a branch line side network, each contact of a relay control section 12 is switched to conduct loopback, a beacon frame generating circuit 14 generates a beacon frame not giving effect on a state of each station and transmits it to the branch line side network. A beacon frame comparator 23 monitors whether or not the beacon frame is received from the branch line side network. When the beacon frame is received from the branch line side network, it is discriminated that the broken line is restored and each contact of the relay control section 12 is switched to release the loopback.
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