| 摘要 |
There is provided a network monitoring system in which nodes are connected to the LAN as a communication medium using the token passing method and only the node to which the communication right was transferred can acquire the data communication right. The node has a communication right transfer instruction discriminating circuit, provided for each node, for discriminating a communication right transfer instruction sent through the LAN; an LAN monitoring instruction discriminating circuit, provided for each node, for discriminating an LAN monitoring instruction sent through the LAN; and a controller. When one of the nodes discriminates the LAN monitoring instruction from the LAN by the discriminating circuit, controller sets this node into the LAN monitoring mode. When the communication right transfer instruction is discriminated by this node in the LAN monitoring mode, the controller indicates the change of the transmission right transfer destination to the upward node and, thereafter, sends the communication right transfer instruction to the downward node. With this system, even if the operating mode of the node connected to the LAN using the token passing method is changed from the normal operating mode to the LAN monitoring mode, the malfunction such as lost of the token does not occur, so that the network monitoring system with the high reliability can be realized.
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