<p>A network system comprises a monitored node (300) connected to a network (50) for isochronal transfer and asynchronous transfer and having a utility function and a monitoring node (200) for monitoring the operating state of the monitored node. The monitored node periodically transmits a command (KA) indicating the normal operating state through an isochronal channel of the network to the monitoring node. When the monitoring node comes not to receive the command indicating the normal operating state from the monitored node, the monitoring node transmits to the monitored node a command that the monitored node executes an abnormality countermeasure processing such as reset, power-off, or cut-off of the network connection.</p>
