Patent ID: 6967969

Claim:
A multiplex communication system comprising: a plurality of networks each of which includes a plurality of nodes; a data relay unit for relaying data frames among the networks; and communication lines connecting the respective networks and the data relay unit, wherein each of the networks shifts into a sleep mode if an event does not occur for a predetermined time therein, wherein each of the nodes is for requesting a predetermined response from the data relay unit upon occurrence of an event in the node and is further for sending a notice of the occurrence of the event upon receiving the predetermined response from the data relay unit, and wherein the data relay unit comprises: activation request sending means for sending to at least a destination network, which includes a destination node for receiving the notice of the occurrence of the event, an activation request for requesting the destination network to be activated when the data relay unit receives a node request for the predetermined response; activation state determination means for determining whether the destination network is activated; and activation, state answering means for sending, when the destination network is activated the predetermined response to a sender network, the sender network including the node that sends the node request for the predetermined response.