Network system, network terminal, and method for specifying location of failure in network system

A network system in which at least one loop comprising plural nodes loop-connected by means of a transmission line and at least one loop comprising either a single node or the plural nodes loop-connected by means of the transmission line are directly connected to a common transmission line having at least one input port and at least one output port in which a signal input through one input port branches and the resulting signals are output from all output ports, a node of the plural nodes included in one of the loops serves as a master node, nodes other than the node serving as the master node serve as slave nodes, nodes present on lower-most streams in respective loops become lower-most stream nodes in the respective loops, and a specific signal pattern is transmitted at regular time intervals within a fixed time period, wherein

• each node includes signal monitoring means for detecting existence/non-existence of a signal transmitted on the transmission line and outputting a monitor signal, and detection means for detecting receiving of the specific signal pattern and outputting a signal indicating undetection when the specific signal pattern has not been received during more than a fixed time period, and detects occurrence of a failure in the network system according to the signal indicating undetection,
• each the nodes which have detected occurrence of the failure, notifies an adjacent node of occurrence of the failure by using a notification signal,
• respective nodes in the network system detect occurrence of the failure according to the notification signal,
• each of the nodes which have detected occurrence of the failure in the respective loops, transmits a specifying signal to an adjacent node,
• a node which has detected that it does not receive the specifying signal, according to the monitor signal output from the signal monitoring means, decides that the failure has occurred on an upper stream of itself, and transmits information of a location of the failure in a corresponding loop in the form of an identifier packet including information which identifies itself, to the corresponding lower-most stream node,
• each of plural lower-most stream nodes decides the location of the failure in a corresponding loop according to the identifier packet and the monitor signal, and transmits information of a decided location of the failure in the corresponding loop in the form of the identification packet such that identifier packets from respective lower-most steam nodes do not collide, and
• each of the nodes which have detected occurrence of the failure and the nodes which have detected occurrence of the failure according the notification signal, specifies the location of the failure in the network system, according to the monitor signal and the identifier packets.

A network terminal used in a network system in which plural nodes are connected by means of a transmission line, and a specific signal pattern is transmitted to the transmission line at regular time intervals within a first fixed time period, said terminal comprising:

• receiving means which receives a signal transmitted on the transmission line;
• signal monitoring means which detects existence/non-existence of the signal transmitted on the transmission and outputs a monitor signal;
• detection means which detects receiving of the specific signal pattern transmitted on the transmission line, and outputs a signal indicating undetection when the specific signal pattern is not received during more than a second fixed time period;
• control means which detects occurrence of the failure according to the signal indicating undetection which is output from the detection means, outputs a notification signal and a specifying signal upon detecting occurrence of the failure, outputs an identifier packet when deciding that the failure has occurred on an upper stream of a corresponding node by detecting that the specifying signal is not received, and decides a location of the failure from the monitor signal and a received identifier packet;
• transmission means which outputs signals toward the transmission line;
• and
• storage means which stores a node identifier for identifying a corresponding node.

A method for specifying a location of a failure in a network system in which at least one loop comprising plural nodes loop-connected by means of a transmission line and at least one loop comprising either a single node or the plural nodes loop-connected by means of the transmission line are directly connected to a common transmission line having at least one input port and at least one output port, in which a signal input through one input port branches and the resulting signals are output from all output ports, a node included in one of the loops serves as a master node, nodes other than the node serving as the master node serve as slave nodes, nodes present on lower-most streams in respective loops become lower-most stream nodes in the respective loops, and a specific signal pattern is transmitted at regular time intervals within a fixed time period, wherein

• nodes detect occurrence of the failure in the network system by detecting that they have not received the specific signal pattern during more than a fixed time period,
• each of the nodes which have detected occurrence of the failure, outputs a notification signal to notify an adjacent node that the failure has occurred,
• respective nodes in the network system detect occurrence of the failure according to the notification signal,
• each of the nodes which have detected occurrence of the failure in the respective loops, outputs a specifying signal to an adjacent node,
• a node decides that the failure has occurred on an upper stream of itself by detecting that it does not receive the specifying signal, and outputs information of the location of the failure in a corresponding loop in the form of an identifier packet including information for identifying itself, to the corresponding lower-most stream node, and
• each of plural lower-most stream nodes, decides the location of the failure in a corresponding loop, from the identifier packet and the monitor signal, and transmits information of a decided location of the failure in the form of an identifier packet such that identifier packets transmitted from the plural lower-most stream nodes do not collide, and
• each of the nodes which have detected occurrence of the failure and the nodes which have detected occurrence of the failure according the notification signal, specifies the location of the failure in the network system, according to the monitor signal and the identifier packets.