Patent ID: 8713353

Claim:
A communication system comprising: a client unit; a first node configured to perform processing in response to a request from said client unit; a second node configured to perform the processing in place of said first node when a fault has occurred in said first node; communication units configured to configure network routes among said client unit, said first node and said second node; and a determining section provided onto a first network route of said network routes and configured to determine whether a signal which is transmitted from said first node to said second node through the first network route has been disconnected, wherein each of said communication units comprises: a switching section configured to perform a switching operation between a second network route of said network routes used when said client unit and said first node perform data communication and a third network route of said network routes used when said client unit and said second node perform data communication, based on the determination result of said determining section, wherein a communication unit of the communication units comprises a communication control section which includes the determining section and the switching section, wherein the communication unit further comprises a plurality of communication ports, and a flow table which is accessible by the communication control section and includes information for controlling a flow of data from the communication unit to a data transfer destination, wherein the information in the flow table includes: flow information which specifies identification information of the flow of data; output port information which specifies a communication port from which the data should be outputted; and operation information at disconnection which shows an operation to be performed when the flow of data has been disconnected, wherein the signal transmitted from the first node to the second node comprises a heartbeat signal which is transmitted from the first node to the second node via the communication unit, wherein if the heartbeat signal is not received by the communication unit for a predetermined period, then the communication unit determines that the flow has been disconnected, and refers to the flow table and performs an operation based on the operation information at disconnection corresponding to the flow, and wherein the communication units comprise an other communication unit which is not on a route for the heartbeat signal being transmitted from the first node to the second node, and a flow from the other communication unit is switched by the communication unit to the second node.