US Patent 9467363 Network system and method of managing topology

In an open flow network, a load of a switch on a secure channel network when a controller maintains and updates a physical topology of the switch in the situation that a network among the switches is in a high delay state. More specifically, the controller sets a flow entry having a rule and an action defined to uniformly control a packet as a flow to each of a plurality of switches. The controller sets to each switch, a circulation flow entry to be deleted when a circulation packet which is mutually transmitted and received among the switches gets not to arrive. Then, when receiving a notice that the circulation flow entry has been deleted, from each switch, the controller detects a failure among the switches.