Patent ID: 8792350

Claim:
A network relay system comprising: a first relay device and a second relay device, wherein the first relay device comprises: a first port, that inputs and outputs data packets, the first port being connected to the second relay device, wherein the input data packets are received from source terminals; a detector that detects a congested state of traffic of data packets to be transferred from the first port to the second relay device, the detector detecting the congested state by detecting that a length of a queue in which a data packet to be output from the first port is temporarily stored exceeds a specified first threshold, and after the congested state is detected, detecting that the congested state is resolved by detecting that the length of the queue becomes smaller than a specified second threshold that is shorter than the specified first threshold; and a first transmitter that transmits a detection notification indicating a detection of the congested state to the second relay device when the congested state is detected, the first transmitter terminating transmission of the detection notification when the detector detects that the congested state is resolved, and the second relay device comprises: a plurality of ports that input and output data packets; a storage which represents a relationship between media access control addresses (MAC addresses) of the source terminals that are the source of the input data packets to the second relay device and ports of the second relay device through which the data packets are input, and further represents destinations to which the input data packets are to be transferred and identification information of ports that outputs the input data packets are associated with each other for each of the plurality of ports; a receiver that receives the detection notification from the first relay device; and a second transmitter that obtains, from the storage, destinations associated with a respective port connected to the first relay device out of the plurality of ports when the detection notification is received, and that transmits a notification of congestion including the MAC addresses of the source terminals in response to the received detection notification to the obtained destinations by using the associated port which is also a port to which the detection notification is input through the first relay device that further forwards the notification of congestion to the source terminals, the source terminals being associated with the destinations.