CONGESTION CONTROL METHOD

PROBLEM TO BE SOLVED: To appropriately control a transmission packet number corresponding to the actual load conditions of a network by reducing a succeeding congestion window size by a lost data amount calculated from selective response information stored in the confirmation response packet of a reception node by a transmission node at the time of detecting packet loss. SOLUTION: The processing part 6 of the layer 4 of the transmission node 1 sets connection by the communication request of an application processing part 5, sets respective parameter initial values for congestion control and waits for confirmation response ACK packet reception. Then, at the time or receiving an ACK packet provided with the selective response SACK information, the congestion window size is not reduced when the reception sequence number is less than a start transmission sequence number SNO and it is reduced when it is more than the SNO. A packet loss event is detected to the point of time of the reduction, the SNO of new transmission data which are not retransmission data to be transmitted next is stored, the unrequired increase and reduction are prevented and throughput decline prevented.