When 3 Duplicate Acks arrive TCP halves its congestion window, but when only 1 or 2 Duplicate Acks arrives what does TCP do ? Does it increase the congestion window like any other non duplicate Ack ?
That reaction to 3 duplicate acks is in TCP Reno. When it receives 1 or 2 duplicate ACK's it shouldn't do anything. The increase of the congestion window occurs after original ACK's are received because they indicate the communication is good and TCP is tries to get to the maximum possible throughput.
来源：https://stackoverflow.com/questions/32954156/does-tcp-increase-its-congestion-window-when-dup-acks-arrive