TCP newreno congestion control Window Scaling simulate

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Hello, I am trying to understand how congestion control works by using the ipfw to simulate the network condition.

the condition are as follows. bandwidth = 4Mbps/s delay = 100ms newreno, packet loss rate = default

You can see that according to the graph#1, according to my understand, if there is a timeout, the window size will drop to 1.

but according to the dump I get from the wireshark window scaling, at time 1.5 instead of timing out, it seems to sudden drop to zero, then there is a steep increase, then another drop. What does it mean? Is it a fast recovery?

And also the marked part in color according to my understanding is (red = Slow Start, Blue = Congestion Avoidance, Green = Fast Recovery)