Hi, so, let's keep it simple as we are not really considering the details of the protocol's implementation.
Let's assume the ssthresh was 3 instead of 4.
Initially, the window size is 1 and Alice sends one segment. Alice gets back an ack, sets the window to 2, and sends 2 segments.
Bob sends back two acks. Upon receiving the first one, Alice sets the window to 3 and because it is equal to ssthresh she enters congestion avoidance. When she receives the second ack, she will increase the window by less than 1 MSS (congestion avoidance).
Therefore, the window would not be 4 at t=1s.
Note: check discord if you haven't, a lot more Q&A action there :)
Let's assume the ssthresh was 3 instead of 4.
Initially, the window size is 1 and Alice sends one segment. Alice gets back an ack, sets the window to 2, and sends 2 segments.
Bob sends back two acks. Upon receiving the first one, Alice sets the window to 3 and because it is equal to ssthresh she enters congestion avoidance. When she receives the second ack, she will increase the window by less than 1 MSS (congestion avoidance).
Therefore, the window would not be 4 at t=1s.
Note: check discord if you haven't, a lot more Q&A action there :)
