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Answer 1

Initially, the connection is in the Slow Start phase because the cwnd (1 MSS) is less than the ssthresh ( 16 MSS). In this phase, the cwnd doubles after each successful transmission.

• Initial: cwnd =1, ssthresh=16
   
• After Tx 1: cwnd $=1^* 2=2$
   
• After Tx 2: cwnd $=2 * 2=4$
   
• After Tx 3: cwnd $=4 * 2=8$
   
• After Tx 4: cwnd $=8^* 2=16$. At this point, cwnd reaches ssthresh, so the connection switches to the Congestion Avoidance phase for the next transmission.

In Congestion Avoidance, cwnd increases by just 1 MSS per transmission (additively).

• After Tx 5: cwnd $=16+1=17$

A timeout occurs during the 6th transmission. This is a severe event, triggering the following actions:

1. The ssthresh is set to half of the current cwnd .

• New ssthresh $=$ floor $(17 / 2)=8$ MSS.

2. The cwnd is reset to 1 MSS.

3. The connection goes back into the Slow Start phase.

Now, we trace the cwnd from its reset state.

• State after timeout: cwnd $=1$, ssthresh $=8$

Slow Start Phase (again):

• After Tx 7: cwnd $=1^* 2=2$
   
• After Tx 8: cwnd $=2 * 2=4$
   
• After Tx 9: cwnd $=4{ }^{\star} 2=8$. The cwnd has reached the new ssthresh value. The connection again switches to Congestion Avoidance.

Congestion Avoidance Phase (again):

• After Tx 10: cwnd $=8+1=9$
   
• After Tx 11: cwnd $=9+1=10$
   
• After Tx 12: cwnd $=10+1=11$ MSS

Thus, at the end of the twelfth transmission, the congestion window size is $11$ MSS.

Answer 2

Here is the Explanation