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2 , 4, 8, 16 , 17 ,18 , 1 , 2 ,4 ,8

At end of ninth transmission congestion window size is 8mss
edited

2 first

4 second

8  3rd

16   4th

17   5th

18(new threshod =9)  time out occure here  6th

1

2

4    9th  Transmission

8  ( window size after 9th transmission)

(There is an ambiguity here if the window size will be 1 MSS or 2 MSS as given in the question )

1. Start MSS=2 MSS
2. Threshold=16 MSS
3. TO= at 6th  transmission

At the congestion detection phase on timeout, the TO timer expires before receiving the ACK for a segment.in this case, the sender reacts as:

• Setting the slow start threshold value = $SST_{new}=C_{win}/2$
• decreasing the cw size to 1MSS.
• resuming the slow start algorithm.

 t=1 2 MSS t=2 4 MSS t=3 8 MSS t=4 16 MSS (Threshold) t=5 17 MSS t=6 18 MSS(Timeout) $SST_{new} =18/2=9$ t=7 2 MSS t=8 4 MSS t=9 8 MSS

At 9th transmission, the congestion window size should be 8MSS.

Note: at $t=1,2,3$ is the slow start phase, $t=4$ is the threshold, and $t=5$ is the congestion avoidance phase.

8 mss  is the correct answer
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