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

At end of ninth transmission congestion window size is 8mss

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2 first

4 second 

8  3^rd

16   4^th

17   5^th

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

1

2

4    9^th  Transmission

8  ( window size after 9^th transmission)

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

Answer 1

1. Start MSS=2 MSS
2. Threshold=16 MSS
3. TO= at 6^th  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 9^th 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.

Answer 2

8 mss  is the correct answer