Size of senders window ?

Question

 

Consider a TCP connection using the slow start congestion control scheme with an initial threshold value of 64 kB and a Maximum Segment Size (MSS) of 2 kB. The receiver’s advertised window is initially 32 kB. The first transmission attempt is numbered 0, and all transmission attempts are successful except for the timeouts on attempt number 4. Which of the following represents size of sender’s congestion window at attempt number 10?

Comments

2,4,8,16,32 now timeout (thrshld=16) again 2,4,8,16(reached thrshld)17,18

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As far as I know, The sender's window size = min(Congestion window, Receiver's advertised window)

Here, Receiver's advertised window is 32 KB, so obviously, Threshold = 16 KB (8 MSS)

So, how are we sending till 32 KB (16 MSS) in slow start phase only ?

@Arjun sir, could you please clarify my doubt. Thankyou.

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MSS=2Kb not 1Kb

Answer 1

1mss -2KB- attempt 0

2mss - 4 KB-attempt 1

4mss -8KB- attempt 2

8mss -16KB attempt 3

16mss - 32KB-attempt 4 (time out new thresold = 8mss or 16KB)

1mss - 2KB-attempt 5

2mss -4KB -attempt 6

4mss -8KB- attempt 7

8mss - 16KB-attempt 8(REACHED THRESHOLD VALUE SO START LINEAR INCREASE)

9mss -18KB- attempt 9

10mss - 20KB-attempt 10 (At 10th attempt sender window size is of 10ms=20KB)

 

Comments

They are asking about 10th attempt not 10th transmission no. So I think it should be 18KB.

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no, it will be 20KB ;

 The first transmission attempt is numbered 0

so, 10th attempt means 11th transmission

Answer 2

The answer should be 20Kb

Attempt number              Window Size

0                                     1

1                                    2

2                                     4

3                                    8

4                                    16 ( slow start threshold set to 8 )

5                                     1

6                                     2

7                                     4

8                                      8  ( slow start ends)

9                                     9  (linear increase starts)

10                                    10

 

10MSS =   20Kb

Answer 3

Th=64

MSS=2

2 4 8 16 32 64 **(TO,New Th=32) 2 4 8 16 ³² 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64

so ans 16 kB.

Answer 4

answer should be 30