#Applied Course

Question

Assume the scenario of AIMD where the size of the congestion window of a TCP connection is 40KB when a timeout occurs, the initial threshold is 38 KB. The MSS is 2KB. At which transmission after a timeout the sender window reaches 20 KB?

The given answer is 12, I am not getting the question in this line “At which transmission after a timeout the sender window reaches 20 KB?” we need to count from starting or after timeout?

Comments

Break down the question

Assume the scenario of AIMD where the size of the congestion window of a TCP connection is 40KB when a timeout occurs

Here, when $C_{wind} = 40\ KB$ or $20\ MSS$ then time out occurs.

Initial threshold $= 38\ KB$ or $19\ MSS$

Transmission	$C_{wind}$	Threshold
1	1	19
2	2
3	4
4	8
5	16
6	19
7	20	Time out occur, so new threshold = $\frac{20}{2} = 10$
8	1	10
9	2
10	4
11	8
12	10

 

So, total 12 transmission require to reach $C_{wind} = 10\ MSS$ or $20\ KB$