Applied Test Series

Question

Consider the effect of using slow start on a line with 12 msec round trip time. The size of the congestion window is set to 40 KB. The sender side threshold is set to 20 KB. After 7th transmission a time-out occurs, after timeout the time taken to send the first full window of 20 KB is (in msec). ? [ Assume window size at the start of the slow start phase is 2 KB, MSS=2KB]

Answer 1

First transmission: 2KB

Second Transmission:  4KB

Third transmission: 8KB

Fourth transmission: 16 KB

Fifth transmission: 20 KB [ Threshold reached]

Sixth transmission: 22 KB

Seventh transmission: 24 KB [ Timeout occurs, new th = 24 / 2 = 12 KB]

Eighth transmission: 2 KB

Ninth transmission: 4 KB

Tenth transmission: 8 KB

Eleventh Transmission: 12 KB [ Th reached]

Twelfth transmission: 14 KB

Thirteenth transmission: 16

Fourteenth transmission: 18 KB

Fifteen transmission: 20 KB

So 8RTT after timeout.

=> 8 x 12 = 96  msec