9. Suppose that the TCP congestion window is set to 18 KB and a timeout occurs. How big will the window be if the next four transmission bursts are all successful

9KB

Explanation:

Assuming the maximum segment size is 1KB.

Thus, after the elapsed time following things will occur

1. There will commence of slow time.

2. There will be a beginning of window congestion at 1.

3. There will be a reset of threshold which is going to be 18KB/2=9KB.

Hence, If the next four transmissions are all successful, then we have

1st transmission: 1 segment, 1KB

2nd transmission: 2 segments, 2KB

3rd transmission: 4 segments, 4KB

4th transmission: 8 segments, 8KB

Following the four successful transmissions, the window size is expected to be 16.

However, since the threshold is 9KB, the window size will equal 9KB.