2. The congestion window size, in segments, of the TCP Reno protocol is plotted
ID: 2248624 • Letter: 2
Question
2. The congestion window size, in segments, of the TCP Reno protocol is plotted below versus transmission round for a sequence of segment transmissions. Using text Figure 3.51 (p. 274) 16 (a) Identify the transmission round intervals over15 14 13 12 transmission round intervals [6,9] and [16,204 which TCP is in slow start. (c) Identify the state(s) TCP could be in during transmission round interval [13,15] size drop after the 5th transmission round size drop old" during the 12th transmission round old" during the 18th transmission round (d) Identify the cause of the congestion window 8 (e) Identify the cause of the congestion window after the 9th transmission roui (f) Determine the value of the "slow start thresh- 93 (g) Determine the value of the "slow start thresh- 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 transmission round (h) During what transmission round is the 84th segment sent? (i) Determine the "slow start threshold" and congestion window sizes in the 21st round assuming that a packet loss is detected after the 17th round by receipt of triple duplicate ACKs.Explanation / Answer
(a) The TCP is in slow start from rounds [1,4] and [10,12] as we see the congestion windows increasing exponentially.
(b) During intervals [6,9] and [16,20], the TCP is in Fast Recovery and in additive increase due to receipt of three duplicate ACKs.
(c)In interval [13,15], the TCP is in Congestion Avoidance as cwnd>ssthresh.
(d) The cause of congestion window size drop after 5th transmission round is due to receipt of 3 duplicate ACKs.
(e) The cause of congestion window size drop after 9th transmission round is due to time out.
(f) The slow start threshold during 12th transmission round is seven.
(g) The slow start threshold during 18th transmission round is five.
(h) By adding th segments during each transmission round, the 84th segment is sent during 11th round.
(i) At 17th round, the congestion window size is 9. So, ss thresh is N-1/2 or 4 and in the next round it starts with congestion window size of 7 and performs additive increase. In 21st round the congestion window size is 10.
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