Consider the following plot of TCP window size as a function of time. Assume TCP
ID: 3675349 • Letter: C
Question
Consider the following plot of TCP window size as a function of time. Assume TCP Reno is the protocol experiencing the behavior shown above, answer the following questions. In all cases, you should provide a short discussion justifying your answer. a, Is TCP slow start operating in interval [6, 16]? Why or why not? b, Is TCP congestion avoidance operating in interval [23, 26]? Why or why not? c, After the 16th transmission round, is segment loss detected by a triple duplicate ACK or by a timeout? d, After the 22nd transmission round, is segment loss detected by a triple duplicate ACK or by a timeout? e, What is the value of Threshold at the 20th transmission round? f, What is the value of Threshold at the 6th transmission round?
Explanation / Answer
a. It is slow start operating in interval of [6,16]. If you see the graph, the congestion is down and it is re-initiating the communication.
b. TCP congestion avoidance is not operating in interval [23,26]. TCP congestion advoidance is operating in the intervals [6,16] and [17,22]
c. After the 16th transmission round, packet loss is recognized by a triple duplicate ACK. If there was a timeout, the congestion window size would have dropped to 1.
d. After the 22nd transmission round, segment loss is detected due to timeout, and hence the congestion window size is set to 1.
e. The threshold is set to half the value of the congestion window when packet loss is detected. When loss is detected during transmission round 20, the congestion windows size is 24. Hence the threshold is 12 during the 20th transmission round.
f. The threshold is set to half the value of the congestion window when packet loss is detected. When loss is detected during transmission round 6, the congestion windows size is 34. Hence the threshold is 17 during the 6th transmission round.