Q3- Consider Figure 1 shown below. Assuming TCP Reno is the protocol experiencin

Question

Q3- Consider Figure 1 shown below. Assuming TCP Reno is the protocol experiencing the behavior shown below; answer the following questions. (2 marks)

a. Identify the intervals of time when TCP slow start (SS) is operating. (0.4 marks)

b. Identify the intervals of time when TCP congestion avoidance (CA) is operating. (0.4 marks)

c. After the 16th transmission round (RTT), is segment loss detected by a triple duplicate ACK (3dupACKs) or by a timeout? (0.2 mark)

d. After the 22nd transmission round (RTT), is segment loss detected by a triple duplicate ACK (3dupACKs) or by a timeout? (0.2 mark)

e. What is the initial value of ssthresh (or threshold) at the first transmission round (RTT)? (0.2 mark)

f. What is the value of ssthresh (or threshold) at the 18th transmission round (RTT)? (0.2 mark)

g. Assuming a packet loss is detected after the 26th transmission round (RTT) by the receipt of a triple duplicate ACK (3dupACKs), what will be the values of the congestion window (cwnd) and ssthresh (or threshold)? (0.4 marks)

Explanation / Answer

a)
TCP slowstart is operating in the intervals [1,6] and [23,26]
b)
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 were 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
f)
During the 1st transmission round, packet 1 is sent; packet 2-3 are sent in the 2nd transmission round; packets 4-7 are sent in the 3rd transmission round; packets 8- 15 are sent in the 4th transmission round; packets 16-31 are sent in the 5th transmission round; packets 32-63 are sent in the 6th transmission round; packets 64 – 96 are sent in the 7th transmission round. Thus packet 70 is sent in the 7th transmission round

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