Assume TCP Reno (meaning Fast Retransmit and Fast Recovery) is the protocol expe
ID: 3572711 • Letter: A
Question
Assume TCP Reno (meaning Fast Retransmit and Fast Recovery) is the protocol experiencing the behavior shown above. Assume that the TCP flow has been operating for some time, meaning that the number of RTTs shown are with respect to when you started observing the flow’s behavior.
a) Identify the time periods when TCP slow start is operating.
b) Identify the time periods when TCP congestion avoidance is operation (AIMD).
c) After the 14th RTT, is the segment loss detected by a triple duplicate ACK or by a timeout?
d) What is the initial value of the ssthreshold, before the first congestion avoidance interval?
e) What is the value of ssthreshold at the 19th RTT?
f) What is the value of ssthreshold at the 24th RTT?
g) Assuming a packet loss is detected after the 25th RTT by the receipt of a triple duplicate ACK, what will be the values of the congestion-window size and of ssthreshold?
45 40 35 30 25 L 20 15 10 10 15 Number of RTTs 20 25Explanation / Answer
Answer :
Assume TCP Reno (meaning Fast Retransmit and Fast Recovery) is the protocol experiencing the behavior shown above. Assume that the TCP flow has been operating for some time, meaning that the number of RTTs shown are with respect to when you started observing the flow’s behavior.
a) Identify the time periods when TCP slow start is operating.
b) Identify the time periods when TCP congestion avoidance is operation (AIMD).
c) After the 14th RTT, is the segment loss detected by a triple duplicate ACK or by a timeout?
d) What is the initial value of the ssthreshold, before the first congestion avoidance interval?
e) What is the value of ssthreshold at the 19th RTT?
f) What is the value of ssthreshold at the 24th RTT?
g) Assuming a packet loss is detected after the 25th RTT by the receipt of a triple duplicate ACK, what will be the values of the congestion-window size and of ssthreshold?
Answer :
a) Identify the time periods when TCP slow start is operating.
Answer :
1-6, 22-25
b) Identify the time periods when TCP congestion avoidance is operation (AIMD).
Answer :
6-14,15-21(also accepting 15-19,6-21)
c) After the 14th RTT, is the segment loss detected by a triple duplicate ACK or by a timeout?
Answer :
Triple Duplicate ACK
d) What is the initial value of the ssthreshold, before the first congestion avoidance interval?
Answer :
32
e) What is the value of ssthreshold at the 19th RTT?
Answer :
20
f) What is the value of ssthreshold at the 24th RTT?
Answer :
12
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