6. Consider the diagram below, showing the size variation of a TCP congestion wi

Question

6. Consider the diagram below, showing the size variation of a TCP congestion window under TCP-Reno congestion management. For each question below, briefly justify your answer.

a. Identify the intervals when TCP slow start is operating.

b. Identify the intervals when TCP congestion avoidance is operating.

c. After the 16th transmission round, is segment loss detected by a triple duplicate ACK or a timeout?

d. After the 22nd transmission round, is segment loss detected by a triple duplicate ACK or a timeout?

e. What is the initial threshold value at the first transmission round?

f. What is the value of the threshold at the 18th round?

g. What is the value of the threshold at the 24nd round?

h. During what round is the 70th segment sent?

i. Assuming that a packet loss is detected after the 26th round by receipt of triple duplicate ACKs, what will be the new congestion window size and threshold?

45- 40 35 30 3 25 E 20 15 10 0 2 4 6 8 10 12 14 16 18 20 22 24 26 Transmission round 18 TCP window size as a function of time

Explanation / Answer

a) Identify the intervals when TCP slow start is operating.

First need to understand what is slow start .

Slow start -> When we send message packets travel together. all this each packet during slow start.It is also possibly the only place in the described as “slow”. so it will called slow start.

So here as per Diagram interval [1,6] and [23,26] is slowstart .

B) Identify the intervals when TCP congestion avoidance is operating.

TCP congestion avoidance -> TCP congestion avoidance phase, though all phases of the process are ultimately directed towards avoidance of congestion. when a packet is lost, it should decrease rapidly, but otherwise should increase “slowly”. As TCP finishes each packets, it notes whether a loss occurred.

So as per Diagram Intervals [6,16] and [17,22] is TCP congestion advoidance

c) After the 16th transmission round, packet loss is recognized by a triple duplicate ACK.

D) After the 22nd transmission round, is segment loss detected to a timeout.In above diagram you can see ongestion window size is set to 1 after 22 round

E) As per above diagram The threshold value is initially 32.

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 16, the congestion windows size is 42. and round 17 ,window is 24 Hence the threshold is 25 during the 18th transmission round.

G) As pe above Diagram When loss is detected during transmission round 22, the congestion windows size is 29. Hence the threshold is 14.5 during the 24th transmission round.

H) As per abobe Diagram you can see Packet 1 is sent in 1 transmision

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 to 31 are sent in the 5th transmission round

packets 32 to 63 are sent in the 6th transmission round

packets 64 to 96 are sent in the 7th transmission round.

Here here it is clear 70 packet are sent in the 7th transmission round.

I)

The threshold will be set to half the current value of the congestion window when the loss occurred and congestion window will be set to the new value. Thus the new values of the threshold and window will be 4 and 7 respectively.

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