Computing TCP's RTT and timeout values
Suppose that TCP's current estimated values for the round trip time (estimatedRTT) and
deviation in the RTT (DevRTT) are
400 msec and 50 msec, respectively (see Section 3.5.3 for a discussion of these variables).
Suppose that the next three measured values of the RTT are 300 msec, 270 msec, and 200 msec respectively.
Compute TCP's new value of DevRTT, estimatedRTT, and the TCP timeout value after each of these three measured RTT values is obtained. Use the values of α = 0.125, and β = 0.25. Round your answers to two decimal places after leading zeros.
Question List
1. What is the estimatedRTT after the first RTT?
2. What is the RTT Deviation for the the first RTT?
3. What is the TCP timeout for the first RTT?
4. What is the estimatedRTT after the second RTT?
5. What is the RTT Deviation for the the second RTT?
6. What is the TCP timeout for the second RTT?
7. What is the estimatedRTT after the third RTT?
8. What is the RTT Deviation for the the third RTT?
9. What is the TCP timeout for the third RTT?
Solution
DevRTT is calculated with the following equation: (1-beta)*DevRTT + beta * |estimatedRTT - sampleRTT|
estimatedRTT is calculated with the following equation: (1-alpha)*estimatedRTT + alpha*sampleRTT
TCP timeout is calculated with the following equation: estimatedRTT + (4*DevRTT)
1. The estimatedRTT for RTT1 is 387.5
2. The DevRTT for RTT1 is 62.5
3. The timeout for RTT1 is 637.5
4. The estimatedRTT for RTT2 is 372.81
5. The DevRTT for RTT2 is 76.25
6. The timeout for RTT2 is 677.81
7. The estimatedRTT for RTT3 is 351.21
8. The DevRTT for RTT3 is 100.39
9. The timeout for RTT3 is 752.77
That's incorrect
That's correct
The answer was: 387.5
The answer was: 62.5
The answer was: 637.5
The answer was: 372.81
The answer was: 76.25
The answer was: 677.81
The answer was: 351.21
The answer was: 100.39
The answer was: 752.77