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
240 msec and 23 msec, respectively (see Section 3.5.3 for a discussion of these variables).
Suppose that the next three measured values of the RTT are 260 msec, 220 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 242.5
2. The DevRTT for RTT1 is 22.25
3. The timeout for RTT1 is 331.5
4. The estimatedRTT for RTT2 is 239.69
5. The DevRTT for RTT2 is 22.31
6. The timeout for RTT2 is 328.94
7. The estimatedRTT for RTT3 is 234.73
8. The DevRTT for RTT3 is 26.66
9. The timeout for RTT3 is 341.35
That's incorrect
That's correct
The answer was: 242.5
The answer was: 22.25
The answer was: 331.5
The answer was: 239.69
The answer was: 22.31
The answer was: 328.94
The answer was: 234.73
The answer was: 26.66
The answer was: 341.35