### 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
270 msec and 15 msec, respectively (see Section 3.5.3 for a discussion of these variables).
Suppose that the next three measured values of the RTT are 400 msec, 330 msec, and 300 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 286.25

2. The DevRTT for RTT1 is 43.75

3. The timeout for RTT1 is 461.25

4. The estimatedRTT for RTT2 is 291.72

5. The DevRTT for RTT2 is 43.75

6. The timeout for RTT2 is 466.72

7. The estimatedRTT for RTT3 is 292.75

8. The DevRTT for RTT3 is 34.88

9. The timeout for RTT3 is 432.29

That's incorrect

That's correct

The answer was: 286.25

The answer was: 43.75

The answer was: 461.25

The answer was: 291.72

The answer was: 43.75

The answer was: 466.72

The answer was: 292.75

The answer was: 34.88

The answer was: 432.29