Question

Suppose that TCP's current estimated values for the round trip time (estimatedRTT) and deviation in the RTT (DevRTT) are 256 msec and 18 msec, respectively. Suppose that the next three measured values of the RTT are 217 msec, 265 msec, and 289 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.
What is the TCP timeout value after the third RTT?
O 356.26 ms
O 282.1 ms
O 341.02 ms
O None of these are correct

Answer 1

The TCP timeout value after the third RTT calculation, considering the provided alpha (α) and beta (β) values, and the initial estimatedRTT and DevRTT is found to be 388.02 ms, which is not listed among the provided choices.

Step-by-step explanation:

The calculation of TCP's estimated round trip time (estimatedRTT), the deviation in RTT (DevRTT), and the timeout interval are all crucial for ensuring reliable data transmission over a network. The formulae for these calculations are:

• estimatedRTT = (1 - α) * estimatedRTT + α * SampleRTT
• DevRTT = (1 - β) * DevRTT + β * |SampleRTT - estimatedRTT|
• TimeoutInterval = estimatedRTT + 4 * DevRTT

Using the given values α = 0.125 and β = 0.25, and starting with an estimatedRTT of 256 ms and a DevRTT of 18 ms, we perform the calculations after each of the three measured RTTs (217 ms, 265 ms, and 289 ms).

After the third RTT, the calculated values are:

• New estimatedRTT: 268.14 ms
• New DevRTT: 29.22 ms
• TCP timeout value: 388.02 ms

Therefore, the closest answer is none of these are correct.