Suppose that the five measured SampleRTT values (see Section 3.5.3) are 106 ms, 120 ms, 140 ms, 90 ms, and 115 ms. Compute the EstimatedRTT after each of these SampleRTT values is obtained, using a value of α = 0.125 and assuming that the value of EstimatedRTT was 100 ms just before the first of these five samples were obtained. Compute also the DevRTT after each sample is obtained, assuming a value of β = 0.25 and assuming the value of DevRTT was 5 ms just before the first of these five samples was obtained. Last, compute the TCP TimeoutInterval after each of these samples is obtained.
Calculate the EstimatedRTT after obtaining the first sample RTT=106ms,
EstimatedRTT = α * SampleRTT+(1- α) * EstimatedRTT
EstimatedRTT =0.125 * 106 + (1-0.125) * 100
=0.125* 106 + 0.875 * 100
=13.25 + 87.5
=100.75ms
Calculate the DevRTT after obtaining the first sample RTT:
DevRTT = β * | SampleRTT- EstimatedRTT|+(1- β)* DevRTT
=0.25 * |106-100.75| + (1-0.25) *5
=0.25 *5.25 + 0.75 * 5
=1.3125 + 3.75
=5.0625ms
Calculate the Timeout Interval after obtaining the first sample RTT:
TimeoutInterval = EstimatedRTT +4* DevRTT
= 100.75 + 4 *5.0625
=121ms
Calculate the EstimatedRTT after obtaining the second sample RTT=120ms,
EstimatedRTT = α * SampleRTT+(1- α) * EstimatedRTT
EstimatedRTT =0.125 * 120 + (1-0.125) * 100.75
=0.125* 120 + 0.875 * 100.75
=15 + 88.15625
=103.15625ms
Calculate the DevRTT after obtaining the second sample RTT:
DevRTT = β * | SampleRTT- EstimatedRTT|+(1- β)* DevRTT
=0.25 * |120-103.15625| + (1-0.25) *5.0625
=0.25 *16.84 + 0.75 * 5.0625
=4.21 + 3.79
=8ms
Calculate the Timeout Interval after obtaining the second sample RTT:
TimeoutInterval = EstimatedRTT +4* DevRTT
= 103.15 + 4 *8
=135.15ms
Calculate the EstimatedRTT after obtaining the third sample RTT=140ms:
EstimatedRTT = α * SampleRTT+(1- α) * EstimatedRTT
EstimatedRTT =0.125 * 140 + (1-0.125) * 103.15
=0.125* 140 + 0.875 * 103.15
=17.5 +90.26
=107.75ms
Calculate the DevRTT after obtaining the third sample RTT:
DevRTT = β * | SampleRTT- EstimatedRTT|+(1- β)* DevRTT
=0.25 * |140-107.75| + (1-0.25) *8
=0.25 *32.25 + 0.75 * 8
=8.06 + 6
=14.06ms
Calculate the Timeout Interval after obtaining the third sample RTT:
TimeoutInterval = EstimatedRTT +4* DevRTT
= 107.75 + 4 *14.06
=164ms
Calculate the EstimatedRTT after obtaining the fourth sample RTT=90ms:
EstimatedRTT = α * SampleRTT+(1- α) * EstimatedRTT
EstimatedRTT =0.125 * 90 + (1-0.125) * 107.75
=0.125* 90 + 0.875 * 107.75
=11.25 +94.28
=105.53ms
Calculate the DevRTT after obtaining the fourth sample RTT:
DevRTT = β * | SampleRTT- EstimatedRTT|+(1- β)* DevRTT
=0.25 * |90-105.53| + (1-0.25) *14.06
=0.25 *15.53 + 0.75 * 14.06
=3.88 + 10.545
=14.42ms
Calculate the Timeout Interval after obtaining the fourth sample RTT:
TimeoutInterval = EstimatedRTT +4* DevRTT
= 105.53 + 4 *14.42
=163.21ms
Calculate the EstimatedRTT after obtaining the fifth sample RTT=115ms:
EstimatedRTT = α * SampleRTT+(1- α) * EstimatedRTT
EstimatedRTT =0.125 * 115 + (1-0.125) * 105.53
=0.125* 115 + 0.875 * 105.53
=14.375 +92.34
=106.715ms
Calculate the DevRTT after obtaining the fifth sample RTT:
DevRTT = β * | SampleRTT- EstimatedRTT|+(1- β)* DevRTT
=0.25 * |115-106.715| + (1-0.25) *14.42
=0.25 *8.285 + 0.75 * 14.42
=2.07 + 10.815
=12.885ms
Calculate the Timeout Interval after obtaining the fifth sample RTT:
TimeoutInterval = EstimatedRTT +4* DevRTT
= 106.715 + 4 *12.885
=158.255ms