This question is from our friend Shujaat
Suppose we have average RTT of 1.5 ms, and RTT variation of 0.5 ms. Suppose further that the next RTT sample is 3 ms.
1) What is the average value of RTT corresponding to the last RTT Sample above.
2) What is the value of RTT variation
3) What is the value of RTO
Sunday, July 12, 2009
[AIT09] RTT and RTO for TCP
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11 comments:
[Nakrop Jinaporn,107936]
What are the values of alfa and beta in your question?
[Nakrop Jinaporn,107936]
Suppose that alfa = 0.5,
E{t(k+1)} = 0.5(1.5ms) + (1-0.5)(3 ms)
= 2.25 ms
[Wattanadej J, 107971]
t(k+1) = 3 ms
RTT variation of 0.5 ms
According to Mr. Nakrop
E{ t(k+1)} = 2.25 ms
suppose Beta is 0.7
variation of RTT at k+1 equal to
(0.7 * 0.5)+ (1 - 0.7) * (3 - 2.25)
which is 0.07875
[Preechai,108021]
according to above
the value of RTO = RTO(k+1)
= min{ub, max{lb, gamma * [t(k+1) + 4*zigma(k+1)]}}
= min{10^5, max{0.2, 1 * [2.25 + 4*0.07875]}}
= 2.565
[Nawat,108113] Is value of alpha,beta are fixed (from lecture note, alpha=7/8, beta=3/4)?
[Karin,107985]
According to Mr.Nawat, The default value for alpha and beta are
alpha = 7/8 , beta = 3/4.
You can see the function
rtt_update(double tao)
in file xxx/tcp/tcp.cc,
which I can't remember the correct path.
Then, the answer for the first question should be 1.6875ms.
(Hasanain/106000) We will use the equations 10.1, 10.2 and 10.3 given in chapter # 10 on page 244 of the text book (Introduction to Network Simulator NS2). By substituting the values provided in the specified equations and using the value alpha=7/8 , beta=3/4 and gamma=1, we get the following results
1)Average value of RTT = 1.6875ms
2)Value of RTT variation = 0.75ms
3)Value of RTO = 6ms
Dear Nakrop and Nawat,
Alpha belongs to (0,1)and Beta belongs to (0,1). The values are usually set to alpha=7/8,beta=3/4. [Intro to NS2, pp. 200]
I think you guys should now be able to compute RTT, right?
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