MadeEasy Subject Test 2019: Computer Networks - Tcp

Question

If TCP RTT is currently 20 ms and following acknowledgement come in after 22,24 and 23 ms respectively. What is new RTT estimate ?

• A. 28.527
• B. 28.82
• C. 20.82
• D. 21.22

Comments

Sorry alpha is given as 0.9 (forgot to mention)

---

yes, the final answer is 20.822 for alpha = 0.9

---

Yes the answer is 20.822

Answer 1

Given: 1) IRTT= $20$ms

2)$\alpha=0.9$

3) NRTT= $22,24,23$ms

Expected RTT can be calculated in TCP as follows:

$\text{ERTT=$\alpha*$IRTT+(1-$\alpha$)*NRTT}$

1. ERTT=$0.9*20+0.1*22=20.2$ ms
2. ERTT=$0.9*20.2+0.1*24=20.58$ ms
3. ERTT=$0.9*20.58+0.1*23=20.82$ ms

Note: each time when we calculated ERTT, it will become IRTT for the next part.

Option (C) is correct.

Answer 2

with smoothing factor=0.9    RTT=20.3ms

with smoothing factor=0.8    RTT=20.6ms