Consider two hosts \(X\) and \(Y\), connected by a single direct link of rate…
2017
Consider two hosts \(X\) and \(Y\), connected by a single direct link of rate 10^6bits/sec. The distance between the two hosts is 10,000km and the propagation speed along the link is 2×10^8m/sec. Host \(X\) sends a file of 50,000 bytes as one large message to host \(Y\) continuously. Let the transmission and propagation delays be \(p\) milliseconds and \(q\) milliseconds respectively. Then the value of \(p\) and \(q\) are
- A.
\(p=50\)and\(q=100\) - B.
\(p=100\)and\(q=50\) - C.
\(p=400\)and\(q=50\) - D.
\(p=50\)and\(q=100\)
Attempted by 102 students.
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Correct answer: C
Transmission delay (p): Message size = 50,000 bytes = 50,000 × 8 = 400,000 bits. Link rate = 1,000,000 bits/s. p = 400,000 / 1,000,000 = 0.4 s = 400 ms.
Propagation delay (q): Distance = 10,000 km = 10,000,000 m. Propagation speed = 2 × 10^8 m/s. q = 10,000,000 / 200,000,000 = 0.05 s = 50 ms.
Conclusion: Therefore p = 400 ms and q = 50 ms. The correct choice is the one that states these values.
Common mistakes: treating bytes as bits (forgetting to multiply by 8) which underestimates transmission delay.
Mixing up transmission and propagation delays or using incorrect distance/speed values can lead to swapped or doubled errors.
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