Suppose two hosts are connected by a point-to-point link and they are…
2023
Suppose two hosts are connected by a point-to-point link and they are configured to use Stop-and-Wait protocol for reliable data transfer. Identify in which one of the following scenarios, the utilization of the link is the lowest.
- A.
Longer link length and lower transmission rate
- B.
Longer link length and higher transmission rate
- C.
Shorter link length and lower transmission rate
- D.
Shorter link length and higher transmission rate
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Correct answer: B
Key idea: In Stop-and-Wait, the sender transmits one frame and then waits for an acknowledgment. The link is utilized only while transmitting the frame; the rest of the round-trip time is idle waiting.
Define variables: frame size L, transmission rate R, one-way propagation delay d.
Approximate utilization: U ≈ (L/R) / ( (L/R) + 2d ). For small ACK size, ACK transmission time is negligible compared to data.
To minimize U, make the numerator (L/R) small and the denominator large: that means a high transmission rate R (small L/R) together with a long propagation delay d.
Therefore, the scenario with a longer link length (large propagation delay) and a higher transmission rate (small transmission time) gives the lowest utilization.
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