The network using CSMA/CD has a bandwidth of 20 mbps. If the maximum…
2025
The network using CSMA/CD has a bandwidth of 20 mbps. If the maximum propagation time is 25μ sec (microsecond), what is the minimum size of the frame?
- A.
500 bits
- B.
1000 bits
- C.
1500 bits
- D.
2000 bits
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Correct answer: B
Key idea: For CSMA/CD the frame transmission time must be at least the round-trip (two-way) propagation time so that a collision can be detected before the sender finishes transmitting.
Calculate round-trip propagation time: 2 × 25 μs = 50 μs.
Compute bits that can be sent in 50 μs at 20 Mbps: bits = 20,000,000 bits/s × 50×10⁻⁶ s = 1000 bits.
Therefore the minimum frame size required to guarantee collision detection is 1000 bits (which is 125 bytes).
Answer: 1000 bits.
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