Topic: Computer Networks
In a computer network using CSMA/CD, the minimum frame size for data transfer is 1500 bytes. What will be the data transfer speed in this network over 1 Km cable, if the signal speed in the cable is 250000 Km/sec and no repeaters are used in this network?
- A. 1 Gbps
- B. 100 Mbps
- C. 500 Mbps
- D. 1.5 Gbps
Answer: D. 1.5 Gbps
Explanation: For CSMA/CD to detect collisions, transmission time ($T_t$) must be $\ge 2 \times$ propagation delay ($T_p$). $T_p = \frac{Distance}{Speed} = \frac{1 km}{250000 km/s} = 4 \mu s$. $T_t = \frac{L}{B} \ge 2 \times T_p$. Length L = $1500 \times 8 = 12000$ bits. $\frac{12000}{B} \ge 8 \mu s \implies B \le \frac{12000}{8 \times 10^{-6}} = 1.5 \times 10^9$ bps = 1.5 Gbps.