Discussion

If the data rate of a ring is 20 Mbps and the signal propagation speed is 200 m/µs, how many bits can be placed on a channel of 200 km?

Answer: B

Correct answer: 20,000 bits

The signal takes

\[ \frac{200\times 10^{3}\ \text{m}}{200\ \text{m}/\mu\text{s}} = 1000\ \mu\text{s} \]

to go round, and at 20 Mbps that interval holds

\[ 20\times 10^{6}\times 10^{-3} = 20{,}000\ \text{bits} \]

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