Suppose a 200-Mbps point-to-point link is being set up between Earth and a new l

Question

Suppose a 200-Mbps point-to-point link is being set up between Earth and a new lunar colony. The distance from the moon to Earth is approximately 385,000 km, and data travels over the link at the speed of light 3x10^8 m/s.

(a) Calculate the minimum RTT (round trip time – the time for the signal togo and come back) for the link.

(b) Suppose Mission Control on Earth wishes to download a 8GB image froma camera on the lunar base. What is the minimum amount of time that will elapse between when the request for the data goes out and the transfer is finished?

Explanation / Answer

Solution:

Minimum RTT = 2 x Propagation

            Propagation = Distance / Speed of Light

                                = 2 x 385000 km / 3 x 108 m/s

                                = 2 x 385000000 m / 3 x 108 m/s

                                = 2 x 385 / 300 sec

                                = 2.57 sec

Delay x Bandwidth = 2.57 sec x 100 Mbits/sec

                               = 257 Mbits

                               = 257/8 MB

                               = 32MB

Solution:

Minimum RTT = 2 x Propagation

            Propagation = Distance / Speed of Light

                                = 2 x 385000 km / 3 x 108 m/s

                                = 2 x 385000000 m / 3 x 108 m/s

                                = 2 x 385 / 300 sec

                                = 2.57 sec

Delay x Bandwidth = 2.57 sec x 200 Mbits/sec

                               = 514 Mbits

                               = 514/8 MB

                               = 64.25MB

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