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Chapter 1: Problem 14
How long does it take to transmit \(x\) KB over a \(y\)-Mbps link? Give your answer as a ratio of \(x\) and \(y\).
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Suppose a 100-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 \(385,000 \mathrm{~km}\), and data travels over the link at the speed of light-3 \(\times 10^{8} \mathrm{~m} / \mathrm{s}\). (a) Calculate the minimum RTT for the link. (b) Using the RTT as the delay, calculate the delay \(\times\) bandwidth product for the link. (c) What is the significance of the delay \(\times\) bandwidth product computed in (b)? (d) A camera on the lunar base takes pictures of Earth and saves them in digital format to disk. Suppose Mission Control on Earth wishes to download the most current image, which is \(25 \mathrm{MB}\). What is the minimum amount of time that will elapse between when the request for the data goes out and the transfer is finished?
Suppose a 128-Kbps point-to-point link is set up between Earth and a rover on Mars. The distance from Earth to Mars (when they are closest together) is approximately \(55 \mathrm{Gm}\), and data travels over the link at the speed of light-3 \(\times 10^{8} \mathrm{~m} / \mathrm{s}\). (a) Calculate the minimum RTT for the link. (b) Calculate the delay \(\times\) bandwidth product for the link. (c) A camera on the rover takes pictures of its surroundings and sends these to Earth. How quickly after a picture is taken can it reach Mission Control on Earth? Assume that each image is \(5 \mathrm{Mb}\) in size.
What differences in traffic patterns account for the fact that STDM is a costeffective form of multiplexing for a voice telephone network and FDM is a costeffective form of multiplexing for television and radio networks, yet we reject both as not being cost-effective for a general-purpose computer network?
One property of addresses is that they are unique; if two nodes had the same address it would be impossible to distinguish between them. What other properties might be useful for network addresses to have? Can you think of any situations in which network (or postal or telephone) addresses might not be unique?
Suppose hosts A and B are connected by a link. Host A continuously transmits the current time from a high-precision clock, at a regular rate, fast enough to consume all the available bandwidth. Host \(\mathrm{B}\) reads these time values and writes them each paired with its own time from a local clock synchronized with A's. Give qualitative examples of B's output assuming the link has (a) high bandwidth, high latency, low jitter (b) low bandwidth, high latency, high jitter (c) high bandwidth, low latency, low jitter, occasional lost data For example, a link with zero jitter, a bandwidth high enough to write on every other clock tick, and a latency of 1 tick might yield something like \((0000,0001)\), \((0002,0003),(0004,0005)\).
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