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Main points of this past exam are: Steady State Probabilities, Random Arrival, Random Departure, Queue Length, Arrival Probability, Departure Probability, Cell Discard Probability, Queue Carrying Traffic, Average Data Rate, Exceeding
Typology: Exams
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: 75 :^5
Give an expression for the virtual cell discard probability for a queue carrying traffic from 30 bursty sources, each with a peak data rate of 8% of the link rate and an average data rate equal to 0.5% of the link rate. 12 such sources can be on without exceeding the link rate and the probability that any given sources is on is 1/16. So the virtual cell discard probability is
i= 12
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The IBA model and virtual cell discard probability can be used to estimate the cell loss for bursty sources. Which is more accurate in each of the following cases? Explain why.
link rate all sending data to a queue large enough to hold one average size burst. Virtual cell discard probability is more accurate in this case. In general, it produces accurate results when the peak rate of the sources is much smaller than the link rate and the buffer is small, as is true here. The IBA model works poorly in these situations.
the link rate all sending data to a queue large enough to hold 30 average size bursts. Here the IBA model is better. It gives good results when the buffer is much larger than the burst size and the peak rate is close to the link rate. The virtual cell discard probability is a poor estimate for the actual cell discard probability in this case.
prefix next hop
What would be the next hop for a packet whose address started with the bits 1011001? 12 Show a binary trie that could be used to represent this routing table.
Suppose that the maximum speed advantage that can be implemented in the technology you are using is 4. If you implement multicast by dedicating some of the 512 ports for recycling, how many external ports can the system have?
ports in this system.
the values for a and b?
x 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 a;b (x) 0 2 4 6 8 10 12 14 1 3 5 7 9 11 13 15
Well the product of a and b is clearly 16, so the possible choices are a = 2 , b = 8 , a = 4 , b = 4 and a = 8 , b = 2. The last of these is the correct choice.
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Assume the system operates as described in class. That is, the fanout sums are computed top to bottom and the copy-range block computes the copy network outputs directly, without any regard for positional unfairness.
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