hwk3-4-Su10 - CNT5106C Computer Networks, Summer 2010...

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CNT5106C Computer Networks, Summer 2010 Instructor: Prof. Ahmed Helmy On the Data link layer, MAC protocols and Wireless Networking [Date Assigned: Jul 7 th , 2010. Due Date: Jul 21 st , 2010] Points: 120 Q1. (9 points: 3 x 3) MAC layer utilization For an Ethernet LAN (shared bus) the data rate was increased from 10Mbps to 100Mbps. I. How will the utilization (U) of this network change? [Calculate U for each case] II. Suggest two ways in which we can return the utilization to what it was before (Increasing or decreasing another parameter and by how much? Show your reasoning.) III. One person argued that increasing the number of stations attached to the LAN would reduce the idle time on the LAN and hence increase the utilization. Do you agree? Q2. (13 point: 3 + 10) I. Why do we need a medium access control (MAC) protocol? Shouldn’t routing, queuing and flow control at the data link layer be sufficient? II. Mention ten MAC protocols and classify them according to their type (e.g., random access, etc.). Q3. (6 points) Reason mathematically about the relationship between the utilization in Aloha and utilization in the slotted Aloha MAC protocols. Q4. (6 points: 3 x 2) I. Which MAC protocol is used in switched (fast/Gigabit) Ethernet, and why? II. What is ‘frame bursting’ in switched Ethernet and why is it used? Q5 . (13 total points) I. (6 points) Derive an expression for the utilization of the token ring release-after- transmission algorithm. Comment on your result showing the effect of the change of ‘ a on the utilization. II. (4 points) Compare this result to utilization of token ring (release after reception) and
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hwk3-4-Su10 - CNT5106C Computer Networks, Summer 2010...

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