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CS158a Spring 2007Practice Midterm 2To study for the midterm I would suggest you: (1) Know how to do (by heart) all the practice problems. (2) Go over your notes at least three times. Second and third time try to see how much you can remember from the first time. (3) Go over the homework problems. (4) Try to create your own problems similar to the ones I have given and solve them. (5) Skim the relevant sections from the book. (6) If you want to study in groups, at this point you are ready to quiz each other. The practice midterm is below. Here are some facts about the actual midterm: (a) It is closed book, closed notes. Nothing will be permitted on your desk except your pen (pencil) and test. (b) You should bring photo ID. (c) There will be more than one version of the test. Each version will be of comparable difficulty. (d) One problem (less typos) on the actual test will be from the practice test. 1. Suppose the delay for a frame to arrive is 100msec and a frame take 10msec to send. If we are using a sliding window of size 11 and the first frame is lost, how many frames will be discarded if we are using the go back n protocol and how many will be discarded if we are using selective repeat? 2. Give three differences between HDLC and PPP. 3. Suppose we have a 1Gbps channels, we have a mean frame length of 20Kbits, and a frame arrival of 10,000frames/sec. What would be the mean delay for this channels assuming that frame arrive according to a Poisson process? What if we split the channel into 10 subchannels using TDM? 4. Briefly define or describe (a) carrier sense, (b) slotted ALOHA, (c)non-persistent CSMA. 5. Briefly define the following terms related to 802.11 (a) RTS, (b) CTS, (c) NAV, (d) fragment burst. 6. Explain with an example the backwards learning algorithm used by bridges to create table entries for LANs in a local internetwork. 7. Give an example situation where Dijkstra's algorithm would have to update an entry at least three times for a distance it has calculated between a pair of nodes. Explain why your example works. 8. Briefly explain the count-to-infinity problem. 9. Consider the graph which consists of an octogon with the vertices labeled A to H. The edges starting around the exterior of the octogon each have weight 2. In addition A is connected to D with weight 3. If A through H represent router and link state routing is used what information would each router put in its link state packet? 10. Explain with an example how the leaky bucket algorithm works. |