Final_Exam_sol - Final Exam, Spring Semester, 2009 Data...

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Final Exam, Spring Semester, 2009 Data Networks Professor: Sunghyun Choi 2008-06-11 (Thu), 10:30am-12:30pm 1. (10 pts, 5 pts each) Indicate the correct answer to each of the following topics, and briefly explain why . (a) The maximum achievable throughputs of slotted ALOHA, unslotted ALOHA, splitting algorithm, CSMA slotted ALOHA, and CSMA/CD can be ordered as follows: unslotted ALOHA < slotted ALOHA < splitting algorithm < CSMA slotted ALOHA < CSMA/CD. A. True B. False Ans. False since the maximum throughputs of CSMA slotted ALOHA and CSMA/CD heavily depend on the propagation and detection delay beta. For example, for large beta, CSMA/CD can perform worse than CSMA slotted ALOHA. (b) Consider an M/M/1, M/M/m, or M/M/ system with arrival rate λ and service rate μ . Suppose that the system starts in steady-state. Then, according to Burke s theorem, the departure process is Poisson with rate . A. True B. False Ans. False since the departure rate is , NOT . 2. (10 pts) Consider a closed Jackson network where the service time at each queue is independent of the number of customers at the queue. Suppose that for a given number of customers, the utilization factor of one of the queues, say queue 1, is strictly larger than the utilization factors of the other queues. Show that as the number of customers increases, the proportion of time that a customer spends in queue 1 approaches unity.
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This note was uploaded on 04/29/2010 for the course CSE 4541.525A taught by Professor Choisunghyun during the Spring '09 term at Seoul National.

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Final_Exam_sol - Final Exam, Spring Semester, 2009 Data...

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