Lecture7

Lecture7 - ECE 340 Lecture 7: Variance & conditional pmf...

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ECE 340 Lecture 7: Variance & conditional pmf Jean Liu Email: Jliu@mrn.org
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Example to review Problem 3.18 A computer reserves a path in a network. To extend the reservation the computer must successfully refresh message before the expiry time. The messages are lost with probability ½. Suppose that it take 10 sec. to send a refresh message and receive acknowledgement. When should the computer start sending a refresh messages in order to have a 99% chance of successfully extending the reservation time.
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10 min. 0 ? Refresh request
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• Let X be the times that a refresh request needs to be sent till successfully received. •S X is {1,2,3,…} • Let Y be the seconds that a refresh request needs to be sent till successfully received. Y is {10,20,30,…} • Success rate of a message is 1/2 What is the set B, which begins with 1 and increases accordingly, has 99% chance of successfully extending reservation?
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pmf of X? 1 11 1 ( ) ( ) () 22 2 kk Xk px p xK == = = 1 1 [] ( ) 2 N k k kB k PB p x ∈= ∑∑ Set B probability ?
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This note was uploaded on 02/10/2010 for the course TBE 2300 taught by Professor Cudeback during the Spring '10 term at Webber.

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Lecture7 - ECE 340 Lecture 7: Variance & conditional pmf...

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