# X2S - Cmpen/EE 362 Exam 2 Solution Fall 2010 Problem 1[10...

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Cmpen/EE 362 Exam 2 Solution Fall 2010 Problem 1. [10 crs,] Consider the cases of a hub and a switch. Each line can carry R bits/second in one direction at a time. If A sends to D at the maximum rate, show the flow of data and rates for each of the two configurations. Solution. A hub sends to everyone. Problem 2. 12 crs. In slotted ALOHA, suppose 10 senders send independently with probability 0.1 each and 1 sender sends independently with probability 0.3. Assume if there is a collision there is no success. What is the probability a slot will have a successful packet. Solution. P(success) = P(1 sent) = .3(.9) + 10(.1)(.9) (.7) = .3758 10 9

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Problem 3. [16 crs. 8/8] a) Draw the feedback shift register circuit with the input on the high degree side for computing the check bits using the CRC polynomial: X + X + X + X + X + X + 1. 1 21 1732 Solution. a) b) If the register is initially all zero, show the entries after two 1's are shifted in. Solution First one 1 0 0 0 1 0 0 0 1 1 1 1 Second 1 adds to 1 shift, creating no feedback. Rest shift.
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X2S - Cmpen/EE 362 Exam 2 Solution Fall 2010 Problem 1[10...

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