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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View Full DocumentProblem 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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 Spring '11
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 Following, Collision Avoidance, one 1 0 0 0 1 0 0 0 1 1 1 1 Second

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