hw4-soln - CS536 Homework 4 due Tue, Apr 28th, 1:30pm May...

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Unformatted text preview: CS536 Homework 4 due Tue, Apr 28th, 1:30pm May 2, 2009 Submit your homework electronically in a text or PDF file. Email your solution to the professor by 1:30pm on Tuesday, Apr 14th. Late submission will not be accepted, nor will collaboration. To receive credit, all submissions should contain this statement at the be- ginning: By turning in this homework submission, I certify that this work was done solely by me. Questions about this homework should be directed to the TAs or the Professor, not to fellow classmates. Problem 1 (10 pts) Suppose two nodes start to transmit at the same time a packet of length L over a broadcast channel of rate R . Denote the propagation delay between the two nodes as d prop . Will there be a collision if d prop < L/R ? Why or why not? Answer. Yes, because the remote senders packet will arrive before the packet is done being transmitted. Problem 2 (10 pts) Suppose a 10 Mbps adapter sends into a channel an infinite stream of 1s using a Manchester encoding. The signal merging from the adaptor has how many transitions per second? Answer. 20 million transitions per second. Problem 3 (10 pts) In CSMA/CD, after the fifth collision, what is the probability that a node chooses K = 4? The result K = 4 corresponds to a delay of how many seconds on a 10 Mbps Ethernet? Answer. After the 5th collision, the adapter chooses from { 0, 1, 2,, 31 } . The probability that it chooses 4 is 1 / 32. It waits 204.8 microseconds. 1 Problem 4 (10 pts) Consider the 4-bit generator G = 1001, and suppose that the data D has the values given below. For each, give the value of the remainder R which serve as the CRC. Show your work. a. 01010101 Answer. 110 (Note that the subtraction is done without carry, see ex- ample in book) b. 10010001 Answer. 001 (Note that the leading 0s will be important for a fixed- width check.) c. 11011011 Answer. 011 d. 01101011 Answer. 111 (Note that even though 1000 < 1001, you still apply the subtraction/xor at that point)....
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This note was uploaded on 10/24/2009 for the course CS 536 taught by Professor Sonia,f during the Spring '08 term at Purdue University-West Lafayette.

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hw4-soln - CS536 Homework 4 due Tue, Apr 28th, 1:30pm May...

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