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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 4bit 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 UniversityWest Lafayette.
 Spring '08
 Sonia,F

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