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EE 444 INTRODUCTION TO COMPUTER NETWORKS Spring 2009 HOMEWORK # 4 Deadline: April 24 2009 @ 23:59 (No late submission is allowed.) Posted on April 17 2009. Question # 1 Given the message 1010001101 and the CRC polynomial P(x) = x 5 +x 4 +x 2 +1. (a) Compute the final message to be sent including the CRC. (b) Show how the receiver performs the CRC check operation on the received message. Show all your work. Question # 2 (a) A channel has a data rate of 4 kbps and a propagation delay of 20 ms. For what range of frame sizes does stop-and-wait give an efficiency of at least 50%? (b) Two nodes n 1 and n 2 communicate using Go-Back-N as the ARQ mechanism with a window size of 4 frames. Assume that n 1 is transmitting and n 2 is receiving. Show the window positions for the following sequence of events. 1. Before n 1 sends any frames. 2. After n 1 sends frames 0, 1, 2 and n 2 acknowledges 0, 1 and the ACKs are received by n 1 . 3.
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This note was uploaded on 04/09/2010 for the course EE ee444 taught by Professor Akan during the Spring '10 term at Middle East Technical University.

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