EL5363-CRC

EL5363-CRC - Concept of Error Detection Code Suppose we...

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Communication Networks © Kang Xi, Polytechnic Institute of NYU 1 Concept of Error Detection Code Suppose we send out a message [1 2 5 8] and an error turns it to [ 2 2 5 8] At the receiver, there is no way to tell whether [ 2 2 5 8] contains an error Solution: append an error detection code to the original message at the sender
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Concept of CRC Question: what kind of error detection code to add Assumption: sender and receiver shares a number 7 Sender: divides the message by 7, and use the remainder as the code msg [1 2 5 8] 1258/7 = 179 + 5/7, so the reminder is 5 Now append 5 to the msg: [1 2 5 8 5 ] When an error occurs, the receiver gets [ 2 2 5 8 5] Receiver takes [2 2 5 8] and divides it by 7 2258/7 = 322 + 4/7, so the reminder is 4 Since 4 is different from the error detection code carried in the msg, the error is detected. EE136: Communication Networks © Kang Xi, Polytechnic University 2
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Important !!! Sender and receiver must know the divisor in
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EL5363-CRC - Concept of Error Detection Code Suppose we...

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