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ISRO | ISRO CS 2013 | Question 39

  • Last Updated : 08 May, 2018

If the frame to be transmitted is 1101011011 and the CRC polynomial to be used for generating checksum is x4+ x + 1, then what is the transmitted frame?
(A) 11010110111011
(B) 11010110111101
(C) 11010110111110
(D) 11010110111001


Answer: (C)

Explanation:

Step-1: 
Append (number of bits in divisor - 1) number
of zeroes at the end of data unit
Data unit = 1101011011, Divisor = 10011,
So, append 4 zeroes at the end.
          = 11010110110000

Step 2
Divide using xor subtraction:      
      _________________
10111) 11010110110000  ( 101000001
       10111
       ------
        10011
        10011
        -------
              10110
              10011
             --------
                10100
                10011
               --------
                  1110


Step 3
Perform Xor-sum of the remainder with the appended
zeroes in data unit.
= 11010110110000 xor (1100)
= 11010110111110 

So, option (C) is correct.

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