If the data frame to be transmitted is 1101011011 and the CRC generator…
2013
If the data frame to be transmitted is 1101011011 and the CRC generator polynomial used for the checksum is x4 + x + 1, what is the transmitted frame?
- A.
11010110111011
- B.
11010110111101
- C.
11010110111110
- D.
11010110111001
Attempted by 118 students.
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Correct answer: C
CONCEPT: In CRC, a generator polynomial of degree r is represented as an (r + 1)-bit divisor. The sender appends r zero bits to the data, performs modulo-2 division, and replaces the zeros with the r-bit remainder.
A valid transmitted frame should divide by the generator with a zero syndrome, because the appended remainder cancels the division remainder.
Convert the polynomial: x4 + x + 1 corresponds to the binary divisor 10011, so r = 4.
Append four zeros to the data: 1101011011 becomes 11010110110000.
Divide 11010110110000 by 10011 using XOR subtraction. The modulo-2 remainder is 1110.
Replace the four appended zeros with 1110, giving 1101011011 + 1110 = 11010110111110.
CROSS-CHECK: Dividing the full frame 11010110111110 by 10011 leaves syndrome 0000, while 11010110111011 leaves a nonzero syndrome.
Result: the transmitted frame is 11010110111110.