1. What is the sending codeword of given data word 101101101 and divisor 1101
- A. 101101101001
- B. 101101101000
- C. 101111010101
- D. 101111011001
- E. None of the above
Ans- A. 101101101001
Solution:- In Data Link layer detecting of error is is done by using CRC
In above example given data word is 101101101 and divisor is 1101
According to CRC if we have divisor bits are n then add n-1 0 bits to data word
now data word is 101101101000 and divisor is 1101
Perform XOR to data word 101101101000 by dividing 1101
here we found CRC=001 , So the sending code word is 101101101001
If Receiver receive 101101101001 then it again perform XOR operation with given divisor 1101
Reminder 0 means Receiver received correct codeword.
2. Consider a binary message (data word) string is 1011001111. Find CRC ( Cyclic redundancy check) for this message if divisor(generator) is given as x6 + x5 + x3 + x2 + 1.
- A. 010110
- B. 100110
- C. 010101
- D. 010111
- E. None of the above
Ans- A. 010110
In Data Link layer detecting of error is is done by using CRC
Given polynomial (generator) is x6 + x5 + x3 + x2 + 1 convert it in binary string by 1101101
In above example given data word is 1011001111 and divisor is 1101101
According to CRC if we have divisor bits are n then add n-1 0 bits to data word here the highest degree of polynomial expression is 6 so add 6 0s to data word
now data word is 1011001111000000 and divisor is 1101101
Perform XOR to data word 1011001111000000 by dividing 1101101
