1) Cyclic redundancy check (CRC) is a method for detecting errors in digital data during transmission over unreliable communication channels. It works by using a generator polynomial to generate a checksum that is appended to the transmitted data. 2) At the sender, the data bits are divided by the generator polynomial to calculate a remainder which becomes the CRC checksum. This checksum is appended to the data before transmission. 3) At the receiver, the received data and checksum are divided again by the same generator polynomial. If the remainder is zero, then no errors were detected in the received data. A non-zero remainder indicates errors were detected.

1. Maharshi Dayanand Saraswati University
Presentation Topic: Cyclic Redundancy Check
Subject : Computer Networks
Class: MCA1
Presented by : Shivangi Tak Submitted to: Praful Sir

2. Welcome To My
Presentation
Topic : Cyclic Redundancy Check

3. 03
01 02
04
Agenda
Error Detection
Method
Cyclic
Redundancy
Check
Performance
of CRC
Advantages of
CRC

4. What is Error Detection ?
 Networks must be able to transfer data from one device
to another with complete accuracy.
 Data can be corrupted during transmission.
 For reliable communication, errors must be detected
and corrected.

6. Cyclic Redundancy Check
 CRC or Cyclic Redundancy Check is a method of
detecting errors in the communication channel.
 CRC uses Generator Polynomial which is available on
both sender and receiver side.

7. CRC Generation At Sender Side
1.Find the Length of Divisor ‘L’
2.Append 0 ‘L-1’bits to the original bits
3.Perform Binary Digit Operation
4.Remainder of the division=CRC A B A XOR B
0 0 0
0 1 1
1 0 1
1 1 0

8. A B A XOR B
0 0 0
0 1 1
1 0 1
1 1 0
1 Find the Length of Divisor ‘L’
2 Append 0 ‘L-1’bits to the original bits
3 Perform Binary Digit Operation
4 Remainder of the division=CRC
Finally, Cyclic Redundancy
check will be generated as
shown.

9. The sender performs a division operation
on the bits being sent and calculates the
remainder. Before sending the actual bits,
the sender adds the remainder at the end
of the actual bits.
(Data Bits+ Remainder)

10. Receiver Side:
Code word received at the receiver
side 100100001
(data + CRC)

11. At The Receiver Side
 Receiver divides received data (data + CRC) with
generator.
 If remainder is zero, data is correctly received.
 Else, there is error.

12. A B A XOR B
0 0 0
0 1 1
1 0 1
1 1 0
Therefore, the remainder is all zeros.
Hence, the data received has no
error.

13. Advantages of CRC
1. Cyclic codes have a very good performance in detecting
single-bit errors, double errors, an odd number of errors.
2. They can easily be implemented in hardware and
software.
3. They are especially fast when implemented in hardware.
4. This has made cyclic codes a good candidate for many
networks.

14. Reference
CRC
https://www.geeksforgeeks.org/error-detection-in-computer-networks/
CRC Error Detection
https://www.youtube.com/watch?v=wQGwfBS3gpk
https://www.geeksforgeeks.org/modulo-2-binary-division/

15. THANK YOU