1. Cyclic Redundancy Check (CRC)
Learning Intention
Be able to perform CRC error checking on simple data

2. Error checking
There are three error checking techniques that you must be comfortable with. These are listed below…
Parity bit (odd and even)
Repetition code
CRC

3. Repetition codes (overview)
One way to detect an error is to send data multiple times. For example. Suppose we are trying to send the data We would send The receive would check to see if the data being sent is consistent. The receiver could also correct basic errors. Suppose the data was received below… The computer would find the common item and chose that bit.

4. Repetition codes – Repeat more times
A repetition code that uses groups of three can only detect a problem that exists in any one of the two bits. The more bits we repeat the lower the probability that errors could occur. However you do not get anything for free. The additional repetition codes will result in larger amounts of data being sent.

5. Cyclic Redundancy Check (CRC)
CRC is an error checking technique which messages can be encoded with that allows a network to check to see if a message has been sent successfully.
It is not limited to networks
It includes two elemtns
A right padded data set
A Divisor (This is known to both the transmitter and the reciever)
It cannot correct data when errors are detected

6. XOR – What is XOR
Build a truth table and examine what the output of following would be…
0 XOR 0
1 XOR 0
O XOR 1
1 XOR 1

7. Example
Message – Polynomial