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

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

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 01101 We would send 000 111 111 000 111 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… 010 111 011 100 101 The computer would find the common item and chose that bit.

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.

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

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

Example Message – 11100101 Polynomial - 11011