Error Detection and Correction.  Corrupted files  Attachments that won’t open  Files that won’t download  Videos that won’t play Errors occur when.

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Presentation transcript:

Error Detection and Correction

 Corrupted files  Attachments that won’t open  Files that won’t download  Videos that won’t play Errors occur when there is a problem with the data, it’s time consuming to fix. Parity checks are used to check the data is OK before it is sent. What is an error and when do errors occur?

Suppose you are sending a stream of data to a server. By adding a parity bit, you enable the server to detect some basic transmission errors. A parity bit is a bit that is added as the leftmost bit of a bit string to ensure that the number of bits that are ‘1’ in the bit string are even or odd.  In an even parity scheme the eighth bit, the parity bit, is set to 1 if the number of 1s in the 7 data bits is odd. It is set to 0 if the number of 1s in the data is even.  In an odd parity scheme the eighth bit, the parity bit, is set to 1 if the number of 1s in the 7 data bits is even. It is set to 0 if the number of 1s in the data is odd. Parity Bit Error detection

Even Parity - what does it look like? A string of data that is ready to send Parity bits have been added to the left hand side of the data The number of bits in a row must always add up to an even number This row is already even – a ‘0’ added to the left hand side This row has an odd number of ‘1’ so a ‘1’ is added This column has an odd number of ‘1’ so a ‘1’ is added This column had an even number of ‘1’ so a ‘0’ is added

Odd and even Parity Here, you always want to get an even number of 1s Here, you always want to get an odd number of 1s

Odd Parity – how would it appear? A string of data that is ready to send The number of bits in a row must always add up to an even number

Odd and even Parity NOTE: Either even or odd parity systems can be used to check data, but you will usually find that most people tend to use the even parity scheme.