SLR12 Error checking Flashcards
What is a parity bit?
Single bit added to a transmission to check for errors - its calculated relating to the data itself
What are the two types of parity bit?
Odd parity and an even parity
How would you make an odd parity bit?
- The total number of 1’s in the bit would have to be odd.
- If they were originally odd, the parity bit would be 0
- If they were originally even, the parity bit would be 1
How would you make an even parity bit?
- The total number of 1’s in the bit would have to be even.
- If they were originally even, the parity bit would be 0
- If they were originally odd, the parity bit would be 1
What is the major problem with parity bits?
Whether using odd or even parity, if an
even number of bits are changed during transmission, the error is not detected - the number will stay odd or stay even
What is majority voting?
Each bit of data is transmitted multiple times and the most commonly occurring value is taken s the correct one.
What is a major pro of majority voting?
It has the capability to check is multiple bits are of the correct value
What is a major con of majority voting?
The volume of data being transmitted is majorly increased, which increases the time taken to transmit the data
What are checksums?
- Adding a value transmitted (determined by the data)
- An algorithm is used to do this, but its not a set one so different systems use different ones
- Recipient removes the checksum, applies the algorithm and sees if they match - if not it is re-transmitted
What are check digits?
- its a type of checksum, which only adds a single digit to the transmitted data
Pros of a check digit
- this reduces the number of algorithms that can calculate the check digit and therefore reduce the variety of errors from this method
What are the levels of efficiency:
- Parity bit
- Check digit
- Checksum
- Majority vote
What are the different types of check digit?
- Parity bit
- Check digit
- Checksum
- Majority vote
