Disadvantages of Parity Bits

What are the disadvantages of parity bits?

I gathered some info but I was hoping someone could expand on t开发者_StackOverflow社区hem.

• Not capable of finding all errors. Only errors which cause an odd number of bits to flip will be detected.

• No way to know which bit is false.

• Not able to correct the data so the data has to be retransmitted.

• On noisy lines, other detection method such as CRC is used to assure that the sent information is received correctly.

There are only two disadvantages to using parity bits:

1. It's N extra bits-per-word that have to be transmitted.
2. Parity checking can't detect all forms of errors.

The advantage is that errors on a noisy line can be caught quickly and only the errant word has to be re-transmitted. However, because a parity check cannot detect all errors, you have to use a higher-level error detection mechanism, like CRC. If an error is detected at that level, the entire block has to be re-transmitted.

So it's a trade-off.

Using a parity bit incurs a fixed bandwidth penalty, but catches certain errors quickly with little re-transmission cost.

The only way to answer the question, "Should I use parity bits?" is with testing of the specific connection in question. Transmission errors are highly localized and you will only know which error correction is best for that connection by testing it.

The advantage is that errors on a noisy line can be caught quickly and only the errant word has to be re-transmitted. However, because a parity check cannot detect all errors, you have to use a higher-level error detection mechanism, like CRC. If an error is detected at that level, the entire block has to be re-transmitted.