Introduction to Error Detection and Correction. Need and Basis for Data Protocols.
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Error Detection and Correction

Many factors can lead to errors during transmission or storage

When binary information is sent across a physical channel such as wire, coax cable, optical fiber or air, there is always the possibility that some bits will be received in error due to interference form other sources; or, due to signal attenuation because of long distances or events like rain or snow, etc.

Binary representation makes it possible to perform coding (changing the original information into a new encoded pattern). Clever coding, or additional information added to the transmission can increase the odds of the sent information being received correctly. We will discuss 3 methods:
Parity checking
Repetition
Redundancy code word checking

Parity Errors

Even parity is set: 1 0 0 is received
Error present, but don’t know which one is the bit in error
Parity method can detect certain errors, but cannot correct them
Odd parity is set: 1111011 0 is received. Error?
Even parity is set: 1111011 0 is received. Error?
Parity checking has a major disadvantage due to its inability to detect even number of inverted bits, e.g. 0011 1001 would go undetected even if the original transmission was 0011 1111, because there are 2 errors (even number of errors)