# noob stuck with Data Communication

Discussion in 'Homework Help' started by lookforterry, Feb 14, 2006.

1. ### lookforterry Thread Starter New Member

Feb 14, 2006
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"In an odd parity checking scheme, what is the value of the parity bit for the following 0101101 sequence. Why? Imagine a communication link that is experiencing interference so every 18th bt is changed from 0 to 1 or from 1 to 0. Does a parity chck detect all errors? why?"

Apr 26, 2005
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3. ### chesart1 Senior Member

Jan 23, 2006
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Hi,

Of course you are correct in being skeptical about the errors a parity check can catch.

Check out this more sophisticated method of detecting errors in data transmission. It is known as CRC which stands for Cyclic Redundancy Check.

http://www.4d.com/docs/CMU/CMU79909.HTM

John

4. ### Papabravo Expert

Feb 24, 2006
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The value of the odd parity bit is one. It is one because that makes the number of ones in the message plus the single parity bit an ODD number. If there was an odd number of ones in the message then the odd parity bit would be zero. Parity checks can only detect a single bit error. In your example(I know it's less than 18 bits) message if you change the first two bits from 01 to 10, and the the parity bit stays the same then the bogus message gets trhough undetected.