Wednesday, August 4, 2010

PARITY BIT

SORRY, THIS BLOG CAME 1 DAY LATE.

                             I WOULD LIKE TO START THE BLOG BY RAISING A QUESTION - WHAT IS PARITY BIT ?         
                                   PARITY BIT IS A BIT THAT IS ADDED TO THE CODE FOR THE DETECTION OF ERROR DURING THE TRANSMISSION OF THE CODE.
                                                        PARITY BIT IS GENERALLY ADDED TO THE LEFTMOST SIDE OF THE CODE.
                                           
                                      THERE ARE TWO TYPES OF PARITY-EVEN PARITY AND ODD PARITY. IN EVEN PARITY, THE BIT ADDED IS SUCH THAT THE NUMBER OF 1s IN THE CODE IS EVEN AND IN ODD PARITY, THE BIT ADDED IS SUCH THAT THE NUMBER OF 1s IN THE BINARY CODE IS ODD.
                                             
                                          NOW, I WOULD TO THROUGH SOME LIGHT ON HOW PARITY BIT CAN BE USED FOR THE DETECTION OF ERROR DURING THE TRANSMISSION OF THE CODE. GENERALLY, AN EVEN PARITY IS CREATED AT THE TRANSMISSION END BY THE ADDITION OF DESIRED BIT. THEN, THE CODE IS TRANSMITTED AND THE PARITY OF THE CODE IS CHECKED AT RECEIVING END. IF THE PARITY OF THE CODE HAS CHANGED FROM EVEN TO ODD, THEN, IT MEANS THAT EITHER 1 OR 3 OR AN ODD NUMBER OF BITS ( EXCEPT THE PARITY BIT ) IN THE CODE HAVE  CHANGED THEIR VALUES DURING TRANSMISSION.
                                       
                                                            BUT, IF THE PARITY OF THE CODE REMAINS SAME, THEN THERE ARE TWO POSSIBILITIES THAT EITHER THE CODE IS SAME (MORE PROBABLE) OR AN EVEN NUMBER OF BITS HAVE CHANGED THEIR VALUES DURING TRANSMISSION( LESS PROBABLE ). THIS IS THE LIMITATION OF THE PARITY BIT. BUT THE CASE OF EVEN CHANGES OF BITS HAPPENS QUITE LESS TIMES, HENCE, THE PARITY BIT METHOD IS A GOOD WAY TO DETECT ERROR IN THE CODES DURING TRANSMISSION.
                           I WOULD LIKE TO EXPLAIN THE ERROR DETECTION PROCESS BY AN EXAMPLE - SUPPOSE 0110001 IS THE CODE TO BE TRANSMITTED(NOTE THAT NUMBER OF 1s IN CODE IS ODD ). NOW, BY ADDING 1 TO THE LEFT OF THE CODE, THE CODE BECOMES EVEN PARITY AND THE NEW CODE IS 10110001. THIS CODE IS TRANSMITTED TO THE RECEIVER WHERE ITS PARITY IS CHECKED. IF THE CODE RECEIVED IS 10100001, THEN , IT MEANS THE PARITY HAS BECOME ODD WHICH CAN BE DETECTED. BUT, IF THE CODE RECEIVED IS 11100001, THEN, THOUGH TWO BITS HAVE CHANGED THEIR VALUES DURING TRANSMISSION, BUT THE PARITY OF THE RECEIVED CODE IS SAME , SO SUCH KIND OF ERRORS CANNOT BE DETECTED USING PARITY BIT.

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