Error Possibility during information transfer corrupts 1 or more bits

Bit Drop -> Bit which is 1 at sending end is received as 0

Bit Pickup ->  Bit 0 at sending end is received as 1

Sender & Receiver follows Algorithm & Encoding to detect error

1. Parity Check ( odd & even) 

Odd Parity System:  Should have totally odd no. of 1’s in data including parity bit. If in data the no. of 1’s is odd, parity is 0 else 1

Even Parity System: Vice versa

Eg: Data: 11101110 – OddParity :111011101 – EvenParity:111011100

Data: 11001101 – OddParity: 110011010 – EvenParity: 110011011

Pros & Cons:

  • Even no. of bit failures cant be detected

  • Used in PC for stroing memory & reading it back

2. Multiple Bit Error Detection scheme

 Causes data files corruption & program corruption 

CRC used 

  • Sending end divides the data by polynomial& remainder is appended to data and sent as CRC Character (CRCC)
  • Receiving end applies same polynomial & divides received data & compares new CRCC with received CRCC & detects multiple bit error
  • Detection of maximum multiple bit failure depends on power of polynomial. 
  • Eg: if data is 11101110 and the divisor polynomial is 1110. Append 000 to data (since divisor is 4 digits add 3 zero) and divide it by 1110.
  • 11101110000/ 1110 (modulo division).  Remainder/CRC is 000.

In pc used for,

  • data transfer between floppy disk controller & floppy disk drive & hard disk controller. 
  • While write CRCC while read check it 

Error Correcting Code

  • ECC does error detection and correction
  • Sending end generates ECC pattern from data bit
  • Identifies failing bits & corrects it

In PC, 

  • Used by hard disk controller for data recorded on hard disk
  • R/W memory uses ECC in PC