Methods of Error Detection

Causes of Data Errors

• Data corruption during transmission due to:

  • Interference (electrical)

  • Packet switching problems

  • Skewing in parallel transmission

Need for Error Checking

• Mandatory to check for transmission errors.

Error Detection Methods

1. Parity Checks

   • Determines if data has changed or corrupted.

   • Based on the even/odd count of 1-bits in a byte.

   • Types:

     • Even Parity: even number of 1-bits.

     • Odd Parity: odd number of 1-bits.

   • Agreement needed between sender and receiver on parity type.

   • Issues: Can't detect 2-bit errors reliably.

2. Checksum

   • Checks for changes or corruption in data.

   • Calculation based on agreed algorithm:

     • Sender computes checksum for data block before transmission.

     • Receiver recalculates and compares.

3. Echo Check

   • Data sent back to sender for verification.

   • Comparison determines if errors occurred.

   • Limitations: unreliability in identifying where errors occurred.

4. Check Digits

   • Final digit in codes to identify input errors (e.g., ISBN, VIN).

   • Can detect various types of input errors (e.g., mis-typed, transpositions).

5. Automatic Repeat reQuests (ARQs)

   • Uses positive/negative acknowledgments and timeout strategies.

   • Error detection through codes, e.g., Cyclic Redundancy Check (CRC).

   • Commands re-transmission on error detection.