Methods of Error Detection

2026 Syllabus Objectives

By the end of this topic, you should be able to:

  1. Understand the need to check for errors after data transmission and how these errors can occur (such as data loss, data gain, and data change due to interference)
  2. Describe the processes involved in error detection methods: parity check (odd and even), checksum, and echo check, including parity byte and parity block check
  3. Describe how a check digit is used to detect errors in data entry and identify examples such as ISBN and bar codes
  4. Describe how an automatic repeat query (ARQ) can be used to establish that data is received without error, including positive/negative acknowledgements and timeout

Why We Need to Check for Errors

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How Errors Occur During Data Transmission

When data travels from one device to another, things can go wrong. This happens because of interference – unwanted signals or problems that disrupt the data as it travels.

Interference can cause three main types of errors:

  • Data loss – some of the data disappears during transmission and never reaches the receiver
  • Data gain – extra, unwanted data is added during transmission
  • Data change – bits flip from 0 to 1 or from 1 to 0, changing the meaning of the data

What Causes Interference?

For wireless technology (like Wi-Fi or mobile networks):

  • Physical barriers such as buildings, walls, or cars can block signals
  • Bad weather conditions like heavy rain or thick clouds interfere with radio waves
  • Other wireless signals or electromagnetic radiation can disrupt transmission

For wired technology (like Ethernet cables):

  • Physical damage to cables over time (degradation)
  • Electrical fields from nearby equipment changing the signal
  • Interruptions or intermittent connections

Why Must We Check for Errors?

Computers expect data to arrive in specific formats. A format is an agreed way of arranging data so both computers and people can understand it correctly.

Example: Consider dates

  • 13/04/14 could mean 13th April 2014 (DD/MM/YY format)
  • But if received as 04/13/14, it could mean 13th April 2014 or 4th March 2014 depending on format (MM/DD/YY)

If data doesn't arrive as expected, serious problems occur:

  • The computer cannot process the data correctly
  • Information becomes difficult or impossible to understand
  • Important work or transactions may fail

An error or corruption means the data received is different from what was sent, making it unreliable or unusable.

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