Checksum & Echo Checks
Computer Science: Cambridge International GCSE, topic 1.2.5
Checksum & Echo Checks
Checksum and echo checks are error detection methods that identify corrupted data during transmission, so it can be resent accurately.
Why errors occur
- Data transmission can be unreliable – errors can happen due to interference.
- This can cause the data to be corrupted:
- Data loss: Some bits of data go missing
- Data gain: Extra, unwanted bits are added
- Data change: Bits altered from a 0 to a 1, or vice versa
- Error detection methods are used to find these corrupted data packets so they can be resent.
Checksum
- Checksum is an error detection method that works as a mathematical check.
- The data is divided into blocks.
- A calculation is performed on each block of data before being sent.
- The result of this calculation is the checksum.
- The checksum is added to the data block and both are sent to the receiver.
- The same calculation is performed on the receiver's data block.
- The new checksum is compared to the one sent by the sender.
Outcome of checksum
- If the two checksum values match → the data is correct.
- If the two do not match → an error has occurred.
- The data packet will be requested to be resent.
- Checksum is widely used in networks and internet data transfer.
Echo check
- Echo check is a method that works by sending data back to the original sender to be verified.
- Data is transmitted from the sender to the receiver.
- The receiver then returns ("echoes") the same data block back to the sender.
- The sender compares the data it sent (original data) with the data it received back.
Outcome of echo check
- If the two data blocks are identical → the data was transmitted successfully.
- If there is a mismatch in data → an error has occurred and the data is sent again.
- Echo check is less efficient than a checksum but simple to use.
Test yourself on Checksum & Echo Checks
Why are error detection methods needed after data transmission?