Error Checking (Cambridge (CIE) O Level Computer Science)
Revision Note
Written by: Robert Hampton
Reviewed by: James Woodhouse
Why Errors Occur
Why do errors occur?
Errors can occur using wired or wireless technology due to interference
Examples of interference include wire degradation or electrical fields changing the signal
Results of interference include:
Data loss - data is lost in transmission
Data gain - additional data is received
Data change - some bits have been changed or flipped
Wireless technology uses radio signals or other electromagnetic signals to transmit data
These signals can be blocked by physical barriers such as buildings, walls, cars or other objects
Interference can be caused by bad weather such as rain or clouds, or by other wireless signals or electromagnetic radiation
Wired technology carries more chance of causing an error as physical components can be damaged, degrade or receive interference from outside signals
Data loss can also occur from interruptions to data transmission such as a blocked signal or if the transmission is intermittent
Why check for errors?
Computers expect data in certain formats
A format is a way of arranging the data so that it can be easily understood by people and by computers
People agree to certain formats so that systems work more efficiently and there is little chance of misunderstanding each other
An example of a format is date and time
Date and time can have multiple formats such as:
13/04/14 (DD/MM/YY)
12/31/2020 (MM/DD/YYYY)
Jul-04-16 (MMM/DD/YY)
If data is not as expected, things can go wrong
For example, if a receiver expected to receive a date in format DD/MM/YY as 03/04/17 but received 04/03/17, did the sender mean 3rd April 2017 or 4th March 2017?
An error or corruption occurs when data received is not as expected and therefore is difficult or impossible to process
Worked Example
Alex receives an email over a wireless connection from a work colleague containing an important document.
Identify what interference Alex could experience when sending this email and identify the outcomes of interference.
Further explain why Alex should check to make sure the document contains no errors.
[4]
Answer
Weather conditions or physical barriers such as building can affect signals, for example bits could be flipped in the document making it hard to understand the original meaning [1]
Alex should be aware that interference can cause wirelessly received data to contain errors or corruption [1]
Data could be lost, additional data could be gained or data could be changed [1]
As Alex received an important work document they need to check for errors so that their work is unaffected and they do not receive incorrect information [1]
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