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Information Processes and Technology

Home > Information Processes and Technology > Communication Systems > Error Detection and Checking

Error detection and checking in communication systems - Suggested answers

Activity 1

1. Define the following terms:
   
   

   Term	Definition
   Parity check	A method of checking for errors in data transmission using an additional bit called a parity bit.
   Odd parity	The number of bits in a character is odd
   Even parity	The number of bits in a character is even
   Parity bit	An additional bit added to data to check if transmission was successful
   Checksum	A method of checking for errors in data transmission by counting the number of bits in a data packet
   Packet	A data group, created by dividing total data into smaller groups
   Cyclic redundancy check	A method of error checking that uses a division process. Data is divided into predetermined lengths and divided by a fixed divisor. When the data is received, the remainder is recalculated. If the remainders do not match, an error in transmission has occurred
   Binary number	Base 2 number system. 0 and 1 are the only values.

   
   
   
2. Under what conditions would a parity bit check fail to show errors?
   Received data may be corrupted during transmission. If, for example, even parity was chosen and the data received had an even number of bits, no error would be detected by parity checking even if the data had been corrupted during transmission.
   
   
3. How are the problems with a checksum error check similar to the problems faced by a parity bit check.
   Checksum counts the number of bits in a data packet. If the count of bits received matches the count of bits sent no error will be detected.
   
   
4. Draw a diagram which explains the problems with a checksum error check. Use the drawing under the heading of checksum to help guide you. However you must be entirely original.
   A diagram which shows data being transmitted and corrupted in some way is required.
   
   
5. Why is CRC more successful in picking up errors than a parity check or a checksum?
   CRC resembles a long division operation in which the quotient is discarded and the remainder becomes the result. Because a division method is used, rather than simply counting the number of bits, a higher rate of error detection is achieved.
   
   
6. Discuss the following statement, “Networks would be entirely unworkable without a method to check for errors.”
   The extent to which networks are free from errors defines their success and usability. Without reliable error checking methods an unacceptable rate of errors could make networks unusable. A discussion which outlines the importance of error checking methods in networks is required.
   
   
7. Discuss the following “Every form of information system is dependent on some reliable form of error checking, without them they would collapse in a bundle.”
   An example of a non computer information system could be used to answer this question. For example, without a way of ensuring that paper based letters reach their intended destinations, our postal system would be completely unworkable.
   
   
8. Look at the following image. The image describes a problem with the checksum error checking method. Explain the problem with checksum.
   The image shows that all the data has arrived, but that its order has been changed. This is similar to an error in transmission which may not be detected by checksum. The same number of bits that have been transmitted may be received but due to errors in transmission the data may be corrupted. Checksum will not detect such an error.

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