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- 1Parity checkingParity checking is one method used to check whether data has been changed or corrupted following transmission from one device or medium to another device or medium.
A byte of data, for example, is allocated a parity bit. this is allocated before transmission takes place. systems that use even parity have an even number of 1-bits; systems that use odd parity have an odd number of 1-bits - 2ARQAUTOMATIC REPEAT REQUEST (ARQ) is another method used to check whether data has been correctly transmitted.
It uses an ACKNOWLEDGEMENT (a message sent by the receiver indicating that data has been received correctly) and TIMEOUT (this is the time allowed to elapse before an acknowledgement is received).
If an acknowledgement isn’t sent back to the sender before timeout occurs, then the message is automatically resent. - 3CHECK SUMCHECKSUM is another way to check if data has been changed or corrupted following data transmission.
Data is sent in blocks and an additional value, the checksum, is also sent at the end of the block of data.
To explain how this works, we will assume the checksum of a block of data is 1 byte in length. This gives a maximum value of 28 − 1 (i.e. 255). The value 0000 0000 is ignored in this calculation. - 4ECHO CHECKWith ECHO CHECK , when data is sent to another device, this data is sent back again to the sender.
The sender compares the two sets of data to check if any errors occurred during the transmission process.
As you will have no doubt worked out, this isn’t very reliable.
If the two sets of data are different, it isn’t known whether the error occurred when sending the data in the first place, or if the error occurred when sending the data back for checking!
However, if no errors occurred then it is another way to check that the data was transmitted correctly.
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- Flashcards on Untitled, created by William Bowles on 20/10/2015.
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- William Bowles
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