When data is sent from one device or component to another there is always a chance that the data might become corrupt/damaged during transfer. Computer have various methods of checking is the data received is correct, method covered in this section include Parity Checks, Checksums and ARQs.
DATA INTEGRITY
Data integrity refers ensuring the data is correct and as it was intended to be. Various methods are used to help ensure data accuracy at the data input stage and at the data transmission stage and receiving stage.
Data accuracy/integrity during data transmission: During data transmission it is possible that data can be damaged through circuitry issues, electromagnetic interference when the signal is travelling via cables. Data could also be deliberately changed or corrupted during data transmission. In some stages data might be completely unreadable in other cases it is possible that binary representations of 1 is changed to a 0 and 0s to 1s. There are three common methods of checking if data has been received with all BIT's still as original.
Parity Check
Checksum
ARQ
PARITY CHECK
There are two type of parity checks, odd parity and even parity. The even parity check adds another BIT to each string of BITs to either make the number of 1s within that string even. For example:
Parity bit added 1 1101000
As seen above; at stage of transmission by adding a Parity BIT of 1 in front of the string 1101000 makes the total number of 1s even, when this is checked by the receiver if there was not an even number of 1s with an even parity check the a request to resend the data might be made.
To cross check this a parity byte is added, by doing this we can often work out which BIT has been changes during the transmission period.
As can be seen in the diagram above there is an odd number of 1s on row five meaning there must be an issue with one of the bits. A parity byte has been sent during transmission (bottom row) and it shows that one of the columns also has an odd number of BITs therefore we know that the issue is with the BIT in the intersection as shown in the diagram.
Where the incorrect BIT can be detected it will be changed and the data accepted, if the incorrect BIT cannot be detected then a ARQ request to resend the data will be made.
CHECKSUM
The checksum method looks at the numeric value of each byte in a block of bytes and sums the total of the predefined block of bytes, that total is then sent with the block of bytes and the check is then made on the receiving end to ensure the sum of the bytes matches the value of the checksum sent.
Above gives an example of a checksum for a block of four bytes. In practice the block of bytes would be much larger. For the purpose of using the checksum method the computers ignore what the actual byte represents and just looks at its numerical value.
ARQ - AUTO REPEAT REQUEST
An Auto Repeat Request (ARQ) is a protocol/rule used with data transfer to check for data transmission errors. It uses to factors, an acknowledgement and a timeout. The acknowledgment works by the receiver sending a message to the sender to acknowledge the data has been received without any known errors. The timeout is the time permitted by the sender for the acknowledgement from the receiver, if a timeout occurs then the sender knows the data may not have been received.
What is data loss in the context of data transmission errors?
What is data gain in the context of data transmission errors?
What is data change in the context of data transmission errors?
What is a parity byte check in data transmission and how does it work?
What is a parity block check in data transmission and how does it work?
How does interference impact data transmission and what are some common forms of interference?
How does the use of parity checks help to detect and prevent data transmission errors?
What is the difference between parity byte checks and parity block checks in data transmission?
How can the use of error correction techniques help to reduce the impact of data transmission errors?
What is the role of redundancy in reducing the impact of data transmission errors during data transmission?
