This document discusses error detection techniques. It defines an error as a condition when output information does not match input information, which can occur during data transmission due to noise. It describes parity check, checksum, and cyclic redundancy check (CRC) as common error detection methods. Parity check involves adding a parity bit to ensure an even or odd number of 1s. Checksum uses addition of data segments and complementing the sum. CRC appends a remainder from binary division of data by a divisor to detect errors.

1. INFORMATION
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ERROR DEDECTION

2. ERROR DEDECTION
Error is a condition when the output information
does not match with the input information.
During transmission, digital signals suffer from
noise that can introduce errors in the binary bits
travelling from one system to other. That means a
0 bit may change to 1 or a 1 bit may change to 0.
Whenever a message is transmitted, it may get
scrambled by noise or data may get corrupted.
A simple example of error-detecting code
is parity check

3. Types of error Dedection
•Parity check
•Checksum
•Cyclic Redundancy Check (CRC)

4. PARITY CHECK
Parity checking at the receiver can detect the presence of an
error if the parity of the receiver signal is different from the
expected parity. That means, if it is known that the parity of the
transmitted signal is always going to be "even" and if the
received signal has an odd parity, then the receiver can
conclude that the received signal is not correct. If an error is
detected, then the receiver will ignore the received byte and
request for retransmission of the same byte to the transmitter.

5. • It is the simplest technique for detecting and correcting
errors.
• Even parity -- Even parity means the number of 1's in the
given word including the parity bit should be even
(2,4,6,....).
• Odd parity -- Odd parity means the number of 1's in the
given word including the parity bit should be odd
(1,3,5,....).
Types of parity check

6. Checksum
• Data is divided into fixed sized frames or segments.
• The sender adds the segments using 1’s complement
arithmetic to get the sum. It then complements the sum
to get the checksum and sends it along with the data
frames.
• The receiver adds the incoming segments along with the
checksum using 1’s complement arithmetic to get the
sum and then complements it.
• If the result is zero, the received frames are accepted;
otherwise, they are discarded.

7. Cyclic Redundancy Check (CRC)
• The sender performs binary division of the data
segment by the divisor. It then appends the
remainder called CRC bits to the end of the data
segment. This makes the resulting data unit
exactly divisible by the divisor.
• The receiver divides the incoming data unit by
the divisor. If there is no remainder, the data unit
is assumed to be correct and is accepted.
Otherwise, it is understood that the data is
corrupted and is therefore rejected.

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