Error Detection Methods In Data Transfer
Detection Methods
VRC(Vertical Redundancy Check)
LRC(Longitudinal Redundancy)
CRC(Cyclical redundancy Check)
Checksum
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| Detection Methods |
VRC(Vertical Redundancy Check)
A parity bit is added to every data unit so that the
total number of 1s(including the parity bit) becomes
“even for even-parity check” or “odd for odd-parity
check”
VRC can detect all single-bit errors.
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| Parity VRC concept |
LRC(Longitudinal Redundancy Check)
Create parity bit of each column into a new data unit,
which is added to the end of the data block
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| LRC(Longitudinal Redundancy Check) |
- Cyclic Redundancy Check (CRC) is and error detection
technique very used in computer network.
- CRC Code are also known as polynomial codes.
F(x) = x6+x4+x3+x+1 = (1 0 1 1 0 1 1) 2
1x6 + 0x5 + 1x4 + 1x3 + 0x2 + 1x + 1
- The message (Data) must be sent with calculated CRC code
so that it should be verified by receiver
- In CRC we have:
Data: which is to be sent
Divisor: Which is known and in both side of CRC sender and
Checker (Its MSB should not be 0)
Remainder: In sender side, it makes the CRC
Detection(cont’d)
Number of 0 (Zero) to add in from of Data is one less than Divisor
Length.
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| Detection(cont’d) |
Detection methods
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| Detection methods |
CRC generator
Binary Division
in a CRC Generator
Now Data to send is:
100100001
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| Binary Divisionin a CRC Checker |
Binary Division
in a CRC Checker
Checksum
Suppose we want to send (7, 11, 12, 0, 6). We can send (7, 11, 12, 0,
6, 36) and receiver checks the sum of the numbers and finds if it is
correct data. We can make it easier for receiver if send the negative
(complement) of the sum, called the checksum.
In this case, we send (7, 11, 12, 0, 6, −36). The receiver can add all
the numbers received (including the checksum). If the result is 0, it
assumes no error; otherwise, there is an error.
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| Checksum |
