Error Detection Methods In Data Transfer

Error Detection Methods In Data Transfer

Detection Methods

VRC(Vertical Redundancy Check)

LRC(Longitudinal Redundancy)

CRC(Cyclical redundancy Check)

Checksum

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.

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

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.

Detection(cont’d)

Detection methods 

Detection methods 

CRC generator

Binary Division

in a CRC Generator

Now Data to send is:

100100001

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.

Checksum