Error Detection in Data Link Layer

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 Sure! Error control in the data link layer ensures that data is transmitted accurately over a network. It involves both error detection and error correction techniques. Here’s a detailed explanation with examples:

Error Detection

Error detection involves identifying errors in the transmitted data. Common techniques include:


  2. Sure! Let’s dive into the different error detection methods used in the data link layer: VRC, LRC, CRC, and Checksum.

    1. Vertical Redundancy Check (VRC)

    VRC, also known as Parity Check, involves adding a parity bit to each data unit (byte). This parity bit ensures that the total number of 1s in the byte (including the parity bit) is even (even parity) or odd (odd parity).

    Example:

    • Data to be sent: 1010001
    • Even parity: Add a parity bit 1 to make the total number of 1s even: 10100011
    • Odd parity: Add a parity bit 0 to keep the total number of 1s odd: 10100010





    At the receiver’s end, the parity of the received data is checked. If it doesn’t match the expected parity, an error is detected.

    2. Longitudinal Redundancy Check (LRC)

    LRC involves adding a block of parity bits across multiple data units. A parity bit is calculated for each bit position across all data units in a block, creating a “longitudinal” set of parity bits.

    Example:

    • Data block:
      1010
1100
1001
    • Calculate parity bits for each column:
      1111 (LRC)
    • Transmitted data block with LRC:
      1010
1100
1001
1111 (LRC)


    At the receiver’s end, the LRC is recalculated and compared with the received LRC to detect errors.

    3. Cyclic Redundancy Check (CRC)

    CRC uses polynomial division to detect errors. The data is treated as a long binary number and divided by a predetermined polynomial divisor. The remainder from this division (CRC value) is appended to the data.

    Example:

    • Data to be sent: 1101011011
    • Polynomial: 1011
    • Perform binary division and append the remainder (CRC) to the data.

    • CRC

    At the receiver’s end, the same polynomial division is performed on the received data. If the remainder is zero, the data is considered error-free.

    4. Checksum

    Checksum involves summing all data units and appending the result as a checksum. The receiver sums the received data units (including the checksum) and checks if the result matches the expected value.

    Example:

    • Data units: 1001, 1100, 1010
    • Sum: 1001 + 1100 + 1010 = 11111
    • Checksum: 11111
    • Transmitted data with checksum: 1001 1100 1010 11111



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