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    Lecture 13 Data Link Layer Error Detection Methods

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    Mahnoor Lab Engr EE
    The document discusses three error detection methods used at the data link layer: 1) Parity-check codes use an extra bit to detect single-bit errors through syndrome calculation. Simple parity can detect odd errors but not bursts. 2) Cyclic redundancy check (CRC) uses a polynomial division technique to generate a checksum that can detect all single and multiple bit errors. 3) Checksum involves adding data sections using 1's complement, complementing the sum, and sending the checksum with data for the receiver to validate no errors.

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    Lecture 13 Data Link Layer Error Detection Methods

    Uploaded by

    Mahnoor Lab Engr EE
    11 views13 pages
    The document discusses three error detection methods used at the data link layer: 1) Parity-check codes use an extra bit to detect single-bit errors through syndrome calculation. Simple parity can detect odd errors but not bursts. 2) Cyclic redundancy check (CRC) uses a polynomial division technique to generate a checksum that can detect all single and multiple bit errors. 3) Checksum involves adding data sections using 1's complement, complementing the sum, and sending the checksum with data for the receiver to validate no errors.

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    Lecture 13 Data Link Layer Error Detection Methods

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    Lecture 13 Data Link Layer Error Detection Methods

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    The document discusses three error detection methods used at the data link layer: 1) Parity-check codes use an extra bit to detect single-bit errors through syndrome calculation. Simple parity can detect odd errors but not bursts. 2) Cyclic redundancy check (CRC) uses a polynomial division technique to generate a checksum that can detect all single and multiple bit errors. 3) Checksum involves adding data sections using 1's complement, complementing the sum, and sending the checksum with data for the receiver to validate no errors.

    Copyright:

    © All Rights Reserved
    Download as PPTX, PDF, TXT or read online from Scribd
    Download as pptx, pdf, or txt
    11 views13 pages

    Lecture 13 Data Link Layer Error Detection Methods

    Uploaded by

    Mahnoor Lab Engr EE
    The document discusses three error detection methods used at the data link layer: 1) Parity-check codes use an extra bit to detect single-bit errors through syndrome calculation. Simple parity can detect odd errors but not bursts. 2) Cyclic redundancy check (CRC) uses a polynomial division technique to generate a checksum that can detect all single and multiple bit errors. 3) Checksum involves adding data sections using 1's complement, complementing the sum, and sending the checksum with data for the receiver to validate no errors.

    Copyright:

    © All Rights Reserved
    Download as PPTX, PDF, TXT or read online from Scribd
    Download as pptx, pdf, or txt
    of 13

    Computer Networks

    Data Link Layer

    LECTURE 13
    DATA LINK LAYER

    DATA LINK CONTROL (DLC)


    Error Detection Methods
    Parity-Check Code
    Cyclic Redundancy Check
    Checksum
    Error Detection
    Simple Parity Check

    A simple parity-check code is a single-bit error-


    detecting code in which n = k + 1.
    Example
    Let us look at some transmission scenarios. Assume
    the sender sends the dataword 1011. The codeword
    created from this dataword is 10111, which is sent to
    the receiver. We examine five cases:
    1. No error occurs; the received codeword is 10111. The
    syndrome is 0. The dataword 1011 is created.
    2. One single-bit error changes a1 . The received
    codeword is 10011. The syndrome is 1. No dataword is
    created.
    3. One single-bit error changes r0 . The received codeword is
    10110. The syndrome is 1. No dataword is created.
    Example (contd.)

    4. An error changes r0 and a second error changes a3 .


    The received codeword is 00110. The syndrome is 0. The
    dataword 0011 is created at the receiver. Note that
    here the dataword is wrongly created due to the
    syndrome value.
    5. Three bits—a3, a2, and a1—are changed by errors.
    The received codeword is 01011. The syndrome is 1.
    The dataword is not created. This shows that the simple
    parity check, guaranteed to detect one single error, can
    also find any odd number of errors.
    Performance

    A Simple parity check can detect all single-bit errors.


    It can detect burst errors only if the total number of
    errors in each data unit is odd.
    Cyclic Redundancy Check
    •Cyclic Redundancy Check (also called polynomial code)
    •Based on modulo-2 binary division
    • No carries (because it's modulo-2)
    • Subtraction is equivalent to XOR
    Division in CRC encoder
    Division in the CRC decoder for two cases
    Checksum

    Example:
    IP header

    1. The data unit is divided into k sections, each of n bits


    2. All sections are added using 1’s complement
    3. The sum is complemented
    4. The checksum is sent with data
    Checksum: Sending

    Suppose the following block of 16 bits is to be sent using


    a checksum of 8 bits.
    10101001 00111001
    The numbers are added using one’s complement
    10101001
    00111001
    ------------
    Sum 11100010
    Checksum 00011101 (Take 1’s complement of Sum)
     The pattern sent is 10101001 00111001 00011101
    Checksum: Receiving

    Now suppose the receiver receives the pattern sent and


    there is no error.
    10101001 00111001 00011101
    When the receiver adds the three sections, it will get all
    1s, which, after complementing, is all 0s and shows
    that there is no error.
    10101001
    00111001
    00011101
    Sum 11111111
    Complement 00000000 means that the pattern is
    OK.

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