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The bit-stuffing technique

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• Difference between bit framing and byte framing
  • Byte framing:

    Impart special meaning to some byte patterns Example: SOH (Start of header) SOT (Start of text) EOT (End of text) ESC (Escape !!!)

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  • Bit framing:

    Do not impart special meaning to some byte patterns Therefore: There is no ESCAPE character in bit-oriented framing protocols !!!!!

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• Avoid using the flag pattern in a frame
  • Fact:

    Bit-oriented framing protocols uses: The bit-stuffing technique         to avoid transmitting a flag pattern in the data portion

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• Bit Stuffing
  • Bit stuffing transmission rule:

    Whenever the sender has transmitted 5 consecutive "1" bits: the sender must insert one 0 bit into the transmission

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    Example:

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  • Bit stuffing receive rule:

    When "011111" is received: Next bit = 0 ===> discard this "0" bit (it was a stuffed 0 bit) Next bit = 1 ===> Next bit = 0 ====> Flag detected Next bit = 1 ====> Transmission error detected

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    Example: