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Selective Acknowledgement

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• Acknowledgement methods
  • Recall:

    An acknowledgement frame contains: Indications in the frames that the frame is an acknowledgement frame (and not e.g., a data frame) A receive sequence number (The receive sequence number differentiates one ACK frame from another ACK frame. We added the receive sequence number to an ACK frame to solve the delayed ACK error: click here)

  • Fact:

    An acknowledgement ACK n (n is the receive sequence number) can be interpreted in different ways !!!

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  • Commonly used meanings assigned to ACK n:

    ACK n acknowlegdes only the frame with sequence number n ACK n acknowlegdes all the frame with sequence number ≤ n−1

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• Selective Acknowledgement
  • Selective Acknowledgement:

    Selective Acknowledgement = an acknowlegdement protocol (= agreement) where: The frame ACK n acknowledges only the data frame n

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  • Comment:

    That's what I have been using all the time without telling you the official name of the protocol....