L26 - Review for Exam 2 part A The Data Link Layer Basic...

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Review for Exam 2 - part A The Data Link Layer Basic principles for reliable communication despite errors: 1. error detection - negligible chance of undetected error. 2. Acknowledgments - re-send if in doubt 3. Sequence number the data. Error detection Details of the CRC polynomial method for generating the Frame check sequence and detecting errors will not be part of this exam.
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Elementary Data Link Protocols stop -and - wait protocol: one frame at a time. For stop-and-wait , one frame at a time, can operate with a one-bit sequence number. The acknowledgment is conveyed by specifying the next expected sequence number .
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Example of operation with some losses or errors: Dashed line indicates loss or error. If variable ACK delay, have Timeout concept - If no response by a certain time, the frame is retransmitted.
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important assumption with variable delay and timeouts: No jumping over in time.
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Error control with multiple frames outstanding Communication is faster, but requires more sequence number bits. Let b be the number of bits in the sequence number. Sending "next expected" sequence number acts as a cumulative acknowledgment. There is a certain maximum window W of number of unacknowledged frames, so as to ensure no ambiguity. The “
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L26 - Review for Exam 2 part A The Data Link Layer Basic...

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