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Chapter 11 Data Link Control and Protocols

Chapter 11 Data Link Control and Protocols. Flow and error control Stop-and-wait ARQ Go-back-N ARQ Selective repeat ARQ. Flow and Error Control. Flow control refers to a set of procedures used to restrict the amount of data that the sender can send before waiting for acknowledgement

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Chapter 11 Data Link Control and Protocols

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  1. Chapter 11 Data Link Control and Protocols Flow and error control Stop-and-wait ARQ Go-back-N ARQ Selective repeat ARQ Data Communications, Kwangwoon University

  2. Flow and Error Control • Flow control refers to a set of procedures used to restrict the amount of data that the sender can send before waiting for acknowledgement • Error control in the data link layer is based on automatic repeat request (ARQ), which is the retransmission of data • Common flow and error control mechanisms • Stop-and-wait ARQ • Go-back-N ARQ • Selective repeat ARQ Data Communications, Kwangwoon University

  3. Stop-and-Wait ARQ: Normal Operation Data Communications, Kwangwoon University

  4. Stop-and-Wait ARQ: Lost Frame Data Communications, Kwangwoon University

  5. Stop-and-Wait ARQ: Lost ACK Data Communications, Kwangwoon University

  6. Stop-and-Wait ARQ: Delayed ACK Data Communications, Kwangwoon University

  7. Stop-and-Wait ARQ: Piggybacking Data Communications, Kwangwoon University

  8. Sliding Window ARQ Flow/Error Control Stop-and-Wait ARQ Sliding Window ARQ Go-back-N ARQ Selective Repeat ARQ Data Communications, Kwangwoon University

  9. Sliding Window: Sender Data Communications, Kwangwoon University

  10. Sliding Window: Receiver Data Communications, Kwangwoon University

  11. Sliding Window: Control Variables Data Communications, Kwangwoon University

  12. Go-Back-N ARQ: Normal Operation Data Communications, Kwangwoon University

  13. Go-Back-N ARQ: Lost Frame Data Communications, Kwangwoon University

  14. Go-Back-N ARQ: Sender Window Size Data Communications, Kwangwoon University

  15. Selective Repeat ARQ: Windows Data Communications, Kwangwoon University

  16. Selective Repeat ARQ: Lost Frame Data Communications, Kwangwoon University

  17. Selective Repeat ARQ: Sender Window Size Data Communications, Kwangwoon University

  18. Aspects of the Mechanisms • Stop-and-wait ARQ • Numbering frames prevents the retaining of duplicate frames • Numbered acknowledgements are needed if an acknowledgement is delayed and the next frame is lost • Go-back-N ARQ • The size of the sender window must be less then 2m; the size of the receiver window is always 1 • Selective repeat ARQ • The size of the sender and receiver window must be at most one-half of 2m Data Communications, Kwangwoon University

  19. Examples • In a Stop-and-Wait ARQ system, the bandwidth of the line is 1 Mbps, and 1 bit takes 20 ms to make a round trip. What is the bandwidth-delay product? If the system data frames are 1000 bits in length, what is the utilization percentage of the link? The bandwidth-delay product is 1  106 20  10-3 = 20,000 bitsThe system can send 20,000 bits during the time it takes for the data to go from the sender to the receiver and then back again. However, the system sends only 1000 bits. We can say that the link utilization is only 1000/20,000, or 5%. For this reason, for a link with high bandwidth or long delay, use of Stop-and-Wait ARQ wastes the capacity of the link • What is the utilization percentage of the link in Example 1 if the link uses Go-Back-N ARQ with a 15-frame sequence? The bandwidth-delay product is still 20,000. The system can send up to 15 frames or 15,000 bits during a round trip. This means the utilization is 15,000/20,000, or 75 percent. Of course, if there are damaged frames, the utilization percentage is much less because frames have to be resent Data Communications, Kwangwoon University

  20. HDLC: NRM Data Communications, Kwangwoon University

  21. HDLC: ABM Data Communications, Kwangwoon University

  22. HDLC: Frame Data Communications, Kwangwoon University

  23. HDLC Frame Types Data Communications, Kwangwoon University

  24. I-Frame Data Communications, Kwangwoon University

  25. S-Frame Control Field Data Communications, Kwangwoon University

  26. U-Frame Control Field Data Communications, Kwangwoon University

  27. Example Data Communications, Kwangwoon University

  28. Example Data Communications, Kwangwoon University

  29. Bit Stuffing and Removal Data Communications, Kwangwoon University

  30. Bit Stuffingin HDLC Data Communications, Kwangwoon University

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