chap11_part2

# Example 114 continued 1 7 what is the utilization

• Notes
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Example 11.4 (continued)

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1 7 What is the utilization percentage of the link in Example 11.4 if we have a protocol that can send up to 15 frames before stopping and worrying about the acknowledgments? Solution The bandwidth-delay product is still 20,000 bits. 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. Example 11.5
1 8 In the Go-Back-N Protocol, the sequence numbers are modulo 2 m , where m is the size of the sequence number field in bits. Note

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1 9 Figure 11.12 Send window for Go-Back-N ARQ
1 10 The send window is an abstract concept defining an imaginary box of size 2 m − 1 with three variables: Sf, Sn, and Ssize. Note

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1 11 The send window can slide one or more slots when a valid acknowledgment arrives. Note
1 12 Figure 11.13 Receive window for Go-Back-N ARQ

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1 13 The receive window is an abstract concept defining an imaginary box of size 1 with one single variable Rn. The window slides when a correct frame has arrived; sliding occurs one slot at a time. Note
1 14 Figure 11.14 Design of Go-Back-N ARQ

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1 15 Figure 11.15 Window size for Go-Back-N ARQ
1 16 In Go-Back-N ARQ, the size of the send window must be less than 2 m ; the size of the receiver window is always 1.

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• Fall '11
• manjunath
• Selective Repeat ARQ, Go-Back-N ARQ, Stop-and-wait ARQ

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