SolStd11 - CHAPTER 11 Data Link Control Solutions to...

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1 CHAPTER 11 Data Link Control Solutions to Odd-Numbered Review Questions and Exercises Review Questions 1. The two main functions of the data link layer are data link control and media access control . Data link control deals with the design and procedures for commu- nication between two adjacent nodes: node-to-node communication. Media access control deals with procedures for sharing the link. 3. In a byte-oriented protocol , data to be carried are 8-bit characters from a coding system. Character-oriented protocols were popular when only text was exchanged by the data link layers. In a bit-oriented protocol , the data section of a frame is a sequence of bits. Bit-oriented protocols are more popular today because we need to send text, graphic, audio, and video which can be better represented by a bit pat- tern than a sequence of characters. 5. Flow control refers to a set of procedures used to restrict the amount of data that the sender can send before waiting for acknowledgment. Error control refers to a set of procedures used to detect and correct errors. 7. In this chapter, we discussed three protocols for noisy channels: the Stop-and-Wait ARQ , the Go-Back-N ARQ , and the Selective-Repeat ARQ . 9. In the Go-Back-N ARQ Protocol , we can send several frames before receiving acknowledgments. If a frame is lost or damaged, all outstanding frames sent before that frame are resent. In the Selective- Repeat ARQ protocol we avoid unnecessary transmission by sending only the frames that are corrupted or missing. Both Go- Back- N and Selective-Repeat Protocols use sliding windows . In Go-Back- N ARQ, if m is the number of bits for the sequence number, then the size of the send win- dow must be at most 2 m 1 ; the size of the receiver window is always 1. In Selec- tive-Repeat ARQ, the size of the sender and receiver window must be at most 2 m 1 . 11. Piggybacking is used to improve the efficiency of bidirectional transmission. When a frame is carrying data from A to B, it can also carry control information
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SolStd11 - CHAPTER 11 Data Link Control Solutions to...

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