450_SampleQuestions_4_solutions

450_SampleQuestions_4_solutions - EE 450 Sample Questions 4...

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1 EE 450 Sample Questions 4 Solutions Summer ’09 ● Nazarian 1. Dataword Number of 1s Parity Codeword a. 1001011 4 (even) 0 0 1001011 b. 0001100 2 (even) 0 0 0001100 c. 1000000 1 (odd) 1 1 1000000 d. 1110111 6 (even) 0 0 1110111 Note: The receiver knows which bit is the parity bit in the codeword (the least significant bit or the most significant bit) - 2. a. b. 0 0
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2 3. a. 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 communication between two adjacent nodes: node-to-node communication. Media access control deals with procedures for sharing the link. b. 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. c. Go-Back-N ARQ is more efficient than Stop-and-Wait ARQ. The second uses pipelining , the first does not. In the first, sender needs to wait for an acknowledgment for each frame before sending the next one. In the second sender can send several frames before receiving an acknowledgment from the receiver. d. 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 both 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 window must be at most 2 m - 1 ; the size of the receiver window is always 1. In Selective-Repeat ARQ, the size of the sender and receiver window must be at most 2 m - 1 . e.
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This note was uploaded on 02/09/2012 for the course EE 450 taught by Professor Zahid during the Spring '06 term at USC.

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450_SampleQuestions_4_solutions - EE 450 Sample Questions 4...

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