3213Assignment2_solutions

3213Assignment2_solutions - CSE 3213 Fall 2009 Exercise 2...

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CSE 3213, Fall 2009 Exercise 2 - solutions Problem 1: If the ratio of error detection bits (EDB) to payload bits remain constant, what are the tradeoffs between: (a) having the error bits applied to smaller blocks of data, i.e. spread out over the sequence (see Figure 1), vs. (b) having the error bits applied to bigger blocks of data (see Figure 2). Figure 1 Figure 2 SOLUTION: Bigger blocks can detect longer burst errors. Smaller blocks reduce latency when sending small frames and reduce the amount of data to be re- transmitted when an error occurs. Problem 2: Suppose a header consists of the following bits: 11111111 11111111 11111111 00000000 11110000 11110000 11000000 11000000 Find the 16-bit Internet checksum for this code. SOLUTION: 1 st 16-bits 11111111 11111111 2 nd 16-bits 11111111 00000000 ---------------------------- sum: 1 11111110 11111111 1-s complement: 11111111 00000000 __________________________________________________________________ 11111111 00000000 3 rd 16-bits 11110000 11110000
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