Interactive end-of-chapter exercises


Supplement to Computer Networking: A Top Down Approach 8th Edition


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Computing an Internet checksum

Consider the two 16-bit words (shown in binary) below. Recall that to compute the Internet checksum of a set of 16-bit words, we compute the one's complement sum [1] of the two words. That is, we add the two numbers together, making sure that any carry into the 17th bit of this initial sum is added back into the 1's place of the resulting sum); we then take the one's complement of the result. Compute the Internet checksum value for these two 16-bit words:


   10111110   10100011      this binary number is 48803 decimal (base 10)

   11000100   00000100      this binary number is 50180 decimal (base 10)



Question List


1. What is the sum of these two 16 bit numbers? Don't put any spaces in your answer

2. Using the sum from question 1, what is the checksum? Don't put any spaces in your answer




Solution


1. The sum of 10111110 10100011 and 11000100 00000100 = 10000010   10101000

2. The internet checksum is the one's complement of the sum: 10000010   10101000 = 01111101   01010111



That's incorrect

That's correct

The answer was: 10000010   10101000

Question 1 of 2

The answer was: 01111101   01010111

Question 2 of 2

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