Interactive end-of-chapter exercises


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:


   11111011   00110000      this binary number is 64304 decimal (base 10)

   10111011   00010111      this binary number is 47895 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 11111011 00110000 and 10111011 00010111 = 10110110   01001000

2. The internet checksum is the one's complement of the sum: 10110110   01001000 = 01001001   10110111



That's incorrect

That's correct

The answer was: 10110110   01001000

Question 1 of 2

The answer was: 01001001   10110111

Question 2 of 2

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We greatly appreciate the work of John Broderick (UMass '21) in helping to develop these interactive problems.

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