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:


   00100111   11000010      this binary number is 10178 decimal (base 10)

   10110011   01100001      this binary number is 45921 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 00100111 11000010 and 10110011 01100001 = 11011011   00100011

2. The internet checksum is the one's complement of the sum: 11011011   00100011 = 00100100   11011100



That's incorrect

That's correct

The answer was: 11011011   00100011

Question 1 of 2

The answer was: 00100100   11011100

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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