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:


   11100001   00110101      this binary number is 57653 decimal (base 10)

   10010000   00101111      this binary number is 36911 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 11100001 00110101 and 10010000 00101111 = 01110001   01100101

2. The internet checksum is the one's complement of the sum: 01110001   01100101 = 10001110   10011010



That's incorrect

That's correct

The answer was: 01110001   01100101

Question 1 of 2

The answer was: 10001110   10011010

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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