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:


   11010111   00101100      this binary number is 55084 decimal (base 10)

   10001111   00111111      this binary number is 36671 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 11010111 00101100 and 10001111 00111111 = 01100110   01101100

2. The internet checksum is the one's complement of the sum: 01100110   01101100 = 10011001   10010011



That's incorrect

That's correct

The answer was: 01100110   01101100

Question 1 of 2

The answer was: 10011001   10010011

Question 2 of 2

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