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:


   11011101   00010111      this binary number is 56599 decimal (base 10)

   00111111   11111001      this binary number is 16377 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 11011101 00010111 and 00111111 11111001 = 00011101   00010001

2. The internet checksum is the one's complement of the sum: 00011101   00010001 = 11100010   11101110



That's incorrect

That's correct

The answer was: 00011101   00010001

Question 1 of 2

The answer was: 11100010   11101110

Question 2 of 2

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