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:


   00100001   10000011      this binary number is 8579 decimal (base 10)

   00110000   01001000      this binary number is 12360 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 00100001 10000011 and 00110000 01001000 = 01010001   11001011

2. The internet checksum is the one's complement of the sum: 01010001   11001011 = 10101110   00110100



That's incorrect

That's correct

The answer was: 01010001   11001011

Question 1 of 2

The answer was: 10101110   00110100

Question 2 of 2

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