Suppose the information portion of packet (D in figure 5.4) contains 10 bytes consisting of the 8-bit unsigned binary ASCII representation of string “Link Layer.” Compute the internet checksum for this data. Can someone explain to me how is this done?
Info in D is: 0111000110101011.
To compute the internet checksum for the given information portion of the packet, which is "0111000110101011" representing the ASCII string "Link Layer" in binary, you need to follow these steps:
Step 1: Split the 10 bytes of data into 16-bit chunks (two bytes).
- "01 11 00 01 10 10 11 01 01 10" (linking adjacent bytes)
Step 2: Add up all the 16-bit chunks (excluding any carry generated):
- 01110001 + 10101101 + 01100110 + carry = partial sum 1
Step 3: Calculate the complement (1's complement) of the partial sum:
- complement(partial sum 1) = 10001110
Step 4: Add the partial sum 1 and its complement:
- partial sum 1 + complement(partial sum 1) = 00000000
Step 5: Take the complement of the result obtained from step 4:
- complement(result of step 4) = 11111111
This resulting 8-bit value, "11111111," is the internet checksum for the given data.
Note: In step 2, if there is any carry generated during the addition of 16-bit chunks, it should be added back to the 16-bit sum (carry generated in this case is 0, so no adjustment is needed). Also, make sure to perform the arithmetic in binary without any decimal conversions.
To compute the Internet checksum for the given data, you need to follow these steps:
Step 1: Divide the data into 16-bit chunks
The given data is "0111000110101011", which consists of 16 bits. Since the Internet checksum operates on 16-bit chunks, we need to split the data into two 16-bit chunks: "0111000110101011" -> "011100011010101" and "1"
Step 2: Add the 16-bit chunks together using one's complement addition
Perform one's complement addition by adding the two 16-bit chunks together. If there's a carry out beyond the 16 bits, add it back to the result until there's no carry.
So, let's perform the addition:
011100011010101
+ 1
----------------
011100011010110
Step 3: Take the one's complement of the result
To get the Internet checksum, we need to take the one's complement of the result obtained from the addition.
Taking the one's complement of "011100011010110" yields:
100011100101001
This is the Internet checksum for the given data, "0111000110101011" or "Link Layer."