Suppose the information portion of a packet (D in Figure 5.3) contains 10
bytes consisting of the 8-bit unsigned binary ASCII representation of string
“Networking.” Compute the Internet checksum for this data.
1010101010110011
1111001111100000
To compute the Internet checksum for a given data, follow these steps:
Step 1: Convert the ASCII characters to their binary representations. The ASCII representation for the string "Networking" is as follows:
N - 01001110
e - 01100101
t - 01110100
w - 01110111
o - 01101111
r - 01110010
k - 01101011
i - 01101001
n - 01101110
g - 01100111
Step 2: Concatenate the binary representations together to form a single string:
010011100110010101110100011101110110111101110010011010110110100101101010011001110
Step 3: Divide the concatenated binary string into 16-bit chunks. In this case, we have 10 bytes, so we get 5 chunks:
0100111001100101
0111010001110111
0110111101101001
0110011101101110
011001110
Step 4: Perform one's complement addition on the 16-bit chunks. Add each chunk together, including any carry-over, and take the one's complement of the result. If there is a carry-over from the addition, add it back to the sum. In this case, the addition would be as follows:
0100111001100101 +
0111010001110111 =
110000101101110
110000101101110 +
0110111101101001 =
0011001001001111
0011001001001111 +
0110011101101110 =
1001100110111101
1001100110111101 +
011001110 =
1001110100010010
Step 5: Finally, take the one's complement of the sum. In this case, the one's complement of the sum is:
0110001011101101
So, the Internet checksum for the data "Networking" is 0110001011101101.
To compute the Internet checksum for a data packet, you need to follow these steps:
Step 1: Convert the ASCII characters in the data packet to their binary representation.
In this case, you have the string "Networking" which consists of 10 characters. Each character needs to be converted to its 8-bit unsigned binary ASCII representation.
Here's the binary representation for each character in the string "Networking":
N: 01001110
e: 01100101
t: 01110100
w: 01110111
o: 01101111
r: 01110010
k: 01101011
i: 01101001
n: 01101110
g: 01100111
Step 2: Group the binary representations into 16-bit words.
Since the checksum algorithm operates on 16-bit words, you need to group the binary representations into pairs of 8-bits.
Here are the 16-bit words formed from the binary representations above:
0100111001100101
0111010001110111
0110111101110010
0110101101101001
0110111001100111
Step 3: Sum up all the 16-bit words.
Add up all the 16-bit words obtained in the previous step.
0100111001100101 +
0111010001110111 +
0110111101110010 +
0110101101101001 +
0110111001100111
The sum is: 01010111100010100
Step 4: Take the one's complement of the sum.
To get the Internet checksum, you need to compute the one's complement of the sum calculated in the previous step. To do this, flip all the bits of the sum.
One's complement of 01010111100010100: 10101000011101011
Step 5: The resulting one's complement is the Internet checksum for the data packet.
The Internet checksum for the data packet "Networking" is 10101000011101011.