Binary Inverse Code summation _TCP/IP

When you look at TCP/IP, you see that there is a header check in the IP protocol and a binary inverse code sum. Not quite understand, the Internet found an answer, recorded below.

Check and verify with 4bit (easy to compute and 16bit is the same).

Suppose the original data is 1100, 1010, 0000 (check digit)


Then they are added by a bitwise-by-group in 4bit. 1100 Take the counter 0011, 1010 take the reverse is 0101, the check digit is 0011 plus 0101 is 1000, fill in to check digit

So the data sent is

1100, 1010, 1000


After receiving the data, the same bitwise reverse addition is added. 0011+0101+0111 = 1111; All 1 indicates the correct. is equal to oneself plus own reverse, then the result certainly should be all 1. If the transmission is correct.