Why does the TCP header contain ACK and SEQ fields?

Question

Since the TCP header is a relatively large overhead, why don't we compress it the way ACK and SEQ use the same field and can still be distinguished by the flags in the header?

Answer 1

Because they are not used exclusively. Below is the most important: connection negotiations, i.e. Three-way handshake:

Three-way handshake http://upload.wikimedia.org/wikipedia/commons/c/c7/300px-Tcp-handshake.png

wikimedia commons. , TCP-, , ACK SEQ ( , , , - ).

Answer 2

- , .

Answer 3

Because they can both be present in the header at the same time. One is to mark the data being sent, the other is what the sender expects in the next packet back. See wikipedia for more details .