TCP header structure
tcp fixed length header of 20bytes
data offset: indicates the total header length tcp
the URG: behalf of the data packet if it contains an emergency
ACK: acknowledgment number, ACK handshake tcp value after successfully transmitted three times in case of holding 1
PSH: indicates whether the received packet tcp to be uploaded directly to the upper application layer, in the cache area represents 0, 1 represents a direct upload *** can be used to send large amounts PSH = tcp packets 0 to disrupt transmission
RST: If received a message to RST = 1, indicating problems with connection to the host of a serious error (such as a host crash), the connection must be released, then re-establish the connection. Or state data previously transmitted to the host in question, host rejection response, TCP segment with the RST flag called a reset segment
SYN: used when establishing a connection, the first secondary handshake. 1
the FIN: a notification to close the other end is connected to this, if the flag data is sent. If FIN = 1, that is, to tell each other: "My data has been sent, you can release the connection", TCP segments with the FIN flag is called the end of the segment
in the process of transmission, ack = seq + segment segment how many packets that pass, this value is limited by the window