Protocol TCP (Transmission Control Protocol) is one of the basic transport protocol on the Internet. This protocol allows to correct errors that may occur during packet transmission, and is a protocol with the establishment of a logical connection - a virtual channel.
Through this channel is transmitted and received packets with the registration of their sequence, manages the flow of packets, organized by the retransmission of distorted packets, and at the end of the session channel is broken. In this case, TCP is the only basic protocol of the family of TCP / IP, with the additional identification system for messages and connection. That is why the application layer protocols FTP, TELNET, providing users with remote access to hosts Internet, are realized by using the protocol TCP.
To identify the TCR-package in the TCP-header, there are two 32-bit identifier, which also play a role count packages.
Their names - Sequence Number and Acknowledgment Number. Also we are interested in a field called Control Bits.
This field size of 6 bits can contain the following command bits (from left right):
URG: Urgent Pointer field significant
ACK: Acknowledgment field significant
PSH: Push Function
RST: Reset the connection
SYN: Synchronize sequence numbers
FIN: No more data from sender