What is TCP (Transmission Control Protocol)?
TCP is a connection-oriented protocol it establishes a logical connection between two computers. Before transferring data, the two computers exchange control messages to make sure a connection has been established, this process is called handshaking. TCP sets up control functions in the Flag field of the Segment Header. Compared to UDP, TCP is a very reliable protocol, and uses PAR (Positive Acknowledgment with Re-transmission) to guarantee that data from one host computer can reach the other host computer safely and correctly.