TCP is a connection-oriented protocol. It means that the involved machines must create a connection before exchanging data. Opening a TCP connection includes exchanging control messages between the machine that starts and the machine that waits for a communication.
First, the client sends an SYN message to the server. Then, if the server is available, it responds to the client with an SYN-ACK. Thus, the client confirms the SYN-ACK by sending an ACK to the server. Finally, the connection is established, and the machines can exchange data.
Potential Connection Problems :