The Transmission Control Protocol (TCP) is a core protocol of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the entire suite is commonly referred to as TCP/IP.
Transmission Control Protocol (TCP) provides connection-oriented traffic with a guaranteed delivery.
TCP uses a three-way handshake.
To start a TCP session, the client sends a SYN (synchronize) packet.
The server responds with a SYN/ACK (synchronize/acknowledge) packet.
The client completes the third part of the handshake with an ACK packet to establish the connection.
SYN ======>
<======= SYN-ACK
ACK =======>