What is the TCP hand shake?

TCP requires three packets to set up a socket connection, before any user data can be sent. This is called the tree way TCP handshake. First the requester sends a SYN packet and expects a SYN-ACK packet, to which the initiator replies with ACK packet plus the first chunk of user data. From there on the TCP connection is established and two sides exchange user data using features such as message acknowledgment, retransmission and timeout.