Most of the application layer protocols (like HTTP, telnet, SMTP etc.) use TCP as a transport protocol. TCP establishes a 3-way handshake between the client and server before any application layer data is transferred.
There are 3 messages involved in the handshake process. They are:
a. Synchronise (SYN) message from client
b. Synchronise (SYN) + Acknowledgement (ACK) from server
c. Acknowledgement (ACK) from client