The Transmission Control Protocol (TCP) is known for its three-way handshake. This is a method of establishing a connection. A connection is the key characteristic of TCP. The alternative protocol in the Transport Layer of TCP/IP is called the User Datagram Protocol (UDP), which does not establish a connection and so is known as a connectionless protocol. The TCP connection is begun with a SYN packet sent by the client to the server and this requests a connection. The server replies with a SYN+ACK package, which says “Yes, OK.” The client then replies with an ACK message, which says “Let’s do it.”