What is the purpose of the TCP three-way handshake?

• A. Establish a reliable connection between client and server.
• B. Encrypt the payload data during transmission.
• C. Close a session immediately after negotiation.
• D. Transmit data without acknowledgments.

Answer: (A)

The main concept being tested is how the TCP three-way handshake establishes a reliable connection before any data starts to flow. The handshake initiates with a client sending a SYN to signal a request to open a connection and to establish an initial sequence number. The server replies with a SYN-ACK, acknowledging the request and supplying its own initial sequence number. The client then sends a final ACK to confirm, completing the setup. This exchange synchronizes both ends, confirms that each side can reach the other, and negotiates the basic parameters needed for reliable transmission, such as sequence spaces and initial flow-control values. Once the handshake finishes, data can be transferred with TCP’s reliability mechanisms—acknowledgments, retransmissions, and in-order delivery. This process is not about encryption, nor about closing a session (that uses a separate teardown), and it isn’t about sending data without acknowledgments—the reliability features come into play once the connection is established.