Which statement correctly describes the function of the TCP three-way handshake?

• A. It establishes a connection by synchronizing sequence numbers and agreeing on initial window size.
• B. It terminates the connection.
• C. It negotiates IP addresses.
• D. It closes the listen socket.

Answer: (A)

The three-way handshake is about starting a reliable connection by coordinating where to begin sending data and how much data can be in flight. The client starts by sending a segment with the SYN flag and its initial sequence number, signaling a new connection. The server replies with a segment that has both SYN and ACK, acknowledging the client’s sequence number and providing its own initial sequence number, which synchronizes both sides. The client then sends a final ACK to acknowledge the server’s SYN, and this completes the setup. The exchange also communicates the initial window size for flow control, so both sides know how much data can be sent before receiving further acknowledgments. Once this handshake finishes, the connection is established and data can be transferred reliably.