What initiates the TCP three-way handshake?

• A. A client sends a SYN to initiate the connection.
• B. A server sends a FIN.
• C. A client sends a RST.
• D. A client sends a data packet.

Answer: (A)

The handshake starts when a client wants to open a TCP connection and sends a segment with the SYN flag set. This SYN is a request to begin communication and to establish the initial sequence numbers. The server then responds with a SYN-ACK, acknowledging the request and proposing its own sequence number, and finally the client sends an ACK to confirm, completing the connection setup. This sequence is the mechanism that initializes a reliable session and ensures both sides are ready to exchange data.

The other actions described are part of other phases. A FIN initiates closing a connection, a RST resets a connection, and a data packet is sent after a connection has already been established. None of these start the handshake, which is specifically triggered by the initial SYN from the client.