Which TCP state indicates a successfully established connection?

The state that signifies a successfully established connection within the TCP (Transmission Control Protocol) state machine is "Established." In this state, a reliable communication link has been set up between two endpoints, allowing them to exchange data. During the establishment of a TCP connection, a three-way handshake process occurs, where both sides confirm the receipt and acknowledgment of packets, thus reaching the Established state.

When transitioned to this state, both the client and server can send and receive data, ensuring that the connection is active and reliable. The other states, such as Closed, New, and Listening, represent different phases of connection management – they indicate either a lack of an established connection, an initiating connection attempt, or a server awaiting inbound connections, respectively. Only the Established state confirms that data transfer can actively take place between the communicating entities.