TCPtilstand

TCPtilstand, often translated as TCP state, refers to the distinct phases a Transmission Control Protocol (TCP) connection progresses through during its lifetime. This state machine is fundamental to TCP's reliable and ordered data delivery.

The cycle typically begins with the LISTEN state, where a server waits for incoming connection requests. Upon receiving a SYN (synchronize) packet, the server transitions to SYN-SENT or SYN-RECEIVED, initiating the three-way handshake. If the handshake is successful, the connection enters the ESTABLISHED state, where data transfer can occur.

During data transfer, connections can also be in states related to managing the flow of data, such as FIN-WAIT-1, FIN-WAIT-2, CLOSE-WAIT, and CLOSING, which are part of the connection termination process. The four-way handshake is used to gracefully close a TCP connection.

The TIME-WAIT state is a crucial final stage for the side that initiated the active close. It exists to ensure that any delayed packets from the previous connection still in transit are handled correctly before the port resources are fully released. Finally, the CLOSED state signifies that the connection is no longer active. Each state has specific rules governing the valid incoming and outgoing TCP segments, ensuring the integrity and reliability of the communication.