Connection state

ConnectionState is the current state of the connection. See Figure 1 for the Pascal declaration of the ConnectionStateType data type. ConnectionStateType is used in StatusInfoType and NotificationInfoType. It defines the client program view of the state of a TCP connection, in a form more readily usable than the formal TCP connection state defined by RFC 793. See Table 1 for the mapping between TCP states and ConnectionStateType.

Figure 1. Pascal declaration of connection state type

   ConnectionStateType =
   (
        CONNECTIONclosing,
        LISTENING,
        NONEXISTENT,
        OPEN,
        RECEIVINGonly,
        SENDINGonly,
        TRYINGtoOPEN
   );

CONNECTIONclosing: Indicates that no more data can be transmitted on this connection, because it is going through the TCP connection closing sequence.
LISTENING: Indicates that you are waiting for a foreign site to open a connection.
NONEXISTENT: Indicates that a connection no longer exists.
OPEN: Indicates that data can go either way on the connection.
RECEIVINGonly: Indicates that data can be received, but cannot be sent on this connection, because the client has done a TcpClose.
SENDINGonly: Indicates that data can be sent out, but cannot be received on this connection, because the foreign application has done a TcpClose or equivalent.
TRYINGtoOPEN: Indicates that you are trying to contact a foreign site to establish a connection.

Table 1 lists the TCP connection states.

Table 1. TCP connection states
TCP State	ConnectionStateType
CLOSED	NONEXISTENT
LAST-ACK, CLOSING, TIME-WAIT	If there is incoming data that the client program has not received, then RECEIVINGonly, otherwise CONNECTIONclosing.
CLOSE-WAIT	If there is incoming data that the client program has not received, then OPEN, otherwise SENDINGonly.
ESTABLISHED	OPEN
FIN-WAIT-1, FIN-WAIT-2	RECEIVINGonly
LISTEN	LISTENING
SYN-SENT, SYN-RECEIVED	TRYINGtoOPEN