SENA PS210W - Manual (Page 45)

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[Established]
It represents “an open connection”. If one of the hosts, the remote host or the Pro Series, accepts
a connection request from the other, the connection is opened and state is changed into
[Established].
[Data]
When it is in [Established] state, data from a host will be transferred to the other one. For easier
understanding of the TCP session operation, we called the state as [Data] state when actual data
transfer is performed. Actually, the [Data] mode is a part of [Established] state as is described in
the RFC 793 [Transmission Control Protocol]. This is a normal state for the data transfer phase of
the connection.
The Pro Series works as either TCP server or client according to the situation. This will be the typical
mode for most applications, since it will transfer the data either from serial port or from TCP port. The
default TCP state is [Listen] which is the same as that of TCP server mode.
1) Typical State Transition
[Listen] --> [Sync-Received] --> [Established] --> [Data] --> [Closed] --> [Listen]
Or
[Listen] --> [Sync-Sent] --> [Established] --> [Data] --> [Closed] --> [Listen]
The initial state is [Listen]. If there are data coming from the serial port, it will connect to the remote
host as a TCP client and then transfer data through the TCP port. If there is incoming connection
request from the remote host, it will accept the connection as a TCP server, and then transfer data
through the serial port. Thus, users can assume that the Pro Series is always connected to the
specified remote host.
2) Operations
Serial data transfer
Whenever the serial device sends data through the serial port of the Pro Series, data will be
accumulated on the serial port buffer of the Pro Series. If the buffer is full or the time gap reaches
the inter-character timeout (See 4.2.6. Serial port parameters for details), the Pro Series connect
to the registered remote host(s). If a TCP session has not been established yet. If the Pro Series
succeeds in connecting to the remote host, the data in the serial port buffer will be transferred to
the host. Otherwise, all the data stored in the buffer will be cleared.
Session disconnection
The connected session will be disconnected when the remote host sends disconnection request