SENA PS400 - Manual (Page 31)

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- 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.
4.1.2 TCP server mode operations
The HelloDevice Pro Series works as a TCP server, and the default TCP state is [Listen] in this mode.
The HelloDevice Pro Series supports only one TCP socket connection per one serial port. If a
connection is currently established, the additional connection requests will be rejected. The remote
host will be either Ethernet-Serial communication devices acting as a TCP client or a socket program
acting as a TCP client running on users ’PC.
1) Typical State Transition
[Listen] --> [Sync-Received] --> [Established] --> [Data] --> [Closed] --> [Listen]
At start-up, an initial TCP state is [Listen]. If there is any incoming TCP connection request, the state
will be changed into [Sync-Received], then [Established], which means a session is opened. For a
while, data will be transferred between the hosts. This is the [Data] state. The session will be
disconnected due to the request of one of them, which is [Closed] state. And then, the state is
automatically changed to its original state, [Listen].
2) Operations
Serial data transfer
When a session has been established, the HelloDevice Pro Series reads the data from the serial
port buffer till internal serial buffer is full or inter-character time interval reaches the time specified
as inter-character timeout value. Then, it transfers the data to the IP address (or domain name) of
the remote host (See Options in section 4.4 for more details on inter-character timeout). If there’s
no remote host connected to the HelloDevice Pro Series, all the incoming data from the serial port
are discarded.
Session disconnection
The connected session will be disconnected when the remote host sends disconnection request
or when no data transfer activity is found through the serial port for a certain amount of time,
which is “Inactivity timeout” (See Options in section 4.4 for details on Inactivity timeout).