Senatek HELLODEVICE LITE SERIES LS100 - Manual (Page 29)

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- Sync-Sent
If the LS100 sends a connection request to a remote host, the state is changed from [Closed] to
[Sync-Sent]. This state is maintained until the remote host accepts the connection request. This
state is valid only in TCP client mode.
- Established
It represents “an open connection”. If one of the hosts accepts a connection request from the
other host, 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.
4.1 TCP Server Mode Operations
4.1.1 Overview
The LS100 works as a TCP server, and the default TCP state is [Listen] in this mode. The LS100
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