RACOM M!DGE2, Руководство пользователя

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Each SCADA protocol like Modbus, DNP3, IEC101, DF1 etc. has its unique message format, most
importantly its unique way of addressing the remote units. The following text is valid for all M!DGE/RipEX
units (further in this
the section called “Protocol Server” referred to as a "Unit") - the special properties
for mobile cellular networks (e.g. limitation of broadcasting) are mentioned here. The basic task for the
protocol server is to check whether a received frame is within the protocol format and is not corrupted.
Most of the SCADA protocols are using some type of Error Detection Code (Checksum, CRC, LRC,
BCC, etc.) for data integrity control, so each Unit calculates this code and checks it against the received
one.
Cellular mobile network operates in IP environment, so the basic task for the Protocol server is to
convert SCADA serial packets to UDP datagrams. The Address translation settings are used to define
the destination IP address and UDP port. Then these UDP datagrams are sent to the M!DGE router,
processed there and are forwarded as unicasts through the mobile network to their destination. When
the gateway defined in the Routing table belongs to the Ethernet LAN, UDP datagrams are instead
forwarded to the Ethernet interface. After reaching the gateway, the datagram is forwarded according
to the Routing table.
When the UDP datagram reaches its final IP destination, it should be in a M!DGE or RipEX router
again. It is processed further according to its UDP port. It can be delivered to the Protocol server where
where the datagram is decapsulated and the data received on the serial interface of the source unit
are forwarded to COM. The UDP port can also be that of a Terminal server (RipEX) or any other special
protocol daemon on Ethernet like Modbus TCP etc. The datagram is then processed according to the
respective settings.
Note
All timeouts in the parameters described below are derived from the time when the packet is
sent into the COM driver, i.e. it includes the transfer time of the packet. Take this into account
especially when there is a low Baud rate set in the COM settings.
M!DGE2 GPRS/UMTS/HSPA+/LTE router – © RACOM s.r.o. 52
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