7.3.5. Protocols
Fig. 7.8: Menu Protocols COM
Generally
Each SCADA protocol like Modbus, DNP3, IEC101, DF1 etc. has its unique message format, most
importantly its unique way of addresing of remote units. The basic task for protocol utility is to check
whether received frame is within protocol format and it is not corrupted. Most of the SCADA protocols
are using some type of Error Detection Codes (Checksum, CRC, LRC, BCC, etc.) for data integrity
control, so RipEX calculates this code and check it with the received one.
RipEX radio network works in IP enviroment, so the basic task for Protocol interface utility 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 RipEX router, processed
there and they are typically forwarded as unicasts to Radio channel to their destination. When the
gateway defined in the Routing table belongs to the Ethernet LAN, UDP datagrams are rather forwarded
to the Ethernet interface. After reaching the gateway (typically a RipEX router again), the datagram is
forwarded according to the Routing table.
Note:
Even if UDP datagrams, they can be acknowledged on the Radio channel (ACK parameter of
Router mode), however they are not acknowledged on Ethernet.
When the UDP datagram reaches its final IP destination, it should be in a RipEX router again (either
its ETH or Radio interface). It is processed further according its UDP port. It can be delivered to COM1(2)
port daemon, where the datagram is decapsulated and the data received on the serial interface of the
source unit are forwarded to COM1(2). The UDP port can also be that of a Terminal server or any
other special protocol daemon on Ethernet like Modbus TCP etc. The datagram is then processed ac-
cordingly to the respective settings.
RipEX uses a unique, sophisticated protocol on Radio channel. This protocol ensures high probability
of data delivery. It also guarantees data integrity even under heavy interference or weak signal conditions
due to the 32 bit CRC used, minimises the probability of collision and retransmits frame when a collision
happens, etc., etc. These features allow for the most efficient SCADA application arrangements to be
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Advanced Configuration
