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Chapter 5
Setup and Configuration
Figure 77: Broadcast RTU Polling
1. Host 2. RMC30 3. Ethernet 4. RTU
Initially, the remote servers establish connections with the host server. The host server is configured to accept a
maximum of three incoming connections.
The host sequentially polls each RTU. Each poll received by the host server is forwarded (i.e. broadcast) to all of
the remote servers. All RTUs receive the request and the appropriate RTU issues a reply. The reply is returned to
the host server, where it is forwarded to the host.
Section 5.4.1.4
Preemptive Raw Socket
Most SCADA protocols are master/slave and support only a single master device. Preemptive Raw Socket offers the
ability to have multiple masters communicate to Remote Terminal Units (RTUs) or Intelligent Electronic Devices
(IEDs) in a protocol-independent manner. For example, the SCADA master polling device is the normal background
process collecting data from the RTUs/IEDs on a permanent TCP connection. Occasionally, RTU/IED maintenance
configuration or control may be required from a different master (on a dynamic TCP connection).
This feature allows a dynamic master to automatically preempt a permanent master. A connection request from
the dynamic master would cause the permanent master to be suspended. Either closing the dynamic connection
or timing out on data packets causes the permanent master session to be resumed.
The illustrates the scenario where all RTUs are connected to Preemptive Raw Socket ports of RMC30 devices.
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Preemptive Raw Socket
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