2. Serial Protocols
ROS® v3.11User Guide
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2.2.1.4. Preemptive Raw Socket
Figure 2.4. Permanent and Dynamic Master Connection Support
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 RTUs/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 permanent TCP connection.
Occasionally, RTU/IED maintenance configuration or control may be required from a different
master (on 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 diagram,
Permanent and Dynamic Master Connection Support
shows the case where
all RTUs are connected to Preemptive Raw Socket ports of RuggedServer devices. The
permanent master is connected to the Raw Socket port of the RuggedServer. Raw Socket
is configured to be connected to all Preemptive Raw Socket ports where polled RTUs are
connected (multiple incoming connection). Preemptive Raw Socket configuration on all ports
connected to RTUs will point to that Raw Socket as a permanent master (IP address and
Remote IP port).
A dynamic master can establish a connection to any Preemptive Raw Socket port at any time
and temporarily suspend the polling process (until the dynamic connection is cleared or times
out).
