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RS400 57 ROS™ v3.5
2.2.1.4 Preemptive Raw Socket
Figure 33: 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 a multiple masters communicate to RTUs/IEDs in 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 preempt a permanent master in an automatic fashion.
A connection request from the dynamic master would cause the permanent master to be
suspended. Either closing dynamic connection or timing out on data packets causes the
permanent master session to be resumed.
Figure shows the case where all RTUs are connected to Preemptive Raw Socket ports of
RuggedServer™ devices. Permanent master is connected to the Raw Socket port of
RuggedS4erver™. 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).
Dynamic master can establish connection to any of Preemptive Raw Socket ports at any time
and temporarily suspend polling process (until dynamic connection is cleared or times out).