Protocols and Layers
In a SCADA system, a Remote Terminal Unit (RTU) generally does not know what it is measuring. It is just following orders and reporting back. It is the master station that must know what the data is, and whose data it is. For this, there are protocols to be followed. Each protocol has two divisions: The Master Protocol, containing statements from master to RTU and the RTU Protocol, containing instructions from RTU to the main computer. Communication between master and RTU forms a model for RTU to Intelligent Electronic Device IED Communications, the most popular being International Electrotechnical Commission (IEC) 60870-5 series and the Distributed Network Protocol Version 3 (DPNP3).
With the drifting towards open standards, on one hand the SCADA systems have been easily integrated with diverse industrial systems, it also has increased the risk of people with lesser knowledge or lesser integrity gaining access and control from the TCP/IP based systems. This exposes them to variety of threats like the Denial of Service attacks, System Downtime, Trojans, keyloggers for password stealing, defamation etc. Hence, dedicated security layers for SCADA systems are needed. In the aftermath of the 9/11 attacks, Departments of Homeland Security of many countries have identified the importance of SCADA systems.
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