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Such systems are considered to be the first‐generation SCADA systems. At that time, the concept of networks were nonexistent in general, and therefore SCADA systems were deployed as stand‐alone systems and there was no connectivity to other systems. Figure 2.1 illustrates the typical architecture of this generation. Typically, a SCADA master uses Wide Area Networks (WANs) to communicate with field devices using communication protocols that were developed by vendors of field devices. In addition, these protocols had limited functionality and they could only do scanning and controlling points within RTUs. The communication between the master and field devices (e.g. RTUs) were performed at the bus level using a proprietary adapter. To avoid a system's failure, two identically equipped mainframe systems are used, one to be a primary with another as backup. The latter will take over when failure of the primary is detected.