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Figure 2.2 depicts a typical second‐generation SCADA architecture. With the development of Local Area Networking (LAN) technologies, the SCADA systems of this generation distribute the processing to multiple systems and assigns a specific function for each station. In addition, multiple stations could be connected to an LAN in order to share information with each other in real time. For instance, the communication server can be set up to communicate with field devices such as PLCs and RTUs. Some stations are distributed as MTU, Historian, and HMI servers. The distribution of system functionality across network‐connected systems increases processing power, reduces the redundancy, and improves reliability of the system as a whole. In this generation, the system failure is addressed by keeping all stations on the LAN in an online state over the operation time and if one station, say the HMI station, fails, another HMI station will take over.

Figure 2.1 First‐generation SCADA architecture.

Figure 2.2 Second‐generation SCADA architecture.