Architecture of SCADA

Generally the SCADA system includes the following components: local processors, operating equipment, PLCs, instruments, remote terminal unit, intelligent electronic device, master terminal unit or host computers and a PC with human machine interface.

Architecture of SCADA

The block diagram of SCADA system shown in the figure represents the basic SCADA architecture. The SCADA (supervisory control and data acquisition) systems are different from distributed control systems that are commonly found in plant sites. When distributed control systems cover the plant site, SCADA system cover much larger geographic areas.

Above figure depicts an integrated SCADA architecture which supports TCP/IP, UDP and other IP based communication protocols as well as industrial protocols like Modbus TCP, Modbus over TCP or Modbus over UDP. These all work over cellular, private radio or satellite networks.

In complex SCADA architectures, there are a variety of wired and wireless media & protocols involved in getting data back to the monitoring site. This allows implementation of powerful IP based SCADA networks over landline, mixed cellular and satellite systems. SCADA communications can utilize a diverse range of wired and wireless media.

The choice of the existing communication depends on the characterization of a number of factors. The factors are remoteness, available communications at the remote sites, existing communications infrastructure, polling frequency and data rates. These factors impact the final decision for SCADA architecture. Therefore, a review of SCADA systems evolution allows us to better understand many security concerns.