SCADA Architectures

SCADA systems have evolved through 3 generations as follows:

First Generation: "Monolithic"
In the first generation computing was done by Mainframe systems. Networks didn’t exist at the time SCADA was developed. Thus SCADA systems were independent systems with no connectivity to other systems. Wide Area Networks were later designed by RTU vendors to communicate with the RTU. The communication protocols used were often proprietary at that time. The first generation SCADA System was redundant since a back-up mainframe system was connected at the bus level and was used in the event of failure of the main mainframe system.

Second Generation: "Distributed"
The processing was distributed across multiple stations which were connected through LAN and they shared information in real time. Each station was responsible for a particular task thus making the size and cost of each station less than the one used in First Generation. The network protocols used were still mostly proprietary.

Third Generation: "Networked"
These are the current generation SCADA systems which use open system architecture rather than a vendor controlled proprietary environment. The SCADA system utilizes open standard and protocols thus distributing functionality across a WAN rather than a LAN. It is easier to connect third party peripheral devices like printers, disk drives, tape drives due to the use of open architecture. WAN protocols such as Internet Protocol (IP) are used for communication between the master station and communications equipment. This on the other hand has put a question on the security of SCADA system which seems to be vulnerable to cyber-warfare and cyber terrorism attacks.