The current day the systems of SCADA (Supervisory Control and Data Acquisition) containing of Remote Terminal Units (RTUs), SCADA hosts, and field devices control and monitor process systems and equipment from multiple locations and replace data from a variety of distributed control systems alongside the wide and local area networks.
The RTUs are pre-programmed to correspond with the SCADA central station and other systems of networked in protocols that are planned to deliver reports on all the input and output devices status in the field. Protocols are alike to languages, which let the units of RTU/SCADA to correspond with each other. All the architectures network are loosely based on International Standards Organization (ISO) standard seven layer Open Systems Interconnection (OSI) model as following:
• Application at Layer 7
• Presentation at Layer 6
• Session at Layer 5
• Transport at Layer 4
• Network at Layer 3
• Data Link at Layer 2
• Physical at Layer 1
The model of OSI object is to set up a framework that will let any network or system to connect and replace messages packets, signals, and addresses. The model creates it possible for communications to become autonomous of the system devised and shield the user from the requirement to understand the network complexity.
In common, the bottom 4 layers cover the physical network, wiring, and protocols of communication the wide and local area networks for example Frame Relay and Ethernet. Transport Control protocol / Internet Protocol (TCP/IP) suite is a diverse open standard which is an alike used of open standard.
The layers of presentation and session generally deal with creating and after that terminating the session between the 2 hosts. Not all of the networks utilize these layers. The Layer 7 (Application) and above is where a characteristic Protocol of PLC/RTU (for example Modbus) will give the data at a characteristic workstation or server of SCADA in a user format from the local PLC and field RTUs systems.
A great part of any complex system of SCADA design is included in corresponding the communication and protocol parameters between relating devices. There are around 200 such application protocols and actual time user layer. These include protocols of proprietary and non- proprietary, some are listed as following:
• Westinghouse
• Omron
• Siemens Sinaut
• Allen Bradley DF1,DH and DH+
• Mitsubishi
• Toshiba
• GE Fanuc
• Modbus RTU / ASCII
• etc
The industry is nowadays moving away from a lot of the proprietary and old protocols.