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Automation Committee
Understanding SCADA Communication Protocols
Module: Basic Concepts
Host:James MondaleWayne Wilson
Reduce background noisePlease mute your phones
Gain working knowledge of communication SCADA Protocols
Learn the basics layers and architectures
Examine various architectures SCADA Protocols
Learn about common Protocol errors that can occur in your SCADA system
Introduction
In telecommunication,• a communication protocol is a system of rules that
allow two or more entities of a communications system to transmit information via any kind of variation of a physical quantity.
• Protocols may be implemented by hardware, software, or a combination of both.
• In SCADA it includes the collecting of the information via;• RTU (remote terminal unit), • PLC's (Programmable Logic Controllers) • IED's (Intelligent electronic devices)
Transferring it back to the central site, carrying out any necessary analysis and control and then displaying that information on a number of operator screens or displays.
DNP3
PROTOCOLS are available for many types of SCADA systems
• Industrial Controls
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DNP3
PROTOCOLS are available for many types of SCADA systems
✓• Process Automation
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DNP3
PROTOCOLS are available for many types of SCADA systems
• Power Systems
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Protocol Layer OverviewThe Open Systems interconnection model (OSI) model is used to define how data communication occurs on computer networks.
Fiber Optic
Scada systems in water & wastewater commonly useModbus or DNP3 .
Modbus and DNP3 are both byte-oriented protocols. Modbus is an application layer protocol, while DNP contains Application and Data Link Layers, with a pseudo-transport layer.
Both protocols are widely used over a variety of physical layers, including RS-232, RS- 422, RS-485, and TCP/IP.
The term “Modbus” typically refers to one of three related protocols: Modbus ASCII, Modbus RTU, or Modbus TCP/IP
Multi Drop network
Message Query initiates from Master
Master can broadcast to all slaves
or a single one
Multi Drop network
Slaves returns a response to only messages addressed to them individuallyBut do not respond to broadcast messages.
Modbus Slaves do not initiate messages on their own
DNP3
DNP3 Slaves can report by exception
Difference between Modbus and DNP3 Communication Protocols
Let’s use Modbus as an example to demonstrate how protocols work
Physical Media
Data Model
Service request from master
Protocol Data Unit (PDU)
Fields in PDU are broken down into Bytes
4 Basic Data types
Slave Address Function
Code
Data Field
CRCError
Check
Function Code field determines read or write and in which field
Slave memory registers
Typical problems
• Hardware problems
• Mis-wired cabling
• Faulty Cable connectors
• Corrosion on connector ends
• Cables not “snapped” into socket
• Poor signals
• Network collisions• Duplicate IP Addressing• Overwriting registers• Polling loop problems
• Software (protocol ) related problems
Questions?
Thank You!The End
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