DNP3 protocol overview in SCADA systems - Step-by-Step Execution

Process Flow - DNP3 protocol overview

Start: Device wants to communicate

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Build DNP3 message frame

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Send frame over network

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Receiver checks frame integrity

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Process commands or data

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Send response frame

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Communication ends or continues

This flow shows how a device builds and sends a DNP3 message, the receiver checks and processes it, then responds.

Execution Sample

SCADA systems

1. Build DNP3 frame with header and data
2. Send frame to remote device
3. Remote device verifies frame
4. Remote device processes data
5. Remote device sends response frame

This sequence shows the step-by-step message exchange in DNP3 communication.

Process Table

Step	Action	Details	Result
1	Build frame	Add header, control, data, CRC	Frame ready to send
2	Send frame	Transmit over TCP/IP or serial	Frame sent to remote device
3	Receive frame	Remote device checks CRC and header	Frame valid or error detected
4	Process frame	Execute commands or read data	Data updated or command executed
5	Send response	Build response frame with status	Response sent back
6	End or continue	Wait for next message or close	Communication cycle complete

💡 Communication ends or continues based on session state

Status Tracker

Variable	Start	After Step 1	After Step 3	After Step 5	Final
Frame	empty	built with header and data	received and validated	response frame built	communication cycle complete
Status	none	none	valid or error	response status set	session open or closed

Key Moments - 3 Insights

Why does the receiver check the CRC in step 3?

The CRC check ensures the frame was not corrupted during transmission, as shown in execution_table step 3.

What happens if the frame is invalid at step 3?

If invalid, the receiver discards the frame and may request retransmission, stopping normal processing (step 4).

Why is a response frame sent back in step 5?

The response confirms the command was received and processed, ensuring reliable communication (step 5).

Visual Quiz - 3 Questions

Look at the execution_table, what is the result after step 3?

A Frame valid or error detected

B Frame ready to send

C Response sent back

D Communication cycle complete

💡 Hint

Check the 'Result' column for step 3 in the execution_table

At which step is the response frame built?

A Step 2

B Step 4

C Step 5

D Step 6

💡 Hint

Look at the 'Action' and 'Details' columns for step 5 in the execution_table

If the CRC check fails, what likely happens next?

A Process frame commands

B Discard frame and request retransmission

C Send response frame with success

D End communication immediately

💡 Hint

Refer to key_moments explanation about step 3 in execution_table

Concept Snapshot

DNP3 protocol sends messages in frames with headers and CRC.
Receiver checks frame integrity before processing.
Commands or data are executed or read.
Response frames confirm successful communication.
Reliable and secure data exchange for SCADA systems.

Full Transcript

The DNP3 protocol works by devices building message frames that include headers, control information, data, and error checks like CRC. These frames are sent over a network to remote devices. The receiver checks the frame's integrity using the CRC to ensure no errors occurred during transmission. If valid, the receiver processes the commands or data contained in the frame. Then, it builds and sends a response frame back to confirm the action. This cycle continues as needed for reliable communication in SCADA systems.