IEC 60870-5 protocol in SCADA systems - Step-by-Step Execution

Process Flow - IEC 60870-5 protocol

Start Communication

↓

Send Frame

↓

Wait for Acknowledgment

↓

Timeout or Error Handling

Yes↓

Process Received Frame

↓

Send Response or Next Frame

↓

Check for More Data

↓

End Communication

Yes↓

Repeat Send Frame Step

The IEC 60870-5 protocol communication flows by sending frames, waiting for acknowledgments, processing received frames, and repeating until communication ends.

Execution Sample

SCADA systems

Send Frame 1
Wait Ack
Receive Frame 2
Send Ack
Repeat or End

This sequence shows sending a frame, waiting for acknowledgment, receiving a frame, sending acknowledgment, then repeating or ending communication.

Process Table

Step	Action	Frame Type	Result	Next Step
1	Send Frame	I-Frame (Information)	Frame 1 sent	Wait for Ack
2	Wait for Acknowledgment	S-Frame (Supervisory)	Ack received	Receive Frame
3	Receive Frame	I-Frame	Frame 2 received	Send Ack
4	Send Acknowledgment	S-Frame	Ack sent	Check for More Data
5	Check for More Data	N/A	More data? Yes	Send Frame
6	Send Frame	I-Frame	Frame 3 sent	Wait for Ack
7	Wait for Acknowledgment	S-Frame	Ack received	Receive Frame
8	Receive Frame	I-Frame	Frame 4 received	Send Ack
9	Send Acknowledgment	S-Frame	Ack sent	Check for More Data
10	Check for More Data	N/A	More data? No	End Communication
11	End Communication	N/A	Communication ended	Stop

💡 Communication ends when no more data is to be sent or received.

Status Tracker

Variable	Start	After Step 1	After Step 3	After Step 6	After Step 8	Final
Sent Frames Count	0	1	1	2	2	2
Received Frames Count	0	0	1	1	2	2
Acknowledgment Status	None	Waiting	Received	Waiting	Received	Completed
Communication State	Idle	Sending	Receiving	Sending	Receiving	Ended

Key Moments - 3 Insights

Why do we wait for an acknowledgment after sending a frame?

Waiting for acknowledgment ensures the other device received the frame correctly before sending the next one, as shown in steps 2 and 7 in the execution table.

What happens if no more data is available to send or receive?

The communication ends gracefully, as seen in step 10 where 'More data? No' leads to ending communication in step 11.

Why are different frame types used like I-Frame and S-Frame?

I-Frames carry actual data, while S-Frames are used for control like acknowledgments, ensuring reliable communication as shown in the alternating steps of sending and acknowledging frames.

Visual Quiz - 3 Questions

Look at the execution table, what is the frame type sent at step 6?

A I-Frame

B S-Frame

C U-Frame

D No frame sent

💡 Hint

Refer to the 'Frame Type' column at step 6 in the execution table.

At which step does the communication end according to the execution table?

A Step 9

B Step 10

C Step 11

D Step 5

💡 Hint

Check the 'Action' and 'Result' columns for the step indicating communication ended.

If acknowledgment is not received after sending a frame, what would likely happen next?

A Proceed to receive next frame

B Timeout or error handling

C Send next frame immediately

D End communication

💡 Hint

Look at the concept flow where waiting for acknowledgment leads to timeout or error if no ack is received.

Concept Snapshot

IEC 60870-5 protocol manages communication by sending information frames (I-Frames) and supervisory frames (S-Frames) for acknowledgments.
Each sent frame waits for an acknowledgment before proceeding.
Communication repeats until no more data is exchanged.
Timeouts handle errors if acknowledgments are missing.
This ensures reliable data transfer in SCADA systems.

Full Transcript

The IEC 60870-5 protocol is a communication method used in SCADA systems to exchange data reliably. It works by sending frames called I-Frames that carry information. After sending a frame, the sender waits for an acknowledgment frame called an S-Frame from the receiver. This confirms the frame was received correctly. If the acknowledgment is not received, the protocol handles errors or timeouts to retry or stop communication. This process repeats, sending and acknowledging frames, until no more data needs to be sent. Then the communication ends cleanly. This step-by-step flow ensures data is transferred safely and reliably between devices in the system.