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.

Practice

1. What is the primary purpose of the IEC 60870-5 protocol in SCADA systems?

easy

A. To encrypt data for secure internet browsing

B. To store historical data in databases

C. To enable communication between power system devices

D. To provide user interface design standards

Solution

1. Step 1: Understand the protocol's role

   IEC 60870-5 is designed for communication in power systems, connecting devices like RTUs and control centers.

2. Step 2: Eliminate unrelated options

   Options about databases, UI design, and internet encryption do not relate to device communication in power systems.

3. Final Answer:

   To enable communication between power system devices -> Option C

4. Quick Check:

   IEC 60870-5 = communication protocol [OK]

Hint: Remember: IEC 60870-5 connects power devices [OK]

Common Mistakes:

• Confusing communication protocol with data storage
• Thinking it handles user interface design
• Assuming it encrypts internet data

2. Which of the following is a correct characteristic of IEC 60870-5 protocol messages?

easy

A. They include structured fields for data and commands

B. They only support wireless communication

C. They use unstructured free text for data

D. They require manual data entry at each device

Solution

1. Step 1: Recall message format

   IEC 60870-5 messages have structured fields to clearly define data and commands.

2. Step 2: Check other options

   Unstructured text, wireless-only support, and manual data entry are incorrect for this protocol.

3. Final Answer:

   They include structured fields for data and commands -> Option A

4. Quick Check:

   Structured messages = They include structured fields for data and commands [OK]

Hint: Look for 'structured fields' in message descriptions [OK]

Common Mistakes:

• Assuming messages are free text
• Believing protocol only supports wireless
• Thinking manual entry is required

3. Given a device using IEC 60870-5-101 protocol, which communication method is it most likely using?

medium

A. Wireless Wi-Fi communication

B. Bluetooth low energy

C. Internet Protocol (IP) over Ethernet

D. Serial communication over RS-232 or RS-485

Solution

1. Step 1: Identify protocol version

   IEC 60870-5-101 is designed for serial communication using RS-232 or RS-485 interfaces.

2. Step 2: Compare options

   Wi-Fi, IP over Ethernet, and Bluetooth are not typical for 101 version; those relate more to 104 or other protocols.

3. Final Answer:

   Serial communication over RS-232 or RS-485 -> Option D

4. Quick Check:

   60870-5-101 = serial comm [OK]

Hint: 101 version means serial communication [OK]

Common Mistakes:

• Confusing 101 with 104 (network-based)
• Assuming wireless communication
• Selecting Ethernet/IP for 101

4. A SCADA engineer configures an IEC 60870-5-104 device but cannot establish communication. The device is set to use serial port settings. What is the likely issue?

medium

A. The serial port baud rate is too high for 104 protocol

B. The device should be configured for network (TCP/IP) communication, not serial

C. The device requires manual data entry to start communication

D. The IEC 60870-5-104 protocol does not support communication

Solution

1. Step 1: Understand protocol communication type

   IEC 60870-5-104 uses network communication over TCP/IP, not serial ports.

2. Step 2: Identify misconfiguration

   Configuring 104 device for serial communication causes failure; it must use network settings.

3. Final Answer:

   The device should be configured for network (TCP/IP) communication, not serial -> Option B

4. Quick Check:

   104 = network, not serial [OK]

Hint: 104 protocol requires TCP/IP network setup [OK]

Common Mistakes:

• Trying to use serial settings with 104
• Changing baud rate unnecessarily
• Thinking manual data entry is needed

5. You need to design a SCADA communication system that supports both serial and network devices using IEC 60870-5 protocols. Which approach best ensures compatibility?

hard

A. Use IEC 60870-5-101 for serial devices and IEC 60870-5-104 for network devices

B. Use only IEC 60870-5-104 for all devices regardless of connection type

C. Use IEC 60870-5-101 for network devices and IEC 60870-5-104 for serial devices

D. Use a custom protocol to replace IEC 60870-5 entirely

Solution

1. Step 1: Identify protocol roles

   IEC 60870-5-101 is designed for serial communication; 104 is designed for network (TCP/IP) communication.

2. Step 2: Match protocols to device types

   Using 101 for serial and 104 for network devices ensures compatibility and proper communication.

3. Step 3: Evaluate other options

   Using only 104 ignores serial devices; swapping roles is incorrect; custom protocol is unnecessary.

4. Final Answer:

   Use IEC 60870-5-101 for serial devices and IEC 60870-5-104 for network devices -> Option A

5. Quick Check:

   101 = serial, 104 = network [OK]

Hint: Match 101 to serial, 104 to network devices [OK]

Common Mistakes:

• Using 104 for serial devices
• Ignoring serial device support
• Trying to replace IEC 60870-5 unnecessarily