IEC 104 APDU Format in SCADA: Explained Simply

The IEC 104 APDU format is a structured data packet used in SCADA systems for communication between control centers and remote devices. It defines how information is packaged and transmitted over networks using the IEC 60870-5-104 protocol to ensure reliable and standardized data exchange.

How It Works

Think of the IEC 104 APDU format as a well-organized envelope that carries messages between a control center and remote devices in a SCADA system. Just like an envelope has a sender, receiver, and message inside, the APDU (Application Protocol Data Unit) contains specific fields that tell the system where the data is from, where it should go, and what the data means.

This format breaks down the communication into parts: a start flag, length, control fields, and the actual data payload. The control fields manage the flow of messages, like traffic lights ensuring data moves smoothly without collisions or loss. The data payload carries the real information, such as sensor readings or commands.

By following this format, devices in a SCADA network can understand each other clearly, even if they come from different manufacturers. It’s like everyone agreeing on a common language and letter format to avoid confusion.

Example

This example shows a simplified IEC 104 APDU frame in hexadecimal form, illustrating its structure:

plaintext

68 0E 00 00 00 00 00 00 00 00 00 00 00 00

Output

Start flag: 0x68
Length: 0x0E (14 bytes)
Control fields: 4 bytes
Data payload: 6 bytes
Checksum and stop flag follow (not shown here)

When to Use

Use the IEC 104 APDU format when you need to connect SCADA control centers with remote substations or devices over TCP/IP networks. It is ideal for electric power systems, water treatment plants, and other critical infrastructure where real-time monitoring and control are essential.

This format helps ensure data is sent reliably and understood correctly, which is crucial for safety and efficiency. For example, a power grid operator uses IEC 104 to receive sensor data and send commands to circuit breakers remotely.

Key Points

• The IEC 104 APDU format structures messages for SCADA communication over networks.
• It includes control fields to manage message flow and data payload for actual information.
• Used mainly in electric power and industrial automation systems.
• Ensures interoperability between devices from different vendors.
• Operates over TCP/IP for real-time, reliable data exchange.

Key Takeaways

IEC 104 APDU format defines the message structure for SCADA communication over TCP/IP.

It ensures reliable and standardized data exchange between control centers and remote devices.

The format includes control fields for managing message flow and a data payload for information.

It is widely used in electric power systems and industrial automation for real-time control.

Using IEC 104 APDU helps devices from different vendors communicate seamlessly.