IEC 60870-5-104
Last updated on 16 October 2025
IEC 60870-5-104 is the protocol widely used in energy and infrastructure networks for telecontrol and SCADA. In this article, I briefly and practically explain what IEC 104 does exactly, which characteristics are important, and how to set up a reliable IEC 60870-5-104 environment — so you can check your configuration faster and more efficiently.
What is IEC 60870-5-104
IEC 60870-5-104 (short: IEC 104) is an Ethernet/TCP/IP extension of the older serial IEC 60870-5-101. The protocol is designed for telecontrol and telemetry and ensures real-time exchange of measurement values, status information, and control commands between Control Centers (Master) and field equipment such as RTUs and IEDs.
Who Communicates with Whom
The typical roles are Master (central SCADA) and Slave (RTU or IED). The Master initiates sessions and polls, while Slaves can also send spontaneous notifications for events. IEC 104 operates over standard TCP/IP networks and usually uses port 2404.
Key Features of IEC 104
- Based on TCP/IP — communication lines run over IP, enabling long distances and modern network architectures.
- Master-Slave structure — the central SCADA acts as Master; RTUs/IEDs respond but can also send spontaneous messages.
- Standardized information objects — data is exchanged as Information Objects with ASDU and IOA addressing (ASDU addresses and IOA).
- Real-time & event-driven — supports periodic polling and spontaneous notifications for rapid reporting.
- Reliable transmission — sequence numbering, acknowledgments, and retransmissions make communication robust, even on unstable networks.
- Specific to energy — IEC 104 is tailored for grid management, station automation, and critical infrastructures.
Technical Terms You should Know
Important terms are ASDU (Application Service Data Unit), IOA (Information Object Address), Information Object, Common Address, and timestamps (timestamps via NTP or protocol). For transport, you often see TCP/IP and the well-known port 2404.
Supported Devices and Applications
IEC 104 can be found on various devices and in different systems. Here’s an overview:
| Application / device | Description |
|---|---|
| RTUs (Remote Terminal Units) | Devices in substations that exchange measurement values, status information, and commands with the central station. |
| IEDs (Intelligent Electronic Devices) | Smart protection and measurement devices that natively support IEC 104. |
| SCADA systems | Central systems that function as Master and receive data, process it, and send control commands. |
| Gateways / Protocol converters | Devices that convert, for example, Modbus or IEC 101 to IEC 104 for IP communication. |
| Network components in energy installations | Switching stations, measurement units, and protection relays that speak IEC 104 for direct SCADA connection. |
Setting up an IEC 104 Environment
When setting up, focus on network, addressing, time synchronization, and security. Below are the practical steps you always check:
1. Network connection
IEC 104 uses port 2404 over TCP/IP. The Master connects to RTU/IED; ensure firewalls allow traffic on port 2404 and that routing/static routes are correctly configured.
2. Configure addressing
Each device gets a unique Common Address, and each data point has an Information Object Address (IOA). Verify that ASDU addresses and IOAs from field equipment exactly match the SCADA configuration.
3. Direction and spontaneous notifications
The Master initiates the session, but Slaves can also send spontaneous notifications for faults or status changes. Carefully set buffer lengths and settings for spontaneous transmission to ensure reliable reporting.
4. Time settings and synchronization
IEC 104 supports timestamps. Use NTP or protocol-based synchronization to ensure events are correctly logged chronologically.
5. Security and segmentation
The original standard has no built-in encryption. For modern networks, implement
6. Testing and monitoring
After configuration, test the connection with SCADA software or special IEC 104 test tools. Check ASDU and IOA addressing, confirmation mechanisms, and whether messages arrive within expected time. For central data storage and logging, you can also look at solutions for remote access and datalogging to keep reporting and history centralized.
Practical Tips and Pitfalls
– Always check if port 2404 is open in both network and host firewalls.
– Watch for overlaps in ASDU/IOA addresses with multiple RTUs.
– Test spontaneous notifications with realistic fault scenarios.
– Use NTP and check timestamps after daylight saving time changes.
Where IEC 104 is Mainly Used
IEC 104 is primarily seen in high and medium voltage stations, substations, hydroelectric power plants, and SCADA environments of utility companies. It is increasingly being applied in infrastructure projects such as tunnels, bridges, and water management installations.
In Summary
IEC 60870-5-104 combines the robust data structure of IEC 101 with modern TCP/IP transport. With standardized Information Objects (ASDU/IOA), support for spontaneous notifications, and mechanisms for reliable transmission, the protocol is suitable for critical infrastructure. Ensure correct addressing, network settings, time synchronization, and layered security (VPN, firewalls, IEC 62351) to have a stable and secure IEC 104 environment.