The Application Service Data Unit (ASDU) is the core of the IEC 60870-5-104 communication protocol. It defines how information is represented and exchanged between a controlling station (SCADA master) and controlled stations such as RTUs or IEDs. If the Application Protocol Data Unit (APDU) is the message envelope, the ASDU is the payload — carrying the actual telemetry… Read More »
Before any data or command exchange can begin, the communication link between the controlling station (master) and controlled stations (RTUs or substation gateways) must be properly established. This process — called link initialization — ensures both sides start from a synchronized state with correct frame sequencing, clear buffers, and ready communication paths. Link initialization is part of the… Read More »
The IEC 60870-5-101 protocol (commonly known as IEC 101) is a serial telecontrol standard widely used in SCADA, power automation, and industrial control systems. It defines how data is formatted and transmitted between a controlling station (master) and controlled stations, such as RTUs or dedicated substation operation and data-handling devices. Each message on the line is called a… Read More »
The Originator Address in IEC 60870-5-101 is an optional but powerful feature that enhances message routing and command traceability in telecontrol and SCADA systems. This one-byte field, located within the Cause of Transmission (COT) section of the ASDU, allows a controlling station to explicitly identify itself when sending commands. In systems with a single master station, this feature… Read More »
Wireshark is the go-to tool for analyzing communication protocols — and it fully supports IEC 60870-5-104 (commonly known as IEC 104). Whether you’re diagnosing network issues, validating SCADA data, or learning how IEC 104 works, Wireshark provides an unmatched level of visibility into the protocol’s Ethernet, TCP, and ASDU layers. This guide shows you how to capture, decode,… Read More »
The IEC 60870-5-104 (IEC 104) protocol is one of the most important standards for modern SCADA and telecontrol systems.It extends the earlier IEC 60870-5-101 serial protocol by enabling communication over Ethernet and TCP/IP networks, allowing utilities and industries to operate over LAN, WAN, or even public IP networks with reliability and scalability. This article explains — in plain… Read More »
Reliable communication in IEC 60870-5-104 depends heavily on properly tuned timeout parameters. The standard defines several timing constants — t0, t1, t2, and t3 — which control connection setup, data acknowledgment, and link supervision between the controlling station (master) and the controlled station (slave/RTU). Misconfigured timeouts can cause link resets, delayed data updates, or even total communication failure.… Read More »
IEC 60870-5-104 is one of the most widely used SCADA communication protocols in power and industrial automation. One of its most critical yet misunderstood components is time synchronization, achieved using the CP56Time2a format. Accurate time coordination across remote terminal units (RTUs), intelligent electronic devices (IEDs), and control centers ensures that every event, command, and alarm can be correctly… Read More »
In the realm of Supervisory Control and Data Acquisition (SCADA) systems, the IEC 60870-5 protocol suite is a fundamental standard for telecontrol and remote communication in power systems and industrial automation. One of the core technical distinctions within the IEC 60870-5-101 profile is between balanced and unbalanced transmission modes. These modes define how communication is initiated and managed… Read More »