When people first hear about IEC 61850, they often assume it is simply another communication protocol like DNP3, Modbus, or IEC 60870-5-104. But this assumption is incorrect. IEC 61850 is not just a protocol—it is a full engineering language designed to describe, model, and structure the functions that make up modern digital substations and power automation systems. Where… Read More »
Every Modbus TCP/IP device listens on TCP port 502. This single port carries all Modbus communication over Ethernet — read requests, write commands, exception responses, and diagnostics. Port 502 is registered with IANA (Internet Assigned Numbers Authority) under the service name “mbap” (Modbus Application Protocol). It has been the standard since the Modbus TCP specification was published in… Read More »
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 »
Modern SCADA and utility automation systems face growing cybersecurity demands. The Distributed Network Protocol (DNP3)—the backbone of many control networks—has evolved to meet them. With the release of IEEE 1815-2020, the DNP3 Secure Authentication Version 6 (SAv6) specification brings authenticated encryption, centralized authorization, and simplified key management directly into the protocol. This article explains how SAv6 improves on… Read More »
DNP3 runs over IP networks using TCP or UDP port 20000. This port number is the standard for communication between SCADA masters and field devices (RTUs, IEDs) in electric utilities, water systems, and oil and gas pipelines. The IANA also registered port 19999 for DNP3 Secure (DNP3 over TLS), though it is rarely used in practice — most… Read More »
The Distributed Network Protocol (DNP3) is recognised for its efficiency and reliability in SCADA and power automation systems. The DNP3 protocol is characterized by three key operational concepts: Report by Exception, Periodic Background Polls, and Balanced Communication. These concepts enable the system to optimize bandwidth utilization while ensuring real-time monitoring of field device status. Report by Exception (unsolicited… Read More »
In a DNP3-based SCADA system, system topology refers to the physical and logical arrangement of how master stations, outstations, and communication devices are connected and interact. Designed for flexibility and reliability, DNP3 supports multiple network configurations that can be tailored to the system size, communication medium, and redundancy requirements. The most common DNP3 topologies include master–slave, multidrop, hierarchical,… 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 »