Originator Address in IEC 60870-5-101 Explained

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 isn’t needed — every command originates from the same source.

However, in multi-master or dual-mode configurations (where some devices act as both controllers and controlled units), the originator address becomes essential for ensuring that responses and acknowledgments are returned to the correct sender.

Why the Originator Address Is Needed

In complex SCADA architectures, it’s common to have multiple control centers or peer stations that communicate with the same group of RTUs.

Without a way to distinguish which controller issued a command, responses could be broadcast system-wide or sent to the wrong device.

By including a unique originator ID within the ASDU, IEC 60870-5-101 ensures that every action confirmation, activation termination, or event report is sent back directly to the initiating controller — not to the entire system.

How It Works

When a command is issued by a dual-mode or non-master station, a non-zero originator address must be placed in the COT field of the ASDU.

Although this has no effect in the control direction of the message itself, it becomes essential when responses are sent in the monitor direction.

The controlled station copies this originator value into any confirmation (activation/termination) or status report it returns.

Intermediate routers or data concentrators must recognize this originator ID and route the response directly back to the correct originating controller — not to every station on the network.

Default and Broadcast Behavior

There is one important exception:

An originator address of 0 acts as a default or broadcast address.

Using a value of zero is equivalent to having no originator field, meaning the response or notification is visible to all stations in the system.

This convention ensures that network-wide or master-level updates — such as state changes or time-tagged events — are delivered to the main control center, even in systems containing intermediate dual-mode controllers.

Conclusion

The Originator Address in IEC 60870-5-101 is an optional but essential feature for multi-master and dual-mode SCADA systems.

It ensures precise message routing by embedding the controller’s unique ID within the Cause of Transmission (COT) field, allowing responses and confirmations to reach the correct source.

A value of zero (0) functions as a broadcast address for system-wide or master-level updates, while the same principle extends into IEC 60870-5-104, where originator addressing supports reliable communication over TCP/IP.

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