DNP3 Master/Outstation Architecture
Key Takeaway
How DNP3 master and outstation roles work — polling, control, time sync, addressing, and multi-master/multi-outstation network topologies.
Quick Answer
DNP3 uses a master/outstation model. The master (SCADA host) polls outstations (RTUs, flow computers) for data and issues control commands. Outstations respond with requested data and can send unsolicited event reports. Each device has a unique DNP3 address (0-65519).
Master Role
- Initiates integrity and event class polls
- Sends control commands (CROB, analog output)
- Issues time synchronization
- Enables unsolicited response acceptance
- Manages event confirmation
Outstation Role
- Responds to master polls with requested data
- Buffers events during communication outages
- Executes received control commands
- Optionally sends unsolicited event reports
- Maintains local clock (synchronized by master)
Addressing
Each DNP3 device has a source address and a destination address. Master address is typically 1. Outstation addresses range from 1 to 65519. Address must be unique on each communication segment.
Network Topologies
- Point-to-point — One master, one outstation (dedicated serial or Ethernet link)
- Multi-drop — One master, multiple outstations on shared RS-485 bus
- Multi-master — Multiple masters polling the same outstation (supported on TCP)
- Data concentrator — Intermediate device that acts as outstation to upstream master and master to downstream outstations
Frequently Asked Questions
Standard polls are initiated by the master. However, with unsolicited responses enabled, the outstation can push event data proactively — a key advantage over Modbus.
DNP3 addresses range from 0 to 65519. Address 65520+ are reserved. Each device on a communication segment must have a unique address.