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DNP3 Protocol Communication Testing

The DNP3 protocol communication test tool

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SUBNET’s ASE2000 Test Set with support for the DNP3 protocol is for SCADA engineers, technicians, substation personnel, IT and others who need to test the communication between a SCADA host and an Intelligent Electronic Device (IED).

The DNP3 (Distributed Network Protocol) protocol was developed to enable communications between data acquisition and control devices such as substation computers, RTUs (Remote Terminal Units), IEDs (Intelligent Electronic Devices), and master stations. The protocol is mainly used in electric utility industry.

The DNP3 protocol mostly falls under the layer 2 of the OSI (Open Systems Interconnect) seven-layer model. This protocol helps in fragmenting data, error checking, controlling link, and multiplexing the user data. Error checking is done using CRC (Cyclical Redundancy Check) codes.

For process automation systems such as SCADA (Supervisory Control and Data Acquisition), bandwidth efficiency is very important. The DNP3 protocol handles the bandwidth usage very efficiently by using event based data reporting. In the DNP3 protocol, the RTU is first interrogated with class 0 poll, which in turn sends all static point data to the Master station. Events are generated by these data points. These events go into one of the three buffers. All the RTUs report the response of these events. The data flag is only set if there is data in the buffers. This ensures that data transmission happens only during relevant data changes. DNP3 protocol thus avoids unnecessary polling all the time even if there is no significant change.

Even though infrequent polling brings bandwidth efficiency, there is danger to miss out event sequences in between the polling. With the DNP3 protocol it is possible to synchronize time with an RTU. With the availability of time stamped data objects, it is easy to reconstruct sequence of events even in between polling. The DNP3 protocol also provides a large set of common point-oriented objects. This removes the need to for bit-mapped data and improves compatibility.

DNP3 protocol was designed for reliability and efficiency but security is not its strong point. However, security authentication features have been gradually added to the protocol. It is now compliant with IEC 62351-5 standard. ECC (elliptic curve cryptography) over DNP3 is also possible.

SUBNET is a member of the DNP3 Users Group Steering Committee. A SUBNET protocol specialist holds the position of Comformance Test Administrator and is also a voting member of the DNP Technical Committee. Visit the DNP3 Users Group website for more information.

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