For a blog that is dedicated to OPC,  the topic of other standards seems to come up a lot.  Gary touched a bit on why that might be in on of his posts (not surprisingly entitled Standards).  It’s because OPC is often used to drive standardization among other compatible specifications.  Over time many of these have emerged such as Modbus from discrete auto manufacturing, BACnet from HVAC and DNP 3.0 which was developed for the Electrical Utility industry.

DNP3 was designed to be an open, standards-based Interoperability protocol between substation computers, RTUs, IEDs (Intelligent Electronic Devices) and master stations.  DNP was originally created by GE Harris in 1990 (who was Westronic, Inc. at the time).  In 1993, the DNP3 specifications where released into the public domain, and ownership of the protocol was given over to the newly formed DNP Users Group. Since that time, the open protocol has gained worldwide acceptance.

You may also be familiar with the other popular protocol in the electrical industry, the IEC 60870-5 specifications which have many of the same features of DNP3 with the exception that it was created by the International Electrotechnical Commission (IEC).  DNP 3.0 and IEC 60870-5 share a common design and both grew from the some of the same ‘roots’.

Both protocols provide basically similar application functionality and were primarily designed for point-to-point or multi-drop serial link architectures, but can work over radio, LAN, etc.   Both protocols are used worldwide for electric power SCADA.  DNP is dominant in North America, Australia, South Africa. IEC is required by legislation in some European countries, and is also common in the Middle East. In most of Asia and South America both are used almost equally.
However DNP has gained wide acceptance in some non-electric power applications, where IEC is not used much beyond the electrical world.

Both protocols offer features that are important to transmission of electrical data or control such as:   
• Time synchronization and Time stamped events
• Freeze/Clear Counters
• Select before operate (a two stage control process for increased security)
• Polled report by exception and Unsolicited Responses

In particular DNP3 offers robust and efficient functionality such as the ability to:   
• Request and respond with multiple data types in single messages
• Segment messages into multiple frames for greater error detection and recovery
• Only report data that has changed in response messages
• Request data items periodically based on priority
• Support time synchronization and a standard time format
• Allow multiple masters and peer-to-peer operations

These optimization and control features are important to SCADA applications that have large numbers of devices in the field, all sharing the same, remote communication channels.  Although DNP and IEC 60870-5 are very common protocols for electrical hardware such as RTUs and IEDs, they are complicated software protocols to implement properly and are not commonly supported by more general software applications such as HMIs, historians or alarm management packages.  Of course, this is where OPC fits into the picture.

Even very feature rich protocols like these can be mapped into OPC specifications using OPC DA 2.0, 3.0, HDA and/or A&E specifications.  Since electrical transmission sites and substations are almost always telemetry type architectures, you will find DNP 3.0 and IEC 60870-5 OPC Servers that take this into account by offering highly configurable communication options, and redundant communication channel support.

Competition due to deregulation and increased legislation aimed at improving reliability and security are driving companies to have better access, history and/or tracking over their field level devices.  This means more higher level applications are needing data from DNP 3.0/IEC 60870-5 devices.  Good thing OPC is around to solve their problems