DNP3 and IEC60870-5-101 IMPLEMENTATIONS IN INTELLIGENT ELECTRICAL DEVICES (IED’S)

1. DNP3 and IEC60870-5-101 IMPLEMENTATIONS IN INTELLIGENT ELECTRICAL DEVICES (IED’S) Distribution 2000 November 9th - 12th 1999 Neil O’Sullivan and Lauri Mikli

2. Introduction • Rationalisation and privatisation in the global electrical distribution industry is forcing utilities to consider new ways to optimise their business from both a performance and cost perspective. • Utilities are increasingly required to meet the performance criteria set by the regulators of these newly privatised companies.

3. Introduction • This is making remote control and automation of their distribution networks a real necessity if they are to meet these requirements. • This paper discusses and compares the two main open architecture protocols to emerge from the proprietary communications era.

4. DNP V3.00 and IEC60870-5-101 • These two open architecture communications protocols are Distributed Network Protocol Version 3.00 (DNP3) and International Electrotechnical Committee 60870-5-101(IEC870) • Both protocols are controlled and maintained by regulatory bodies. • The DNP User Group and the International Electrotechnical Committee respectively.

5. DNP3 History • DNP was originally created by Westronics Inc (now GE Harris ) in 1990. • In 1993 the DNP V3.00 protocol specification document set was released into the public domain. • Ownership of the protocol was given to the DNP User Group in October 1993. • Today there are user group chapters in the USA, Latin America, China and Australia.

6. IEC870 History • IEC 870 was based on IEC60870-5 • It is controlled and maintained by IEC Technical Committee 57 Working Group 3 • Documentation was released in parts between 1990 and 1995 • Addendum 2 Supplementary Definitions due to be released January 2000.

7. Reporting Model • This paper looks at slave implementations of these protocols. • It is important to choose the protocol network topology which best supports the electricity utility’s needs. • Points to consider are the communications medium, network topology and whether continuous polling or unsolicited reporting is required.

8. Unsolicited Reporting • If unsolicited / report by exception reporting is required then DNP3’s balanced transmission is the best solution because it supports point to multipoint communications. • IEC870 does support balanced transmission, report by exception communications but it is limited to point to point communications only. It would not be suitable for point to multipoint communications. • This is because IEC870 does not support Master addressing in the message structure and doesn’t support collision avoidance.

9. Protocol Architecture • Both DNP3 and IEC870 use a simplified 3 layer version of the Open System Interconnection (OSI) 7 layer reference model known as the Enhanced Performance Architecture (EPA). • It is important to know this basic design in order to understand the various terminology and principles involved with using either protocol.

10. APPLICATION APPLICATION PRESENTATION SESSION TRANSPORT (DNP3 LIMITED TRANSPORT) NETWORK DATA LINK DATA LINK PHYSICAL PHYSICAL Protocol Architecture OSI 7 LAYER MODEL 3 LAYER ENHANCED PERFORMANCE ARCHITECTURE

11. DNP V3.00 - IEC870 compatibility • DNP3 and IEC870 are not compatible but because of the EPA standard common to both protocols are often confused to be compatible.

12. Physical Layer • Physical Layer • The physical layer refers to the physical media over which the protocol is transmitted. • This is usually a physical medium such as RS-232, RS-485 or V23 FSK using media such as landline, fibre optic, radio or satellite. • Nu-Lec’s Optimised Family controllers provide a onboard 9600Baud RS232 interface and a V23 FSK audio tone modem as well as a radio power supply.

13. Transport Layer • DNP Pseudo-Transport Layer • The DNP protocol varies from the EPA 3 layer model by adding a fourth layer - a pseudo-transport layer. The pseudo-transport layer segments application layer messages into multiple link messages and provides a segment tracking mechanism.

14. Application Layer • Application Layer • The application layer builds messages based on the need for, or the availability of, user data. Once messages are built, they are passed down to the data link layer and eventually communicated over the physical layer. • The application layer uses function codes to indicate the purpose, or requested operation, of the message.

15. Application Layer • Application Layer functions include • Reporting - Polled or Unsolicited Responses • Time Synchronisation • Read/Write message identification • Digital Control Commands eg Select before Operate, Direct Operate • Freeze and Clear commands for counters • Time-stamped events • Data Groups/classes

16. DNP V3.00 Subset Levels • The DNP protocol is specified in a 4 volume set of protocol documents called the basic 4 set. • Historically it was possible for both a master vendor and an slave vendor to claim support for the DNP protocol without the devices being able to fully communicate with one another. • Therefore Subset levels were introduced in 1995.

17. DNP V3.00 Subset Levels • Level 1 • This is the simplest implementation of DNP. • Intended for use between a master station and a small end device (eg. Meter, relay or capacitor bank controller). • The input and output points of the slave devices are typically local to the device.

18. DNP V3.00 Subset Levels • Level 2 • This level of implementation defines a slightly larger subset of DNP features • It is intended to be used between a master station or data concentrator and a medium Slave • The input and output points of the slave device would be local to the device. • The functionality available in the Nu-Lec Optimised Family of products require Level 2 functionality.

19. DNP V3.00 Subset Levels • Level 3 • This level of implementation is the largest subset of DNP. • It is intended for use between a master and a large size slave device (e.g. Slave, Data Concentrator). • There are not yet many slaves with full level 3 compliance in the market place.

20. IEC 60870-5-101 and its companion standards • We believe there appears to be much confusion in relation to IEC companion standards 60870-5-101 and 60870-5-103. • Some of this confusion arises because DNP3 is specified in three levels and anyone who understands DNP naturally assumes 60870-5-101 has a similar set of levels and subset level functionality.

21. IEC 60870-5-101 and its companion standards • This is not the case • The 60870-5-103 companion standard is an extension, not a subset, of the 60870-5-101 standard and is designed for specific use in data interchange between protection equipment and a substation control system. • The 60870-5 standard for Transmission Protocols consists of five basic parts (60870-5-1 to 5) and a set of companion standards (eg 60870-5-101 and 103).

22. 60870-5 standard for Transmission Protocols • The following documents define 60870-5. • IEC 60870-5-103 Informative Interface of Protection Equipment • IEC 60870-5-101 Basic Telecontrol Tasks • IEC 60870-5-5 Basic Application Functions • IEC 60870-5-4 Definition and Coding of Application Information Elements • IEC 60870-5-3 General Structure of Application Data • IEC 60870-5-2 Link Transmission Procedures • IEC 60870-5-1 Transmission Frame Format

23. Device Interoperability • Both protocols have incorporated detailed compliance tables in their standards. • These tables provide a standard format for easy checking of the functions and data types supported by an implementation. • DNP3 is defined in a Device Profile • IEC870 is defined in a Interoperability Statement

24. DNP V3.00 Device Profile • The Device Profile document defines compliance with various application and link layer issues such as implementation level and deviations from the basic level criteria. • The Implementation Table defines the data objects and message types supported by the device.

25. IEC870 Interoperability Statement • It contains information about the device’s support of all EPA layers. • This information includes data such as supported network configuration, transmission details, link transmission procedure, and implemented data objects.

26. Compliance Test Procedures • One of DNP communications protocol’s strengths are the very detailed compliance certification test procedures produced and maintained, by the DNP V3.00 user group. • Currently available for slave implementation levels 1 and 2. • At present testing is a weakness of the IEC870 protocol because there are currently no official certification procedures available.

27. Comparison Between DNP3 and IEC870 • The protocols have many similarities in their functionality. Each permits: • Collection of binary (digital) data • Collection of analogue data • Collection, freezing and clearing of counters • Single pass or two-pass control of binary (digital) outputs • Single pass or two-pass control of analog outputs • Reporting of binary and analog events (report by exception) • Time synchronisation • Time-stamping events • Grouping data objects • File Transfer

28. Comparison Between DNP3 and IEC870 • The protocols have also have many differences in their functionality. • DNP does not conform exactly to the frame format specified by the IEC • DNP only uses balanced link services. 60870-5-101 may use balanced or unbalanced services. • DNP supports only a single addressing format. 60870-5-101 allows most of the options specified in 60870-5-2.

29. Comparison Between DNP3 and IEC870 • Differences • The DNP3 addressing format supports peer-to-peer operation, the IEC870 format does not. • DNP3 introduces a pseudo-transport layer (OSI layer 4) to build application data messages larger than a single data link frame. • Each IEC870 message must be contained in a single data link frame.

30. Comparison Between DNP3 and IEC870 • Differences • DNP groups data into four classes. This may be used to prioritise event reporting. One class is for “static” data: current values of inputs; the other three are for “event” data: reporting changes. • IEC groups data into two classes, and while not explicitly stated in the 60870-5-101 standard, one class is intended for “cyclic” data, and the other class is for all other data.

31. Comparison Between DNP3 and IEC870 • Differences • DNP is maintained by the technical committee of the DNP User Group. This body provides information about the protocol, and clarifies ambiguous areas of the protocol definition. The IEC does not provide information to clarify the interpretation of its standards. Questions are best addressed to a vendor of a product that supports 60870-5-101.

32. Conclusion • Both DNP V3.00 and IEC 60870-5-101 communications protocols go a long way to solving the interoperability problems common in previous generations of remote control systems. • Selecting the correct protocol for your utility depends very much on your SCADA master system’s ability to support one or both of these protocols and your network topology.

33. Conclusion • In fact, there would be benefits to ensure both protocols are supported by their Master stations. • This would provide the absolute maximum in flexibility of choice when interfacing to IEDs. • It is obvious from this paper that the IEC870 protocol has still not matured to the same level as DNP3 but this is coming.