7 Preview of IEC 60870-5 7.1 What is IEC 60870-5? IEC 60870-5 refers to a collection of standards produced by the International Electrotechnical Commission, or IEC , to provide an open standard for the transmission of SCADA telemetry control and information. The standard provides a detailed functional description for telecontrol equipment and systems for controlling geographically widespread processes, in other words for SCADA systems. The standard is intended for application in the electrical industries, and has data objects that are specifically intended for such applications, however it is not limited to such applications as it has data objects that are applicable to general SCADA applications in any industry. Nevertheless, the IEC 60870-5 protocol is primarily used in the electrical industries of European countries. When the IEC 60870-5 set of standards was initially completed in 1995 with the publication of the IEC 870-5-101 profile, it covered only transmission over relatively low bandwidth bit-serial communication circuits. With the increasingly widespread use of network communications technology, IEC 60870-5 now also provides for communications over networks using the TCP/IP protocol suite. This same sequence of development occurred for DNP3. In this preview, the main features of IEC 60870-5 are described under the headings listed below. These areas are all examined in greater detail in the subsequent chapters of Fundamentals and Advanced considerations of IEC 60870-5, in which the protocol will be described in detail by focussing on the protocol specification from the physical level through to the user application level. • Standards • System topology • Message structure • Addressing
Preview of IEC 60870-5 171 7.2 Standards • Message transport • Application and user level functions • Application data objects • Interoperability IEC 60870 refers to a standard produced in a number of parts between 1988 and 2000 by the International Electrotechnical Commission, or IEC. The IEC is an organization made up from national committees from around the world, and its role is to promote international cooperation on standardization in the electrical and electronic fields. This standard was originally referenced as IEC 870, but the prefix ‘60’ has subsequently been added. The IEC 60870 standard is structured in hierarchical manner, comprising six parts plus a number of companion standards. Each part is then made up of a number of sections, each of which has been published separately in a progressive manner. In addition to the main parts, there are four ‘companion’ standards that provide the fine details of the standard for a particular field of application. The companion standards extend the definition provided by the main parts of the standard by adding specific information objects for the field of application. The structure of the IEC 60870 standard is illustrated in Figure 7.1, following. This shows the main parts of the standard, plus the sections and companion standards concerned with transmission protocols. Near the bottom of the figure, the companion standard IEC 60870-5-101 may be seen. This is titled ‘Companion standard for basic telecontrol tasks’. It is in fact this document that is most often meant when IEC 870 or IEC 60870 is discussed in the context of SCADA systems. This is because it was only with the release of this document that a full definition for a complete SCADA transmission protocol was created, as it is this document that provides all of the application level data objects that are necessary for SCADA operation. Nevertheless, although IEC 60870-5-101 completes the definition for the transmission protocol, it includes many references to the details contained in Sections 1 to 5 of Part 5. The fourth companion standard, IEC 60870-5-104 is also of particular importance in understanding the standard as it is used today, because it defines the transport of IEC 60870-5 application messages over networks. Its full title is ‘Network Access using Standard Transport Profiles’ which is referring to its use of TCP/IP for the transport and network protocols. This companion standard was published in December 2000, some six years after the IEC 60870-5-101 was published. It of course provides a very different physical and data transport mechanism to IEC 60870-101, but leaves most of the higher application level functions and data objects unaltered. The standards are discussed in greater detail in a following section of this course. The key points to note from this preview are the hierarchical structure of the standard, the fact that it has been progressively developed and issued, and the fact that the two main describing documents are the profiles IEC 60870-5-101 and more recently IEC 60870-5-104.
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