Fundamentals of IEC 60870-5

The chapter discusses the International Electrotechnical Commission (IEC) 60870-5 standard. The companion standard sections or simply companion standards—IEC 60870-5-101 to IEC 60870-5-104—are each separate application protocols intended for specific purposes. They provide definitions of application level data objects and functions to completely define a working protocol. They are also referred to as profiles, and may sometimes be given the shorthand references T101, T102, T103, and T104, where T stands for telecontrol. IEC 60870-5-1 1990 describes the operation of the physical and data link layers in terms of the services provided to higher layers, and provides a choice of four data link frame types identified as FT1.1, FT1.2, FT2, and FT3, each with a different level of security against data errors. The chapter also discusses the link transmission procedures that represents the four-frame formats from IEC 60870-5-1, and describes the internal processes in terms of service primitives and transmission procedures. IEC 60870-5-5 1995 describes transmission protocol's highest level functions, which are those application functions that are above layer 7 of the open systems interconnection (OSI) model. IEC 60870-5 is based on the three-layer enhanced performance architecture or enhanced performance architecture model for data communications. For the first defined companion standard IEC 60870-5-101 or T101 profile, a four-layer model provides an accurate representation of the architecture of the protocol. In the case of the networked version IEC 60870-5-104 or the T104 profile, additional layers of the OSI model must be included to provide transport of messages over networks using standard network protocols.