Historical
IEC 61158-5-20 Ed. 2.0 en:2010
Industrial communication networks - Fieldbus specifications - Part 5-20: Application layer service definition - Type 20 element
"IEC 61158-5-20:2010(E) specifies the structure and services of the type 20 IEC fieldbus Application Layer, in conformance with the OSI Basic Reference Model (ISO/IEC 7498) and the OSI Application Layer Structure (ISO/IEC 9545). This second edition cancels and replaces the first edition published in 2007 and constitutes a technical revision. The main change with respect to the previous edition is Revised VFD ASE, see 6.2.1."
International Electrotechnical Commission [iec]