IEC 61158-5-2:2019 (E) defines the services provided to the FAL user at the boundary between the user and the application layer of the fieldbus reference model, and Systems Management at the boundary between the application layer and Systems Management of the fieldbus reference model. This standard specifies the structure and services of the Type 2 fieldbus application layer, in conformance with the OSI Basic Reference Model (ISO/IEC 7498-1) and the OSI application layer structure (ISO/IEC 9545)This fourth edition cancels and replaces the third edition published in 2014. This edition constitutes a technical revision.This edition includes the following significant technical changes with respect to the previous edition:- addition of a data type in 5.3.2;- clarifications of Object management ASE in 6.2.1;- extensions of General ASE in 6.2.1.2.1;- extensions/clarifications of Identity ASE in 6.2.1.2.2;- update of Message Router ASE in 6.2.1.2.4;- extensions/clarifications of Time Sync ASE in 6.2.1.2.6;- updates of Parameter ASE in 6.2.1.2.7;- updates of FAL ASE service specification in 6.2.1.3;- extensions/clarifications of Connection manager ASE in 6.2.2;- extensions/clarifications of Connection ASE in 6.2.3;- extensions/clarifications of Application type in 6.3.1.4.5.- miscellaneous editorial corrections.