This Recommendation | International Standard refines the description of the Application Layer contained in the Basic Reference Model for OSI (ITU-T Rec. X.200 | ISO/IEC 7498-1). It provides a framework for coordinating the development of existing and future Application Layer Recommendations and Standards. It is provided for reference by Application Layer Recommendations and Standards. In particular this Recommendation | International Standard: a) defines the nature of Recommendations and Standards in the Application Layer and the relationships among them; b) defines the architectural framework in which individual OSI Application Layer protocols are developed. c) defines concepts which provide a flexible approach to structuring in the Application Layer; d) defines the categories of identifiable objects which are necessary for the specification and operation of protocols; e) relates distributed information processing activities to the Recommendations and Standards in the Application Layer; f) structures, and relates, specifications in Application Layer Recommendations and Standards; g) identifies the various kinds of specification necessary in Application Layer Recommendations and Standards. This Recommendation | International Standard is provided for reference by Application Layer Recommendations and Standards. Its purpose is to facilitate a coherent and modular approach to the structuring of specifications for Application Layer behaviour. It neither specifies services nor protocols for OSI; nor is it an implementation specification for systems, nor a basis for appraising the conformance of implementations