IEC 61158-6-12:2010 specifies the protocol of the Type 12 fieldbus application layer, in conformance with the OSI Basic Reference Model (ISO/IEC 7498-1) and the OSI application layer structure (ISO/IEC 9545). It defines the protocol provided to define the wire-representation of the service primitives defined in IEC 61158-5-12:2010, and the externally visible behavior associated with their transfer. This second edition cancels and replaces the first edition published in 2007 and constitutes a technical revision. The main changes with respect to the previous edition are: bug fixes and editorial improvements.