IEC 61158-6-20:2010(E) specifies the protocol of the Type 20 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 61158-5-20:2010, 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: revised Identify FAL PDU, see 5.3.2 and revised Read device variables with status FAL PDU, see 5.3.9.