GB/T 47014.4-2026 Industrial communication networks—Fieldbus specifications—Type 2 elements:EtherNet/IP, ControlNet and DeviceNet specifications—Part 4:Application layer protocol specification

Scope

1.1 Overview
The Fieldbus Application Layer (FAL) provides a method for user programs to access the Fieldbus communication environment. In this regard, FAL can be regarded as a "window" between corresponding applications.
This document provides common elements for time-critical and non-time-critical message communication between applications in an automation environment and Type 2 Fieldbus-specific devices. "Time-critical" refers to the existence of a time window within which one or more specified actions must be completed with a specified degree of certainty. If the specified actions cannot be completed within this time window, there is a risk of failure for the application requesting the actions, and this could also pose additional risks to equipment, factories, and even human lives.
This document specifies the interaction between remote applications and defines the externally visible behavior provided by the Type 2 Fieldbus application layer, including the following aspects:
—— Formal abstract syntax, which defines the application layer protocol data units exchanged between communication application entities;
—— Transport syntax, which defines the encoding rules applicable to application layer protocol data units;
—— Application context state machines, which define the externally visible application service behavior between communication application entities;
—— Application relationship state machines, which define the externally visible communication behavior between communication application entities.
The purpose of this document is to specify the protocol used for the following:
—— Specifying the representation of service primitives defined in GB/T 47014.3—2026 on the network;
—— Specifying the externally visible behavior associated with their transmission.
This document specifies the Type 2 Fieldbus application layer protocol, which complies with the OSI Basic Reference Mo

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