工业通信网络 现场总线规范第 6-27 部分：应用层协议规范 类型 27 元素

[中文适用范围]： Fieldbus Application Layer (FAL)为用户程序提供访问现场总线通信环境的手段。FAL可以被视为“相应应用程序之间的窗口”。本部分IEC 61158为自动化环境中的应用程序之间的基本时间关键和非时间关键消息通信提供通用元素，并针对Type 27现场总线提供特定材料。“时间关键”表示存在一个时间窗口，在该窗口内需要以一定的确定性完成一个或多个指定动作。未能在时间窗口内完成指定动作可能会导致请求动作的应用程序失败，进而对设备、工厂甚至人身安全造成风险。本文档以抽象方式定义了Type 27现场总线应用层提供的外部可见行为，包括：定义通信应用实体之间传递的应用层协议数据单元的抽象语法、传输语法、定义通信应用实体之间可见的应用服务行为的应用上下文状态机，以及定义通信应用实体之间可见的通信行为的应用关系状态机。本文档的目的是定义协议，以定义IEC 61158-5-27中定义的服务原语的线表示，并定义与其传输相关的外部可见行为。本文档规定了Type 27现场总线应用层的协议，符合OSI基本参考模型(ISO/IEC 7498-1)和OSI应用层结构(ISO/IEC 9545)。 [外文原描述]： IEC 61158-6-27:2023 provides common elements for basic time-critical and non-time-critical messaging communications between application programs in an automation environment and material specific to Type 27 fieldbus. The term "time-critical" is used to represent the presence of a time-window, within which one or more specified actions are required to be completed with some defined level of certainty. Failure to complete specified actions within the time window risks failure of the applications requesting the actions, with attendant risk to equipment, plant and possibly human life. This document defines in an abstract way the externally visible behavior provided by the Type 27 fieldbus application layer in terms of the abstract syntax defining the application layer protocol data units conveyed between communicating application entities, the transfer syntax defining the application layer protocol data units conveyed between communicating application entities, the application context state machines defining the application service behavior visibly between communicating application entities, and the application relationship state machines defining the communication behavior visibly between communicating application entities.