Description of BS EN IEC 61158-5-26:2023 2023

1.1 General The fieldbus application layer (FAL) provides user programs with a means to access the fieldbus communication environment. In this respect, the FAL can be viewed as a "window between corresponding application programs." This part of IEC 61158 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 2 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 International Standard defines in an abstract way the externally visible service provided by the Type 2 fieldbus application layer in terms of: a) an abstract model for defining application resources (objects) capable of being manipulated by users via the use of the FAL service, b) the primitive actions and events of the service; c) the parameters associated with each primitive action and event, and the form which they take; and d) the interrelationship between these actions and events, and their valid sequences. The purpose of this document is to define the services provided to: a) the FAL user at the boundary between the user and the application layer of the fieldbus reference model, and b) Systems Management at the boundary between the application layer and Systems Management of the fieldbus reference model. This document specifies the structure and services of the Type 2 fieldbus application layer, in conformance with the OSI Basic Reference Model (ISO/IEC 7498-1) and the OSI application layer structure (ISO/IEC 9545). FAL services and protocols are provided by FAL application-entities (AE) contained within the application processes. The FAL AE is composed of a set of object-oriented application service elements (ASEs) and a layer management entity (LME) that manages the AE. The ASEs provide communication services that operate on a set of related application process object (APO) classes. One of the FAL ASEs is a management ASE that provides a common set of services for the management of the instances of FAL classes. Although these services specify, from the perspective of applications, how request and responses are issued and delivered, they do not include a specification of what the requesting and responding applications are to do with them. That is, the behavioral aspects of the applications are not specified; only a definition of what requests and responses they can send/receive is specified. This permits greater flexibility to the 318 FAL users in standardizing such object behavior. In addition to these services, some supporting services are also defined in this document to provide access to the FAL to control certain aspects of its operation. 1.2 Specifications [...] 1.3 Conformance [...]

Standard Number	BS EN IEC 61158-5-26:2023
Title	Industrial communication networks. Fieldbus specifications - Application layer service definition. Type 26 elements
Status	Definitive
Publication Date	2023-04-28
Replaces	BS EN IEC 61158-5-26:2019
Identical National Standard Of	EN 61158-5-X Ed.5.0, IEC 61158-5-X Ed.5.0
Descriptors	Definitions, Application layer (OSI), Open systems interconnection, Industrial, Communication networks
ICS	25.040.40 Industrial process measurement and control, 35.100.70 Application layer, 35.110 Networking
Committee	GEL/65
ISBN	978 0 539 13668 5
Publisher	BSI
Pages	122

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