IEC 61158-6-25:2019

Industrial communication networks - Fieldbus specifications - Part 6-25: Application layer protocol specification - Type 25 elements

IEC 61158-6-25:2019 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 specifies interactions between remote applications and defines the externally visible behavior provided by the Type 2 fieldbus application layer. The purpose of this document is to define the protocol provided to
a) define the wire-representation of the service primitives defined in this document, and
b) define the externally visible behavior associated with their transfer. This document specifies the protocol 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).

Réseaux de communication industriels - Spécifications des bus de terrain - Partie 6-25: Spécification du protocole de la couche application - Éléments de type 25

L'IEC 61158-6-25:2019 La couche application de bus de terrain (FAL, Fieldbus Application Layer) fournit aux programmes d’utilisateur un moyen d’accéder à l’environnement de communication du bus de terrain. A cet égard, la FAL peut être vue comme une "fenêtre entre des programmes d'application correspondants".
L'IEC 61158-6-25:2019 fournit les éléments communs pour les communications de messagerie de base prioritaires et non prioritaires entre des programmes d'application dans un environnement d'automation et le matériau spécifique au bus de terrain de type 25. On utilise le terme "prioritaire" pour traduire la présence d’une fenêtre temporelle, à l’intérieur de laquelle une ou plusieurs actions spécifiées doivent être terminées avec un niveau de certitude défini. Si les actions spécifiées ne sont pas réalisées dans la fenêtre temporelle, les applications demandant les actions risquent de connaître une défaillance, avec les risques que cela comporte pour les équipements, les installations et éventuellement la vie humaine.
Le présent document définit de manière abstraite le comportement, visible par un observateur externe, assuré par les différents types de la couche application de bus de terrain, en termes
a) de syntaxe abstraite définissant les unités de données de protocole de la couche application, transmises entre les entités d'application en communication;
b) de syntaxe de transfert définissant les unités de données de protocole de la couche application, transmises entre les entités d'application en communication;
c) de diagramme d'états de contexte d'application définissant le comportement de service d'application observable entre les entités d'application en communication; et
d) de diagrammes d'états de relations d'applications définissant le comportement de communication visible entre les entités d'application en communication.

General Information

• Status: Published
• Publication Date: 19-Jun-2019
• ICS: 25.040.40 - Industrial process measurement and control
• ICS: 35.100.70 - Application layer
• ICS: 35.110 - Networking
• Technical Committee: SC 65C - Industrial networks
• Drafting Committee: WG 9 - TC 65/SC 65C/WG 9
• Current Stage: PPUB - Publication issued
• Start Date: 20-Jun-2019
• Completion Date: 26-Apr-2019

Overview

IEC 61158-6-25:2019 - "Industrial communication networks - Fieldbus specifications - Part 6-25: Application layer protocol specification - Type 25 elements" defines the application-layer protocol for Type 2 fieldbus systems used in industrial automation. The standard specifies the wire-representation of service primitives and the externally visible behaviour of the Fieldbus Application Layer (FAL), covering both time‑critical (with defined time-windows) and non‑time‑critical messaging between automation application programs. It conforms to the OSI Basic Reference Model (ISO/IEC 7498-1) and the OSI application layer structure (ISO/IEC 9545).

Key topics and technical requirements

• Fieldbus Application Layer (FAL) structure: Definition of Type S and Type N FAL elements, including abstract and transfer syntaxes.
• PDU types and encoding rules: Specification of FAL PDUs such as CyclicData-PDU, MulticastData-PDU, PtoPData-PDU, Aliveinfo, Inq/Ninq, Reply, RetransEnq/Confirm/Nak, and encoding/serialization rules (unsigned, octet strings, SEQUENCE).
• State machines and protocol machines: Formal definitions of FAL service protocol machine (FSPM), Application Relationship Protocol Machine (ARPM), and Data Link Layer mapping protocol machine (DMPM) to describe externally visible behaviour and control sequences.
• Cyclic vs. acyclic communication: Mechanisms for cyclic transmission (periodic exchange) and acyclic/RT transmissions (on-demand, remote control).
• Reliability and retransmission: Protocol elements addressing retransmission control, sequence numbering and reception status to support dependable message delivery.
• Mapping and QoS: DLL mapping, communication ports, Quality of Service considerations and references to DSCP and IEEE 802.1Q for traffic classification and VLAN tagging.
• Conformance & interoperability: Rules for conformance testing and the externally visible interface between remote applications.

Practical applications and who uses this standard

IEC 61158-6-25 is applicable to designers and implementers of industrial communication solutions where robust application-layer behaviour is required:

• Automation system integrators implementing deterministic fieldbus communication for PLCs, DCS, remote I/O and motion control.
• Field device and gateway vendors developing Type 2 fieldbus stacks and ensuring interoperability.
• Control and safety engineers specifying time‑critical messaging for process and factory automation.
• Network architects and OEMs who need to map application-layer requirements to lower-layer QoS and VLAN configurations.

Typical use cases include time-critical control loops, distributed I/O, supervised safety functions and mixed time-critical/non-time-critical messaging in process plants and manufacturing lines.

Related standards

• IEC 61158 (other parts) - Fieldbus series
• ISO/IEC 7498-1 - OSI Basic Reference Model
• ISO/IEC 9545 - OSI application layer structure
• IEEE 802.1Q and DSCP references for VLAN/traffic classification

Keywords: IEC 61158-6-25, Fieldbus, Type 25, application layer, FAL, industrial communication networks, time-critical messaging, cyclic communication, PDUs, OSI.

Standards Content (Sample)

IEC 61158-6-25 ®
Edition 1.0 2019-06
INTERNATIONAL
STANDARD
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Industrial communication networks – Fieldbus specifications –
Part 6-25: Application layer protocol specification – Type 25 elements

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IEC 61158-6-25 ®
Edition 1.0 2019-06
INTERNATIONAL
STANDARD
colour
inside
Industrial communication networks – Fieldbus specifications –

Part 6-25: Application layer protocol specification – Type 25 elements

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 25.040.40; 35.100.70; 35.110 ISBN 978-2-8322-7015-8

– 2 – IEC 61158-6-25:2019 © IEC 2019
CONTENTS
FOREWORD . 7
INTRODUCTION . 9
1 Scope . 10
1.1 General . 10
1.2 Specification . 11
1.3 Conformance . 11
2 Normative references . 11
3 Terms, definitions, symbols, abbreviations and conventions . 12
3.1 Reference model terms and definitions . 12
3.1.1 ISO/IEC 7498-1 terms . 12
3.1.2 ISO/IEC 8822 terms . 12
3.1.3 ISO/IEC 9545 terms . 12
3.1.4 ISO/IEC 8824-1 terms . 13
3.2 Additional Type 25 terms and definitions . 13
3.3 Symbols and abbreviations . 15
3.4 Conventions . 16
3.4.1 General conventions . 16
3.4.2 Conventions for class definitions . 16
3.4.3 Conventions for bit description in octets . 16
3.4.4 Conventions for state machine descriptions . 17
4 FAL syntax description . 18
4.1 FAL PDU type S abstract syntax . 18
4.1.1 Basic abstract syntax . 18
4.2 FAL PDU type N abstract syntax . 22
4.2.1 Basic abstract syntax . 22
4.2.2 CyclicData-PDU . 22
4.2.3 MulticastData-PDU . 23
4.2.4 PtoPData-PDU . 23
4.2.5 Aliveinfo-PDU . 23
4.2.6 Aliveinfo6-PDU . 23
4.2.7 Inq-PDU . 24
4.2.8 Ninq-PDU . 24
4.2.9 Reply-PDU . 24
4.2.10 RetransEnq-PDU . 24
4.2.11 RetransConfirm-PDU . 24
4.2.12 RetransNak-PDU . 25
4.3 Data type assignments for type S . 25
4.4 Data type assignments for type N . 25
5 FAL transfer syntax . 26
5.1 Encoding rules . 26
5.1.1 Unsigned encoding . 26
5.1.2 Octet string encoding . 27
5.1.3 SEQUENCE encoding . 27
5.2 FALPDU type S elements encoding. 27
5.2.1 RCL_header . 27
5.2.2 RHE-PDU . 28

5.2.3 LCC-PDU . 30
5.2.4 LCA-PDU . 30
5.2.5 LCN-PDU . 31
5.2.6 LNA-PDU . 32
5.2.7 SCR-PDU . 32
5.2.8 Cyclic_S-PDU . 32
5.2.9 Cyclic_header . 33
5.2.10 Control-PDU . 33
5.2.11 RMTCTL-PDU. 33
5.2.12 INFO-PDU . 34
5.3 FALPDU type N elements encoding . 35
5.3.1 General . 35
5.3.2 FALAR-N Header . 35
5.3.3 CyclicData-PDU . 49
5.3.4 MulticastData-PDU . 50
5.3.5 PtoP Data-PDU. 50
5.3.6 Aliveinfo-PDU . 50
5.3.7 Aliveinfo6-PDU . 53
5.3.8 Inq-PDU . 54
5.3.9 Ninq-PDU . 55
5.3.10 Reply-PDU . 55
5.3.11 RetransEnq-PDU . 56
5.3.12 RetransConfirm-PDU . 56
5.3.13 RetransNak-PDU . 57
6 Structure of the FAL protocol state machine . 58
7 FAL service protocol machine (FSPM) . 58
7.1 Overview. 58
7.2 FSPM type S . 58
7.2.1 Overview . 58
7.2.2 Interface of cyclic communication to FAL users . 59
7.2.3 State machine of FSPM . 61
7.3 FSPM type N . 62
7.3.1 Overview . 62
7.3.2 FSPM . 63
8 Application relationship protocol machine (ARPM) . 65
8.1 ARPM type S . 65
8.1.1 Overview . 65
8.1.2 Cyclic control . 66
8.1.3 Remote control . 70
8.1.4 RCL communication control . 75
8.1.5 RT communication control . 79
8.2 ARPM type N . 83
8.2.1 Overview . 83
8.2.2 General control . 83
8.2.3 Cyclic transmission control . 85
8.2.4 Acyclic transmission control . 90
8.2.5 RT communication control . 105
9 DLL mapping protocol machine (DMPM) . 121

– 4 – IEC 61158-6-25:2019 © IEC 2019
9.1 DMPM type S . 121
9.2 DMPM type N . 122
9.2.1 General . 122
9.2.2 Communication port in transport layer . 122
9.2.3 Quality of Service . 122
Bibliography . 124

Figure 1 – Bit description in octets . 16
Figure 2 – hd_sa . 35
Figure 3 – hd_da . 36
Figure 4 – Valid sequence number for reception message . 40
Figure 5 – hd_m_ctl . 40
Figure 6 – Valid reception packet sequence number . 44
Figure 7 – Node-list . 55
Figure 8 – Relationships between protocol machines . 58
Figure 9 – Structure of FSPM type S . 59
Figure 10 – Shared memory allocation in type S network . 61
Figure 11 – Structure of FSPM type N . 63
Figure 12 – Structure of ARPM type S . 66
Figure 13 – Sequence of cyclic communication . 67
Figure 14 – The primitives for cyclic control . 67
Figure 15 – The primitives for Remote control . 70
Figure 16 – The primitives for RCL communication control . 75
Figure 17 – The primitives for RT communication control . 80
Figure 18 – Structure of ARPM type N . 83
Figure 19 – Primitives of Cyclic transmission control . 85
Figure 20 – Primitives of acyclic transmission control . 91
Figure 21 – DSCP format . 123
Figure 22 – IEEE 802.1Q tag frame format . 123

Table 1 – State transition descriptions . 17
Table 2 – Descriptions of state machine elements . 17
Table 3 – Conventions used in state machine . 17
Table 4 – Frame Class . 27
Table 5 – DA_STaddress – DA_STaddress . 27
Table 6 – DA_MACaddress . 27
Table 7 – CMD field format . 28
Table 8 – Send Direction . 28
Table 9 – RHE ReceiveStatus . 29
Table 10 – Physical Linkdown . 29
Table 11 – RHE_pattern 1~4 . 30
Table 12 – LCC-Kind . 30
Table 13 – RCL Status . 31
Table 14 – hd_h_type . 35

Table 15 – Usage of Mgn or Lnn . 37
Table 16 – Detailed conditions for sequence number check of reception message . 39
Table 17 – Valid bits of hd_m_ctl . 40
Table 18 – Specified TCD . 41
Table 19 – hd_pkind . 42
Table 20 – PDU with an effective hd_pseq . 42
Table 21 – Detailed conditions for sequence number check of reception packet
(Multicast communication with retransmission). 44
Table 22 – Detailed conditions for packet sequence number check . 45
Table 23 – Relation between message transmission/reception . 46
Table 24 – hd_mode . 46
Table 25 – Message priority level . 46
Table 26 – Value of α . 47
Table 27 – Example of header information for a UDP message fragmentation . 47
Table 28 – Example of header information for a TCP message fragmentation . 47
Table 29 – inqid_inq_sa value. 48
Table 30 – inqid_tr_adr value . 48
Table 31 – inqid_inq_seq value . 49
Table 32 – Relationship between inqid_id_seq and inqid_tr_adr . 49
Table 33 – Type of an alive-message . 51
Table 34 – Type of an alive-message protocol . 51
Table 35 – Time of each al_mode . 52
Table 36 – Status change of tasks . 52
Table 37 – Change of tasks content . 52
Table 38 – The threshold of transmission factor . 60
Table 39 – Example of the traffic control configuration menu . 60
Table 40 – Cyclic data state table . 61
Table 41 – Acyclic data state table. 62
Table 42 – Cyclic data state table . 64
Table 43 – Acyclic data state table. 64
Table 44 – Cyclic control state table . 68
Table 45 – Cyclic control functions. 69
Table 46 – Cyclic control variables. 70
Table 47 – Remote control state table . 71
Table 48 – Remote control functions . 74
Table 49 – Remote control variables . 75
Table 50 – RCL communication control state table . 76
Table 51 – RCL communication control functions . 77
Table 52 – RCL communication control variables . 79
Table 53 – RT communication control state table . 80
Table 54 – RT communication control functions . 82
Table 55 – RT communication control variables . 82
Table 56 – Cyclic transmission control state table . 86

– 6 – IEC 61158-6-25:2019 © IEC 2019
Table 57 – Cyclic transmission control functions . 88
Table 58 – Cyclic transmission control variables . 90
Table 59 – Acyclic transmission control state table . 91
Table 60 – Acyclic transmission control functions . 101
Table 61 – Acyclic transmission control variables . 104
Table 62 – RT communication control state table . 105
Table 63 – RT communication control functions . 116
Table 64 – RT communication control variables . 120
Table 65 – ARPM to DL mapping . 122
Table 66 – Assignment policy of communication ports . 122
Table 67 – Default DSCP, IEEE 802.1D and IEEE 802.1Q priority mapping . 123

INTERNATIONAL ELECTROTECHNICAL COMMISSION
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INDUSTRIAL COMMUNICATION NETWORKS –
FIELDBUS SPECIFICATIONS –
Part 6-25: Application layer protocol specification –
Type 25 elements
FOREWORD
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International Standard IEC 61158-6-25 has been prepared by subcommittee 65C: Industrial
networks, of IEC technical committee 65: Industrial-process measurement, control and
automation.
The text of this International Standard is based on the following documents:
FDIS Report on voting
65C/948/FDIS 65C/956/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

– 8 – IEC 61158-6-25:2019 © IEC 2019
A list of all parts in the IEC 61158 series, published under the general title Industrial
communication networks – Fieldbus specifications, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
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related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
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INTRODUCTION
This document is one of a series produced to facilitate the interconnection of automation
system components. It is related to other standards in the set as defined by the “three-layer”
fieldbus reference model described in IEC 61158-1.
The application protocol provides the application service by making use of the services
available from the data-link or other immediately lower layer. The primary aim of this
document is to provide a set of rules for communication expressed in terms of the procedures
to be carried out by peer application entities (AEs) at the time of communication. These rules
for communication are intended to provide a sound basis for development in order to serve a
variety of purposes:
• as a guide for implementers and designers;
• for use in the testing and procurement of equipment;
• as part of an agreement for the admittance of systems into the open systems environment;
• as a refinement to the understanding of time-critical communications within OSI.
This document is concerned, in particular, with the communication and interworking of
sensors, effectors and other automation devices. By using this document together with other
standards positioned within the OSI or fieldbus reference models, otherwise incompatible
systems may work together in any combination.

– 10 – IEC 61158-6-25:2019 © IEC 2019
INDUSTRIAL COMMUNICATION NETWORKS –
FIELDBUS SPECIFICATIONS –
Part 6-25: Application layer protocol specification –
Type 25 elements
1 Scope
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 International Standard 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 25 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
different Types of the fieldbus Application Layer in terms of:
a) the abstract syntax defining the application layer protocol data units conveyed between
communicating application entities,
b) the transfer syntax defining the application layer protocol data units conveyed between
communicating application entities,
c) the application context state machine defining the application service behavior visible
between communicating application entities; and
d) the application relationship state machines defining the communication behavior visible
between communicating application entities.
The purpose of this document is to define the protocol provided to:
a) define the wire-representation of the service primitives defined in IEC 61158-5-25, and
b) define the externally visible behavior associated with their transfer.
This document specifies the protocol of the IEC 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 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 Specification
The principal objective of this document is to specify the syntax and behavior of the
application layer protocol that conveys the application layer services defined in
IEC 61158-5-25. A secondary objective is to provide migration paths from previously-existing
industrial communications protocols. It is this latter objective which gives rise to the diversity
of protocols standardized in subparts of IEC 61158-6.
1.3 Conformance
This document does not specify individual implementations or products, nor does it constrain
the implementations of application layer entities within industrial automation systems.
There is no conformance of equipment to the application layer service definition standard.
Instead, conformance is achieved through implementation of this application layer protocol
specification.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements of this document. For dated references, only the edition
cited applies. For undated references, the latest edition of the referenced document (including
any amendments) applies.
NOTE All parts of the IEC 61158 series, as well as IEC 61784-1 and IEC 61784-2 are maintained simultaneously.
Cross-references to these documents within the text therefore refer to the editions as dated in this list of normative
references.
IEC 61158-3-25:2019, Industrial communication networks – Fieldbus specifications –
Part 3-25: Data-link layer service definition – Type 25 elements
IEC 61158-5-25:2019, Industrial communication networks – Fieldbus specifications –
Part 5-25: Application layer service definition – Type 25 elements
ISO/IEC 7498-1, Information technology – Open Systems Interconnection – Basic Reference
Model: The Basic Model
ISO/IEC 8822, Information technology – Open Systems Interconnection – Presentation
service definition
ISO/IEC 9545, Information technology – Open Systems Interconnection – Application Layer
structure
ISO/IEC 8824-1, Information technology – Abstract Syntax Notation One (ASN.1):
Specification of basic notation
ISO/IEC/IEEE 8802-3, Information technology – Telecommunications and information
exchange between systems – Local and metropolitan area networks – Specific requirements –
Part 3: Standard for Ethernet
IEEE Std 802.1D, IEEE Standard for Local and metropolitan area networks – Media access
Control (MAC) Bridges; available at http://www.ieee.org [viewed 2018-09-17]

– 12 – IEC 61158-6-25:2019 © IEC 2019
IEEE Std 802.1Q, IEEE Standard for Local and metropolitan area networks – Bridges and
Bridged Networks; available at http://www.ieee.org [viewed 2018-09-17]
IETF RFC 768, User Datagram Protocol; available at http://www.ietf.org> [viewed 2018-09-17]
IETF RFC 791, Internet Protocol; available at http://www.ietf.org> [viewed 2018-09-17]
3 Terms, definitions, symbols, abbreviations and conventions
For the purposes of this document, the following terms, definitions, symbols, abbreviations
and conventions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1 Reference model terms and definitions
3.1.1 ISO/IEC 7498-1 terms
For the purposes of this document, the following terms given in ISO/IEC 7498-1 apply:
application entity;
application process;
application protocol data unit;
application service element;
application entity invocation;
application process invocation;
application transaction;
real open system;
transfer syntax.
3.1.2 ISO/IEC 8822 terms
For the purposes of this document, the following terms given in ISO/IEC 8822 apply:
a) abstract syntax;
presentation context.
3.1.3 ISO/IEC 9545 terms
For the purposes of this document, the following terms given in ISO/IEC 9545 apply:
a) application-association;
application-context;
application context name;
application-entity-invocation;
application-entity-type;
application-process-invocation;
application-process-type;
application-service-element;
application control service element.
3.1.4 ISO/IEC 8824-1 terms
For the purposes of this document, the following terms given in ISO/IEC 8824-1 apply:
a) object identifier;
type.
3.2 Additional Type 25 terms and definitions
For the purpose of this document, the following definitions also apply.
NOTE Many definitions are common to more than one protocol Type; they are not necessarily used by all protocol
Types.
3.2.1
ADP message
message conveyed by an autonomous decentralized system protocol
3.2.2
alive-message
message reporting own node state, periodically transmitted
3.2.3
block
basic unit of data transferred in a cyclic communication, each having a size of 64 octets
3.2.4
category N_ f
category of an autonomous decentralized system protocol (full specifications) in type N
3.2.5
category N_l
category of an autonomous decentralized system protocol (light weight specifications) in
type N
3.2.6
control communication
acyclic data communication for higher time-critical applications in type S network
3.2.7
cyclic communication
periodic data communication for real-time communication
3.2.8
cyclic transfer memory
memory which is allocated to each node in the data field, which each node transmits
periodically for the purpose of sharing of this memory area logically
3.2.9
data field
logical place through which specific data passes, corresponding to real networks
3.2.10
domain
administrative set consisting of multiple data fields

– 14 – IEC 61158-6-25:2019 © IEC 2019
3.2.11
duplex LAN
two different network-paths between end nodes
3.2.12
equipment
physical hardware connected to the network
EXAMPLE Station, device, and server.
3.2.13
information communication
acyclic data communication for lower time-critical application in type S network
3.2.14
logical node, node
equipment in data fields, where an autonomous decentralized system’s function is installed
3.2.15
message mode
identifier that indicates the uses of a message (whether an online message or a test message)
EXAMPLE Online message or a test message.
3.2.16
multicast group
group of nodes belonging to a data field to determine whether to receive same data from other
node
3.2.17
node list
bit array structure of specifying a node to receive a request data
3.2.18
node mode
identifier that indicates the usage of a node
EXAMPLE Online node or a test node.
3.2.19
primary local area network
local area network (LAN) used in normal state in a duplex LAN system
3.2.20
priority control
transmission order control for the packets arrived from networks, according to the virtual local
area network (VLAN)
3.2.21
ring control communication
control for the type S ring network using ring control (RCL) frames
3.2.22
remote control
control for other nodes connected to a network
3.2.23
secondary local area network
local area network (LAN) for backup of a primary LAN in a duplex LAN system

3.2.24
transaction code
information to identify the characteristics of the message within a PDU
3.3 Symbols and abbreviations
ADP Autonomous Decentralized Protocol
ADS-net Autonomous Decentralized System – network
AE Application Entity
AL Application Layer
AP Application Process
APDU Application Protocol Data Unit
APO Application Process Object
AR Application Relationship
AREP Application Relationship Endpoint
ARPM Application Relationship Protocol Machine
ASCII American Standard Code for Information Interchange
ASE Application Service Element
ASN.1 Abstract Syntax Notation 1
CRC Cyclic Redundancy Check
DF Data Field
Dfn Data Field Number
DLL Data-link Layer
Dmn
...

IEC 61158-6-25 ®
Edition 1.0 2019-06
INTERNATIONAL
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INTERNATIONALE
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Industrial communication networks – Fieldbus specifications –
Part 6-25: Application layer protocol specification – Type 25 elements

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IEC 61158-6-25 ®
Edition 1.0 2019-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Industrial communication networks – Fieldbus specifications –

Part 6-25: Application layer protocol specification – Type 25 elements

Réseaux de communication industriels – Spécifications des bus de terrain –

Partie 6-25: Spécification du protocole de la couche application – Éléments

de type 25
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 25.040.40; 35.100.70; 35.110 ISBN 978-2-8322-9173-3

– 2 – IEC 61158-6-25:2019 © IEC 2019
CONTENTS
FOREWORD . 7
INTRODUCTION . 9
1 Scope . 10
1.1 General . 10
1.2 Specification . 11
1.3 Conformance . 11
2 Normative references . 11
3 Terms, definitions, symbols, abbreviations and conventions . 12
3.1 Reference model terms and definitions . 12
3.1.1 ISO/IEC 7498-1 terms . 12
3.1.2 ISO/IEC 8822 terms . 12
3.1.3 ISO/IEC 9545 terms . 12
3.1.4 ISO/IEC 8824-1 terms . 13
3.2 Additional Type 25 terms and definitions . 13
3.3 Symbols and abbreviations . 15
3.4 Conventions . 16
3.4.1 General conventions . 16
3.4.2 Conventions for class definitions . 16
3.4.3 Conventions for bit description in octets . 16
3.4.4 Conventions for state machine descriptions . 17
4 FAL syntax description . 18
4.1 FAL PDU type S abstract syntax . 18
4.1.1 Basic abstract syntax . 18
4.2 FAL PDU type N abstract syntax . 22
4.2.1 Basic abstract syntax . 22
4.2.2 CyclicData-PDU . 22
4.2.3 MulticastData-PDU . 23
4.2.4 PtoPData-PDU . 23
4.2.5 Aliveinfo-PDU . 23
4.2.6 Aliveinfo6-PDU . 23
4.2.7 Inq-PDU . 24
4.2.8 Ninq-PDU . 24
4.2.9 Reply-PDU . 24
4.2.10 RetransEnq-PDU . 24
4.2.11 RetransConfirm-PDU . 24
4.2.12 RetransNak-PDU . 25
4.3 Data type assignments for type S . 25
4.4 Data type assignments for type N . 25
5 FAL transfer syntax . 26
5.1 Encoding rules . 26
5.1.1 Unsigned encoding . 26
5.1.2 Octet string encoding . 27
5.1.3 SEQUENCE encoding . 27
5.2 FALPDU type S elements encoding. 27
5.2.1 RCL_header . 27
5.2.2 RHE-PDU . 28

5.2.3 LCC-PDU . 30
5.2.4 LCA-PDU . 30
5.2.5 LCN-PDU . 31
5.2.6 LNA-PDU . 32
5.2.7 SCR-PDU . 32
5.2.8 Cyclic_S-PDU . 32
5.2.9 Cyclic_header . 33
5.2.10 Control-PDU . 33
5.2.11 RMTCTL-PDU. 33
5.2.12 INFO-PDU . 34
5.3 FALPDU type N elements encoding . 35
5.3.1 General . 35
5.3.2 FALAR-N Header . 35
5.3.3 CyclicData-PDU . 49
5.3.4 MulticastData-PDU . 50
5.3.5 PtoP Data-PDU. 50
5.3.6 Aliveinfo-PDU . 50
5.3.7 Aliveinfo6-PDU . 53
5.3.8 Inq-PDU . 54
5.3.9 Ninq-PDU . 55
5.3.10 Reply-PDU . 55
5.3.11 RetransEnq-PDU . 56
5.3.12 RetransConfirm-PDU . 56
5.3.13 RetransNak-PDU . 57
6 Structure of the FAL protocol state machine . 58
7 FAL service protocol machine (FSPM) . 58
7.1 Overview. 58
7.2 FSPM type S . 58
7.2.1 Overview . 58
7.2.2 Interface of cyclic communication to FAL users . 59
7.2.3 State machine of FSPM . 61
7.3 FSPM type N . 62
7.3.1 Overview . 62
7.3.2 FSPM . 63
8 Application relationship protocol machine (ARPM) . 65
8.1 ARPM type S . 65
8.1.1 Overview . 65
8.1.2 Cyclic control . 66
8.1.3 Remote control . 70
8.1.4 RCL communication control . 75
8.1.5 RT communication control . 79
8.2 ARPM type N . 83
8.2.1 Overview . 83
8.2.2 General control . 83
8.2.3 Cyclic transmission control . 85
8.2.4 Acyclic transmission control . 90
8.2.5 RT communication control . 105
9 DLL mapping protocol machine (DMPM) . 121

– 4 – IEC 61158-6-25:2019 © IEC 2019
9.1 DMPM type S . 121
9.2 DMPM type N . 122
9.2.1 General . 122
9.2.2 Communication port in transport layer . 122
9.2.3 Quality of Service . 122
Bibliography . 124

Figure 1 – Bit description in octets . 16
Figure 2 – hd_sa . 35
Figure 3 – hd_da . 36
Figure 4 – Valid sequence number for reception message . 40
Figure 5 – hd_m_ctl . 40
Figure 6 – Valid reception packet sequence number . 44
Figure 7 – Node-list . 55
Figure 8 – Relationships between protocol machines . 58
Figure 9 – Structure of FSPM type S . 59
Figure 10 – Shared memory allocation in type S network . 61
Figure 11 – Structure of FSPM type N . 63
Figure 12 – Structure of ARPM type S . 66
Figure 13 – Sequence of cyclic communication . 67
Figure 14 – The primitives for cyclic control . 67
Figure 15 – The primitives for Remote control . 70
Figure 16 – The primitives for RCL communication control . 75
Figure 17 – The primitives for RT communication control . 80
Figure 18 – Structure of ARPM type N . 83
Figure 19 – Primitives of Cyclic transmission control . 85
Figure 20 – Primitives of acyclic transmission control . 91
Figure 21 – DSCP format . 123
Figure 22 – IEEE 802.1Q tag frame format . 123

Table 1 – State transition descriptions . 17
Table 2 – Descriptions of state machine elements . 17
Table 3 – Conventions used in state machine . 17
Table 4 – Frame Class . 27
Table 5 – DA_STaddress – DA_STaddress . 27
Table 6 – DA_MACaddress . 27
Table 7 – CMD field format . 28
Table 8 – Send Direction . 28
Table 9 – RHE ReceiveStatus . 29
Table 10 – Physical Linkdown . 29
Table 11 – RHE_pattern 1~4 . 30
Table 12 – LCC-Kind . 30
Table 13 – RCL Status . 31
Table 14 – hd_h_type . 35

Table 15 – Usage of Mgn or Lnn . 37
Table 16 – Detailed conditions for sequence number check of reception message . 39
Table 17 – Valid bits of hd_m_ctl . 40
Table 18 – Specified TCD . 41
Table 19 – hd_pkind . 42
Table 20 – PDU with an effective hd_pseq . 42
Table 21 – Detailed conditions for sequence number check of reception packet
(Multicast communication with retransmission). 44
Table 22 – Detailed conditions for packet sequence number check . 45
Table 23 – Relation between message transmission/reception . 46
Table 24 – hd_mode . 46
Table 25 – Message priority level . 46
Table 26 – Value of α . 47
Table 27 – Example of header information for a UDP message fragmentation . 47
Table 28 – Example of header information for a TCP message fragmentation . 47
Table 29 – inqid_inq_sa value. 48
Table 30 – inqid_tr_adr value . 48
Table 31 – inqid_inq_seq value . 49
Table 32 – Relationship between inqid_id_seq and inqid_tr_adr . 49
Table 33 – Type of an alive-message . 51
Table 34 – Type of an alive-message protocol . 51
Table 35 – Time of each al_mode . 52
Table 36 – Status change of tasks . 52
Table 37 – Change of tasks content . 52
Table 38 – The threshold of transmission factor . 60
Table 39 – Example of the traffic control configuration menu . 60
Table 40 – Cyclic data state table . 61
Table 41 – Acyclic data state table. 62
Table 42 – Cyclic data state table . 64
Table 43 – Acyclic data state table. 64
Table 44 – Cyclic control state table . 68
Table 45 – Cyclic control functions. 69
Table 46 – Cyclic control variables. 70
Table 47 – Remote control state table . 71
Table 48 – Remote control functions . 74
Table 49 – Remote control variables . 75
Table 50 – RCL communication control state table . 76
Table 51 – RCL communication control functions . 77
Table 52 – RCL communication control variables . 79
Table 53 – RT communication control state table . 80
Table 54 – RT communication control functions . 82
Table 55 – RT communication control variables . 82
Table 56 – Cyclic transmission control state table . 86

– 6 – IEC 61158-6-25:2019 © IEC 2019
Table 57 – Cyclic transmission control functions . 88
Table 58 – Cyclic transmission control variables . 90
Table 59 – Acyclic transmission control state table . 91
Table 60 – Acyclic transmission control functions . 101
Table 61 – Acyclic transmission control variables . 104
Table 62 – RT communication control state table . 105
Table 63 – RT communication control functions . 116
Table 64 – RT communication control variables . 120
Table 65 – ARPM to DL mapping . 122
Table 66 – Assignment policy of communication ports . 122
Table 67 – Default DSCP, IEEE 802.1D and IEEE 802.1Q priority mapping . 123

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INDUSTRIAL COMMUNICATION NETWORKS –
FIELDBUS SPECIFICATIONS –
Part 6-25: Application layer protocol specification –
Type 25 elements
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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international co-operation on all questions concerning standardization in the electrical and electronic fields. To
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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61158-6-25 has been prepared by subcommittee 65C: Industrial
networks, of IEC technical committee 65: Industrial-process measurement, control and
automation.
The text of this International Standard is based on the following documents:
FDIS Report on voting
65C/948/FDIS 65C/956/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

– 8 – IEC 61158-6-25:2019 © IEC 2019
A list of all parts in the IEC 61158 series, published under the general title Industrial
communication networks – Fieldbus specifications, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
INTRODUCTION
This document is one of a series produced to facilitate the interconnection of automation
system components. It is related to other standards in the set as defined by the “three-layer”
fieldbus reference model described in IEC 61158-1.
The application protocol provides the application service by making use of the services
available from the data-link or other immediately lower layer. The primary aim of this
document is to provide a set of rules for communication expressed in terms of the procedures
to be carried out by peer application entities (AEs) at the time of communication. These rules
for communication are intended to provide a sound basis for development in order to serve a
variety of purposes:
• as a guide for implementers and designers;
• for use in the testing and procurement of equipment;
• as part of an agreement for the admittance of systems into the open systems environment;
• as a refinement to the understanding of time-critical communications within OSI.
This document is concerned, in particular, with the communication and interworking of
sensors, effectors and other automation devices. By using this document together with other
standards positioned within the OSI or fieldbus reference models, otherwise incompatible
systems may work together in any combination.

– 10 – IEC 61158-6-25:2019 © IEC 2019
INDUSTRIAL COMMUNICATION NETWORKS –
FIELDBUS SPECIFICATIONS –
Part 6-25: Application layer protocol specification –
Type 25 elements
1 Scope
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 International Standard 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 25 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
different Types of the fieldbus Application Layer in terms of:
a) the abstract syntax defining the application layer protocol data units conveyed between
communicating application entities,
b) the transfer syntax defining the application layer protocol data units conveyed between
communicating application entities,
c) the application context state machine defining the application service behavior visible
between communicating application entities; and
d) the application relationship state machines defining the communication behavior visible
between communicating application entities.
The purpose of this document is to define the protocol provided to:
a) define the wire-representation of the service primitives defined in IEC 61158-5-25, and
b) define the externally visible behavior associated with their transfer.
This document specifies the protocol of the IEC 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 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 Specification
The principal objective of this document is to specify the syntax and behavior of the
application layer protocol that conveys the application layer services defined in
IEC 61158-5-25. A secondary objective is to provide migration paths from previously-existing
industrial communications protocols. It is this latter objective which gives rise to the diversity
of protocols standardized in subparts of IEC 61158-6.
1.3 Conformance
This document does not specify individual implementations or products, nor does it constrain
the implementations of application layer entities within industrial automation systems.
There is no conformance of equipment to the application layer service definition standard.
Instead, conformance is achieved through implementation of this application layer protocol
specification.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements of this document. For dated references, only the edition
cited applies. For undated references, the latest edition of the referenced document (including
any amendments) applies.
NOTE All parts of the IEC 61158 series, as well as IEC 61784-1 and IEC 61784-2 are maintained simultaneously.
Cross-references to these documents within the text therefore refer to the editions as dated in this list of normative
references.
IEC 61158-3-25:2019, Industrial communication networks – Fieldbus specifications –
Part 3-25: Data-link layer service definition – Type 25 elements
IEC 61158-5-25:2019, Industrial communication networks – Fieldbus specifications –
Part 5-25: Application layer service definition – Type 25 elements
ISO/IEC 7498-1, Information technology – Open Systems Interconnection – Basic Reference
Model: The Basic Model
ISO/IEC 8822, Information technology – Open Systems Interconnection – Presentation
service definition
ISO/IEC 9545, Information technology – Open Systems Interconnection – Application Layer
structure
ISO/IEC 8824-1, Information technology – Abstract Syntax Notation One (ASN.1):
Specification of basic notation
ISO/IEC/IEEE 8802-3, Information technology – Telecommunications and information
exchange between systems – Local and metropolitan area networks – Specific requirements –
Part 3: Standard for Ethernet
IEEE Std 802.1D, IEEE Standard for Local and metropolitan area networks – Media access
Control (MAC) Bridges; available at http://www.ieee.org [viewed 2018-09-17]

– 12 – IEC 61158-6-25:2019 © IEC 2019
IEEE Std 802.1Q, IEEE Standard for Local and metropolitan area networks – Bridges and
Bridged Networks; available at http://www.ieee.org [viewed 2018-09-17]
IETF RFC 768, User Datagram Protocol; available at http://www.ietf.org> [viewed 2018-09-17]
IETF RFC 791, Internet Protocol; available at http://www.ietf.org> [viewed 2018-09-17]
3 Terms, definitions, symbols, abbreviations and conventions
For the purposes of this document, the following terms, definitions, symbols, abbreviations
and conventions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1 Reference model terms and definitions
3.1.1 ISO/IEC 7498-1 terms
For the purposes of this document, the following terms given in ISO/IEC 7498-1 apply:
a) application entity;
b) application process;
c) application protocol data unit;
d) application service element;
e) application entity invocation;
f) application process invocation;
g) application transaction;
h) real open system;
i) transfer syntax.
3.1.2 ISO/IEC 8822 terms
For the purposes of this document, the following terms given in ISO/IEC 8822 apply:
a) abstract syntax;
b) presentation context.
3.1.3 ISO/IEC 9545 terms
For the purposes of this document, the following terms given in ISO/IEC 9545 apply:
a) application-association;
b) application-context;
c) application context name;
d) application-entity-invocation;
e) application-entity-type;
f) application-process-invocation;
g) application-process-type;
h) application-service-element;

i) application control service element.
3.1.4 ISO/IEC 8824-1 terms
For the purposes of this document, the following terms given in ISO/IEC 8824-1 apply:
a) object identifier;
b) type.
3.2 Additional Type 25 terms and definitions
For the purpose of this document, the following definitions also apply.
NOTE Many definitions are common to more than one protocol Type; they are not necessarily used by all protocol
Types.
3.2.1
ADP message
message conveyed by an autonomous decentralized system protocol
3.2.2
alive-message
message reporting own node state, periodically transmitted
3.2.3
block
basic unit of data transferred in a cyclic communication, each having a size of 64 octets
3.2.4
category N_ f
category of an autonomous decentralized system protocol (full specifications) in type N
3.2.5
category N_l
category of an autonomous decentralized system protocol (light
...