SIST EN 61158-3-7:2008

Industrial communication networks - Fieldbus specifications - Part 3-7: Data-link layer service definition - Type 7 elements

It provides common elements for basic time-critical messaging communications between devices in an automation environment. 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. It includes the following significant changes with respect to the previous edition deletion of the former Type 6 fieldbus, and the placeholder for a Type 5 fieldbus data-link layer, for lack of market relevance; addition of new types of fieldbuses; division of this part into multiple parts numbered.

Industrielle Kommunikationsnetze - Feldbusse - Teil 3-7: Dienstfestlegungen des Data Link Layer (Sicherungsschicht) - Typ 7-Elemente

Réseaux de communication industriels - Spécifications des bus de terrain - Partie 3-7: Définition des services des couches de liaison de données - Eléments de type 7

La CEI 61158-3-7:2007 définit de manière abstraite le service visible de l'extérieur fourni par la couche de liaison de données de bus de terrain de Type 7 en termes:
- d'actions et événements primitifs du service;
- de paramètres associés à chaque action primitive et événement primitif, et la forme qu'ils prennent;
- de l'interrelation entre ces actions et événements, et leurs séquences valides. Cette première édition et ses parties associées de la sous-série CEI 61158-3 annulent et remplacent la CEI 61158-3:2003. La présente édition de cette partie constitue une révision rédactionnelle. Cette édition inclut les modifications suivante:
- suppression du précédent bus de terrain de Type 6, et du paramètre fictif pour une couche de liaison de données des bus de terrain de Type 5, en raison d'un manque de pertinence avec le marché;
- ajout de nouveaux types de bus de terrain; division de cette partie en plusieurs parties numérotées 3-1, 3-2,..., 3-19. La présente version bilingue (2013-07) correspond à la version anglaise monolingue publiée en 2007-12.

Industrijska komunikacijska omrežja - Specifikacije za procesna vodila - 3-7. del: Definicija opravil na nivoju podatkovnih povezav - Elementi tipa 7 (IEC 61158-3-7:2007)

General Information

• Status: Published
• Publication Date: 15-Apr-2008
• ICS: 25.040.40 - Industrial process measurement and control
• ICS: 35.100.20 - Data link layer
• ICS: 35.110 - Networking
• Technical Committee: MOV - Measuring equipment for electromagnetic quantities
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 14-Mar-2008
• Due Date: 19-May-2008
• Completion Date: 16-Apr-2008
• Mandate: M/490 - Standardisation mandate to the European Standardisation Organisations (ESOs) to support European Smart Grid deployment
• Ref Project: EN 61158-3-7:2008 - Industrial communication networks - Fieldbus specifications - Part 3-7: Data-link layer service definition - Type 7 elements

Relations

• Replaces: SIST EN 61158-3:2004 - Digital data communication for measurement and control - Fieldbus for use in industrial control systems -- Part 3: Data link service definition
• Effective Date: 29-Jan-2023
• Revised: SIST EN 61158-3:2004 - Digital data communication for measurement and control - Fieldbus for use in industrial control systems -- Part 3: Data link service definition
• Effective Date: 07-Jun-2022

Overview

EN 61158-3-7:2008 - Industrial communication networks - Fieldbus specifications - Part 3-7: Data‑link layer service definition - Type 7 elements (CLC / IEC 61158-3-7) defines the abstract, externally visible services of the Type 7 fieldbus data‑link layer for time‑critical messaging in automation systems. The standard specifies the primitives, parameters and valid sequences used at the boundary between the application layer and the data‑link layer, and between the data‑link layer and systems management. It is part of the IEC/EN 61158 fieldbus series and supersedes the older EN 61158-3:2004 with reorganization of fieldbus types.

Key topics

• Time‑critical messaging: Defines services intended for communications that must complete within a specified time window to avoid equipment, process or safety failures.
• Abstract service definition: Describes primitives (actions/events), parameter formats and allowed sequences rather than low‑level bit/byte encodings.
• Buffer and message services: Coverage includes buffer writing/reading/transfer and both unacknowledged and acknowledged message transfer services. Example primitive names in the document include DL‑Put, DL‑Get, DL‑Buffer‑Sent, DL‑Buffer‑Received, DL‑Message and DL‑Message‑Ack.
• Medium allocation and timing concepts: High‑level mechanisms for medium access and deterministic delivery appropriate to fieldbus environments.
• Conformance and scope: Defines what constitutes the Type 7 data‑link layer service and how it complements the OSI reference model; notes on intellectual property and permitted protocol type combinations (see IEC 61784 series).

Applications

• Real‑time and safety‑relevant automation where deterministic device‑to‑device messaging is required - e.g., PLC networks, motion control, process control loops and industrial safety systems.
• Use cases where failing to meet strict timing windows risks plant equipment, production continuity or human safety.
• Specification guidance for designing and validating data‑link implementations, protocol stacks and interoperability between field devices and system management tools.

Who should use this standard

• Control system architects, fieldbus protocol designers and firmware developers implementing Type 7 data‑link layers.
• System integrators and OEMs selecting or validating fieldbus components for time‑critical automation.
• Test houses and certification bodies assessing conformance to Type 7 data‑link services.

Related standards

• IEC/EN 61158 series (other parts 3-1 … 3-19) - fieldbus protocol types
• IEC 61784 series - profiles and allowed layer combinations
• EN/ISO references to the OSI Basic Reference Model (ISO/IEC 7498)

This standard is primarily conceptual and intended to guide implementers and integrators in achieving deterministic, time‑critical fieldbus communications consistent with the IEC/EN fieldbus family.

Standards Content (Sample)

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Industrijska komunikacijska omrežja - Specifikacije za procesna vodila - 3-7. del: Definicija opravil na nivoju podatkovnih povezav - Elementi tipa 7 (IEC 61158-3-7:2007)Industrielle Kommunikationsnetze - Feldbusse - Teil 3-7: Dienstfestlegungen des Data Link Layer (Sicherungsschicht) - Typ 7-ElementeRéseaux de communication industriels - Spécifications des bus de terrain - Partie 3-7: Définition des services des couches de liaison de données - Eléments de type 7Industrial communication networks - Fieldbus specifications - Part 3-7: Data-link layer service definition - Type 7 elements35.110OmreževanjeNetworking35.100.20Podatkovni povezovalni slojData link layer25.040.40Merjenje in krmiljenje industrijskih postopkovIndustrial process measurement and controlICS:Ta slovenski standard je istoveten z:EN 61158-3-7:2008SIST EN 61158-3-7:2008en,de01-junij-2008SIST EN 61158-3-7:2008SLOVENSKI
STANDARDSIST EN 61158-3:20041DGRPHãþD

EUROPEAN STANDARD EN 61158-3-7 NORME EUROPÉENNE
EUROPÄISCHE NORM February 2008
CENELEC European Committee for Electrotechnical Standardization Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung
Central Secretariat: rue de Stassart 35, B - 1050 Brussels
© 2008 CENELEC -
All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 61158-3-7:2008 E
ICS 35.100.20; 25.040.40 Partially supersedes EN 61158-3:2004
English version
Industrial communication networks -
Fieldbus specifications -
Part 3-7: Data-link layer service definition -
Type 7 elements (IEC 61158-3-7:2007)
Réseaux de communication industriels -
Spécifications des bus de terrain -
Partie 3-7: Définition des services
des couches de liaison de données -
Eléments de type 7 (CEI 61158-3-7:2007)
Industrielle Kommunikationsnetze -
Feldbusse -
Teil 3-7: Dienstfestlegungen des
Data Link Layer (Sicherungsschicht) -
Typ 7-Elemente (IEC 61158-3-7:2007)
This European Standard was approved by CENELEC on 2008-02-01. CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the Central Secretariat has the same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Cyprus, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom.
- 2 -
Foreword The text of document 65C/473/FDIS, future edition 1 of IEC 61158-3-7, prepared by SC 65C, Industrial networks, of IEC TC 65, Industrial-process measurement, control and automation, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as EN 61158-3-7 on 2008-02-01. This and the other parts of the EN 61158-3 series supersede EN 61158-3:2004. With respect to EN 61158-3:2004 the following changes were made: – deletion of Type 6 fieldbus, and the placeholder for a Type 5 fieldbus data-link layer, for lack of market relevance; – addition of new fieldbus types; – partition into multiple parts numbered 3-1, 3-2, …, 3-19. The following dates were fixed: – latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement
(dop)
2008-11-01 – latest date by which the national standards conflicting
with the EN have to be withdrawn
(dow)
2011-02-01 NOTE
Use of some of the associated protocol types is restricted by their intellectual-property-right holders. In all cases, the commitment to limited release of intellectual-property-rights made by the holders of those rights permits a particular data-link layer protocol type to be used with physical layer and application layer protocols in type combinations as specified explicitly in the EN 61784 series. Use of the various protocol types in other combinations may require permission from their respective intellectual-property-right holders. Annex ZA has been added by CENELEC. __________ Endorsement notice The text of the International Standard IEC 61158-3-7:2007 was approved by CENELEC as a European Standard without any modification. In the official version, for Bibliography, the following notes have to be added for the standards indicated: IEC 61158-2 NOTE
Harmonized as EN 61158-2:2008 (not modified). IEC 61158-4-7 NOTE
Harmonized as EN 61158-4-7:2008 (not modified). IEC 61158-5-7 NOTE
Harmonized as EN 61158-5-7:2008 (not modified). IEC 61158-6-7 NOTE
Harmonized as EN 61158-6-7:2008 (not modified). IEC 61784-1 NOTE
Harmonized as EN 61784-1:2008 (not modified). __________
- 3 - EN 61158-3-7:2008 Annex ZA
(normative)
Normative references to international publications with their corresponding European publications
The following referenced documents are indispensable for the application 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
When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD applies.
Publication Year Title EN/HD Year
ISO/IEC 7498-1 -1) Information technology - Open Systems Interconnection - Basic Reference Model:
The Basic Model EN ISO/IEC 7498-119952)
ISO/IEC 7498-3 -1) Information technology - Open Systems Interconnection - Basic Reference Model: Naming and addressing - -
ISO/IEC 10731 -1) Information technology - Open Systems Interconnection - Basic Reference Model - Conventions for the definition of OSI services- -
1) Undated reference. 2) Valid edition at date of issue. SIST EN 61158-3-7:2008

IEC 61158-3-7Edition 1.0 2007-12INTERNATIONAL STANDARD
Industrial communication networks – Fieldbus specifications –
Part 3-7: Data-link layer service definition – Type 7 elements
INTERNATIONAL ELECTROTECHNICAL COMMISSION VICS 35.100.20; 25.040.40 PRICE CODEISBN 2-8318-9413-1SIST EN 61158-3-7:2008

– 2 – 61158-3-7 © IEC:2007(E) CONTENTS FOREWORD.4 INTRODUCTION.6 1 Scope.7 1.1 Overview.7 1.2 Specifications.7 1.3 Conformance.7 2 Normative references.8 3 Terms, definitions, symbols, abbreviations and conventions.8 3.1 Reference model terms and definitions.8 3.2 Service convention terms and definitions.9 3.3 Data-link service terms and definitions.9 3.4 Symbols and abbreviations.13 3.5 Common conventions.14 4 Data-link layer services and concepts.16 4.1 Field of application, object.16 4.2 General description of services.16 4.3 Sequences of primitives.21 4.4 Buffer writing.22 4.5 Buffer reading.24 4.6 Buffer transfer.25 4.7 Explicit request for buffer transfer.26 4.8 Unacknowledged message transfer.30 4.9 Acknowledged message transfer.32 Bibliography.35
Figure 1 – Relationships of DLSAPs, DLSAP-addresses and group DL-addresses.11 Figure 2 – General description of medium allocation.20 Figure 3 – Primitives associated with the buffer writing service.23 Figure 4 – Primitives associated with the buffer reading service.24 Figure 5 – Primitives associated with the buffer transfer service.25 Figure 6 – Primitives associated with the specified explicit request for a buffer transfer.28 Figure 7 – Primitives associated with the free explicit request for a buffer transfer.29 Figure 8 – Primitives associated with the unacknowledged message transfer request service.31 Figure 9 – Primitives associated with the acknowledged message transfer request service.33
Table 1 – Summary of DL-services and primitives for buffer transfers.22 Table 2 – Summary of DL-services and primitives for message exchanges.22 Table 3 – DL-Put primitives and parameters.23 Table 4 – DL-Get primitives and parameters.24 Table 5 – DL-Buffer-Sent primitive and parameter.26 Table 6 – DL-Buffer-Received primitive and parameter.26 Table 7 – DL-Spec-Update primitives and parameters.28 Table 8 – DL-Free-Update primitives and parameters.30 SIST EN 61158-3-7:2008

61158-3-7 © IEC:2007(E) – 3 –
Table 9 – DL-Message primitives and parameters.31 Table 10 – DL-Message-Ack primitives and parameters.33
– 4 – 61158-3-7 © IEC:2007(E) INTERNATIONAL ELECTROTECHNICAL COMMISSION ____________ INDUSTRIAL COMMUNICATION NETWORKS – FIELDBUS SPECIFICATIONS –
Part 3-7: Data-link layer service definition – Type 7 elements
FOREWORD 1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory work. International, governmental and non-governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for Standardization (ISO) in accordance with conditions determined by agreement between the two organizations. 2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international consensus of opinion on the relevant subjects since each technical committee has representation from all interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any misinterpretation by any end user. 4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications transparently to the maximum extent possible in their national and regional publications. Any divergence between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter. 5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any equipment declared to be in conformity with an IEC Publication. 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 members of its technical committees and IEC National Committees for any personal injury, property damage or other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC Publications.
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. NOTE
Use of some of the associated protocol types is restricted by their intellectual-property-right holders. In all cases, the commitment to limited release of intellectual-property-rights made by the holders of those rights permits a particular data-link layer protocol type to be used with physical layer and application layer protocols in type combinations as specified explicitly in the IEC 61784 series. Use of the various protocol types in other combinations may require permission of their respective intellectual-property-right holders. International Standard IEC 61158-3-7 has been prepared by subcommittee 65C: Industrial networks, of IEC technical committee 65: Industrial-process measurement, control and automation. This first edition and its companion parts of the IEC 61158-3 subseries cancel and replace IEC 61158-3:2003. This edition of this part constitutes an editorial revision. This edition includes the following significant changes with respect to the previous edition: a) deletion of the former Type 6 fieldbus, and the placeholder for a Type 5 fieldbus data-link layer, for lack of market relevance; b) addition of new types of fieldbuses; c) division of this part into multiple parts numbered 3-1, 3-2, …, 3-19. SIST EN 61158-3-7:2008

61158-3-7 © IEC:2007(E) – 5 –
The text of this standard is based on the following documents: FDIS Report on voting 65C/473/FDIS 65C/484/RVD
Full information on the voting for the approval of this standard can be found in the report on voting indicated in the above table. This publication has been drafted in accordance with ISO/IEC Directives, Part 2. The committee has decided that the contents of this publication will remain unchanged until the maintenance result 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. NOTE
The revision of this standard will be synchronized with the other parts of the IEC 61158 series. The list of all the parts of the IEC 61158 series, under the general title Industrial communication networks – Fieldbus specifications, can be found on the IEC web site. SIST EN 61158-3-7:2008

– 6 – 61158-3-7 © IEC:2007(E) INTRODUCTION This part of IEC 61158 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/TR 61158-1. Throughout the set of fieldbus standards, the term “service” refers to the abstract capability provided by one layer of the OSI Basic Reference Model to the layer immediately above. Thus, the data-link layer service defined in this standard is a conceptual architectural service, independent of administrative and implementation divisions. SIST EN 61158-3-7:2008

61158-3-7 © IEC:2007(E) – 7 –
INDUSTRIAL COMMUNICATION NETWORKS – FIELDBUS SPECIFICATIONS –
Part 3-7: Data-link layer service definition – Type 7 elements
1 Scope 1.1 Overview This part of IEC 61158 provides common elements for basic time-critical messaging communications between devices in an automation environment. 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 standard defines in an abstract way the externally visible service provided by the Type 7 fieldbus data-link layer in terms of a) the primitive actions and events of the service; b) the parameters associated with each primitive action and event, and the form which they take; and c) the interrelationship between these actions and events, and their valid sequences. The purpose of this standard is to define the services provided to • the Type 7 fieldbus application layer at the boundary between the application and data-link layers of the fieldbus reference model, and • systems management at the boundary between the data-link layer and systems management of the fieldbus reference model. 1.2 Specifications The principal objective of this standard is to specify the characteristics of conceptual data-link layer services suitable for time-critical communications, and thus supplement the OSI Basic Reference Model in guiding the development of data-link protocols for time-critical communications. A secondary objective is to provide migration paths from previously-existing industrial communications protocols. This specification may be used as the basis for formal DL-Programming-Interfaces. Nevertheless, it is not a formal programming interface, and any such interface will need to address implementation issues not covered by this specification, including a) the sizes and octet ordering of various multi-octet service parameters, and b) the correlation of paired request and confirm, or indication and response, primitives. 1.3 Conformance This standard does not specify individual implementations or products, nor does it constrain the implementations of data-link entities within industrial automation systems. There is no conformance of equipment to this data-link layer service definition standard. Instead, conformance is achieved through implementation of the corresponding data-link protocol that fulfills the Type 7 data-link layer services defined in this standard. SIST EN 61158-3-7:2008

– 8 – 61158-3-7 © IEC:2007(E) 2 Normative references The following referenced documents are indispensable for the application 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. ISO/IEC 7498-1, Information technology – Open Systems Interconnection – Basic Reference Model: The Basic Model ISO/IEC 7498-3, Information technology – Open Systems Interconnection – Basic Reference Model: Naming and addressing ISO/IEC 10731, Information technology – Open Systems Interconnection – Basic Reference Model – Conventions for the definition of OSI services 3 Terms, definitions, symbols, abbreviations and conventions For the purposes of this document, the following terms, definitions, symbols, abbreviations and conventions apply. 3.1 Reference model terms and definitions This standard is based in part on the concepts developed in ISO/IEC 7498-1 and ISO/IEC 7498-3, and makes use of the following terms defined therein: 3.1.1 DL-address [7498-3]3.1.2 DL-connection [7498-1]3.1.3 DL-connection-end-point [7498-1]3.1.4 DL-connection-end-point-identifier [7498-1]3.1.5 correspondent (N)-entities
correspondent DL-entities
(N=2)
correspondent Ph-entities
(N=1) [7498-1]3.1.6 (N)-entity
DL-entity
(N=2)
Ph-entity
(N=1) [7498-1]3.1.7 flow control [7498-1]3.1.8 (N)-layer
DL-layer
(N=2)
Ph-layer
(N=1) [7498-1]3.1.9 DL-name [7498-3]3.1.10 peer-entities [7498-1]3.1.11 primitive name [7498-3]3.1.12 DL-protocol [7498-1]3.1.13 DL-protocol-connection-identifier [7498-1]3.1.14 DL-protocol-data-unit [7498-1]SIST EN 61158-3-7:2008

61158-3-7 © IEC:2007(E) – 9 –
3.1.15 DL-relay [7498-1]3.1.16 (N)-service
DL-service
(N=2)
Ph-service
(N=1) [7498-1]3.1.17 (N)-service-access-point
DL-service-access-point
(N=2)
Ph-service-access-point
(N=1) [7498-1]3.1.18 DL-service-data-unit [7498-1]3.1.19 DLS-user-data [7498-1] 3.2 Service convention terms and definitions This standard also makes use of the following terms defined in ISO/IEC 10731 as they apply to the data-link layer: 3.2.1 acceptor 3.2.2 confirm (primitive);
requestor.deliver (primitive) 3.2.3 deliver (primitive) 3.2.4 DL-service-primitive;
primitive 3.2.5 DL-service-provider 3.2.6 DL-service-user 3.2.7 indication (primitive);
acceptor.deliver (primitive) 3.2.8 multi-peer 3.2.9 request (primitive);
requestor.submit (primitive) 3.2.10 requestor 3.2.11 response (primitive);
acceptor.submit (primitive) 3.2.12 submit (primitive) 3.3 Data-link service terms and definitions 3.3.1
acknowledgement response DLPDU information that the recipient of an acknowledged message emits in order to signal either the proper reception of the message or the lack of available resources to store the message, received by the DLE on the local link that emitted the message which requested the acknowledgement SIST EN 61158-3-7:2008

– 10 – 61158-3-7 © IEC:2007(E) 3.3.2
basic cycle sequence of scanning by the bus-arbitrator of a) a set of DLCEP-identifiers for variables, requests, and cyclical application messages; b) plus a window provided for aperiodic exchanges; c) plus a window provided for message services; d) plus a window provided for synchronization 3.3.3
basic transaction succession of DLPDUs related to a single DL-service instance 3.3.4
bus-arbitrator (BA) DLE that controls each data producer's right to access the medium NOTE
At any given instant one and only one bus-arbitrator is active in each DL-segment of a DL-subnetwork. 3.3.5
control field portion of an emitted or received DLPDU that gives the nature of the data exchanged and the type of exchange 3.3.6
destination address three octets specifying the DL-segment of the DLE to whom the message is sent, and the destination DLSAP’s sub-address within the local link 3.3.7
DL-segment, link, local link single DL-subnetwork in which any of the connected DLEs may communicate directly, without any intervening DL-relaying, whenever all of those DLEs that are participating in an instance of communication are simultaneously attentive to the DL-subnetwork during the period(s) of attempted communication 3.3.8
DL-segment, local link set of devices that respect the DL-protocol and that are interconnected through a PhL. Only one bus-arbitrator is active on a single DL-segment 3.3.9
DLCEP-identifier two octets specifying a link-local DLCEP-identifier associated with a system variable. A DLCEP-identifier uniquely designates a single DL-accessible variable within the local link 3.3.10
DLCEP-identifier DLPDU information that a bus-arbitrator emits to allocate the local link to a data publisher for the purpose of exchanging a variable 3.3.11
DLSAP distinctive point at which DL-services are provided by a single DL-entity to a single higher-layer entity NOTE
This definition, derived from ISO/IEC 7498-1, is repeated here to facilitate understanding of the critical distinction between DLSAPs and their DL-addresses. SIST EN 61158-3-7:2008

61158-3-7 © IEC:2007(E) – 11 –
PhSAP PhSAP DL-entity DLS-user-entity DLS-user-entity DLSAP DLSAP DLSAP DLSAP-
addresses group DL-
address DLSAP-
address Ph-layer DL-layer DLS-users DLSAP-
address
NOTE 1
DLSAPs and PhSAPs are depicted as ovals spanning the boundary between two adjacent layers. NOTE 2
DL-addresses are depicted as designating small gaps (points of access) in the DLL portion of a DLSAP. NOTE 3
A single DL-entity may have multiple DLSAP-addresses and group DL-addresses associated with a single DLSAP. Figure 1 – Relationships of DLSAPs, DLSAP-addresses and group DL-addresses 3.3.12
DL(SAP)-address either an individual DLSAP-address, designating a single DLSAP of a single DLS-user, or a group DL-address potentially designating multiple DLSAPs, each of a single DLS-user NOTE
This terminology is chosen because ISO/IEC 7498-3 does not permit the use of the term DLSAP-address to designate more than a single DLSAP at a single DLS-user. 3.3.13
(individual) DLSAP-address DL-address that designates only one DLSAP within the extended link NOTE
A single DL-entity may have multiple DLSAP-addresses associated with a single DLSAP. 3.3.14
end of message transaction indication DLPDU information that the source entity of a message emits in order to return link access control to the bus-arbitrator at the end of a message transaction 3.3.15
extended link DL-subnetwork, consisting of the maximal set of links interconnected by DL-relays, sharing a single DL-name (DL-address) space, in which any of the connected DL-entities may communicate, one with another, either directly or with the assistance of one or more of those intervening DL-relay entities NOTE
An extended link may be composed of just a single link. SIST EN 61158-3-7:2008

– 12 – 61158-3-7 © IEC:2007(E) 3.3.16
frame denigrated synonym for DLPDU 3.3.17
group DL-address DL-address that potentially designates more than one DLSAP within the extended link. A single DL-entity may have multiple group DL-addresses associated with a single DLSAP. A single DL-entity also may have a single group DL-address associated with more than one DLSAP 3.3.18
identified variable (or simply "variable") DLL system variable for which an associated DLCEP-identifier has been defined 3.3.19
invalid DLCEP-identifier DLCEP-identifier not recognized locally 3.3.20
macrocycle set of basic cycles needed for all cyclical DLCEP-identifiers to be scanned 3.3.21
message DLPDU identifier information that a bus-arbitrator emits to allocate the medium to a source DLE for a message transfer 3.3.22
message response DLPDU information that a data publisher emits in response to a message identifier DLPDU. This information is received and retained by the desired destination entity or entities 3.3.23
node single DL-entity as it appears on one local link 3.3.24
periodic scanning of variables action by the bus-arbitrator that guarantees the cyclical exchange of variables NOTE
This is the basic principle of the Type 7 DL-service and protocol. 3.3.25
published identified variable variable that corresponds to a DLCEP-identifier for which the DLE emits data 3.3.26
receiving DLS-user DL-service user that acts as a recipient of DLS-user-data NOTE
A DL-service user can be concurrently both a sending and receiving DLS-user. 3.3.27
request DLPDU identifier the information that a bus-arbitrator emits to allocate the medium to the initiator of an explicit request for a buffer transfer SIST EN 61158-3-7:2008

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3.3.28
request response DLPDU the information that the initiator of an explicit request for a buffer transfer emits in response to a request identifier DLPDU. This information is received by the bus-arbitrator 3.3.29
sending DLS-user DL-service user that acts as a source of DLS-user-data 3.3.30
source address three octets specifying the local link-id of the entity sending the message, and the source DLSAP’s sub-address within the local link 3.3.31
subscribed identified variable variable that corresponds to a DLCEP-identifier for which the DLE receives data 3.3.32
triggered message scanning function of a bus-arbitrator that makes it possible to transfer messages 3.3.33
triggered periodic scanning of messages function of a bus-arbitrator that makes it possible to request triggered message exchanges cyclically 3.3.34
triggered periodic scanning of variables function of a bus-arbitrator that makes it possible to request triggered variable transfers cyclically 3.3.35
triggered scanning of variables function of a bus-arbitrator that makes possible the non-cyclical exchange of variables 3.3.36
turnaround time time interval between reception or emission of the last MAC symbol of a DLPDU, signaled by a SILENCE indication from the PhL, and the reception or emission of the first MAC symbol of the subsequent DLPDU, signaled by an ACTIVITY indication from the PhL, both as measured in a given station 3.3.37
variable response DLPDU information that a data producer emits in response to a DLCEP-identifier DLPDU, which also alerts data consumers to the relevance of the immediately time-proximate DLPDU. 3.4 Symbols and abbreviations 3.4.1 BA Bus-arbitrator
3.4.2 B_Dat_Cons Buffer which contains the value of the subscribed data
3.4.3 B_Dat_Prod Buffer which contains the value of the published data
– 14 – 61158-3-7 © IEC:2007(E) 3.4.4 B_Req1/2 Buffer containing the list of DL-identifiers that are the object of a specified explicit request for a transfer at the priority 1 (urgent) or 2 (normal) 3.4.5 DL- Data-link layer (as a prefix) 3.4.6 DLC DL-connection 3.4.7 DLCEP DL-connection-end-point 3.4.8 DLE DL-entity (the local active instance of the data-link layer) 3.4.9 DLL DL-layer 3.4.10 DLPCI DL-protocol-control-information 3.4.11 DLPDU DL-protocol-data-unit 3.4.12 DLM DL-management 3.4.13 DLME DL-management Entity (the local active instance of DL-management) 3.4.14 DLMS DL-management Service 3.4.15 DLS DL-service 3.4.16 DLSAP DL-service-access-point 3.4.17 DLSDU DL-service-data-unit 3.4.18 FIFO First-in first-out (queuing method) 3.4.19 OSI Open systems interconnection 3.4.20 Ph- Physical layer (as a prefix) 3.4.21 PhE Ph-entity (the local active instance of the physical layer) 3.4.22 PhL Ph-layer 3.4.23 Q_IDRQ1/2 Queue for the DL-identifiers requested, received by the BA at priority 1 (urgent) or 2 (normal) 3.4.24 Q_Msg_Aper Queue which contains messages to be emitted that are associated with aperiodic exchanges 3.4.25 Q_Msg_Cyc Queue which contains messages to be emitted that are associated with cyclical exchanges 3.4.26 Q_Req1/2 Queue containing the list of DL-identifiers that are the object of a free explicit request for a transfer at the priority 1 (urgent) or 2 (normal) 3.4.27 QoS Quality of service 3.4.28 RQ_Inhibit Indicator used to manage explicit requests for buffer transfers 3.5 Common conventions This standard uses the descriptive conventions given in ISO/IEC 10731. The service model, service primitives, and time-sequence diagrams used are entirely abstract descriptions; they do not represent a specification for implementation. SIST EN 61158-3-7:2008

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Service primitives, used to represent service user/service provider interactions (see ISO/IEC 10731), convey parameters that indicate information available in the user/provider interaction. This standard uses a tabular format to describe the component parameters of the DLS primitives. The parameters that apply to each group of DLS primitives are set out in tables throughout the remainder of this standard. Each table consists of up to six columns, containing the name of the service parameter, and a column each for those primitives and parameter-transfer directions used by the DLS: ⎯ the request primitive’s input parameters; ⎯ the request primitive’s output parameters; ⎯ the indication primitive’s output parameters; ⎯ the response primitive’s input parameters; and ⎯ the confirm primitive’s output parameters. NOTE
The request, indication, response and confirm primitives are also known as requestor.submit, acceptor.deliver, acceptor.submit, and requestor.deliver primitives, respectively (see ISO/IEC 10731). One parameter (or part of it) is listed in each row of each table. Under the appropriate service primitive columns, a code is used to specify the type of usage of the parameter on the primitive and parameter direction specified in the column: M — parameter is mandatory for the primitive; U — parameter is a User option, and may or may not be provided depending on the dynamic usage of the DLS-user. When not provided, a default value for the parameter is assumed; C — parameter is conditional upon other parameters or upon the environment of the DLS-user;
(blank) — parameter is never present. Some entries are further qualified by items in brackets. These may be a) a parameter-specific constraint (=) indicates that the parameter is semantically equivalent to the parameter in the service primitive to its immediate left in the table. b) an indication that some note applies to the entry (n) indicates that the following note n contains additional information pertaining to the parameter and its use. In any particular interface, not all parameters need be explicitly stated. Some may be implicitly associated with the DLSAP at which the primitive is issued. The diagrams used to describe the sequence of primitives are composed of: a) vertical lines, representing the user-DLL interface; b) lines with arrows representing the time sequence of the primitives at the interface; c) dotted lines, defining the relationships between the primitives. When no dotted lines exist, the action is local. Two types of dotted lines are used: 1) long, crossing the service provider area to reach the remote user, defining a direct action on the remote entity; 2) short, beginning or ending at the middle of the service provider area. This defines an action to or from the bus-arbitrator. SIST EN 61158-3-7:2008

– 16 – 61158-3-7 © IEC:2007(E) 4 Data-link layer services and concepts 4.1 Field of application, object 4.1.1 Field of application This standard applies to a data-link layer appropriate for the exchange of data between transmitters, actuators, and programmable controllers within a manufacturing process. 4.1.2 Object This standard specifies the DLL services. The object is to define: a) the services provided at the conceptual interface between the DLE and the DLS-users, and b) the role of the bus-arbitrator. The standard is based on services provided by the physical layer (IEC 61158-2) to the conceptual interface between the physical and data-link layers. 4.2 General description of services 4.2.1 General Two types of data transmission services are provided: a) the first handles connection-oriented buffer transfers between pre-established point-to-multipoint DLCs on the same local link; b) the second handles acknowledged or unacknowledged connectionless message transfers between single DLSAPs, or unacknowledged message transfers from a single DLSAP to a group of DLSAPs on the extended link. NOTE
The standard term for data exchanged between DLS-users is DLS-user-data, or DLSDU [ISO/IEC 7498-1]. For purposes of clarity, the expressions "buffer transfer" and "message transfer" are used to distinguish between the two types of communications services, connection-oriented and connectionless, respectively, that are offered by this DLS, There are also two types of buffer transfer services: 1)- cyclical buffer transfer. Variable names and periods are defined when the system is configured, and are based on application needs. Cyclical exchanges are automatically triggered by the communications system without the user requesting them, 2) explicit request for buffer transfer. Upon user request the value(s) of one or more variables are circulated. The message transfer service also has two forms: 3) cyclical messages transfer. Resources and periods are defined when the system is configured and are based on application needs. Cyclical transfers are automatically triggered by the communications system without the user requesting them, 4) aperiodic message transfer. Upon user request one or more messages are circulated. 4.2.2 Addressing The DL-addressing model for a system includes two different types of addressing: one for buffer transfer services and the other for message transfer services. For buffer transfers: each variable in the system is associated with a DLCEP-identifier that characterizes it within the system in a unique manner. Entities participating in a buffer transfer are not identified explicitly. Rather, they are identified indirectly as subscriber(s) or publisher of the identified variable. SIST EN 61158-3-7:2008

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Each variable has only one publisher. For message transfer: one or more DLSAP-addresses are defined within each DLE. These DLSAP-addresses give access to a message transfer service. Each DLSAP-address identifies an access point to a message service linked to a DLS-user entity. Variable addressing is restricted to the local link. The addressing mechanism makes it possible to identify variables and exchanges independent of the producing and consuming DLEs. For buffer transfers all relationships between the various DLS-users are known and defined when the system is configured. Each DLCEP-identifier characterizes a single system variable and thus establishes a relationship between the unique publisher of the variable and the subscriber(s) of the variable. Buffer transfers use the local broadcast medium and are restricted to the local link: the DLCEP-identifier and the value of a variable are made available to all DLEs on the local link. The DLCEP-identifier associated with the variable allows each DLE to recognize whether or not it is the publisher or a subscriber of the value associated with the identified variable. Message transfers use the local broadcast medium, and bridges to traverse the extended link. During the message transaction two DLSAP-addresses are indicated in order to establish contact between the communicating entities. a) A 24-bit destination DL(SAP)-address that encodes the link-id of the destination local link and the sub-address of the destination DLSAP or group of DLSAPs within that local link. b) A 24-bit source DLSAP-address that encodes the link-id of the source DLE’s local link and the sub-address of the source DLSAP within that local link. Each DLSAP-address specifies a DLS-user of the message service (for both emission and reception). This DL-address is unique within the extended link. 4.2.3 Flow control Dynamic flow control for the exchange of variables is unnecessary. The volume of data exchanged as a result of cyclical traffic is constant, and is defined upon configuration of the system in a manner compatible with local link capacity. Subscribers store only the last value received; a new exchange overrides the previous value. An acknowledgement mechanism makes it possible to control message transfer flows. In addition, sequence numbering of messages avoids message duplication. A subscriber accepts a message only if that subscriber can store the message. In no case can a message overwrite a previously received message. 4.2.4 Detection of DLPDU duplication/loss Detection mechanisms apply to errors resulting from communications problems or out-of-service DLEs. DLPDU loss is accounted for in the finite state machines that describe the DL-protocol. Duplication of a DLPDU can only occur with message transfers. The sequence numbering mechanism makes it possible to detect message duplication and avoid delivery of duplicate messages. SIST EN 61158-3-7:2008

– 18 – 61158-3-7 © IEC:2007(E) 4.2.5 Overall description of medium allocation 4.2.5.1 General An element known as the bus-arbitrator (BA) controls the right of each data publisher to access the medium. It does this by emitting a DLPDU containing a link-local DL-identifier — either a DLSAP-address or a DLCEP-address. At any given instant there should be only one active bus-arbitrator on each local link. Each transaction belongs to one of the three medium allocation classes defined below: a) cyclical buffer transfers, message transfers or service request polling, b) explicit request for buffer transfer, c) explicit request for message transfer. 4.2.5.2 Cyclical buffer transfers, message transfers or service request polling 4.2.5.2.1 General The bus-arbitrator initiates transactions in a configured order. When one transaction has been completed the bus-arbitrator begins the following transaction according to guidelines defined when the system is configured. The procedure for each type of transaction is as follows: 4.2.5.2.2 Buffer transfer For a buffer transfer, a basic transaction consists of the following phases. a) The bus-arbitrator broadcasts a variable DLCEP-identifier DLPDU. b) The sole publisher of the information required then broadcasts a variable response DLPDU. During this phase subscribers take the information from the local link. Figure 2 shows the various phases of a buffer transfer transaction. NOTE
The term "publisher" designates the sole DLE connected to the local link that is configured as having the responsibility of emitting the variable associated with the bus-arbitrator-emitted DLCEP-identifier DLPDU immediately preceding on the local link. The term “subscriber” refers to any DLE which is configured to receive copies of a published variable and make those copies available to an associated DLS-user. During a buffer transfer the publisher can, using specific features of the response DLPDU, transmit to the BA an explicit request for additional buffer transfers or message transfers. 4.2.5.2.3 Message transfer For a message transfer, a basic transaction consists of the following phases. a) The bus-arbitrator broadcasts a message DL-identifier DLPDU. b) The addressed DLE sends a message DLPDU. c) If the message DLPDU is addressed to a single DLSAP and requests an acknowledgement, the DLE associated with that DLSAP-address sends an acknowledgement DLPDU. Steps b) and c) may be repeated a limited number of times if an expected acknowledgment DLPDU is not received error-free. d) The originally-addressed DLE concludes the message exchange sequence by transmitting an end-of-transaction DLPDU to the bus-arbitrator. 4.2.5.2.4 Service request polling For a service request poll, a basic transaction consists of the following phases. a) The bus-arbitrator broadcasts a request DL-identifier DLPDU. SIST EN 61158-3-7:2008

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b) The initiator of the request replies with a request response DLPDU. c) At a subsequent time of the bus-arbitrator’s choosing, one or more requested transactions identical in form to the cyclical buffer transfer transaction follow. 4.2.5.3 Explicit request for buffer transfer The bus-arbitrator services an explicit request for buffer transfer according to guidelines defined when the system is configured. The procedure employe
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