SIST EN IEC 61158-4-4:2019

SLOVENSKI STANDARD
01-november-2019
Nadomešča:
SIST EN 61158-4-4:2015
Industrijska komunikacijska omrežja - Specifikacije za procesna vodila - 4-4. del:
Specifikacija protokola na ravni podatkovnih povezav - Elementi tipa 4 (IEC 61158-
4-4:2019)
Industrial communication networks - Fieldbus specifications - Part 4-4: Data-link layer
protocol specification - Type 4 elements (IEC 61158-4-4:2019)
Industrielle Kommunikationsnetze - Feldbusse - Teil 4-4: Protokollspezifikation des Data
Link Layer (Sicherungsschicht) - Typ 4-Elemente (IEC 61158-4-4:2019)
Réseaux de communication industriels - Spécifications des bus de terrain - Partie 4-4:
Spécification du protocole de la couche liaison de données - Eléments de type 4 (IEC
61158-4-4:2019)
Ta slovenski standard je istoveten z: EN IEC 61158-4-4:2019
ICS:
25.040.40 Merjenje in krmiljenje Industrial process
industrijskih postopkov measurement and control
35.100.20 Podatkovni povezovalni sloj Data link layer
35.110 Omreževanje Networking
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 61158-4-4

NORME EUROPÉENNE
EUROPÄISCHE NORM
June 2019
Supersedes EN 61158-4-4:2014
ICS 25.040.40; 35.100.20; 35.110
English Version
Industrial communication networks - Fieldbus specifications -
Part 4-4: Data-link layer protocol specification - Type 4 elements
(IEC 61158-4-4:2019)
Réseaux de communication industriels - Spécifications des Industrielle Kommunikationsnetze - Feldbusse - Teil 4-4:
bus de terrain - Partie 4-4: Spécification du protocole de la Protokollspezifikation des Data Link Layer
couche liaison de données - Eléments de type 4 (Sicherungsschicht) - Typ 4-Elemente
(IEC 61158-4-4:2019) (IEC 61158-4-4:2019)
This European Standard was approved by CENELEC on 2019-05-23. 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 CEN-CENELEC
Management Centre 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 CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2019 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 61158-4-4:2019 E

European foreword
The text of document 65C/946/FDIS, future edition 3 of IEC 61158-4-4, 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 approved by CENELEC as EN IEC 61158-4-4:2019.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2020-02-23
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2022-05-23
document have to be withdrawn
This document supersedes EN 61158-4-4:2014.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.

Endorsement notice
The text of the International Standard IEC 61158-4-4:2019 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 61158-1:2019 NOTE Harmonized as EN IEC 61158-1:2019 (not modified)
IEC 61158-2:2014 NOTE Harmonized as EN 61158-2:2014 (not modified)
IEC 61158-3-4:2019 NOTE Harmonized as EN IEC 61158-3-4:2019 (not modified)
IEC 61158-5-4:2019 NOTE Harmonized as EN IEC 61158-5-4:2019 (not modified)
IEC 61784-1:2019 NOTE Harmonized as EN IEC 61784-1:2019 (not modified)
IEC 61784-2:2019 NOTE Harmonized as EN IEC 61784-2:2019 (not modified)
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
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 1  Where an International Publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.
NOTE 2  Up-to-date information on the latest versions of the European Standards listed in this annex is available here:
www.cenelec.eu.
Publication Year Title EN/HD Year
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
IEC 61158-4-4 ®
Edition 3.0 2019-04
INTERNATIONAL
STANDARD
Industrial communication networks – Fieldbus specifications –

Part 4-4: Data-link layer protocol specification – Type 4 elements

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 25.040.40; 35.100.20; 35.110 ISBN 978-2-8322-6774-5

– 2 – IEC 61158-4-4:2019 © IEC 2019
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
1.1 General . 7
1.2 Specifications . 7
1.3 Procedures . 7
1.4 Applicability . 7
1.5 Conformance . 7
2 Normative references . 8
3 Terms, definitions, symbols and abbreviations . 8
3.1 Reference model terms and definitions . 8
3.2 Service convention terms and definitions . 10
3.3 Terms and definitions. 11
3.4 Symbols and abbreviations . 14
4 Data Link Protocol Definition . 14
4.1 Overview of the DL-protocol . 14
4.2 General structure and encoding of PhIDUs and DLPDUs, and related
elements of procedure . 26
4.3 DLPDU-specific structure, encoding and elements of procedure . 33
4.4 DL-service elements of procedure . 37
4.5 Route mechanism . 40
4.6 Link-access system . 43
4.7 Local variables, counters and queues . 44
Bibliography . 46

Figure 1 – Relationship of PhE, DLE and DLS-user . 15
Figure 2 – DLE state diagram for confirmed and unconfirmed, unacknowledged
DLPDUs . 17
Figure 3 – DLE state diagram for confirmed acknowledged DLPDUs . 18
Figure 4 – DLE state diagram for unconfirmed acknowledged DLPDUs . 19
Figure 5 – Full duplex DLE receive state diagram . 20
Figure 6 – Full duplex DLE transmit state diagram . 20
Figure 7 – Link access example . 23
Figure 8 – Simple Type 4-route format . 29
Figure 9 – Extended Type 4-route format . 29
Figure 10 – Complex Type 4-route format . 30
Figure 11 – Immediate Type 4-route format . 30
Figure 12 – IP Type 4-route format . 31
Figure 13 – Control-status format. 32
Figure 14 – Data-field-format . 32
Figure 15 – Source / destination designator . 41
Figure 16 – Simple Type 4-route generation . 41
Figure 17 – Extended Type 4-route generation . 41
Figure 18 – Complex and IP Type 4-route generation . 42
Figure 19 – Simple DL-route generation . 42

IEC 61158-4-4:2019 © IEC 2019 – 3 –
Figure 20 – Extended DL-route generation . 43
Figure 21 – Complex and IP DL-route generation . 43

Table 1 – Summary structure of DLPDUs . 33
Table 2 – Structure of confirmed DLPDUs . 34
Table 3 – Structure of unconfirmed DLPDUs . 35
Table 4 – Structure of acknowledge DLPDU . 36
Table 5 – Structure of immediate-reply DLPDU . 36

– 4 – IEC 61158-4-4:2019 © IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INDUSTRIAL COMMUNICATION NETWORKS –
FIELDBUS SPECIFICATIONS –
Part 4-4: Data-link layer protocol specification –
Type 4 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 itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
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.
Attention is drawn to the fact that the use of the associated protocol type is restricted by its
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 layer protocol type to
be used with other layer protocols of the same type, or in other type combinations explicitly
authorized by its intellectual-property-right holders.
NOTE Combinations of protocol types are specified in IEC 61784-1 and IEC 61784-2.
International Standard IEC 61158-4-4 has been prepared by subcommittee 65C: Industrial
networks, of IEC technical committee 65: Industrial-process measurement, control and
automation.
This third edition cancels and replaces the second edition published in 2014. This edition
constitutes a technical revision.

IEC 61158-4-4:2019 © IEC 2019 – 5 –
This edition includes the following significant technical changes with respect to the previous
edition:
a) additional user parameters to services;
b) additional services to support distributed objects;
c) additional secure services;
The text of this International Standard is based on the following documents:
FDIS Report on voting
65C/946/FDIS 65C/955/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 ISO/IEC Directives, Part 2.
A list of all the parts of 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.
A bilingual version of this publication may be issued at a later date.

– 6 – IEC 61158-4-4:2019 © IEC 2019
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 data-link protocol provides the data-link service by making use of the services available
from the physical 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 data-link
entities (DLEs) 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:
a) as a guide for implementors and designers;
b) for use in the testing and procurement of equipment;
c) as part of an agreement for the admittance of systems into the open systems environment;
d) 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.

IEC 61158-4-4:2019 © IEC 2019 – 7 –
INDUSTRIAL COMMUNICATION NETWORKS –
FIELDBUS SPECIFICATIONS –
Part 4-4: Data-link layer protocol specification –
Type 4 elements
1 Scope
1.1 General
The data-link layer provides basic time-critical messaging communications between devices in
an automation environment.
This protocol provides a means of connecting devices through a partial mesh network, such
that most failures of an interconnection between two devices can be circumvented. In
common practice the devices are interconnected in a non-redundant hierarchical manner
reflecting application needs
1.2 Specifications
This document specifies
a) procedures for the timely transfer of data and control information from one data-link user
entity to a peer user entity, and among the data-link entities forming the distributed data-
link service provider;
b) the structure of the fieldbus DLPDUs used for the transfer of data and control information
by the protocol of this document, and their representation as physical interface data units.
1.3 Procedures
The procedures are defined in terms of
a) the interactions between peer DL-entities (DLEs) through the exchange of fieldbus
DLPDUs;
b) the interactions between a DL-service (DLS) provider and a DLS-user in the same system
through the exchange of DLS primitives;
c) the interactions between a DLS-provider and a Ph-service provider in the same system
through the exchange of Ph-service primitives.
1.4 Applicability
These procedures are applicable to instances of communication between systems which
support time-critical communications services within the data-link layer of the OSI or fieldbus
reference models, and which require the ability to interconnect in an open systems
interconnection environment.
Profiles provide a simple multi-attribute means of summarizing an implementation’s
capabilities, and thus its applicability to various time-critical communications needs.
1.5 Conformance
This document also specifies conformance requirements for systems implementing these
procedures. This document does not contain tests to demonstrate compliance with such
requirements.
– 8 – IEC 61158-4-4:2019 © IEC 2019
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.
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 and abbreviations
For the purposes of this document, the following terms, definitions, symbols and abbreviations
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
This document 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 called-DL-address [7498-3]
3.1.2 calling-DL-address [7498-3]
3.1.3 centralized multi-end-point-connection [7498-1]
3.1.4 correspondent (N)-entities [7498-1]
correspondent DL-entities  (N=2)
correspondent Ph-entities  (N=1)
3.1.5 demultiplexing [7498-1]
3.1.6 DL-address [7498-3]
3.1.7 DL-address-mapping [7498-1]
3.1.8 DL-connection [7498-1]
3.1.9 DL-connection-end-point [7498-1]
3.1.10 DL-connection-end-point-identifier [7498-1]
3.1.11 DL-connection-mode transmission [7498-1]

IEC 61158-4-4:2019 © IEC 2019 – 9 –
3.1.12 DL-connectionless-mode transmission [7498-1]
3.1.13 DL-data-sink [7498-1]
3.1.14 DL-data-source [7498-1]
3.1.15 DL-duplex-transmission [7498-1]
3.1.16 DL-facility [7498-1]
3.1.17 DL-local-view [7498-3]
3.1.18 DL-name [7498-3]
3.1.19 DL-protocol [7498-1]
3.1.20 DL-protocol-connection-identifier [7498-1]
3.1.21 DL-protocol-control-information [7498-1]
3.1.22 DL-protocol-data-unit [7498-1]
3.1.23 DL-protocol-version-identifier [7498-1]
3.1.24 DL-relay [7498-1]
3.1.25 DL-service-connection-identifier [7498-1]
3.1.26 DL-service-data-unit [7498-1]
3.1.27 DL-simplex-transmission [7498-1]
3.1.28 DL-subsystem [7498-1]
3.1.29 DL-user-data [7498-1]
3.1.30 flow control [7498-1]
3.1.31 layer-management [7498-1]
3.1.32 multiplexing [7498-3]
3.1.33 naming-(addressing)-authority [7498-3]
3.1.34 naming-(addressing)-domain [7498-3]
3.1.35 naming-(addressing)-subdomain [7498-3]
3.1.36 (N)-entity [7498-1]
DL-entity
Ph-entity
3.1.37 (N)-interface-data-unit [7498-1]
DL-service-data-unit  (N=2)
Ph-interface-data-unit  (N=1)
3.1.38 (N)-layer [7498-1]
DL-layer  (N=2)
Ph-layer  (N=1)
3.1.39 (N)-service
[7498-1]
DL-service  (N=2)
Ph-service  (N=1)
– 10 – IEC 61158-4-4:2019 © IEC 2019
3.1.40 (N)-service-access-point [7498-1]
DL-service-access-point  (N=2)
Ph-service-access-point  (N=1)
3.1.41 (N)-service-access-point-address
[7498-1]
DL-service-access-point-address  (N=2)
Ph-service-access-point-address  (N=1)
3.1.42 peer-entities
[7498-1]
3.1.43 Ph-interface-control-information [7498-1]
3.1.44 Ph-interface-data [7498-1]
3.1.45 primitive name [7498-3]
3.1.46 reassembling [7498-1]
3.1.47 recombining [7498-1]
3.1.48 reset [7498-1]
3.1.49 responding-DL-address [7498-3]
3.1.50 routing [7498-1]
3.1.51 segmenting [7498-1]
3.1.52 sequencing [7498-1]
3.1.53 splitting [7498-1]
3.1.54 synonymous name [7498-3]
3.1.55 systems-management [7498-1]
3.2 Service convention terms and definitions
This document 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 asymmetrical service
3.2.3 confirm (primitive);
requestor.deliver (primitive)
3.2.4 deliver (primitive)
3.2.5 DL-confirmed-facility
3.2.6 DL-facility
3.2.7 DL-local-view
3.2.8 DL-mandatory-facility
3.2.9 DL-non-confirmed-facility
3.2.10 DL-provider-initiated-facility
3.2.11 DL-provider-optional-facility
3.2.12 DL-service-primitive;
primitive
IEC 61158-4-4:2019 © IEC 2019 – 11 –
3.2.13 DL-service-provider
3.2.14 DL-service-user
3.2.15 DL-user-optional-facility
3.2.16 indication (primitive)
acceptor.deliver (primitive)
3.2.17 multi-peer
3.2.18 request (primitive);
requestor.submit (primitive)
3.2.19 requestor
3.2.20 response (primitive);
acceptor.submit (primitive)
3.2.21 submit (primitive)
3.2.22 symmetrical service
3.3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.3.1
broadcast-Node-address
address used to send broadcasts to all DLEs on a Link
Note 1 to entry: All DLEs on a Link receive all DLPDUs where the first Node-address is equal to the Broadcast-
Node-Address. Such DLPDUs are always Unconfirmed, and their receipt is never acknowledged. The value of a
Broadcast-Node-address is 126.
3.3.2
destination-DL-route
holds a sequence of DL-route-elements, describing the complete route to the destination
Note 1 to entry: This includes both the destination DLSAP and a local component meaningful to the destination
DLS-user.
3.3.3
DL-route
combination of a Destination-DL-route and a Source-DL-route
3.3.4
DL-route-element
octet holding a Node-address or an address used by the DLS-user
3.3.5
DLSAP
distinctive point at which DL-services are provided by a single DL-entity to a single higher-
layer entity.
Note 1 to entry: This definition, derived from ISO/IEC 7498-1, is repeated here to facilitate understanding of the
critical distinction between DLSAPs and their DL-addresses.
3.3.6
DL(SAP)-address
an individual DLSAP-address, designating a single DLSAP of a single DLS-user

– 12 – IEC 61158-4-4:2019 © IEC 2019
3.3.7
(individual) DLSAP-address
DL-address that designates only one DLSAP within the extended link
Note 1 to entry: A single DL-entity may have multiple DLSAP-addresses associated with a single DLSAP.
3.3.8
frame
denigrated synonym for DLPDU
3.3.9
IPNetID
identification of a unique IP network
Note 1 to entry: An IPNetID is translated into an IP-address and a UPD port number.
3.3.10
IPNetTable
definition of the relation between IPNetID, IP address, UPD port number and Router
NodeAddress, where IPNetID is used as index in the table
3.3.11
IP Range net
definition of the use of the IP network for local access, where nodes can be accessed directly
on the same subnet as the client, or through a local Router where the subnets are configured
in the local Router
3.3.12
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
3.3.13
no-Confirm-Node-address
address used to indicate that a request or response is Unconfirmed
Note 1 to entry: The value of a No-Confirm-Node-address is 0.
3.3.14
node
single DL-entity as it appears on one local link
3.3.15
node-address
address which uniquely identifies a DLE on a Link
Note 1 to entry: The value of a Node-address can be in the range of 0 to 127, with the values 0, 126 and 127
reserved for special purposes.
3.3.16
normal class device
device which replies to requests from other normal class devices, and initiates transmissions
Note 1 to entry: Such a device can act as a server (responder) and as a client (requestor) – this is also called a
peer.
3.3.17
Type 4-route
a route that holds a sequence of Type 4-route-elements

IEC 61158-4-4:2019 © IEC 2019 – 13 –
Note 1 to entry: A Type 4-route is defined as an encoded DL-route, with one of the formats used when
transmitting the DLPDU on the Link. The Type 4-route format can be Simple, Extended, Complex, Immediate or IP.
3.3.18
Type 4-route-element
octet, holding a 7-bit DL-route-element or Remaining-route-length, and a 1-bit source/
destination designator
3.3.19
receiving DLS-user
DL-service user that acts as a recipient of DL-user-data
Note 1 to entry: A DL-service user can be concurrently both a sending and receiving DLS-user.
3.3.20
sending DLS-user
DL-service user that acts as a source of DL-user-data
3.3.21
service-Node-address
address reserved for service purposes only
Note 1 to entry: All DLEs on a Link receive all DLPDUs where the first Node-address is equal to the Service-
Node-Address. Such DLPDUs can be Confirmed or Unconfirmed, and their receipt may or may not be
acknowledged. The Service-Node-Address can be used on Links with only two DLEs – the requesting Normal class
DLE and the responding Simple or Normal class DLE. The value of the Service-Node-Address is 127.
3.3.22
simple class device
device which replies to requests from normal class devices, and can act as a server or
responder only
3.3.23
source-DL-route
a route that holds a sequence of DL-route-elements, describing the complete route back to
the source
3.3.24
UDP port number
port number from where a Server can receive requests
Note 1 to entry: The UDP port number is 34378 for Normal UDP port. The UDP port number is 34379 for Secure
UDP port.
Note 2 to entry: These UDP port numbers are registered with the IANA (Internet Assigned Numbers Authority).
Note 3 to entry: There are two different UPD port numbers: Normal UDP port and Secure UDP port.
3.3.25
UDP range net
definition of the use of the IP network for remote access, where a node cannot be accessed
directly on the same subnet as the client
Note 1 to entry: The IPNetTable holds a NAT Router IP address and access to the node is obtained through this
NAT Router.
Note 2 to entry: The NAT Router shall hold a table that translates the UDP port number to the actual server node
IP address and UDP port number.
3.3.26
Virtual link-access token
basis for the link-access system

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Note 1 to entry: It is called virtual because the token is not explicitly sent from one normal-class DLE to another,
but implicitly passed as the link is idle.
3.4 Symbols and abbreviations
3.4.1 Constants, variables, counters and queues
3.4.1.1 BNA broadcast node address
3.4.1.2 C(LAC) link access counter
3.4.1.3 C(LIC) link idle counter
3.4.1.4 SNA service node address
3.4.1.5 NCNA no confirm node address
3.4.1.6 Q(UR) user request queue
3.4.1.7 V(ACPDU) acknowledge confirmed PDU
3.4.1.8 V(AUPDU) acknowledge unconfirmed PDU
3.4.1.9 V(BR) bit rate
3.4.1.10 V(DC) device class (simple or normal)
3.4.1.11 V(DMRT) default max retry time
3.4.1.12 V(MID) max indication delay
3.4.1.13 V(NA) node address
3.4.1.14 V(NDLE) number of DLEs
3.4.1.15 V(PNR) permitted number of retries
3.4.1.16 IPNetTable Table to convert IPNetID to IP-addresses
3.4.2 Miscellaneous
3.4.2.1 RCL/ACK response comes later / acknowledge
4 Data Link Protocol Definition
4.1 Overview of the DL-protocol
The DLL provides connectionless data transfer services for limited-size DLSDUs from one
DLS-user to one or more (broadcast) DLS-users.
A DLE is implicitly connected to one PhE and to a single DLSAP. This means that when a
local DLS-user issues a service primitive at a certain DLSAP, the DLE and hence the Link is
implicitly selected.
A DLE always delivers received DLSDUs at the same DLSAP, and hence to the same DLS-
user.
This concept is illustrated in Figure 1.

IEC 61158-4-4:2019 © IEC 2019 – 15 –
Application
Layer
DLS-user DLS-user
DLSAP DLSAP
Data Link
DLE DLE
Layer
Physical
PhE PhE
Layer
Figure 1 – Relationship of PhE, DLE and DLS-user
Each DLE has a Node-address. Node-addresses uniquely identify DLEs within the same Link.
A DL-route-element is an octet, which can hold a Node-address, or an address used by the
DLS-user.
A Destination-DL-route holds a sequence of DL-route-elements, describing the complete route
to the destination.
A Source-DL-route holds a sequence of DL-route-elements, describing the complete route
back to the source.
A DL-route is defined as a Destination-DL-route and a Source-DL-route.
4.1.1 Functional classes
The functional class of a DLE determines its capabilities, and thus the complexity of
conforming implementations. Two functional classes are defined:
• Simple class, including only responder functionality (server).
• Normal class, including initiator and responder functionality (client and server, also called
peer).
4.1.2 Functions of the DLL
The functions of the DLL are those necessary to bridge the gap between the services
available from the PhL and those offered to DLS-users. The functions are:
As a responder (in Simple class or Normal class DLEs):
a) Receive a DLPDU from a remote DLE, perform frame check, parse the received DLPDU
into its DL-protocol information and data components, and generate a DLS-user indication
primitive. Possibly wait for a DLS-user request or response primitive, convert it to a
DLPDU, and send that DLPDU to the remote DLE.
b) Receive a single PhIDU specifying LINK-IDLE, and use that to time-out when waiting for a
DLS-user request primitive.
As an initiator (in Normal class DLEs):

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c) Convert a DLS-user request primitive to a DLPDU, queue it, and send it to a remote DLE
(or all DLEs at the Link if broadcast) at the first opportunity. Possibly wait for an
Acknowledge or Immediate-reply DLPDU from the remote DLE, and (if an Immediate-reply
DLPDU is received) generate a DLS-user indication primitive.
d) Receive an SPDU, and use the associated data to check or gain Link-access
synchronization.
e) Receive a single PhIDU specifying LINK-IDLE, use that to keep Link-access synchronized,
and possibly to initiate sending a DLPDU from the queue if the queue is not empty, or if
the queue is empty, to send an SPDU for Link-access synchronization.
These functions are illustrated in Figure 2 to Figure 4.
4.1.2.1 Acknowledged vs. confirmed
The terms acknowledged and unacknowledged are used to describe whether the receiving
DLE must acknowledge the receipt of a DLPDU or not. The terms confirmed and unconfirmed
are used to describe whether the receiving DLS-user must confirm the receipt of a DLSDU or
not.
The variable V(ACPDU) – Acknowledge Confirmed PDU – defines whether the DLE must
acknowledge the receipt of Confirmed DLPDUs. The variable V(AUPDU) – Acknowledge
Unconfirmed PDU – defines whether the DLE must acknowledge the receipt of Unconfirmed
DLPDUs.
A special case is when the first Node-address in a received DLPDU is equal to the Broadcast-
Node-address (BNA). In this case, the receiving DLE shall never acknowledge the receipt of
the DLPDU.
4.1.2.2 Half-duplex and full duplex
Unless otherwise stated, the PhL is assumed to support half-duplex transfer. However, a PhL
supporting full duplex is allowed.
Full duplex systems allow up to 125 DLEs on a Link, all of Normal class. Each DLE is allowed
to transmit immediately, that is, there is no Link Access system. DLEs supporting full duplex
PhEs have separate state machines for receive and transmit, as illustrated in Figure 5 and
Figure 6.
In full duplex systems, Confirmed as well as Unconfirmed DLPDUs are unacknowledged.
PhLs supporting full duplex shall not provide Link-Idle indications.

IEC 61158-4-4:2019 © IEC 2019 – 17 –
Indication to DLS-
user
Error OK
Receive DLPDU
Queue DLPDU
START-OF-ACTIVITY
indication from PhE
Request from DLS-user
Idle
Token received and
queue not empty
Send DLPDU
from queue
Figure 2 – DLE state diagram for confirmed and unconfirmed, unacknowledged DLPDUs

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Wait for request
or response
from DLS-user
Response from DLS-
user or 30 bit idle
Indication to DLS-
Request from
user
DLS-user
Send Acknowledge
DLPDU
Error OK
Send Immediate-
Receive DLPDU reply DLPDU
Queue DLPDU
START-OF-ACTIVITY
indication from PhE
Request from DLS-user
Idle
Error indication to
DLS-user
Error indication to
DLS-user
Token received and
queue not empty
Retransmission
not allowed
Retransmission
not allowed
Retransmission
Send DLPDU
allowed
from queue
Retransmission
allowed
Queue DLPDU for
retransmission if
allowed
Retransmit DLPDU
Wait for Immediate-
immediately if
reply or Acknowledge
allowed
Indication to DLS-
DLPDU
user
Received RCL/ACK
35 bit idle
Received Wait Received
START-OF-ACTIVITY
immediate reply
indication from PhE
Receive DLPDU
Error
Figure 3 – DLE state diagram for confirmed acknowledged DLPDUs

IEC 61158-4-4:2019 © IEC 2019 – 19 –
Indication to DLS-
user
Send Acknowledge
Error OK
DLPDU
Receive DLPDU
Queue DLPDU
START-OF-ACTIVITY
indication from PhE
Request from DLS-user
Idle
Error indication to
DLS-user
Error indication to
DLS-user
Token received and
queue not empty
Retransmission
not allowed
Retransmission
not allowed
Retransmission
Send DLPDU
allowed
from queue
Retransmission
allowed
Queue DLPDU for
retransmission if
allowed
Retransmit DLPDU
Wait for Acknowledge
immediately if
DLPDU
allowed
Received RCL/ACK
35 bit idle
Received Wait
START-OF-ACTIVITY
indication from PhE
Receive DLPDU
Error
Figure 4 – DLE state diagram for unconfirmed acknowledged DLPDUs

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Indication to DLS-
user
Error OK
Receive DLPDU
START-OF-ACTIVITY
indication from PhE
Idle
Figure 5 – Full duplex DLE receive state diagram
Queue DLPDU
Request from DLS-user
Idle
Queue not empty
Send DLPDU
from queue
Figure 6 – Full duplex DLE transmit state diagram
4.1.2.3 DLPDU types
Four different types of DLPDUs are defined.
a) Confirmed – used to send confirmed requests between DLS-users.
b) Unconfirmed – used to send responses or unconfirmed requests between DLS-users.

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c) Acknowledge – used by DLEs to acknowledge receipt of Confirmed or Unconfirmed
DLPDUs. The receipt of Acknowledge DLPDUs shall never be acknowledged.
d) Immediate-reply – used to send responses between DLS-users. The receipt of Immediate-
reply DLPDUs shall never be acknowledged.
4.1.2.4 SPDU types
Only one type of SPDU (Support Protocol Data Unit) is defined.
a) Sync – used to send Link access synchronization information between DLEs. An SPDU
holds the Node-address of the DLE holding the Virtual Link-access token. An SPDU can
be "stand-alone" or part of an Acknowledge or Immediate-reply DLPDU.
4.1.2.5 Responder role, receiving a DLPDU from the PhE
This action includes a sequence of steps, as described in the following.
a) Receive a single PhIDU specifying START-OF-ACTIVITY. This PhIDU holds a Node address.
This address is examined to determine whether its value is equal to the Node-address of
this DLE, or equal to the Broadcast-Node-address (BNA) or the Service-Node-Address
(SNA). If not, ignore this sequence and wait for the next PhIDU specifying START-OF-
CTIVITY.
A
b) Receive a sequence of PhIDUs from the PhE, specifying DATA, concatenate them to a
received DLPDU, compute a frame check sequence over the entire sequence of received
data as specified by the value of V(FCM) – FrameCheckMethod, and, if necessary, check
for the proper value. If the value is not correct, ignore the DLPDU and wait for the next
PhIDU specifying START-OF-ACTIVITY.
c) Convert the received DLPDU into its DL-protocol control information and data
components.
d) Generate a DLS-user indication primitive.
e) If the DLPDU received from the remote DLE is of type Confirmed, and the receipt of the
DLPDU shall be acknowledged, according to the rules described in 4.1.2.1, wait for a
request or response primitive from the local DLS-user.
If no request or response primitive is issued from the local DLS-user in time (before a
PhIDU specifying "LINK-IDLE for 30 bit periods" is received from the PhE), generate and
immediately send an Acknowledge DLPDU. This DLPDU shall specify "Wait" if this DLE is
of Simple class, and "Response Comes Later / Acknowledge" ("RCL/ACK") if this DLE is of
Normal class.
If a response primitive is issued from the local DLS-user in time, generate and
immediately send an Acknowledge DLPDU, specifying "Wait" if this DLE is of Simple
class, and "RCL/ACK" i
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