EN 61158-3-21:2012

SLOVENSKI STANDARD
01-julij-2012
Industrijska komunikacijska omrežja - Specifikacije za procesna vodila - 3-21. del:
Definicija opravil na nivoju podatkovnih povezav - Elementi tipa 21 (IEC 61158-3-
21:2010)
Industrial communication networks - Fieldbus specifications - Part 3-21: Data-link layer
service definition - Type 21 elements (IEC 61158-3-21:2010)
Industrielle Kommunikationsnetze - Feldbusse - Teil 3-21: Dienstfestlegungen des Data
Link Layer (Sicherungsschicht) - Typ 21-Elemente (IEC 61158-3-21:2010)
Réseaux de communication industriels - Spécifications des bus de terrain - Partie 3-21:
Définition des services de couche liaison de données - Eléments de Type 21 (IEC 61158
-3-21:2010)
Ta slovenski standard je istoveten z: EN 61158-3-21:2012
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 61158-3-21
NORME EUROPÉENNE
May 2012
EUROPÄISCHE NORM
ICS 25.040.40; 35.100.20; 35.110

English version
Industrial communication networks -
Fieldbus specifications -
Part 3-21: Data-link layer service definition -
Type 21 elements
(IEC 61158-3-21:2010)
Réseaux de communication industriels -  Industrielle Kommunikationsnetze -
Spécifications des bus de terrain - Feldbusse -
Partie 3-21: Définition des services de Teil 3-19: Dienstfestlegungen des Data
couche liaison de données - Link Layer (Sicherungsschicht) -
Eléments de Type 21 Typ 21-Elemente
(CEI 61158-3-21:2010) (IEC 61158-3-21:2010)

This European Standard was approved by CENELEC on 2012-03-28. 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, Romania, Slovakia, Slovenia,
Spain, Sweden, Switzerland, Turkey and the United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Management Centre: Avenue Marnix 17, B - 1000 Brussels

© 2012 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 61158-3-21:2012 E
Foreword
The text of document 65C/604/FDIS, future edition 1 of IEC 61158-3-21, 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 61158-3-21:2012.

The following dates are fixed:
(dop) 2012-12-28
• latest date by which the document has
to be implemented at national level by
publication of an identical national
standard or by endorsement
(dow) 2015-03-28
• latest date by which the national
standards conflicting with the
document have to be withdrawn
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such patent
rights.
Endorsement notice
The text of the International Standard IEC 61158-3-21:2010 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/TR 61158-1:2010 NOTE  Harmonized as CLC/TR 61158-1:2010 (not modified).
IEC 61158-5-21:2010 NOTE  Harmonized as EN 61158-5-21:2012 (not modified).
IEC 61158-6-21:2010 NOTE  Harmonized as EN 61158-6-21:2012 (not modified).

- 3 - EN 61158-3-21:2012
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. 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

IEC 61158-2 2010 Industrial communication networks - Fieldbus EN 61158-2 2010
specifications -
Part 2: Physical layer specification and service
definition
IEC 61158-4-21 2010 Industrial communication networks - Fieldbus EN 61158-4-21 2012
specifications -
Part 4-21: Data-link layer protocol
specification - Type 21 elements

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 8802-3 2000 Information technology - Telecommunications - -
and information exchange between systems -
Local and metropolitan area networks -
Specific requirements -
Part 3: Carrier sense multiple access with
collision detection (CSMA/CD) access method
and physical layer specifications

ISO/IEC 10731 1994 Information technology - Open Systems - -
Interconnection - Basic reference model -
Conventions for the definition of OSI services

IEC 61158-3-21 ®
Edition 1.0 2010-08
INTERNATIONAL
STANDARD
Industrial communication networks – Fieldbus specifications –
Part 3 21: Data-link layer service definition – Type 21 elements

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
X
ICS 25.04.40; 35.100.20; 35.110 ISBN 978-2-88912-079-6
– 2 – 61158-3-21 © IEC:2010(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.10
3.3 Data link service terms and definitions .10
3.4 Symbols and abbreviations.13
3.5 Conventions .14
4 Data-link layer services and concepts.15
4.1 General .15
4.2 Detailed description of the data service .19
4.3 Detailed description of the sporadic data service.21
4.4 Detailed description of network control message service .23
5 Data link management services .26
5.1 General .26
5.2 Data link management service (DLMS) facilities .26
5.3 Data link management service (DLMS).26
5.4 Overview of interactions .27
5.5 Detailed specification of service and interactions.29
6 MAC control service .37
6.1 General .37
6.2 MAC control service .37
6.3 Overview of interactions .37
6.4 Detailed specification of service and interactions.38
7 Ph-control service .40
7.1 General .40
7.2 Ph-control service .40
7.3 Overview of interactions .40
7.4 Detailed specification of service and interactions.41
Bibliography.44

Figure 1 – Full-duplex flow control .16
Figure 2 – Sequence diagram of DL-DATA service .16
Figure 3 – Sequence diagram of DL-SPDATA service .17
Figure 4 – Sequence diagram of NCM service primitive .17
Figure 5 – Relationships of DLSAPs, DLSAP-addresses, and group DL-addresses .18
Figure 6 – DL-DATA service .19
Figure 7 – Sequence diagram of Reset, Set-value, Get-value, SAP-allocation, SAP-
deallocation, Get-SAP information and Get-diagnostic information service primitives .28
Figure 8 – Sequence diagram of Event service primitive .29

61158-3-21 © IEC:2010(E) – 3 –
Figure 9 – Sequence diagram of MAC-reset and MAC-forward-control service primitive.38
Figure 10 – Sequence diagram of Ph-reset and Ph-get-link-status service primitive.41
Figure 11 – Sequence diagram of Ph-link-status-change service primitive .41

Table 1 – Destination DL-address .18
Table 2 – Primitives and parameters used in DL-DATA service.20
Table 3 – DL-DATA Primitives and Parameters.20
Table 4 – Primitives and parameters used in DL-SPDATA service .22
Table 5 – DL-SPDATA Primitives and Parameters .22
Table 6 – Primitives and parameters used on DL-NCM_SND service .23
Table 7 – DL-NCM_SND Primitives and Parameters .24
Table 8 – Summary of Network Control Message Type .25
Table 9 – Summary of DL-management primitives and parameters .28
Table 10 – DLM-RESET primitives and parameters.29
Table 11 – DLM-SET_VALUE primitives and parameters .30
Table 12 – DLM-GET_VALUE primitives and parameters .31
Table 13 – DLM-SAP_ALLOC primitives and parameters .32
Table 14 – DLM-SAP_DEALLOC primitives and parameters .33
Table 15 – DLM-GET_SAP_INFO primitives and parameters .33
Table 16 – DLM-GET_DIAG primitives and parameters.34
Table 17 – DLM-EVENT primitives and parameters.35
Table 18 – DLM event identifier .36
Table 19 – DLM-GET_PATH primitives and parameters .36
Table 20 – Summary of MAC control primitives and parameters.38
Table 21 – MAC-RESET primitives and parameters .38
Table 22 – MAC-FW_CTRL primitives and parameters .39
Table 23 – Summary of Ph-control primitives and parameters.40
Table 24 – Ph-RESET primitives and parameters.41
Table 25 – Ph-GET_LINK_STATUS primitives and parameters .42
Table 26 – Ph-LINK_STATUS _CHANGE primitives and parameters .43

– 4 – 61158-3-21 © IEC:2010(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INDUSTRIAL COMMUNICATION NETWORKS –
FIELDBUS SPECIFICATIONS –
Part 3-21: Data-link layer service definition –
Type 21 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.
NOTE 1 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 profile parts. Use of the various protocol types in other combinations
may require permission of their respective intellectual-property-right holders.
International Standard IEC 61158-3-21:2010 has been prepared by subcommittee 65C:
Industrial networks, of IEC technical committee 65: Industrial-process measurement, control
and automation.
This standard cancels and replaces IEC/PAS 62573 published in 2008. This first edition
constitutes a technical revision.

61158-3-21 © IEC:2010(E) – 5 –
The text of this standard is based on the following documents:
FDIS Report on voting
65C/604/FDIS 65C/618/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.
A list of all parts of the IEC 61158 series, published under the general title Industrial
communication networks – Fieldbus specifications, can be found on the IEC web site.
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.
NOTE 2 The revision of this standard will be synchronized with the other parts of the IEC 61158 series.

– 6 – 61158-3-21 © IEC:2010(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.

61158-3-21 © IEC:2010(E) – 7 –
INDUSTRIAL COMMUNICATION NETWORKS –
FIELDBUS SPECIFICATIONS –
Part 3-21: Data-link layer service definition –
Type 21 elements
1 Scope
1.1 Overview
This part of IEC 61158 provides the common elements for basic time-critical messaging
communications between devices in an automation environment. The term “time-critical” in
this context means the prioritized full-duplex collision-free time-deterministic communication,
of which one or more specified actions are required to be completed with some defined level
of certainty. Failure to complete specified actions within the required time risks the 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 21 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 that they
take; and
c) the interrelationships between these actions and events, and their valid sequences.
The purpose of this standard is to define the services provided to:
• The Type 21 application layer at the boundary between the application and DLLs of the
fieldbus reference model;
• Systems management at the boundary between the DLL and the systems management of
the fieldbus reference model.
1.2 Specifications
The principal objective of this standard is to specify the characteristics of conceptual DLL
services suitable for time-critical communications, and to 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 standard may be used as the basis for formal data link programming interfaces.
Nevertheless, it is not a formal programming interface, and any such interface will need to
address implementation issues not covered by this standard, including:
a) The sizes and octet ordering of various multi-octet service parameters;
b) The correlation of paired primitives for request and confirm, or indication and response.
1.3 Conformance
This standard does not specify individual implementations or products, nor do they constrain
the implementations of data-link entities within industrial automation systems.

– 8 – 61158-3-21 © IEC:2010(E)
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 fulfils the Type 21 DLL services defined in this standard.
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.
IEC 61158-2:2010 , Industrial communication networks – Fieldbus specifications – Part 2:
Physical layer specification and service definition
IEC 61158-4-21:2010 , Industrial communication networks – Fieldbus specifications –
Part 4-21: Data-link layer protocol specification – Type 21 elements
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 8802-3:2000, Information technology – Telecommunications and information
exchange between systems – Local and metropolitan area networks – Specific requirements –
Part 3: Carrier sense multiple access with collision detection (CSMA/CD) access method and
physical layer specifications
ISO/IEC 10731:1994, Information technology – Open Systems Interconnection – Basic
Reference Model – Conventions for the definition of OSI services
3 Terms, definitions, symbols, abbreviations, and conventions
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 [ISO/IEC 7498-3]
3.1.2 DL-address-mapping [ISO/IEC 7498-1]
3.1.3 called-DL-address
[ISO/IEC 7498-3]
3.1.4 calling-DL-address [ISO/IEC 7498-3]
3.1.5 centralized multi-end-point-connection [ISO/IEC 7498-1]
3.1.6 DL-connection [ISO/IEC 7498-1]
3.1.7 DL-connection-end-point [ISO/IEC 7498-1]
3.1.8 DL-connection-end-point-identifier [ISO/IEC 7498-1]
3.1.9 DL-connection-mode transmission [ISO/IEC 7498-1]
3.1.10 DL-connectionless-mode transmission
[ISO/IEC 7498-1]
—————————
To be published.
61158-3-21 © IEC:2010(E) – 9 –
3.1.11 correspondent (N)-entities [ISO/IEC 7498-1]
correspondent DL-entities  (N=2)
correspondent Ph-entities  (N=1)
3.1.12 DL-duplex-transmission [ISO/IEC 7498-1]
3.1.13 (N)-entity [ISO/IEC 7498-1]
DL-entity  (N=2)
Ph-entity  (N=1)
3.1.14 DL-facility [ISO/IEC 7498-1]
3.1.15 flow control
[ISO/IEC 7498-1]
3.1.16 (N)-layer [ISO/IEC 7498-1]
DL-layer  (N=2)
Ph-layer  (N=1)
3.1.17 layer-management [ISO/IEC 7498-1]
3.1.18 DL-local-view [ISO/IEC 7498-3]
3.1.19 DL-name
[ISO/IEC 7498-3]
3.1.20 naming-(addressing)-domain [ISO/IEC 7498-3]
3.1.21 peer-entities [ISO/IEC 7498-1]
3.1.22 primitive name [ISO/IEC 7498-3]
3.1.23 DL-protocol [ISO/IEC 7498-1]
3.1.24 DL-protocol-connection-identifier [ISO/IEC 7498-1]
3.1.25 DL-protocol-data-unit [ISO/IEC 7498-1]
3.1.26 DL-relay [ISO/IEC 7498-1]
3.1.27 Reset [ISO/IEC 7498-1]
3.1.28 responding-DL-address [ISO/IEC 7498-3]
3.1.29 Routing [ISO/IEC 7498-1]
3.1.30 Segmenting [ISO/IEC 7498-1]
3.1.31 (N)-service [ISO/IEC 7498-1]
DL-service  (N=2)
Ph-service  (N=1)
3.1.32 (N)-service-access-point [ISO/IEC 7498-1]
DL-service-access-point  (N=2)
Ph-service-access-point  (N=1)
3.1.33 DL-service-access-point-address [ISO/IEC 7498-3]
3.1.34 DL-service-connection-identifier [ISO/IEC 7498-1]
3.1.35 DL-service-data-unit [ISO/IEC 7498-1]
3.1.36 DL-simplex-transmission [ISO/IEC 7498-1]
3.1.37 DL-subsystem [ISO/IEC 7498-1]
3.1.38 systems-management [ISO/IEC 7498-1]
3.1.39 DLS-user-data [ISO/IEC 7498-1]

– 10 – 61158-3-21 © IEC:2010(E)
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 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-protocol-machine
3.2.11 DL-provider-initiated-facility
3.2.12 DL-provider-optional-facility
3.2.13 DL-service-primitive;
primitive
3.2.14 DL-service-provider
3.2.15 DL-service-user
3.2.16 DLS-user-optional-facility
3.2.17 indication (primitive);
acceptor.deliver (primitive)
3.2.18 multi-peer
3.2.19 request (primitive);
requestor.submit (primitive)
3.2.20 requestor
3.2.21 response (primitive);
acceptor.submit (primitive)
3.2.22 submit (primitive)
3.2.23 symmetrical service
3.3 Data link service terms and definitions
3.3.1
DL-segment, link, local link
single data link (DL) subnetwork in which any of the connected data link entities (DLEs) may
communicate directly, without any intervening data link 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
3.3.2
Data link service access point (DLSAP)
distinctive point at which DL-services are provided by a single DLE 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.

61158-3-21 © IEC:2010(E) – 11 –
3.3.3
DLSAP address
either an individual DLSAP address designating a single DLSAP of a single data link service
(DLS) user (DLS-user), or a group DL-address potentially designating multiple DLSAPs, each
of a single DLS-user
NOTE This terminology was 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.
3.3.4
(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.
3.3.5
Data link connection endpoint address (DLCEP-address)
DL-address that designates either:
a) one peer DL-connection-end-point;
b) one multi-peer publisher DL-connection-end-point, and implicitly the corresponding set of
subscriber DL-connection-end-points, where each DL-connection-end-point exists within a
distinct DLSAP and is associated with a corresponding distinct DLSAP-address.
3.3.6
Frame check sequence (FCS) error
error that occurs when the computed frame check sequence value after reception of all the
octets in a data link protocol data unit (DLPDU) does not match the expected residual
3.3.7
frame
synonym for DLPDU
3.3.8
network management
management functions and services that perform network initialization, configuration, and
error handling
3.3.9
protocol
convention on the data formats, time sequences, and error correction for data exchange in
communication systems
3.3.10
receiving DLS-user
DL-service user that acts as a recipient of DLS-user data
NOTE A DL-service user can be both a sending and receiving DLS-user concurrently.
3.3.11
sending DLS-user
DL-service user that acts as a source of DLS-user data
3.3.12
device
single DLE as it appears on one local link

– 12 – 61158-3-21 © IEC:2010(E)
3.3.13
DL– entity identifier
address that designates the (single) DLE associated with a single device on a specific local
link
3.3.14
device unique identification
unique 8 octet identification to identify a Type 21 device in a network. This ID is a combination
of a 6 octet ISO/IEC 8802-3:2000 MAC address and 2 octet DL-address
3.3.15
ring
active network where each node is connected in series to two other devices
NOTE A ring may also be referred to as a loop.
3.3.16
linear topology
topology where the devices are connected in series, with two devices each connected to only
one other device, and all others each connected to two other devices, for example, connected
in a line
3.3.17
R-port
port in a communication device that is part of a ring structure
3.3.18
real-time
ability of a system to provide a required result in a bounded time
3.3.19
real-time communication
transfer of data in real-time
3.3.20
Real-time Ethernet (RTE)
ISO/IEC 8802-3:2000 based network that includes real-time communication
NOTE 1 Other communications can be supported, providing that the real-time communication is not compromised.
NOTE 2 This definition is base on, but not limited to, ISO/IEC 8802-3:2000. It could be applicable to other
IEEE802 specifications, e.g., IEEE802.11.
3.3.21
RTE end device
device with at least one active RTE port
3.3.22
RTE port
media access control (MAC) sublayer point where an RTE is attached to a local area network
(LAN)
NOTE This definition is derived from that of bridge port in ISO/IEC 10038: 1993, as applied to local MAC bridges.
3.3.23
switched network
network also containing switches
NOTE Switched network means that the network is based on IEEE802.1D and IEEE802.1Q with MAC bridges and
priority operations.
61158-3-21 © IEC:2010(E) – 13 –
3.3.24
link
transmission path between two adjacent nodes [derived from ISO/IEC 11801]
3.4 Symbols and abbreviations
3.4.1 Common symbols and abbreviations
DL data link (used as a prefix or adjective)
DLC data link connection
DLCEP data link connection endpoint
DLE data link entity (the local active instance of the DLL)
DLL data link layer
DLPDU data link protocol data unit
DLPM data link protocol machine
DLM data link management
DLME data link management entity (the local active instance of DLM)
DLMS data link management service
DLS data link service
DLSAP data link service-access-point
DLSDU data link service-data-unit
FIFO first-in, first-out (queuing method)
NMT network management
OSI Open Systems Interconnection
Ph- physical layer (as a prefix)
PHY physical interface transceiver
PhL physical layer
RTE Real-time Ethernet
IEC International Electrotechnical Commission
IP Internet Protocol ( see RFC 791)
ISO International Organization for Standardization
MAC media access control
NRT non-real-time
PDU protocol data unit
SAP service access point
RT real-time
TCP Transmission Control Protocol (see RFC 793)
UDP User Datagram Protocol (see RFC 768)

3.4.2 Type 21: Additional symbols and abbreviations
EFR extremely fast recovery
GD general device
LNM line network manager
PO power on
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PnP plug and play
RNM ring network manager
RNMP primary ring network manager
RNMS secondary ring network manager
RNAC ring network auto configuration
UID device unique identification
Type 21 NMIB Type 21 network management information base

3.5 Conventions
3.5.1 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.
Service primitives, used to represent service user/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 for each of those primitives and
parameter-transfer directions used by the DLS, including
• the request primitive’s input parameters;
• the request primitive’s output parameters;
• the indication primitive’s output parameters;
• the response primitive’s input parameters;
• the confirmation primitive’s output parameters.
NOTE The request, indication, response and confirmation primitives are also known as requestor.submit,
acceptor.deliver, acceptor.submit, and requestor.deliver primitives, respectively (see ISO/IEC 10731).
One parameter, or a portion of it, is listed in each row of each table. Under the appropriate
service primitive columns, a code is used to specify how the parameter is used, and its
direction:
M parameter: mandatory for the primitive;
U parameter: a user option that may or may not be provided depending on the
dynamic use 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 parentheses. These may be one of:
a) (=) A parameter-specific constraint indicating that the parameter is semantically
equivalent to the parameter in the service primitive to its immediate left in the table;

61158-3-21 © IEC:2010(E) – 15 –
b) (n) An indication that following note n contains additional information pertaining to the
parameter and its use.
In any particular interface, not all parameters shall be stated explicitly. Some may be implicitly
associated with the DLSAP at which the primitive is issued.
In the diagrams illustrating these interfaces, dashed lines indicate cause and effect or time
sequence relationships, and wavy lines indicate that events occur at approximately the same
time.
3.5.2 Additional conventions
In the diagrams illustrating the DLS and DLM interfaces, dashed lines indicate cause and
effect or time sequence relationships between actions at different stations, while solid lines
with arrows indicate cause and effect time sequence relationships that occur within the DLE
provider at a single station.
The following notation, a shortened form of the primitive classes defined in 3.5.1, is used in
the figures and tables.
req: request primitive
ind: indication primitive
cnf: confirmation primitive (confirmation)
rsp: response primitive
4 Data-link layer services and concepts
4.1 General
4.1.1 Overview
This standard specifies the Type 21 data link services for an ISO/IEC 8802-3:2000 based
time-deterministic control network, which is one of the communication networks for RTE. The
communication services support timing demands typical of high-performance automation
applications. They do not change the basic principles of ISO/IEC 8802-3:2000, but extend it
toward RTE. Thus, it is possible to continue to use standard Ethernet hardware, infrastructure
components, or test and measurement equipment, such as network analyzers.
The Type 21 DLL provides reliable and transparent data communication between two Type 21
end devices. The Type 21 DLL also guarantees abstract transparent data transfer between
DL-users so that DLL provides flexible and convenient network connectivity to network users.
4.1.2 Overview of full duplex flow control
A Type 21 device is based on an integrated switch with two ports (ring ports) connected to the
ring. Therefore, a Type 21 network system is made up of full-duplex, collision-free switching
devices configured as a ring or a line network. Figure 1 shows the full-duplex flow control
procedure in a Type 21 network system. Type 21 guarantees collision-free data transmission
between two devices linked by a full-duplex Ethernet connection so that the Type 21 DLL
provides reliable, transparent, and collision-free data transmission to the DLS-users.

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Type 21 Type 21
Rx Tx Rx Tx Rx Tx Rx Tx
MAC/DLL MAC/DLL
Forwarding Forwarding
MAC1 MAC2 MAC1 MAC2
Control Control
PHY1 PHY2 PHY1 PHY2
Figure 1 – Full-duplex flow control
4.1.3 Types and classes of DL-layer service
4.1.3.1 Overview
The DLS provides transparent and reliable data transmission between DLS-users over
Type 21. The DLS is based on services provided by the physical layer of
ISO/IEC 8802-3:2000 to the conceptual interface between the physical and data link layers.
Three types of data transmission services are provided.
Data service (DL-DATA)
Data service is used to transmit a Type 21 frame to a destination device or devices using the
priority option. DL-DATA service is a queued service using the RT-queue.
Sporadic data service (DL-SPDATA)
Sporadic data service is used to transmit a common protocol frame, such as TCP/IP or UDP.
Type 21 data link layer transmits without modification any received DLSDUs generated by a
DLS-user. In this case, DLSDU is assumed to include DLPDU. DL-SPDATA is a queued
service using the NRT-queue.
Network control message
Network-control-message service is used by the DL-management entity to share network-
related information with the other devices in a Type 21 network segment.
4.1.3.2 Primitives of the data service
The sequence of primitives for the data service is shown in Figure 2.
DL-DATA request and DL-DATA indication correspond to the MA-DATA request and MA-
DATA indication defined by ISO/IEC 8802-3:2000, respectively.

Figure 2 – Sequence diagram of DL-DATA service

61158-3-21 © IEC:2010(E) – 17 –
The sender DLS-user prepares a DLSDU for a single receiver-side DLS-user, or for multiple
DLS-users. The DLSDU is passed to the local DLE via the DLS interface by means of a
DL-DATA request primitive. The DLE queues the service request, and the queued service
request is transmitted by the DLPM to the receiver DLE or to multiple DLEs.
The receiving DLE(s) attempt to deliver the received DLSDU to the specified DLS-user(s).
There is no confirmation of correct receipt at the remote DLEs or of delivery to the intended
DLS-user(s); acknowledgements do not occur. When the DLSDU is transmitted, it reaches all
receiver-side DLEs at about the same time, ignoring signal propagation delays. Each DLE
addressed by the DLSDU that has received the data error-free, passes the DLSDU and
associated addressing information to the local DLS-user by means of a DL-DATA indication
primitive.
4.1.3.3 Primitives of the sporadic data service
The sequence of primitives for the sporadic data service is shown in Figure 3. DL-SPDATA
request and DL-SPDATA indication correspond to the MA-DATA request and MA-DATA
indication defined by ISO/IEC 8802-3:2000, respectively.

Figure 3 – Sequence diagram of DL-SPDATA service
DL-SPDATA service is used to transmit other protocol frames, such as TCP/IP or UDP.
DL-SPDATA service is transmitted through both R-ports using the non-real-time (NRT) queue
without referring to the path table and without modification of the received DLSDU.
4.1.3.4 Primitives of the network control message service
The sequence of primitives for the network control message service is shown in Figure 4.
DL-NCM_SND request and DL-NCM_SND indication correspond to the MA-DATA request and
MA-DATA indication defined by ISO/IEC8802-3:2000, respectively.

Figure 4 – Sequence diagram of NCM service primitive

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The DL-NCM_SND service is used to transmit a network control message. The DL-NCM_SND
service is transmitted to one or both R-ports through the real-time (RT) queue.
4.1.3.5 Addressing
Figure 5 shows the Relationships of DLSAPs, DLSAP-addresses, and group DL-addresses.
DLS-user-entity
DLS-user-entity
DLS-users
DLSAP DLSAP DLSAP
DLSAP-
address DLSAP-
DLSAP-
...