IEC 61784-2-15:2023

IEC 61784-2-15 ®
Edition 1.0 2023-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Industrial networks – Profiles –
Part 2-15: Additional real-time fieldbus profiles based on ISO/IEC/IEEE 8802-3 –
CPF 15
Réseaux industriels – Profils –
Partie 2-15: Profils de bus de terrain supplémentaires pour les réseaux en temps
réel fondés sur l’ISO/IEC/IEEE 8802-3 – CPF 15

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.

Droits de reproduction réservés. Sauf indication contraire, aucune partie de cette publication ne peut être reproduite ni
utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie et
les microfilms, sans l'accord écrit de l'IEC ou du Comité national de l'IEC du pays du demandeur. Si vous avez des
questions sur le copyright de l'IEC ou si vous désirez obtenir des droits supplémentaires sur cette publication, utilisez
les coordonnées ci-après ou contactez le Comité national de l'IEC de votre pays de résidence.

IEC Secretariat Tel.: +41 22 919 02 11
3, rue de Varembé info@iec.ch
CH-1211 Geneva 20 www.iec.ch
Switzerland
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigendum or an amendment might have been published.

IEC publications search - webstore.iec.ch/advsearchform IEC Products & Services Portal - products.iec.ch
The advanced search enables to find IEC publications by a Discover our powerful search engine and read freely all the
variety of criteria (reference number, text, technical publications previews. With a subscription you will always have
committee, …). It also gives information on projects, replaced access to up to date content tailored to your needs.
and withdrawn publications.
Electropedia - www.electropedia.org
IEC Just Published - webstore.iec.ch/justpublished
The world's leading online dictionary on electrotechnology,
Stay up to date on all new IEC publications. Just Published
containing more than 22 300 terminological entries in English
details all new publications released. Available online and once
and French, with equivalent terms in 19 additional languages.
a month by email.
Also known as the International Electrotechnical Vocabulary

(IEV) online.
IEC Customer Service Centre - webstore.iec.ch/csc
If you wish to give us your feedback on this publication or need
further assistance, please contact the Customer Service
Centre: sales@iec.ch.
A propos de l'IEC
La Commission Electrotechnique Internationale (IEC) est la première organisation mondiale qui élabore et publie des
Normes internationales pour tout ce qui a trait à l'électricité, à l'électronique et aux technologies apparentées.

A propos des publications IEC
Le contenu technique des publications IEC est constamment revu. Veuillez vous assurer que vous possédez l’édition la
plus récente, un corrigendum ou amendement peut avoir été publié.

Recherche de publications IEC - Découvrez notre puissant moteur de recherche et consultez
webstore.iec.ch/advsearchform gratuitement tous les aperçus des publications. Avec un
La recherche avancée permet de trouver des publications IEC abonnement, vous aurez toujours accès à un contenu à jour
en utilisant différents critères (numéro de référence, texte, adapté à vos besoins.
comité d’études, …). Elle donne aussi des informations sur les
projets et les publications remplacées ou retirées. Electropedia - www.electropedia.org

Le premier dictionnaire d'électrotechnologie en ligne au monde,
IEC Just Published - webstore.iec.ch/justpublished
avec plus de 22 300 articles terminologiques en anglais et en
Restez informé sur les nouvelles publications IEC. Just
français, ainsi que les termes équivalents dans 19 langues
Published détaille les nouvelles publications parues.
additionnelles. Egalement appelé Vocabulaire
Disponible en ligne et une fois par mois par email.
Electrotechnique International (IEV) en ligne.

Service Clients - webstore.iec.ch/csc
Si vous désirez nous donner des commentaires sur cette
publication ou si vous avez des questions contactez-nous:
sales@iec.ch.
IEC Products & Services Portal - products.iec.ch

IEC 61784-2-15 ®
Edition 1.0 2023-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Industrial networks – Profiles –

Part 2-15: Additional real-time fieldbus profiles based on ISO/IEC/IEEE 8802-3 –

CPF 15
Réseaux industriels – Profils –

Partie 2-15: Profils de bus de terrain supplémentaires pour les réseaux en

temps réel fondés sur l’ISO/IEC/IEEE 8802-3 – CPF 15

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 35.100.20; 35.240.50 ISBN 978-2-8322-6904-6

– 2 – IEC 61784-2-15:2023 © IEC 2023
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms, definitions, abbreviated terms, acronyms, and conventions . 7
3.1 Terms and definitions . 7
3.2 Abbreviated terms and acronyms . 7
3.3 Symbols . 8
3.4 Conventions . 8
4 CPF 15 (MODBUS-RTPS) – RTE communication profiles . 9
4.1 General overview . 9
4.2 CP 15/1 . 9
4.2.1 Physical layer . 9
4.2.2 Data-link layer . 9
4.2.3 Application layer . 9
4.2.4 Performance indicator selection . 10
4.3 CP 15/2 . 14
4.3.1 Physical layer . 14
4.3.2 Data-link layer . 14
4.3.3 Application layer . 14
4.3.4 Performance indicator selection . 15
Bibliography . 20

Table 1 – CPF 15 symbols . 8
Table 2 – CP 15/1: AL service selection . 10
Table 3 – CP 15/1: AL protocol selection . 10
Table 4 – CP 15/1: PI overview . 10
Table 5 – CP 15/1: PI dependency matrix . 11
Table 6 – CP 15/2: AL service selection . 15
Table 7 – CP 15/2: AL protocol selection . 15
Table 8 – CP 15/2: PI overview . 15
Table 9 – CP 15/2: PI dependency matrix . 16

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INDUSTRIAL NETWORKS –
PROFILES –
Part 2-15: Additional real-time fieldbus profiles
based on ISO/IEC/IEEE 8802-3 –
CPF 15
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 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 layer protocol type to
be used with other layer protocols of the same type, or in other type combinations explicitly
authorized by their respective intellectual property right holders.
NOTE Combinations of protocol types are specified in the IEC 61784-1 series and the IEC 61784-2 series.
IEC 61784-2-15 has been prepared by subcommittee 65C: Industrial networks, of IEC technical
committee 65: Industrial-process measurement, control and automation. It is an International
Standard.
This first edition, together with the other parts of the same series, cancels and replaces the
fourth edition of IEC 61784-2 published in 2019. This first edition constitutes a technical revision.

– 4 – IEC 61784-2-15:2023 © IEC 2023
This edition includes the following significant technical changes with respect to
IEC 61784-2:2019:
a) split of the original IEC 61784-2 into several subparts, one subpart for the material of a
generic nature, and one subpart for each Communication Profile Family specified in the
original document.
The text of this International Standard is based on the following documents:
Draft Report on voting
65C/1209/FDIS 65C/1237/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A list of all parts of the IEC 61784-2 series, published under the general title
Industrial networks – Profiles – Part 2: Additional real-time fieldbus profiles based on
ISO/IEC/IEEE 8802-3, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
INTRODUCTION
The IEC 61784-2 series provides additional Communication Profiles (CP) to the existing
Communication Profile Families (CPF) of the IEC 61784-1 series and additional CPFs with one
or more CPs. These profiles meet the industrial automation market objective of identifying Real-
Time Ethernet (RTE) communication networks coexisting with ISO/IEC/IEEE 8802-3 –
commonly known as Ethernet. These RTE communication networks use provisions of
ISO/IEC/IEEE 8802-3 for the lower communication stack layers and additionally provide more
predictable and reliable real-time data transfer and means for support of precise
synchronization of automation equipment.
More specifically, these profiles help to correctly state the compliance of RTE communication
networks with ISO/IEC/IEEE 8802-3, and to avoid the spreading of divergent implementations.
Adoption of Ethernet technology for industrial communication between controllers and even for
communication with field devices promotes the use of Internet technologies in the field area.
This availability would be unacceptable if it causes the loss of features required in the field area
for industrial communication automation networks, such as:
• real-time,
• synchronized actions between field devices like drives,
• efficient, frequent exchange of very small data records.
These new RTE profiles can take advantage of the improvements of Ethernet networks in terms
of transmission bandwidth and network span.
Another implicit but essential requirement is that the typical Ethernet communication
capabilities, as used in the office world, are fully retained, so that the software involved remains
applicable.
The market is in need of several network solutions, each with different performance
characteristics and functional capabilities, matching the diverse application requirements. RTE
performance indicators, whose values will be provided with RTE devices based on
communication profiles specified in the IEC 61784-2 series, enable the user to match network
devices with application-dependent performance requirements of an RTE network.

– 6 – IEC 61784-2-15:2023 © IEC 2023
INDUSTRIAL NETWORKS –
PROFILES –
Part 2-15: Additional real-time fieldbus profiles
based on ISO/IEC/IEEE 8802-3 –
CPF 15
1 Scope
This part of IEC 61784-2 defines Communication Profile Family 15 (CPF 15). CPF 15 specifies
a set of Real-Time Ethernet (RTE) communication profiles (CPs) and related network
components based on the IEC 61158 series (Type 15), ISO/IEC/IEEE 8802-3 and other
standards.
For each RTE communication profile, this document also specifies the relevant RTE
performance indicators and the dependencies between these RTE performance indicators.
NOTE 1 All CPs are based on standards or draft standards or International Standards published by the IEC or on
standards or International Standards established by other standards bodies or open standards processes.
NOTE 2 The RTE communication profiles use ISO/IEC/IEEE 8802-3 communication networks and its related
network components and in some cases amend those standards to obtain RTE features.
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 the IEC 61784-1 series and the IEC 61784-2 series, are
maintained simultaneously. Cross-references to these documents within the text therefore refer to the editions as
dated in this list of normative references.
IEC 61158 (all parts), Industrial communication networks – Fieldbus specifications
IEC 61158-5-15:2010, Industrial communication networks – Fieldbus specifications – Part 5-15:
Application layer service definition – Type 15 elements
IEC 61158-6-15:2010, Industrial communication networks – Fieldbus specifications – Part 6-15:
Application layer protocol specification – Type 15 elements
IEC 61784-2-0:2023, Industrial networks – Profiles – Part 2-0: Additional real-time fieldbus
profiles based on ISO/IEC/IEEE 8802-3 – General concepts and terminology
ISO/IEC/IEEE 8802-3, Telecommunications and exchange between information technology
systems – Requirements for local and metropolitan area networks – Part 3: Standard for
Ethernet
IEEE Std 802-2014, IEEE Standard for Local and Metropolitan Area Networks: Overview and
Architecture
IEEE Std 802.1AB-2016, IEEE Standard for Local and metropolitan area networks – Station and
Media Access Control Connectivity Discovery

IEEE Std 802.1AS-2020, IEEE Standard for Local and Metropolitan Area Networks – Timing
and Synchronization for Time-Sensitive Applications
IEEE Std 802.1Q-2018, IEEE Standard for Local and Metropolitan Area Networks – Bridges and
Bridged Networks
IETF RFC 768, J. Postel, User Datagram Protocol, August 1980, available at
https://www.rfc-editor.org/info/rfc768 [viewed 2022-02-18]
IETF RFC 791, J. Postel, Internet Protocol, September 1981, available at
https://www.rfc-editor.org/info/rfc791 [viewed 2022-02-18]
IETF RFC 792, J. Postel, Internet Control Message Protocol, September 1981, available at
https://www.rfc-editor.org/info/rfc792 [viewed 2022-02-18]
IETF RFC 793, J. Postel, Transmission Control Protocol, September 1981, available at
https://www.rfc-editor.org/info/rfc793 [viewed 2022-02-18]
IETF RFC 1305, D. Mills, Network Time Protocol (Version 3) Specification, Implementation and
Analysis, March 1992, available at https://www.rfc-editor.org/info/rfc1305 [viewed 2022-02-18]
IETF RFC 2988, V. Paxson, M. Allman, Computing TCP's Retransmission Timer, November
2000, available at https://www.rfc-editor.org/info/rfc2988 [viewed 2022-02-18]
3 Terms, definitions, abbreviated terms, acronyms, and conventions
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 61784-2-0,
ISO/IEC/IEEE 8802-3, IEEE Std 802-2014, IEEE Std 802.1AB-2016, IEEE Std 802.1AS-2020
and IEEE Std 802.1Q-2018 apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.2 Abbreviated terms and acronyms
For the purposes of this document, abbreviated terms and acronyms defined in IEC 61784-2-0
and the following apply.
CP Communication Profile [according to IEC 61784-1-0]
CPF Communication Profile Family [according to IEC 61784-1-0]
nternet Assigned Numbers Authority
IANA I
ICMP Internet Control Message Protocol (see IETF RFC 792)
IETF Internet Engineering Task Force
IP Internet Protocol (see IETF RFC 791)
LLDP Link Layer Discovery Protocol (see IEEE Std 802.1AB-2016)
NoS Number of Switches
Phy PHY Physical layer entity sublayer (see ISO/IEC/IEEE 8802-3)
PI Performance indicator
RSTP Rapid Spanning Tree Algorithm and Protocol (see IEEE Std 802.1Q-2018)

– 8 – IEC 61784-2-15:2023 © IEC 2023
RTO Retransmission Time Out
[according to IETF RFC 2988 – Computing TCP's Retransmission Timer]
RTPS Real-Time Publish-Subscribe
TCP Transmission Control Protocol (see IETF RFC 793)
UDP User Datagram Protocol (see IETF RFC 768)
3.3 Symbols
For the purposes of this document, symbols defined in IEC 61784-2-0 and Table 1 apply.
NOTE Definitions of symbols in this Subclause 3.3 do not use the italic font, as they are already identified as
symbols.
Table 1 – CPF 15 symbols
Symbol Definition Unit
D_size Data size octets
DT Delivery time µs
DT_lf Delivery time when a frame is lost µs
DT_lfh Delivery time when a frame is lost and the configuration is reliable with heartbeat µs
DT_lfp Delivery time when a frame is lost and the configuration is reliable periodic µs
DT_n Delivery time for the NACK message µs
H Period of the heartbeat, which is a configured parameter µs
N_Sw Number of switches between end-stations –
RTO TCP retransmission time out parameter µs
STT_r Stack traversal time of the receiver µs
STT_r1 Part of the stack traversal time of the receiver that is independent of D-size µs
STT_r2 Part of the stack traversal time of the receiver that depends linearly on D_size µs
STT_s Stack traversal time of the sender µs
STT_s1 Part of the stack traversal time of the sender that is independent of D_size µs
STT_s2 Part of the stack traversal time of the sender that depends linearly on D_size µs
T Period, which is a configured parameter µs
T_wire Time per octet on a wire segment µs
TD_Sw Time delay in switch µs
3.4 Conventions
For the purposes of this document, the conventions defined in IEC 61784-2-0 apply.

4 CPF 15 (MODBUS-RTPS) – RTE communication profiles
4.1 General overview
Communication Profile Family 15 defines profiles based on ISO/IEC/IEEE 8802-3,
IETF RFC 791 (IP), IETF RFC 793 (TCP), IETF RFC 768 (UDP), IEC 61158-5-15 and
IEC 61158-6-15, which specify the communication system protocols commonly known as
Modbus® and Modbus TCP, and RTPS (Real-Time Publish-Subscribe).
In this document, the following communication profiles are specified for CPF 15:
– Profile 15/1
Is a profile using Modbus TCP
– Profile 15/2
Is a profile using RTPS.
For both profiles the communication is assumed to be full-duplex, with network topologies built
via switches.
These communication profiles can be active at the same time on the same device and network,
and as such they do not constitute alternative profiles, but can provide complementary and
concurrent functionality.
4.2 CP 15/1
4.2.1 Physical layer
The physical layer of CP 15/1 is as specified in ISO/IEC/IEEE 8802-3.
4.2.2 Data-link layer
The data-link layer of CP 15/1 is as specified in ISO/IEC/IEEE 8802-3.
4.2.3 Application layer
4.2.3.1 General
The application layer of CP 15/1 is mapped on TCP (IETF RFC 793), using TCP Port Number
502, registered with IANA, over IP (IETF RFC 791), as described in IEC 61158-5-15 and
IEC 61158-6-15.
4.2.3.2 AL service selection
The application layer services are defined in IEC 61158-5-15. Table 2 shows the subclauses
included in this profile.
___________
1 Modbus is a trademark of Schneider Automation Inc registered in the United States of America and other

countries. This information is given for the convenience of users of this document and does not constitute an

endorsement by IEC of the trademark holder or any of its products. Compliance with this profile does not require
use of the trademark Modbus. Use of the trademark Modbus requires permission from Schneider Automation Inc.

– 10 – IEC 61784-2-15:2023 © IEC 2023
Table 2 – CP 15/1: AL service selection
Clause Header Presence Constraints
Whole Application layer services definition (Type 15) Partial Subclauses qualified
document as Common or
Client/Server
4.2.3.3 AL protocol selection
The application layer protocols are defined in IEC 61158-6-15. Table 3 shows the subclauses
included in this profile.
Table 3 – CP 15/1: AL protocol selection
Clause Header Presence Constraints
Whole Application layer protocol specification (Type 15) Partial Subclauses qualified
document as Common or
Client/Server
4.2.4 Performance indicator selection
4.2.4.1 Performance indicator overview
Table 4 provides an overview of the CP 15/1 performance indicators.
Table 4 – CP 15/1: PI overview
Performance indicator Applicable Constraints
Delivery time YES —
Number of end-stations YES —
Basic network topology YES —
Number of switches between end-stations YES —
Throughput RTE YES —
Non-RTE bandwidth YES —
Time synchronization accuracy YES Provided with NTP (IETF RFC 1305)
Non-time-based synchronization accuracy YES —
Redundancy recovery time YES —

4.2.4.2 Performance indicator dependencies
4.2.4.2.1 Dependency matrix
Table 5 provides the CP 15/1 performance indicator dependency matrix.

Table 5 – CP 15/1: PI dependency matrix
Influencing PI
Dependent PI
Delivery time NO YES YES NO NO NO NO YES
4.2.4.2.2 4.2.4.2.24 4.2.4.2.3 4.2.4.2.4
4.2.4.2.24
Number of NO NO YES NO NO NO NO NO
end-stations 4.2.4.2.5 4.2.4.2.6
Basic network NO YES YES NO NO NO NO NO
topology 4.2.4.2.7 4.2.4.2.8
Number of NO YES YES NO NO NO NO NO
switches 4.2.4.2.9 4.2.4.2.10
between
end-stations
Throughput NO NO NO NO YES NO NO YES
RTE 4.2.4.2.11 4.2.4.2.12 4.2.4.2.13
Non-RTE NO NO NO NO YES NO NO YES
bandwidth 4.2.4.2.14 4.2.4.2.15
Time NO NO YES YES NO NO NO YES
synchronization 4.2.4.2.16 4.2.4.2.17 4.2.4.2.18
accuracy
Non-time-based NO NO YES YES NO NO NO YES
synchronization 4.2.4.2.19 4.2.4.2.20 4.2.4.2.21
accuracy
Redundancy NO NO YES YES NO NO NO NO
recovery time 4.2.4.2.22 4.2.4.2.23

4.2.4.2.2 Delivery time and basic network topology
The following network topologies are supported:
• Star,
• Linear (embedded or bus),
• Ring,
• Redundant ring,
• Mesh.
The network topology influences the delivery time indirectly by influencing the number of
switches to be traversed and the queuing and directly when supporting redundancy, by reacting
differently in case of failures.
CP 15/1 has no switch technology dependencies.
Delivery time
Number of
end-stations
Basic network
topology
Number of
switches
between
end-stations
Throughput RTE
Non-RTE
bandwidth
Time synchroni-
zation accuracy
Non-time-based
synchronization
accuracy
Redundancy
recovery time
– 12 – IEC 61784-2-15:2023 © IEC 2023
4.2.4.2.3 Delivery time and non-time-based synchronization accuracy
In a scan situation, it may affect the delivery time of the response/confirmation, due to queues
on switches. It does not affect non-scan situations.
4.2.4.2.4 Delivery time and redundancy recovery time
This dependency is applicable only when the network topology supports redundancy.
4.2.4.2.5 Number of end-stations and basic network topology
This indirect dependency is bounded in practice by the number of switches that have to be
traversed, given the same number of connected end-stations, for different topologies.
4.2.4.2.6 Number of end-stations and number of switches between end-stations
The number of end-stations, for a given topology, depends on the number and kind of switches:
there must be enough switches with enough ports.
4.2.4.2.7 Basic network topology and number of end-stations
Some topologies, e.g. linear, have limits on the number of nodes.
4.2.4.2.8 Basic network topology and number of switches between end-stations
The realization of some topologies requires a minimum number of switches, with a minimum
number of ports, given a number of end-stations.
4.2.4.2.9 Number of switches between end-stations and number of end-stations
For certain topologies, like linear, the number of switches between end-stations depends on the
number of end-stations. Considering the limit on the number of ports per switch, this
dependency is generally present.
4.2.4.2.10 Number of switches between end-stations and basic network topology
Some topologies allow for fewer switches given a number of nodes, e.g. the star topology.
4.2.4.2.11 Throughput RTE and non-RTE bandwidth
The application is responsible for limiting non-RTE traffic, which can otherwise impact the
throughput RTE.
4.2.4.2.12 Throughput RTE and non-time-based synchronization accuracy
In a scan situation the throughput may be affected, due to queues on switches. It is not affected
in non-scan situations.
4.2.4.2.13 Throughput RTE and redundancy recovery time
There is throughput RTE disruption when recovery takes place.
4.2.4.2.14 non-RTE bandwidth and throughput RTE
The application is responsible for limiting RTE traffic if non-RTE bandwidth has to be made
available.
4.2.4.2.15 non-RTE bandwidth and redundancy recovery time
There is non-RTE bandwidth disruption when recovery takes place.

4.2.4.2.16 Time synchronization accuracy and basic network topology
Some topologies, e.g. linear, affect the NTP accuracy due to the presence of variable delays.
4.2.4.2.17 Time synchronization accuracy and number of switches between end-
stations
Switches cause variable delays, affecting the NTP accuracy.
4.2.4.2.18 Time synchronization accuracy and redundancy recovery time
There is disruption when recovery takes place.
4.2.4.2.19 Non-time-based synchronization accuracy and basic network topology
Some topologies, e.g. the star topology, allow for a better non-time-based synchronization
accuracy.
4.2.4.2.20 Non-time-based synchronization accuracy and number of switches
between end-stations
Switches cause variable delays, affecting the accuracy.
4.2.4.2.21 Non-time-based synchronization accuracy and redundancy recovery time
There is disruption when recovery takes place.
4.2.4.2.22 Redundancy recovery time and basic network topology
The redundancy recovery time, when supported by the topology, is topology dependent.
4.2.4.2.23 Redundancy recovery time and number of switches between end-stations
The redundancy recovery time, when supported by the topology, is dependent on the number
of switches.
4.2.4.2.24 Calculation of delivery time
The performance indicator delivery time can be calculated by Formula (1):
DT = STT_s + N_Sw x TD_Sw + (N_Sw + 1) × T_wire x D_size + STT_r (1)

where
DT is the delivery time;
STT_s is the stack traversal time of the sender;
N_Sw is the number of switches between end-stations;
TD_Sw is the time delay in switch;
T_wire is the time per octet on a wire segment;
D_size is the data size in octets;
STT_r is the stack traversal time of the receiver.

– 14 – IEC 61784-2-15:2023 © IEC 2023
The performance indicator delivery time, in case of one lost frame, can be calculated by
Formula (2):
DT_lf = 2 × DT + RTO (2)
where
DT_lf is the delivery time when a frame is lost;
DT is as computed in Formula (1);
RTO is the TCP retransmission time out parameter.
NOTE RTO is a dynamic parameter, computed with an algorithm configured using an initial value and a minimum
value, see IETF RFC 2988 (Computing TCP’s Retransmission Timer). The configuration values of RTO differ between
TCP implementations.
4.3 CP 15/2
4.3.1 Physical layer
The physical layer of CP 15/2 is as specified in ISO/IEC/IEEE 8802-3.
4.3.2 Data-link layer
The data-link layer of CP 15/2 is as specified in ISO/IEC/IEEE 8802-3.
4.3.3 Application layer
4.3.3.1 General
The application layer of CP 15/2 is mapped on UDP (IETF RFC 768), over IP (IETF RFC 791),
as described in IEC 61158-5-15 and IEC 61158-6-15.
CP 15/2 uses three UDP ports. The actual values can be configured in the field by setting the
parameters 'portBaseNumber' and 'portGroupNumber' as from Formulae (3), (4) and (5).
Implementations of CP 15/2 shall support configuring these two parameters.
port1 = portBaseNumber + 10 × portGroupNumber (3)

port2 = 1 + portBaseNumber + 10 × portGroupNumber (4)

port3 = 2 + portBaseNumber + 10 × portGroupNumber (5)

The default configuration is to set the values portBaseNumber = 7400 and portGroupNumber =
0, which results in the use of ports 7400, 7401, and 7402. These ports are registered with IANA
as:
• 7400 RTPS Discovery,
• 7401 RTPS Data-Distribution User-Traffic,
• 7402 RTPS Data-Distribution Meta-Traffic.

4.3.3.2 AL service selection
The application layer services are defined in IEC 61158-5-15. Table 6 shows the subclauses
included in this profile.
Table 6 – CP 15/2: AL service selection
Clause Header Presence Constraints
Whole document Application layer services definition (Type 15) Partial Subclauses qualified as
Common or Publish/Subscribe
4.3.3.3 AL protocol selection
The application layer protocols are defined in IEC 61158-6-15. Table 7 shows the subclauses
included in this profile.
Table 7 – CP 15/2: AL protocol selection
Clause Header Presence Constraints
Whole document Application layer protocol specification (Type 15) Partial Subclauses qualified as
Common or
Publish/Subscribe
4.3.4 Performance indicator selection
4.3.4.1 Performance indicator overview
Table 8 provides an overview of the CP 15/2 performance indicators.
Table 8 – CP 15/2: PI overview
Performance indicator Applicable Constraints
Delivery time YES —
Number of end-stations YES —
Basic network topology YES —
Number of switches between end-stations YES —
Throughput RTE YES —
Non-RTE bandwidth YES —
Redundancy recovery time YES —

4.3.4.2 Performance indicator dependencies
4.3.4.2.1 Dependency matrix
Table 9 provides the CP 15/2 performance indicator dependency matrix.

– 16 – IEC 61784-2-15:2023 © IEC 2023
Table 9 – CP 15/2: PI dependency matrix
Influencing PI
Dependent PI
Delivery time YES
YES YES
NO 4.3.4.2.2 NO NO
4.3.4.2.16 4.3.4.2.3
4.3.4.2.16
Number of end- NO YES
NO NO NO NO
stations 4.3.4.2.4 4.3.4.2.5
Basic network YES YES
NO NO NO NO
topology 4.3.4.2.6 4.3.4.2.7
Number of switches YES YES
NO NO NO NO
between end-stations 4.3.4.2.8 4.3.4.2.9
Throughput RTE YES YES
NO NO NO NO
4.3.4.2.10 4.3.4.2.11
Non-RTE bandwidth YES YES
NO NO NO NO
4.3.4.2.12 4.3.4.2.13
Redundancy YES YES
NO NO NO NO
recovery time 4.3.4.2.14 4.3.4.2.15

4.3.4.2.2 Delivery time and basic network topology
The following network topologies are supported:
• Star,
• Linear (embedded or bus),
• Ring,
• Redundant ring,
• Mesh.
The network topology influences the delivery time indirectly by influencing the number of
switches to be traversed and the queuing and directly when supporting redundancy, by reacting
differently in case of failures.
CP 15/2 has no switch technology dependencies.
4.3.4.2.3 Delivery time and redundancy recovery time
This dependency is applicable only when the network topology supports redundancy.
4.3.4.2.4 Number of end-stations and basic network topology
Indirect dependency bounded in practice by the number of switches that have to be traversed,
given the same number of connected end-stations, for different topologies.
4.3.4.2.5 Number of end-stations and number of switches between end-stations
The number of end-stations, for a given topology, depends on the number and kind of switches:
there shall be enough switches with enough ports.
Delivery time
Number of
end-stations
Basic
network
topology
Number of
switches
between
end-stations
Throughput
RTE
Non-RTE
bandwidth
Redundancy
recovery
time
4.3.4.2.6 Basic network topology and number of end-stations
Some topologies, e.g. linear, have limits on the number of nodes.
4.3.4.2.7 Basic network topology and number of switches between end-stations
The realization of some topologies requires a minimum number of switches, with a minimum
number of ports, given a number of end-stations.
4.3.4.2.8 Number of switches between end-stations and number of end-stations
For certain topologies, like linear, the number of switches between end-stations depends on the
number of end-stations. Considering the limit on the number of ports per switch, this
dependency is generally present.
4.3.4.2.9 Number of switches between end-stations and basic network topology
Some topologies allow for fewer switches given a number of nodes, e.g. the star topology.
4.3.4.2.10 Throughput RTE and non-RTE bandwidth
The application is responsible for limiting non-RTE traffic, which can otherwise impact the
throughput RTE.
4.3.4.2.11 Throughput RTE and redundancy recovery time
There is throughput RTE disruption when recovery takes place.
4.3.4.2.12 non-RTE bandwidth and throughput RTE
The application is responsible for limiting RTE traffic if non-RTE bandwidth has to be made
available.
4.3.4.2.13 non-RTE bandwidth and redundancy recovery time
There is non-RTE bandwidth disruption when recovery takes place.
4.3.4.2.14 Redundancy recovery time and basic network topology
The redundancy recovery time, when supported by the topology, is topology dependent.
4.3.4.2.15 Redundancy recovery time and number of switches between end-stations
The redundancy recovery time, when supported by the topology, is dependent on the number
of switches.
4.3.4.2.16 Calculation of delivery time
The performance indicator delivery time can be calculated using the Formulae (6), (7) and (8).
STT_s = STT_s1 + SST_s2 × D_size (6)

where
STT_s is the stack traversal time of the sender;
STT_s1 is the part of the stack traversal time of the sender that is independent of the data
size;
– 18 – IEC 61784-2-15:2023 © IEC 2023
STT_s2 is the part of the stack traversal time of the sender that depends linearly on the size
of the data D_size; this is because the stack performs a memory copy so it is
affected by the speed of the memory system;
D_size is the data size in octets.
STT_r = STT_r1 + SST_r2 × D_size (7)

where
STT_r is the stack traversal time of the receiver;
STT_r1 is the part of the stack traversal time of the receiver that is independent of the data
size;
STT_r2 is the part of the stack traversal time of the receiver that depends linearly on the
size of the data D_size; this is because the stack performs a memory copy so it is
affected by the speed of the memory system;
D_size is the data size in octets.
DT = STT_s + N_Sw × TD_Sw + (N_Sw + 1) × T_wire x D_size + STT_r (8)

where
DT is the delivery time;
STT_s is the stack traversal time of the sender;
N_Sw is the number of switches between end-stations;
TD_Sw is the time delay in switch;
T_wire is the time per octet on a wire segment;
D_size is the data size in octets;
STT_r is the stack traversal time of the receiver.
The performance indicator delivery time, in case of one lost frame, depends on how the
communication between end-stations under consideration is configured:
a) best effort;
b) reliable periodic;
c) reliable with heartbeat.
If best effort, then the delivery time in case of a lost frame does not apply, since that frame is
not retransmitted.
If reliable periodic then, in case of one lost frame, the performance indicator delivery time can
be calculated by the Formula (9).
DT_lfp = 2 × DT + DT_n + T (9)

where
DT_lfp is the delivery time when a frame is lost and the configuration is reliable periodic;
DT is as computed in Formula (8);
DT_n is the delivery time for the NACK message, computed again using Formula (8), but
with a D_size of 16 octets;
T is the period, which is a configured parameter.

NOTE 1 A typical value for the period T is 10 ms.
If reliable with heartbeat then, in case of one lost frame, the performance indicator delivery time
can be calculated by the Formula (10).
DT_lfh = 2 × DT + DT_n + H (10)

where
DT_lfh is the delivery time when a frame is lost and the configuration is reliable with
heartbeat;
DT is as computed in Formula (8);
DT_n is the delivery time for the NACK message, computed again using Formula (8), but
with a D_size of 16 octets;
H is the period of the heartbeat, which is a configured parameter.
NOTE 2 A typical value for the period heartbeat is between 100 ms and 1 s (it has a system monitoring role and
does not carry any data).
– 20 – IEC 61784-2-15:2023 © IEC 2023
Bibliography
IEC 61158-1, Industrial communication networks – Fieldbus specifications – Part 1: Overview
and guidance for the IEC 61158 and IEC 61784 series
IEC 61158-2, Industrial communication networks – Fieldbus specifications – Part 2: Physical
layer spe
...