IEC 61784-2-21:2023

IEC 61784-2-21 ®
Edition 1.0 2023-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Industrial networks – Profiles –
Part 2-21: Additional real-time fieldbus profiles based on ISO/IEC/IEEE 8802-3 –
CPF 21
Réseaux industriels – Profils –
Partie 2-21: Profils de bus de terrain supplémentaires pour les réseaux en temps
réel fondés sur l’ISO/IEC/IEEE 8802-3 – CPF 21

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IEC 61784-2-21 ®
Edition 1.0 2023-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Industrial networks – Profiles –

Part 2-21: Additional real-time fieldbus profiles based on ISO/IEC/IEEE 8802-3 –

CPF 21
Réseaux industriels – Profils –

Partie 2-21: Profils de bus de terrain supplémentaires pour les réseaux en

temps réel fondés sur l’ISO/IEC/IEEE 8802-3 – CPF 21

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 35.100.20; 35.240.50 ISBN 978-2-8322-6914-5

– 2 – IEC 61784-2-21:2023 © 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 . 8
3.3 Symbols . 8
3.4 Conventions . 9
4 CPF 21 (FL-net) – RTE communication profiles . 10
4.1 General overview . 10
4.2 CP 21/1 . 10
4.2.1 Physical layer . 10
4.2.2 Data-link layer . 10
4.2.3 Application layer . 13
4.2.4 Performance indicator selection . 17
Bibliography . 25

Figure 1 – Protocol stack for Type 26 fieldbus . 11

Table 1 – CPF 21 symbols . 9
Table 2 – CPF 21: Overview of profile sets . 10
Table 3 – DL-layer protocol / service suite selection . 12
Table 4 – Data transmission service selection . 12
Table 5 – Port number selection . 13
Table 6 – IP address selection . 13
Table 7 – CP 21/1: AL service selection . 14
Table 8 – Service selection of Subclause 6.5.4 and 6.5.6 . 15
Table 9 – CP 21/1: AL protocol selection . 16
Table 10 – Protocol selection of Subclause 5.2 . 17
Table 11 – CP 21/1: Performance indicator overview . 18
Table 12 – CP 21/1: Performance indicator dependency matrix . 18
Table 13 – CP 21/1: Consistent set of PIs for CM1 and CM2 (Erate = 100 Mbit/s) . 24
Table 14 – CP 21/1: Consistent set of PIs for CM1, CM2 and CM3 (Erate = 100 Mbit/s) . 24
Table 15 – CP 21/1: Consistent set of PIs for CM1, CM2 and CM3
(Erate = 1 000 Mbit/s) . 24

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INDUSTRIAL NETWORKS –
PROFILES –
Part 2-21: Additional real-time fieldbus profiles
based on ISO/IEC/IEEE 8802-3 –
CPF 21
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
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 61784-2-21 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 61784-2-21:2023 © 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;
b) expand Common-memory-area as a new Common-memory-area-3 (CM3);
c) add new services and the protocols with expansion of Common-memory-area:
– Extended-cyclic-data service and the protocol;
– Extended-participation-req service and the protocol;
– Extended-network-parameter-read service and the protocol;
– Extended-network-parameter-write service and the protocol;
d) add new Table for CP 21/1: Consistent set of PIs with CM3.
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 61784-2-21:2023 © IEC 2023
INDUSTRIAL NETWORKS –
PROFILES –
Part 2-21: Additional real-time fieldbus profiles
based on ISO/IEC/IEEE 8802-3 –
CPF 21
1 Scope
This part of IEC 61784-2 defines Communication Profile Family 21 (CPF 21). CPF 21 specifies
a Real-Time Ethernet (RTE) communication profile (CP) and related network components based
on the IEC 61158 series (Type 26), 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 profile uses 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 61158-5-26:2023, Industrial communication networks – Fieldbus specifications – Part 5-26:
Application layer service definition – Type 26 elements
IEC 61158-6-26:2023, Industrial communication networks – Fieldbus specifications – Part 6-26:
Application layer protocol specification – Type 26 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
IEC 61784-5-21, Industrial communication networks – Profiles – Part 5-21: Installation of
fieldbuses – Installation profiles for CPF 21
IEC 61918, Industrial communication networks – Installation of communication networks in
industrial premises
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 in Bridged Local Area Networks
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 796, J. Postel, Address mappings, September 1981, available at
https://www.rfc-editor.org/info/rfc796 [viewed 2022-02-18]
IETF RFC 826, D. Plummer, An Ethernet Address Resolution Protocol: Or Converting Network
Protocol Addresses to 48.bit Ethernet Address for Transmission on Ethernet Hardware,
November 1982, available at https://www.rfc-editor.org/info/rfc826 [viewed 2022-02-18]
IETF RFC 894, C. Hornig, A Standard for the Transmission of IP Datagrams over Ethernet, April
1984, available at https://www.rfc-editor.org/info/rfc894 [viewed 2022-02-18]
IETF RFC 919, J.C. Mogul, Broadcasting Internet Datagrams, October 1984, available at
https://www.rfc-editor.org/info/rfc919 [viewed 2022-02-18]
IETF RFC 922, J.C. Mogul, Broadcasting Internet datagrams in the presence of subnets,
October 1984, available at https://www.rfc-editor.org/info/rfc922 [viewed 2022-02-18]
IETF RFC 950, J.C. Mogul and J. Postel, Internet Standard Subnetting Procedure, August 1985,
available at https://www.rfc-editor.org/info/rfc950 [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

– 8 – IEC 61784-2-21:2023 © IEC 2023
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.
ARP Address Resolution Protocol (see IETF RFC 826)
CP Communication Profile [according to IEC 61784-1-0]
CPF Communication Profile Family [according to IEC 61784-1-0]
FA Factory Automation
FCS Frame check sequence
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)
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 21 symbols
Symbol Definition Unit
BW Total bandwidth in %, and the 100 % is Erate %
BWnrt Non-RTE bandwidth %
BWrte Bandwidth used for the RTE communications %
Cd µs
Signal propagation delay on the cable segment #i
i
Clen m
Cable length of a cable segment #i
i
Cpd Signal propagation delay on the cabling path between sending and receiving end-stations µs
µs/m
Cε
Cable prppagation delay constant per meter on the cable segment #i
i
DT Delivery time µs
DVct Total volume of the cyclic-data sent out by all end-stations Octets
Erate Ethernet data-transmission rate Mbit/s
NoC Number of cable segments between sending and receiving end-stations
NoS Number of switches (including Hub) between sending and receiving end-stations
STTsr Sender and Receiver stack traversal time including Phy, MAC, IP, UDP or TCP and FAL µs
i
processing time of end-station #i
Tct Sum total of the transmission time of all Cyclic-data frames by all end-stations µs
Tctn
Total number of Cyclic-data frames sent out by end-station #i
i
Tcs Sum total of the transmission time up to the permissible count of general Ethernet frame µs
including the general-purpose-server-command transmission
Tms Sum total of the transmission time up to the permissible count of message-data frame µs
sporadically requested during one Tttkr time period
Tnn The total number of nodes participating in the logical ring
Trmt Refresh-cycle-measurement time which is the elapsed time period from the time after µs
obtaining the token by an end-station until the time the end-station obtains the token once
again
TRrte Throughput RTE Octets/s
Ttf Packet frame transmission time µs
Tsw Latency of the switch (including Hub) #i µs
i
Tsw Sum total of the switch (including Hub) latencies on the connection path between sending µs
and receiving end-stations
Ttk Transmission time of the token frames out of all end-stations including the inter-frame µs
space time for sending out the token frame immediately after sending out the final-cyclic-
data frame
Ttkif Inter-frame space time for sending out the token frame immediately after sending out the µs
i
final-cyclic-data frame by end-station #i
Tttkr Target-token-rotation time µs

3.4 Conventions
For the purposes of this document, the conventions defined in IEC 61784-2-0 apply.

– 10 – IEC 61784-2-21:2023 © IEC 2023
4 CPF 21 (FL-net ) – RTE communication profiles
4.1 General overview
Communication Profile Family 21 defines the communication profile based on IEC 61158-5-26
and IEC 61158-6-26 which corresponds to the communication systems commonly known as
FL-net.
• Profile 21/1 (FL-net)
This profile constitutes an FL-net communication system with star topology. It contains a
selection of AL services and protocol definitions from IEC 61158-5-26 and IEC 61158-6-26.
Table 2 shows the overview of FL-net profile set.
Table 2 – CPF 21: Overview of profile sets
Layer Profile 21/1
Application IEC 61158-5-26, IEC 61158-6-26
Data-link a set of the off-the-shelf protocol suite as follows:
IETF RFC 768(UDP), IETF RFC 793(TCP)
IETF RFC 791(IP)
IETF RFC 919, IETF RFC 922
IETF RFC 792, IETF RFC 950
IETF RFC 894 / ISO/IEC/IEEE 8802-3 Ethernet MAC
IETF RFC 826
Physical ISO/IEC/IEEE 8802-3 Phy

4.2 CP 21/1
4.2.1 Physical layer
The physical layer of 100 Mbit/s and 1 000 Mbit/s shall be according to ISO/IEC/IEEE 8802-3.
Connectors, cables and the installation guideline are specified in IEC 61784-5-21 and
IEC 61918.
4.2.2 Data-link layer
4.2.2.1 Overview
Functions of the intermediate OSI layers, layers 3 through 6, are consolidated into the
IEC 61158 data-link layer of a Type 26 fieldbus.
Three kinds of Type 26 data transmission services are defined in IEC 61158-5-26 and
IEC 61158-6-26, which are Cyclic-data transmission (CT), Message-data transmission (MT) and
General-purpose-server-command transmission (CS).
The Cyclic-data transmission and the Message-data transmission are performed as message
transfer services through UDP communication channels. The General-purpose-server-
command transmission is performed as server-command transfer service through the
communication channels of UDP or TCP.
___________
FL-net is the trade name of the JEMA/FL-net: the Japan Electrical Manufacturers’ Association / the Factory
Automation Link network. 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 trade name. Use of the trade name requires permission of the trade name holder.

The service interface to the UDP and/or TCP channels of the DL-layer for Type 26 FAL services
is by means of any off-the-shelf UDP and TCP protocol suite, and the requirement to the DL-
layer service is not peculiar and is minimal and general.
Figure 1 shows the protocol stack for a Type 26 fieldbus, the OSI layers and the equivalent
layers in the IEC 61158 basic fieldbus reference model.
OSI layer IEC 61158 layer
7 Application
Application (FAL)
6 Presentation null
IEC 61158-5-26
IEC 61158-6-26
5 Session null
Data-link
4 Transport
IETF RFC 768, (IETF RFC 793)
IETF RFC 791
3 Network IETF RFC 919, IETF RFC 922
(IETF RFC 792, IETF RFC 950)
IETF RFC 894/
ISO/IEC/IEEE 8802-3 MAC
2 Data-link
(IETF RFC 826)
Physical
1 Physical
ISO/IEC/IEEE 8802-3 Phy
Figure 1 – Protocol stack for Type 26 fieldbus
4.2.2.2 DL-layer service and protocol suite selection
Table 3 specifies the DL-layer protocol/service suite selection for the MT, the CT and the CS
services of CPF 21.
– 12 – IEC 61784-2-21:2023 © IEC 2023
Table 3 – DL-layer protocol / service suite selection
OSI equivalent Corresponding Usage Constraint
layer service DL protocol /Service
UDP: IETF RFC 768 M Used for MT and CT services
UDP: IETF RFC 768 Used for CS service.
The value of "Check-sum" is set to zero (0) at
Transport layer O
sender node, and the check-sum verification
is not performed at receiver nodes.
TCP: IETF RFC 793 O Used for CS service
IP: IETF RFC 791 Used for CT, MT and CS services.
M
A broadcast communication function is
mandatory fundamental function.
ICMP: IETF RFC 792 O Used for CT, MT and CS services
Broadcast related: Used for CT, MT and CS services.
IETF RFC 919
Network layer M
A broadcast communication function is
mandatory fundamental function.
Broadcast related: Used for CT, MT and CS services.
IETF RFC 922
M
A broadcast communication function is
mandatory fundamental function.
Subnet related: IETF RFC 950 O Used for CT, MT and CS services
Ethernet: IETF RFC 894 M Used for CT, MT and CS services
Data-link layer
ARP: IETF RFC 826 O Used for CT, MT and CS services
Physical layer ISO/IEC/IEEE 8802-3 M Used for CT, MT and CS services

The DL-layer service shall specify a broadcast communication function as the mandatory
fundamental function as CPF 21 lower layer, and any other special main functions are not
specified or required as of mandatory for the DL-layer service except for the constraints shown
in Table 4.
Table 4 specifies the data transmission service selection.
Table 4 – Data transmission service selection
Data transmission service Usage Constraint
CT and MT service DL-SAP assignment: See Table 5.
M
Network address and Node number: See Table 6.
CS service through UDP Default selection for CS service.
M DL-SAP assignment: See Table 5.
Network address and Node number: See Table 6.
CS service through TCP Alternative selection for CS service
O DL-SAP assignment: See Table 5.
Network address and Node number: See Table 6.

Table 5 – Port number selection
Data transmission Service Channel type Usage Port number assigned / Constraint
Reception for CT
including AR-control, Token frame
UDP M 55 000
excluding Extended-cyclic-data
frame
Reception for MT
UDP M 55 001
including AR-control reception
Reception for AR-control:
AR-Control.Participation-req frame, UDP M 55 002
AR-Control.Trigger frame
Transmission for MT and CT
UDP M 55 003
including AR-control transmission
Reception for CS UDP M 55 004
Reception for CS TCP O 55 004
Transmission for CS UDP M 55 004
Transmission for CS TCP O 55 004
Reception for:
Extended-cyclic-data frame,
UDP M 55 005
AR-Control.Extended-participation-
req frame.
NOTE AR-control performs the FAL services coordination, the token passing control to establish and maintain a
logical ring for right to send out data among nodes, the control for new node addition and member node drop-out,
the logical-ring recovery, and the error handling with delivery confirmation and retransmission.

Table 6 – IP address selection
IP address Usage Constraint
192.168.250.N M Default selection.
Subnet mask = 255.255.255.0 "N" is identical to the node number of 1 to 254.
Destination node number "N = 255" is for broadcasting.
192.168.200.N O Alternative selection.
Subnet mask = 255.255.255.0 N" is identical to the node number of 1 to 254.
Destination node number "N = 255" is for broadcasting.
NOTE IP address is picked and assigned out of the Class C IP address defined in IETF RFC 796, and each node
number of 1 to 254 is identical to the host address in Class C IP address with subnet mask of 255.255.255.0.

4.2.3 Application layer
4.2.3.1 AL service selection
Table 7 specifies the AL service selection within IEC 61158-5-26.
In addition, AL services are mapped onto the UDP/TCP/IP protocol suite, and corresponding
minimum requirements shall be supported and implemented in accordance with IETF RFC 768,
IETF RFC 791, IETF RFC 793, IETF RFC 894, IETF RFC 919, IETF RFC 922 and these
subsequent documents which supersede them.

– 14 – IEC 61784-2-21:2023 © IEC 2023
Table 7 – CP 21/1: AL service selection
Clause Header Presence Constraints
1 Scope YES —
2 Normative references YES —
3 Terms, definitions, symbols, abbreviated terms and YES —
conventions
4 Concepts YES —
5 Data type ASE YES —
6 Communication model specification – —
6.1 General YES —
6.2 Protocol stack for Type 26 fieldbus YES —
6.3 Overview of Type 26 communication model YES —
6.4 Cyclic data communication service with Common- YES —
memory
6.5 ASEs — —
6.5.1 Overview of Type 26 ASEs YES —
6.5.2 Type 26 specific conventions for FAL service common YES —
parameters
6.5.3 Cyclic-data ASE YES —
6.5.4 Message-data ASE YES See Table 8.
6.5.5 Communication load measurement ASE YES —
6.5.6 Network management ASE YES See Table 8.
6.5.7 General purpose command server ASE YES —
6.5.8 AR ASE YES –
6.5.9 FAL ASE summary YES —
Table 8 – Service selection of Subclause 6.5.4 and 6.5.6
Service ref. Service name Usage Constraint
6.5.4.3.2 Byte block read service O —
6.5.4.3.3 Byte block write service O —
6.5.4.3.4 Word block read service O —
6.5.4.3.5 Word block write service O —
6.5.4.3.6 Network parameter read service M —
6.5.4.3.7 Extended network parameter read service M —
6.5.4.3.8 Network parameter write service O —
6.5.4.3.9 Extended network parameter write service O —
6.5.4.3.10 Stop command service O —
6.5.4.3.11 Operation command service O —
6.5.4.3.12 Profile read service M —
6.5.4.3.13 Transparent message service O —
6.5.4.3.14 Log data read service M —
6.5.4.3.15 Log data clear service M —
6.5.4.3.16 Message return service M —
6.5.4.3.17 Vendor specific message service O —
6.5.4.3.18 Set remote node configuration parameter —
M
service
6.5.4.3.19 Read remote participating node management —
M
information parameter service
6.5.4.3.20 Read remote node management information —
M
parameter service
6.5.4.3.21 Read remote node setting information —
M
parameter service
6.5.6.3.8 Reset node service O —

4.2.3.2 AL protocol selection
Table 9 specifies the AL protocol selection within IEC 61158-6-26.
In addition, AL protocol is mapped onto the UDP/TCP/IP protocol suite, and corresponding
minimum requirements shall be supported and implemented in accordance with IETF RFC 768,
IETF RFC 791, IETF RFC 793, IETF RFC 894, IETF RFC 919, IETF RFC 922 and these
subsequent documents which supersede them.

– 16 – IEC 61784-2-21:2023 © IEC 2023
Table 9 – CP 21/1: AL protocol selection
Clause Header Presence Constraints
1 Scope YES —
2 Normative references YES —
3 Terms, definitions, symbols, abbreviated terms and YES —
conventions
4 FAL syntax description — —
4.1 General YES —
4.2 Overview of Type 26 fieldbus YES —
4.3 Operating principle YES —
4.4 FAL PDU abstract syntax YES —
4.5 Data type assignments YES —
5 Transfer syntax — —
5.1 Encoding rules YES —
5.2 PDU elements encoding YES See Table 10.
6 FAL protocol state machines structure — —
6.1 Overview YES —
6.2 Common variables, parameters, timers, counters, lists YES —
and queues
6.3 Functions used in state tables YES —
7 FAL service protocol machine(FSPM) — —
7.1 Overview YES —
7.2 Cyclic-data protocol machine YES —
7.3 Message data protocol machine YES —
7.4 Load measurement protocol machine YES —
7.5 General purpose communication server protocol YES —
machine
7.6 Network management protocol machine YES —
8 Application relationship protocol machine (ARPM) — —
8.1 Overview YES —
8.2 Cyclic-TX/RX control YES —
8.3 Message-TX/RX control YES —
8.4 Command server TX/RX control YES —
8.5 AR control YES —
9 DLL mapping protocol machine (DMPM) – —
9.1 Overview YES —
9.2 Mapping of DMPM service primitives and DLL service YES —
primitives
9.3 Mapping DMPM service port to DL-SAP YES —
9.4 Mapping of Network address to each node YES —

Table 10 – Protocol selection of Subclause 5.2
Service ref. Service name Usage Constraint
5.2.1 FALARHeader M —
5.2.2 Transparent-msg PDU O —
5.2.3 Token-PDU M —
5.2.4 Participation-req PDU M —
5.2.5 Byte-block-read PDUs O —
5.2.6 Byte-block-write PDUs O —
5.2.7 Word-block-read PDUs O —
5.2.8 Word-block-write PDUs O —
5.2.9 Network-parameter-read PDUs M —
5.2.10 Network-parameter-write PDUs O —
5.2.11 Stop-command PDUs O —
5.2.12 Operation-command PDUs O —
5.2.13 Profile-read PDUs M —
5.2.14 Trigger-PDU M —
5.2.15 Log-data-read PDUs M —
5.2.16 Log-data-clear PDUs M —
5.2.17 Message-return PDUs M —
5.2.18 Vendor-specific-msg PDUs O —
5.2.19 Start-TK-hld-time-mrmt PDUs M —
5.2.20 Terminate-TK-hld-time-mrmt PDUs M —
5.2.21 Start-GP_Comm-sndr-log PDUs M —
5.2.22 Terminate-GP_Comm-sndr-log PDUs M —
5.2.23 Set-remote-node-config-para PDUs M —
5.2.24 Read-rmt-partici-node-mgt-info-para PDUs M —
5.2.25 Read-rmt- node-mgt-info-para PDUs M —
5.2.26 Read-rmt-node-set-info-para PDUs M —
5.2.27 Reset-node PDUs O —
5.2.28 Cyclic-data PDUs M —
5.2.29 Extended-participation-req PDU M —
5.2.30 Extended-network-parameter-read PDUs M —
5.2.31 Extended-network-parameter-write PDUs O —

4.2.4 Performance indicator selection
4.2.4.1 Performance indicator overview
Table 11 shows the performance indicators overview of CP 21/1.

– 18 – IEC 61784-2-21:2023 © IEC 2023
Table 11 – CP 21/1: Performance indicator overview
Performance indicator Applicable Constraints
Delivery time YES —
Number of end-stations YES —
Basic network topology YES Star topology
Number of switches between end-stations YES Switches or Hubs which are
recommended by the CP 21/1 should be
used
Throughput RTE YES —
Non-RTE bandwidth YES —
Time synchronization accuracy NO —
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 12 shows the dependencies between performance indicators for CP 21/1.
Table 12 – CP 21/1: Performance indicator dependency matrix
Influencing PI
Dependent PI
Delivery time NO NO YES YES YES NO NO
Number of end- NO NO YES YES YES NO NO
stations
Basic network NO NO NO NO NO NO NO
topology
Number of switches YES YES NO YES YES NO NO
between end-stations
Throughput RTE YES YES NO YES NO NO NO
Non-RTE bandwidth YES YES NO YES YES NO NO
Non-time-based NO NO NO NO NO NO NO
synchronization
accuracy
Redundancy recovery NO NO NO NO NO NO NO
time
4.2.4.2.2 Delivery time
Maximum delivery time in normal, steady state in operation is specified by the application users
with consideration of Type 26 operating principle defined in IEC 61158-6-26, 4.3.
Delivery time
Number of
end-stations
Basic network
topology
Number of
switches
between end-
stations
Throughput RTE
Non-RTE
bandwidth
Non time-based
synchronization
accuracy
Redundancy
recovery time
The operating principle for Type 26 data transmission is on the basis of token passing. A token
is passed from node to node, and only a node which holds the token can primarily perform the
data transmission. A logical ring is formed to hand over the token from node to node and the
token is circulated on the logical ring at a constant rate.
The Type 26 data transmission service has two kind of data transmission: the Cyclic-data
transmission and the Message-data transmission.
The maximum delivery time of the Type 26 data transmission is as follows:
• The maximum delivery time meets both case of no transmission error and one lost frame in
general, and is identical to the waiting time period for the token circulation to a node;
• With regard to the cyclic-data transmission, the maximum delivery time is identical to the
waiting time period for the token circulation to a node and is equivalent to the cyclic time
period of the cyclic-data transmission;
• With regard to the message-data transmission, however, the maximum delivery time is
dependent on the message-data transmission rate by other nodes. In the case of no
message-data transmission from any other nodes at the time, the maximum delivery time is
the waiting time period for the token circulation to a node as well as that of the cyclic-data
transmission.
The delivery time for payload conveyance between any two end-stations depends on the signal
propagation delay on the cable, the intermediate switch device latency, the variable length
packet transmit time and the stack traversal time including Phy, MAC, IP, UDP or TCP and FAL
processing both of the sender and the receiver nodes, and the delivery time can be calculated
using Formulae (1), (2), (
...