IEC 61158-4-28:2023

IEC 61158-4-28 ®
Edition 1.0 2023-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Industrial communication networks – Fieldbus specifications –
Part 4-28: Data-link layer protocol specification – Type 28 elements

Réseaux de communication industriels – Spécifications des bus de terrain –
Partie 4-28: Spécification du protocole de la couche liaison de données –
Éléments de type 28
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IEC 61158-4-28 ®
Edition 1.0 2023-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Industrial communication networks – Fieldbus specifications –

Part 4-28: Data-link layer protocol specification – Type 28 elements

Réseaux de communication industriels – Spécifications des bus de terrain –

Partie 4-28: Spécification du protocole de la couche liaison de données –

Éléments de type 28
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 25.040 ISBN 978-2-8322-6557-4

– 2 – IEC 61158-4-28:2023 © IEC 2023
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
1.1 General . 8
1.2 Specifications . 8
1.3 Procedures . 8
1.4 Applicability . 8
1.5 Conformance . 8
2 Normative references . 9
3 Terms, definitions, symbols, abbreviated terms and conventions . 9
3.1 Reference model terms and definitions . 9
3.2 Service convention terms and definitions . 11
3.3 Common terms and definitions . 12
3.4 Additional Type 28 terms and definitions . 13
3.5 Additional Type 28 symbols and abbreviations . 15
4 Overview of the DL-protocol . 16
4.1 DLL protocol architecture . 16
4.2 DLL working mechanism . 18
4.2.1 Node . 18
4.2.2 Addressing . 18
4.2.3 Multicast . 19
4.2.4 Resource mapping and scheduling . 19
5 DLPDU structure . 21
5.1 Universal DLPDU structure . 21
5.2 Basic configuration DLPDU . 23
5.3 Address assignment DLPDU . 25
5.4 Multicast assignment DLPDU . 25
5.5 Resource allocation DLPDU . 26
5.6 Access notification DLPDU . 28
5.7 Resource application DLPDU . 29
5.8 Resource release DLPDU . 30
5.9 Status query DLPDU . 30
5.10 Status response DLPDU . 31
5.11 Announcement DLPDU . 32
5.12 Clock synchronization DLPDU. 33
5.13 Common DLPDU . 34
6 Working procedure . 35
6.1 Initialization procedure . 35
6.1.1 Basic configuration . 35
6.1.2 Resource mapping configuration . 35
6.2 DLL node management procedure . 37
6.2.1 DLL maintenance . 37
6.2.2 Node join . 38
6.2.3 Node query . 39
6.2.4 Node leave . 39
6.3 Data transmission procedure . 40

6.4 Clock synchronization procedure . 42
7 State machine . 44
7.1 DLDE state machine . 44
7.2 DLME state machine . 47
7.3 DLCE state machine . 48
8 Error handling . 49
8.1 General . 49
8.2 Possible sources and characteristics of errors . 49
8.3 Error handling of MN / TN . 50
8.4 PhL error source . 50
8.4.1 General . 50
8.4.2 Lost connection . 50
8.4.3 CRC error . 50
8.4.4 Buffer overflow . 50
8.4.5 Symbol resource conflict . 50
8.4.6 Symbol resource insufficient . 50
Annex A (informative) Example for NodeID and MAC address mapping . 51
Annex B (informative) Example for multicast group working mechanism . 52
Bibliography . 53

Figure 1 – Relationships of DLSAPs, DLSAP-addresses and group DL-addresses . 12
Figure 2 – Bitmap data type diagram. 15
Figure 3 – DLL in Type 28 protocol stack architecture . 16
Figure 4 – Relationship of the fieldbus DLL to other fieldbus layers and to users of the
fieldbus DLS . 17
Figure 5 – Type 28 DLL protocol architecture diagram . 17
Figure 6 – Resource mapping between DLL and PhL . 20
Figure 7 – DLL resource mapping message queue scheduling diagram . 21
Figure 8 – Universal DLPDU structure . 22
Figure 9 – Basic configuration DLPDU structure . 23
Figure 10 – General configuration block structure . 24
Figure 11 – Address allocation DLPDU structure. 25
Figure 12 – Multicast assignment DLPDU structure. 26
Figure 13 – Resource allocation DLPDU structure . 27
Figure 14 – Access notification DLPDU structure . 28
Figure 15 – Resource application DLPDU structure. 29
Figure 16 – Resource release DLPDU structure . 30
Figure 17 – Status query DLPDU structure . 31
Figure 18 – Status response DLPDU structure . 31
Figure 19 – Announcement DLPDU structure . 32
Figure 20 – Clock synchronization DLPDU structure . 34
Figure 21 – Common DLPDU structure . 35
Figure 22 – Resource mapping configuration diagram . 36
Figure 23 – Initial access configuration procedure diagram . 37
Figure 24 – The random access configuration procedure diagram . 38

– 4 – IEC 61158-4-28:2023 © IEC 2023
Figure 25 – Node leave procedure diagram . 40
Figure 26 – DLS data sending procedure diagram . 41
Figure 27 – DLS data receiving procedure diagram . 42
Figure 28 – Clock synchronization delay measurement procedure diagram . 43
Figure 29 – Clock register structure diagram . 43
Figure 30 – Clock synchronization procedure . 44
Figure 31 – DLDE state machine . 45
Figure 32 – DLME state machine . 47
Figure 33 – DLCE state machine . 48
Figure B.1 – Multicast working mechanism diagram . 52

Table 1 – NodeID address assignment of Type 28 DLL . 18
Table 2 – NodeID and MAC address mapping table . 18
Table 3 – Members of multicast group mapping table . 19
Table 4 – DLDE state transition . 46
Table 5 – DLME state machine state transition . 48
Table 6 – DLCE state machine state transition . 49
Table A.1 – Example of NodeID and MAC address mapping table saved on TN . 51

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INDUSTRIAL COMMUNICATION NETWORKS –
FIELDBUS SPECIFICATIONS –
Part 4-28: Data-link layer protocol specification –
Type 28 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,
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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
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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
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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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
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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
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
Attention is drawn to the fact that the use of the associated protocol type is restricted by its
intellectual-property-right holders. In all cases, the commitment to limited release of intellectual-
property-rights made by the holders of those rights permits a layer protocol type to be used with
other layer protocols of the same type, or in other type combinations explicitly authorized by its
intellectual-property-right holders.
NOTE Combinations of protocol types are specified in the IEC 61784-1 series and the IEC 61784-2 series.
IEC 61158-4-28 has been prepared by subcommittee 65C: Industrial networks, of IEC technical
committee 65: Industrial-process measurement, control and automation. It is an International
Standard.
– 6 – IEC 61158-4-28:2023 © IEC 2023
The text of this International Standard is based on the following documents:
Draft Report on voting
65C/1206/FDIS 65C/1235/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 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 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.
IMPORTANT – The "colour inside" logo on the cover page of this document indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this document using a colour printer.

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 61158-1.
The data-link protocol provides the data-link service by making use of the services available
from the physical layer. The primary aim of this document is to provide a set of rules for
communication expressed in terms of the procedures to be carried out by peer data-link entities
(DLEs) at the time of communication. These rules for communication are intended to provide a
sound basis for development in order to serve a variety of purposes:
a) as a guide for implementers and designers;
b) for use in the testing and procurement of equipment;
c) as part of an agreement for the admittance of systems into the open systems environment;
d) as a refinement to the understanding of time-critical communications within OSI.
This document is concerned, in particular, with the communication and interworking of sensors,
effectors and other automation devices. By using this document together with other standard
positioned within the OSI or fieldbus reference models, otherwise incompatible systems could
work together in any combination.

– 8 – IEC 61158-4-28:2023 © IEC 2023
INDUSTRIAL COMMUNICATION NETWORKS –
FIELDBUS SPECIFICATIONS –
Part 4-28: Data-link layer protocol specification –
Type 28 elements
1 Scope
1.1 General
The data-link layer provides several types of messaging communications between devices in
an automation environment.
This part of IEC 61158 provides a means of connecting devices through a partial mesh network,
such that most failures of an interconnection between two devices can be circumvented. In
common practice, the devices are interconnected in a non-redundant hierarchical manner
reflecting application needs.
1.2 Specifications
This document specifies
a) procedures for the timely transfer of data and control information from one data-link user
entity to a peer user entity, and among the data-link entities forming the distributed data-
link service provider;
b) the structure of the fieldbus DLPDUs used for the transfer of data and control information
by the protocol of this document, and their representation as physical interface data units.
1.3 Procedures
The procedures are defined in terms of
a) the interactions between peer DL-entities (DLEs) through the exchange of the fieldbus
DLPDUs;
b) the interactions between a DL-service (DLS) provider and a DLS-user in the same system
through the exchange of DLS primitives;
c) the interactions between a DLS-provider and a Ph-service provider in the same system
through the exchange of Ph-service primitives.
1.4 Applicability
These procedures are applicable to instances of communication between systems which
support time-critical communications services within the data-link layer of the OSI or the
fieldbus reference models, and which require the ability to interconnect in an open systems
interconnection environment.
1.5 Conformance
This document also specifies conformance requirements for systems implementing these
procedures. This document does not contain tests to demonstrate compliance with such
requirements.
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 61158-2:2023, Industrial communication networks – Fieldbus specifications – Part 2:
Physical layer specification and service definition
IEC 61158-3-28:2023, Industrial communication networks – Fieldbus specifications – Part 3-28:
Data-link layer service definition – Type 28 elements
ISO/IEC 7498-1:1994, Information technology – Open Systems Interconnection – Basic
Reference Model – Basic Reference Model: The Basic Model
ISO/IEC 7498-3:1997, Information technology – Open Systems Interconnection – Basic
Reference Model: Naming and addressing
ISO/IEC 10731:1994, Information technology – Open Systems Interconnection – Basic
Reference Model – Conventions for the definition of OSI services
ISO/IEC 8886:1996, Information technology – Open Systems Interconnection – Data link
service definition
ISO/IEC/IEEE 8802-3:2021, Information technology – Telecommunications and information
exchange between systems – Local and metropolitan area networks – Specific requirements –
Part 3: Standard for Ethernet
3 Terms, definitions, symbols, abbreviated terms and conventions
For the purposes of this document, the following terms, definitions, symbols and abbreviated
terms 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
3.1 Reference model terms and definitions
This document is based in part on the concepts developed in ISO/IEC 7498-1 and
ISO/IEC 7498-3, and makes use of the following terms defined therein:
3.1.1 called-DL-address [ISO/IEC 7498-3]
3.1.2 calling-DL-address [ISO/IEC 7498-3]
3.1.3 centralized multi-end-point-connection [ISO/IEC 7498-1]
3.1.4 correspondent (N)-entities [ISO/IEC 7498-1]
correspondent DL-entities (N=2)
correspondent Ph-entities (N=1)
3.1.5 Demultiplexing [ISO/IEC 7498-1]

– 10 – IEC 61158-4-28:2023 © IEC 2023
3.1.6 DL-address [ISO/IEC 7498-3]
3.1.7 DL-address-mapping ISO/IEC 7498-1]
3.1.8 DL-connection [ISO/IEC 7498-1]
3.1.9 DL-connection-end-point [ISO/IEC 7498-1]
3.1.10 DL-connection-end-point-identifier [ISO/IEC 7498-1]
3.1.11 DL-connection-mode transmission [ISO/IEC 7498-1]
3.1.12 DL-connectionless-mode transmission [ISO/IEC 7498-1]
3.1.13 DL-data-sink [ISO/IEC 7498-1]
3.1.14 DL-data-source [ISO/IEC 7498-1]
3.1.15 DL-duplex-transmission [ISO/IEC 7498-1]
3.1.16 DL-facility [ISO/IEC 7498-1]
3.1.17 DL-local-view [ISO/IEC 7498-3]
3.1.18 DL-name [ISO/IEC 7498-3]
3.1.19 DL-protocol [ISO/IEC 7498-1]
3.1.20 DL-protocol-connection-identifier [ISO/IEC 7498-1]
3.1.21 DL-protocol-control-information [ISO/IEC 7498-1]
3.1.22 DL-protocol-data-unit [ISO/IEC 7498-1]
3.1.23 DL-protocol-version-identifier [ISO/IEC 7498-1]
3.1.24 DL-relay [ISO/IEC 7498-1]
3.1.25 DL-service-connection-identifier [ISO/IEC 7498-1]
3.1.26 DL-service-data-unit [ISO/IEC 7498-1]
3.1.27 DL-simplex-transmission [ISO/IEC 7498-1]
3.1.28 DL-subsystem [ISO/IEC 7498-1]
3.1.29 DL-user-data [ISO/IEC 7498-1]
3.1.30 flow control [ISO/IEC 7498-1]
3.1.31 layer-management [ISO/IEC 7498-1]
3.1.32 Multiplexing [ISO/IEC 7498-3]
3.1.33 naming-(addressing)-authority [ISO/IEC 7498-3]
3.1.34 naming-(addressing)-domain [ISO/IEC 7498-3]
3.1.35 naming-(addressing)-subdomain [ISO/IEC 7498-3]
3.1.36 (N)-entity [ISO/IEC 7498-1]
DL-entity
Ph-entity
3.1.37 (N)-interface-data-unit [ISO/IEC 7498-1]
DL-service-data-unit (N=2)
Ph-interface-data-unit (N=1)
3.1.38 (N)-layer [ISO/IEC 7498-1]
DL-layer (N=2)
Ph-layer (N=1)
3.1.39 (N)-service [ISO/IEC 7498-1]
DL-service (N=2)
Ph-service (N=1)
3.1.40 (N)-service-access-point [ISO/IEC 7498-1]
DL-service-access-point (N=2)
Ph-service-access-point (N=1)
3.1.41 (N)-service-access-point-address [ISO/IEC 7498-1]
DL-service-access-point-address (N=2)
Ph-service-access-point-address (N=1)
3.1.42 peer-entities [ISO/IEC 7498-1]
3.1.43 Ph-interface-control-information [ISO/IEC 7498-1]
3.1.44 Ph-interface-data [ISO/IEC 7498-1]
3.1.45 primitive name [ISO/IEC 7498-3]
3.1.46 Reassembling [ISO/IEC 7498-1]
3.1.47 Recombining [ISO/IEC 7498-1]
3.1.48 Reset [ISO/IEC 7498-1]
3.1.49 responding-DL-address [ISO/IEC 7498-3]
3.1.50 Routing [ISO/IEC 7498-1]
3.1.51 Segmenting [ISO/IEC 7498-1]
3.1.52 Sequencing [ISO/IEC 7498-1]
3.1.53 Splitting [ISO/IEC 7498-1]
3.1.54 Synonymous name [ISO/IEC 7498-3]
3.1.55 Systems-management [ISO/IEC 7498-1]
3.2 Service convention terms and definitions
This document also makes use of the following terms defined in ISO/IEC 10731 as they apply
to the data-link layer:
3.2.1 acceptor
3.2.2 asymmetrical service
3.2.3 confirm (primitive);
requestor.deliver (primitive)
3.2.4 deliver (primitive)
3.2.5 DL-confirmed-facility
3.2.6 DL-facility
3.2.7 DL-local-view
3.2.8 DL-mandatory-facility
3.2.9 DL-non-confirmed-facility
3.2.10 DL-provider-initiated-facility
3.2.11 DL-provider-optional-facility
3.2.12 DL-service-primitive;
primitive
3.2.13 DL-service-provider
3.2.14 DL-service-user
3.2.15 DLS-user-optional-facility
3.2.16 indication (primitive);
acceptor.deliver (primitive)
3.2.17 multi-peer
3.2.18 request (primitive);
requestor.submit (primitive)
3.2.19 requestor
– 12 – IEC 61158-4-28:2023 © IEC 2023
3.2.20 response (primitive);
acceptor.submit (primitive)
3.2.21 submit (primitive)
3.2.22 symmetrical service
3.3 Common terms and definitions
For the purposes of this document, the following terms and definitions apply.
NOTE Many definitions are common to more than one protocol Type; they are not necessarily used by all protocol
types.
3.3.1
DL-segment, link, local link
single DL-subnetwork in which any of the connected DLEs may communicate directly, without
any intervening DL-relaying, whenever all of those DLEs that are participating in an instance of
communication are simultaneously attentive to the DL-subnetwork during the period(s) of
attempted communication
3.3.2
DLSAP
distinctive point at which DL-services are provided by a single DL-entity to a single higher-layer
entity
Note 1 to entry: This definition, derived from ISO/IEC 7498-1, is repeated here to facilitate understanding of the
critical distinction between DLSAPs and their DL-addresses (see Figure 1).

Note 2 to entry: DLSAPs and PhSAPs are depicted as ovals spanning the boundary between two adjacent layers.
Note 3 to entry: DL-addresses are depicted as designating small gaps (points of access) in the DLL portion of a
DLSAP.
Note 4 to entry: A single DL-entity may have multiple DLSAP-addresses and group DL-addresses associated with
a single DLSAP.
Figure 1 – Relationships of DLSAPs, DLSAP-addresses and group DL-addresses

3.3.3
DL(SAP)-address
either an individual DLSAP-address, designating a single DLSAP of a single DLS user, or a
group DL-address potentially designating multiple DLSAPs where each DLSAP is from a single
DLS-user
Note 1 to entry: This terminology is chosen because ISO/IEC 7498-3 does not permit the use of the term DLSAP
address to designate more than a single DLSAP at a single DLS-user.
3.3.4
(individual) DLSAP-address
DL-address that designates only one DLSAP within the extended link
Note 1 to entry: A single DL-entity may have multiple DLSAP-addresses associated with a single DLSAP.
3.3.5
extended link
DL-subnetwork, consisting of the maximal set of links interconnected by DL-relays, sharing a
single DL-name (DL-address) space, in which any of the connected DL-entities may
communicate, one with another, either directly or with the assistance of one or more of those
intervening DL-relay entities
Note 1 to entry: An extended link may be composed of just a single link.
3.3.6
frame
denigrated synonym for DLPDU
3.3.7
group DL-address
DL-address that potentially designates more than one DLSAP within the extended link
Note 1 to entry: A single DL-entity may have multiple group DL-addresses associated with a single DLSAP. A single
DL-entity may also have a single group DL-address associated with more than one DLSAP.
3.3.8
node
single DL-entity as it appears on one local link
3.3.9
receiving DLS-user
DL-service user that acts as a recipient of DLS-user-data
Note 1 to entry: A DL-service user can be concurrently both a sending and receiving DLS-user.
3.3.10
sending DLS-user
DL-service user that acts as a source of DLS-user-data
3.4 Additional Type 28 terms and definitions
3.4.1
control device
device that controls all field devices for logical operations, timing, calculations, etc.
3.4.2
management node
device for allocating and managing Type 28 network physical communication resources

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3.4.3
terminal node
device in Type 28 network that communicates based on allocated physical communication
resources
3.4.4
clock synchronization
clock calibration of the terminal node device
3.4.5
cyclic time
time of cyclic processing of a device or module
3.4.6
RT data
data sensitive to time deterministic requirements
3.4.7
non-RT data
data insensitive to time deterministic requirements
3.4.8
orthogonal frequency division multiplexing (OFDM) symbol
minimum data transmission unit in time domain that include all subcarriers in frequency based
on OFDM technology
3.4.9
upper sideband
subcarriers with a frequency range from 16,896 MHz to 32,256 MHz on an OFDM symbol
3.4.10
lower sideband
subcarriers with a frequency range from 1,536 MHz to 16,896 MHz on an OFDM symbol
3.4.11
carrier mode
data transfer mode over available resources made up of OFDM symbols
3.4.12
working mode
OFDM operation in a specific transmission mode, RS coding, convolutional coding, and
modulation mode
3.4.13
cyclic frame
signal frames which are processed in a regular and repetitive manner
3.4.14
cyclic symbol
OFDM symbols in signal frames which are processed in a regular and repetitive manner
3.4.15
code block
octet sequence of data interaction between the Type 28 physical layer entity and the Type 28
data-link layer entity
3.4.16
data transmission channel
logical channel of the Type 28 data-link layer mapped by the determined physical
communication resource for transmitting data-link layer data frames
3.4.17
BITMAP
bitmap format type including Width and Mask_Info information and the length range from
2 octets to 256 octets
Note 1 to entry: See Figure 2.
Note 2 to entry: Width has 1octet, its value indicates the number of the octets of Mask_Info.
Note 3 to entry: Mask_Info represented by bit. The octet length is Width value and the bit length is Width × 8.

Figure 2 – Bitmap data type diagram
3.5 Additional Type 28 symbols and abbreviations
AL Application layer
C/S Client/Server
CLMDTA Connection-less Mode Data Transmission with Acknowledge
CLMDTNA Connection-less Mode Data Transmission with No Acknowledge
CLMDTRA Connection-less Mode Data Transmission with Request and Acknowledge
CLMDTRRNA Connection-less Mode Data Transmission with Request and Response but No
Acknowledge
CMDTA Connection Mode Data Transmission with Acknowledge
CMDTNA Connection Mode Data Transmission with No Acknowledge
DL- Data-link layer (as a prefix)
DLCSS Data-link clock synchronization service
DLDE Data-link data entity
DLE Data-link entity
DLL Data-link layer
DLM Data-link management
DLME Data-link management entity
DLMS Data-link management service
DLMS-user Data-link management service user
DLS Data-link service
DLP Data-link protocol
DLS-user Data-link service user
DTC Data transmission channel
DTS Data transmission service

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DLSDU Data-link service data unit
DLPDU Data-link protocol data unit
MAC Medium access control
MN Management node
NodeID Node identifier
nRT non-Real-Time
OFDM Orthogonal Frequency Division Multiplexing
PhL Physical layer
PhL- Physical layer (as a prefix)
RT Real-Time
RTA Real-Time acyclic
RTC Real-Time cyclic
SAP Service access point
TM Transmit mode
TN Terminal node
4 Overview of the DL-protocol
4.1 DLL protocol architecture
Figure 3 illustrates the position of DLL on the protocol stack architecture of the Type 28.

Figure 3 – DLL in Type 28 protocol stack architecture
Type 28 data-link service (DLS) is provided by the Type 28 data-link protocol (DLP) making use
of the services available from the Type 28 physical layer (PhL). The DLS characteristics and
function defined in this document should be exploited by the higher-level protocol. Type 28 DLL

provides data-link management service (DLMS) for system management. The relationship
between the standards for the fieldbus DLS, the fieldbus DLP, the fieldbus application protocol
and systems management are illustrated in Figure 4.

Figure 4 – Relationship of the fieldbus DLL to other fieldbus
layers and to users of the fieldbus DLS
The services provided by Type 28 DLL to upper users include DLS, DLMS and data-link clock
synchronization service (DLCSS). Data-link layer entity (DLE) includes data-link clock entity
(DLCE), data-link data entity (DLDE) and data-link management entity (DLME). Based on the
communication resource allocation scheme for PhL provided by the Type 28 DLMS, DLS
provides data transmission service with different RT levels through connection and connection-
less service. Figure 5 shows the Type 28 DLL protocol architecture.

Figure 5 – Type 28 DLL protocol architecture diagram
DLS: DLS exploits data transmission channel (DTC) established based on PhL OFDM symbol
resources to implement the encapsulation and transmission for application data or protocol data.
After the state machine of Type 28 DLS is started, DLS provides the connection and the
connection-less data transmission service based on DLDE for different RT requirements
through different DTCs. These channels should be pre-configured and allocated on demand.

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DLMS: DLMS provides system management service, including node joining, node leaving,
configuration of network parameters, and establishment, update and release of DTCs, etc. Type
28 DLL configures DLME through DLMS, and then implements the encapsulation and parsing
of DLPDU including ISO/IEC/IEEE 8802-3 Ethernet DLPDU in DLDE and the corresponding
service function subsets to form the Type 28 mac sublayer as shown in Figure 3.
DLCSS: DLCSS provides the clock synchronization service based on the PhL service access
point (PhL-SAP), defining delay measurement, clock synchronization and clock interrupt
services.
4.2 DLL working mechanism
4.2.1 Node
Type 28 network contains at least one management node (MN) and 0 to 253 terminal nodes
(TN). Only one active MN is allowed in the network. The MN should configure all available nodes
in the network and manage node access to the network. The TN works normally after it is
authorised by MN. The TN sends the data after the MN confirms the available DTC resources
...