IEC 61158-4-4:2014

IEC 61158-4-4 ®
Edition 2.0 2014-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Industrial communication networks – Fieldbus specifications –
Part 4-4: Data-link layer protocol specification – Type 4 elements

Réseaux de communication industriels – Spécifications des bus de terrain –
Partie 4-4: Spécification du protocole de la couche liaison de données –
Eléments de type 4
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IEC 61158-4-4 ®
Edition 2.0 2014-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Industrial communication networks – Fieldbus specifications –

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

Réseaux de communication industriels – Spécifications des bus de terrain –

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

Eléments de type 4
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX X
ICS 25.040.40; 35.100.20; 35.110 ISBN 978-2-8322-1722-1

– 2 – IEC 61158-4-4:2014 © IEC 2014

CONTENTS
FOREWORD . 4

INTRODUCTION . 6

1 Scope . 7

1.1 General . 7

1.2 Specifications . 7

1.3 Procedures . 7

1.4 Applicability . 7

1.5 Conformance . 7
2 Normative references . 8
3 Terms, definitions, symbols and abbreviations . 8
3.1 Reference model terms and definitions . 8
3.2 Service convention terms and definitions . 10
3.3 Terms and definitions . 11
3.4 Symbols and abbreviations . 14
4 Data Link Protocol Definition . 14
4.1 Overview of the DL-protocol . 14
4.2 General structure and encoding of PhIDUs and DLPDUs, and related
elements of procedure . 26
4.3 DLPDU-specific structure, encoding and elements of procedure . 33
4.4 DL-service elements of procedure . 37
4.5 Route mechanism . 40
4.6 Link-access system . 43
4.7 Local variables, counters and queues . 44
Bibliography . 46

Figure 1 – Relationship of PhE, DLE and DLS-user . 15
Figure 2 – DLE state diagram for confirmed and unconfirmed, unacknowledged
DLPDUs . 17
Figure 3 – DLE state diagram for confirmed acknowledged DLPDUs . 18
Figure 4 – DLE state diagram for unconfirmed acknowledged DLPDUs . 19
Figure 5 – Full duplex DLE receive state diagram . 20

Figure 6 – Full duplex DLE transmit state diagram . 20
Figure 7 – Link access example . 23
Figure 8 – Simple Type 4-route format . 29
Figure 9 – Extended Type 4-route format . 29
Figure 10 – Complex Type 4-route format . 30
Figure 11 – Immediate Type 4-route format . 30
Figure 12 – IP Type 4-route format . 31
Figure 13 – Control-status format. 32
Figure 14 – Data-field-format . 32
Figure 15 – Source / destination designator . 41
Figure 16 – Simple Type 4-route generation . 41
Figure 17 – Extended Type 4-route generation . 41
Figure 18 – Complex and IP Type 4-route generation . 42

Figure 19 – Simple DL-route generation . 42

Figure 20 – Extended DL-route generation . 43

Figure 21 – Complex and IP DL-route generation . 43

Table 1 – Summary structure of DLPDUs . 33

Table 2 – Structure of confirmed DLPDUs . 34

Table 3 – Structure of unconfirmed DLPDUs . 35

Table 4 – Structure of acknowledge DLPDU . 36

Table 5 – Structure of immediate-reply DLPDU . 36

– 4 – IEC 61158-4-4:2014 © IEC 2014

INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
INDUSTRIAL COMMUNICATION NETWORKS –

FIELDBUS SPECIFICATIONS –
Part 4-4: Data-link layer protocol specification –

Type 4 elements
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
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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
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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
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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 the associated protocol type is restricted by its
intellectual-property-right holders. In all cases, the commitment to limited release of
intellectual-property-rights made by the holders of those rights permits a layer protocol type to
be used with other layer protocols of the same type, or in other type combinations explicitly
authorized by its intellectual-property-right holders.
NOTE Combinations of protocol types are specified in IEC 61784-1 and IEC 61784-2.
International Standard IEC 61158-4-4 has been prepared by subcommittee 65C: Industrial
networks, of IEC technical committee 65: Industrial-process measurement, control and
automation.
This second edition cancels and replaces the first edition published in 2007. This edition
constitutes an editorial revision with only minor editorial changes.

This edition includes the following significant changes with respect to the previous edition:

a) editorial improvements;
b) editorial corrections.
The text of this standard is based on the following documents:

FDIS Report on voting
65C/762/FDIS 65C/772/RVD
Full information on the voting for the approval of this standard can be found in the report on

voting indicated in the above table.
This publication has been drafted in accordance with ISO/IEC Directives, Part 2.
A list of all the parts of the IEC 61158 series, under the general title Industrial communication
networks – Fieldbus specifications, can be found on the IEC web site.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under http://webstore.iec.ch in the data related
to the specific publication. At this date, the publication will be:
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
– 6 – IEC 61158-4-4:2014 © IEC 2014

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 standard is to provide a set of rules for

communication expressed in terms of the procedures to be carried out by peer data-link

entities (DLEs) at the time of communication. These rules for communication are intended to

provide a sound basis for development in order to serve a variety of purposes:

a) as a guide for implementors and designers;
b) for use in the testing and procurement of equipment;
c) as part of an agreement for the admittance of systems into the open systems environment;
d) as a refinement to the understanding of time-critical communications within OSI.
This standard is concerned, in particular, with the communication and interworking of sensors,
effectors and other automation devices. By using this standard together with other standards
positioned within the OSI or fieldbus reference models, otherwise incompatible systems may
work together in any combination.

INDUSTRIAL COMMUNICATION NETWORKS –

FIELDBUS SPECIFICATIONS –
Part 4-4: Data-link layer protocol specification –

Type 4 elements
1 Scope
1.1 General
The data-link layer provides basic time-critical messaging communications between devices in
an automation environment.
This protocol provides a means of connecting devices through a partial mesh network, such
that most failures of an interconnection between two devices can be circumvented. In
common practice the devices are interconnected in a non-redundant hierarchical manner
reflecting application needs
1.2 Specifications
This standard 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 standard, and their representation as physical interface data units.
1.3 Procedures
The procedures are defined in terms of
a) the interactions between peer DL-entities (DLEs) through the exchange of fieldbus
DLPDUs;
b) the interactions between a DL-service (DLS) provider and a DLS-user in the same system
through the exchange of DLS primitives;
c) the interactions between a DLS-provider and a Ph-service provider in the same system
through the exchange of Ph-service primitives.

1.4 Applicability
These procedures are applicable to instances of communication between systems which
support time-critical communications services within the data-link layer of the OSI or fieldbus
reference models, and which require the ability to interconnect in an open systems
interconnection environment.
Profiles provide a simple multi-attribute means of summarizing an implementation’s
capabilities, and thus its applicability to various time-critical communications needs.
1.5 Conformance
This standard also specifies conformance requirements for systems implementing these
procedures. This standard does not contain tests to demonstrate compliance with such
requirements.
– 8 – IEC 61158-4-4:2014 © IEC 2014

2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and

are indispensable for its application. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any

amendments) applies.
NOTE All parts of the IEC 61158 series, as well as IEC 61784-1 and IEC 61784-2 are maintained simultaneously.

Cross-references to these documents within the text therefore refer to the editions as dated in this list of normative
references.
ISO/IEC 7498-1, Information technology – Open Systems Interconnection – Basic Reference
Model: The Basic Model
ISO/IEC 7498-3, Information technology – Open Systems Interconnection – Basic Reference
Model: Naming and addressing
ISO/IEC 10731, Information technology – Open Systems Interconnection – Basic Reference
Model – Conventions for the definition of OSI services
3 Terms, definitions, symbols and abbreviations
For the purposes of this document, the following terms, definitions, symbols and abbreviations
apply.
3.1 Reference model terms and definitions
This standard is based in part on the concepts developed in ISO/IEC 7498-1 and
ISO/IEC 7498-3, and makes use of the following terms defined therein.
3.1.1 called-DL-address [7498-3]
3.1.2 calling-DL-address [7498-3]
3.1.3 centralized multi-end-point-connection [7498-1]
3.1.4 correspondent (N)-entities [7498-1]
correspondent DL-entities  (N=2)
correspondent Ph-entities  (N=1)
3.1.5 demultiplexing [7498-1]
3.1.6 DL-address [7498-3]
3.1.7 DL-address-mapping [7498-1]
3.1.8 DL-connection [7498-1]
3.1.9 DL-connection-end-point [7498-1]
3.1.10 DL-connection-end-point-identifier [7498-1]
3.1.11 DL-connection-mode transmission [7498-1]
3.1.12 DL-connectionless-mode transmission [7498-1]
3.1.13 DL-data-sink [7498-1]
3.1.14 DL-data-source [7498-1]

3.1.15 DL-duplex-transmission [7498-1]

3.1.16 DL-facility [7498-1]
3.1.17 DL-local-view [7498-3]
3.1.18 DL-name [7498-3]
3.1.19 DL-protocol [7498-1]
3.1.20 DL-protocol-connection-identifier [7498-1]

3.1.21 DL-protocol-control-information [7498-1]
3.1.22 DL-protocol-data-unit [7498-1]
3.1.23 DL-protocol-version-identifier [7498-1]
3.1.24 DL-relay [7498-1]
3.1.25 DL-service-connection-identifier [7498-1]
3.1.26 DL-service-data-unit [7498-1]
3.1.27 DL-simplex-transmission [7498-1]
3.1.28 DL-subsystem [7498-1]
3.1.29 DL-user-data [7498-1]
3.1.30 flow control [7498-1]
3.1.31 layer-management [7498-1]
3.1.32 multiplexing [7498-3]
3.1.33 naming-(addressing)-authority [7498-3]
3.1.34 naming-(addressing)-domain [7498-3]
3.1.35 naming-(addressing)-subdomain [7498-3]
3.1.36 (N)-entity [7498-1]
DL-entity
Ph-entity
3.1.37 (N)-interface-data-unit [7498-1]
DL-service-data-unit  (N=2)
Ph-interface-data-unit  (N=1)
3.1.38 (N)-layer
[7498-1]
DL-layer  (N=2)
Ph-layer  (N=1)
3.1.39 (N)-service [7498-1]
DL-service  (N=2)
Ph-service  (N=1)
3.1.40 (N)-service-access-point [7498-1]
DL-service-access-point  (N=2)
Ph-service-access-point  (N=1)

– 10 – IEC 61158-4-4:2014 © IEC 2014

3.1.41 (N)-service-access-point-address [7498-1]
DL-service-access-point-address  (N=2)

Ph-service-access-point-address  (N=1)

3.1.42 peer-entities [7498-1]
3.1.43 Ph-interface-control-information [7498-1]

3.1.44 Ph-interface-data [7498-1]

3.1.45 primitive name [7498-3]

3.1.46 reassembling [7498-1]
3.1.47 recombining [7498-1]
3.1.48 reset [7498-1]
3.1.49 responding-DL-address [7498-3]
3.1.50 routing [7498-1]
3.1.51 segmenting [7498-1]
3.1.52 sequencing [7498-1]
3.1.53 splitting [7498-1]
3.1.54 synonymous name [7498-3]
3.1.55 systems-management [7498-1]
3.2 Service convention terms and definitions
This standard also makes use of the following terms defined in ISO/IEC 10731 as they apply
to the data-link layer:
3.2.1 acceptor
3.2.2 asymmetrical service
3.2.3 confirm (primitive);
requestor.deliver (primitive)
3.2.4 deliver (primitive)
3.2.5 DL-confirmed-facility
3.2.6 DL-facility
3.2.7 DL-local-view
3.2.8 DL-mandatory-facility
3.2.9 DL-non-confirmed-facility
3.2.10 DL-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 DL-user-optional-facility

3.2.16 indication (primitive)
acceptor.deliver (primitive)
3.2.17 multi-peer
3.2.18 request (primitive);
requestor.submit (primitive)
3.2.19 requestor
3.2.20 response (primitive);
acceptor.submit (primitive)
3.2.21 submit (primitive)
3.2.22 symmetrical service
3.3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.3.1
broadcast-Node-address
address used to send broadcasts to all DLEs on a Link
Note 1 to entry:  All DLEs on a Link receive all DLPDUs where the first Node-address is equal to the Broadcast-
Node-Address. Such DLPDUs are always Unconfirmed, and their receipt is never acknowledged. The value of a
Broadcast-Node-address is 126.
3.3.2
destination-DL-route
holds a sequence of DL-route-elements, describing the complete route to the destination
Note 1 to entry:  This includes both the destination DLSAP and a local component meaningful to the destination
DLS-user.
3.3.3
DL-route
combination of a Destination-DL-route and a Source-DL-route
3.3.4
DL-route-element
octet holding a Node-address or an address used by the DLS-user
3.3.5
DLSAP
distinctive point at which DL-services are provided by a single DL-entity to a single higher-
layer entity.
Note 1 to entry:  This definition, derived from ISO/IEC 7498-1, is repeated here to facilitate understanding of the
critical distinction between DLSAPs and their DL-addresses.
3.3.6
DL(SAP)-address
an individual DLSAP-address, designating a single DLSAP of a single DLS-user
3.3.7
(individual) DLSAP-address
DL-address that designates only one DLSAP within the extended link

– 12 – IEC 61158-4-4:2014 © IEC 2014

Note 1 to entry:  A single DL-entity may have multiple DLSAP-addresses associated with a single DLSAP.

3.3.8
frame
denigrated synonym for DLPDU
3.3.9
IPNetID
identification of a unique IP network

Note 1 to entry:  An IPNetID is translated into an IP-address and a UPD port number.

3.3.10
IPNetTable
definition of the relation between IPNetID, IP address, UPD port number and Router
NodeAddress, where IPNetID is used as index in the table
3.3.11
IP Range net
defines use for local access, where nodes can be accessed directly on the same subnet as
the client, or through a local Router where the subnets are configured in the local Router
3.3.12
Local link
single DL-subnetwork in which any of the connected DLEs may communicate directly, without
any intervening DL-relaying, whenever all of those DLEs that are participating in an instance
of communication are simultaneously attentive to the DL-subnetwork during the period(s) of
attempted communication
3.3.13
no-Confirm-Node-address
address used to indicate that a request or response is Unconfirmed
Note 1 to entry:  The value of a No-Confirm-Node-address is 0.
3.3.14
node
single DL-entity as it appears on one local link
3.3.15
node-address
address which uniquely identifies a DLE on a Link

Note 1 to entry:  The value of a Node-address can be in the range of 0 to 127, with the values 0, 126 and 127
reserved for special purposes.
3.3.16
normal class device
device which replies to requests from other normal class devices, and initiates transmissions
Note 1 to entry:  Such a device can act as a server (responder) and as a client (requestor) - this is also called a
peer.
3.3.17
Type 4-route
holds a sequence of Type 4-route-elements
Note 1 to entry:  A Type 4-route is defined as an encoded DL-route, with one of the formats used when
transmitting the DLPDU on the Link. The Type 4-route format can be Simple, Extended, Complex, Immediate or IP.

3.3.18
Type 4-route-element
octet, holding a 7-bit DL-route-element or Remaining-route-length, and a 1-bit source/

destination designator
3.3.19
receiving DLS-user
DL-service user that acts as a recipient of DL-user-data

Note 1 to entry:  A DL-service user can be concurrently both a sending and receiving DLS-user.

3.3.20
sending DLS-user
DL-service user that acts as a source of DL-user-data
3.3.21
service-Node-address
address reserved for service purposes only
Note 1 to entry:  All DLEs on a Link receive all DLPDUs where the first Node-address is equal to the Service-
Node-Address. Such DLPDUs can be Confirmed or Unconfirmed, and their receipt may or may not be
acknowledged. The Service-Node-Address can be used on Links with only two DLEs - the requesting Normal class
DLE and the responding Simple or Normal class DLE. The value of the Service-Node-Address is 127.
3.3.22
simple class device
device which replies to requests from normal class devices, and can act as a server or
responder only
3.3.23
source-DL-route
holds a sequence of DL-route-elements, describing the complete route back to the source
3.3.24
UDP port number
port number from where a Server can receive requests
Note 1 to entry:  The UDP port number is 34378 for Normal UDP port. The UDP port number is 34379 for Secure
UDP port.
Note 2 to entry:  These UDP port numbers are registered with the IANA (Internet Assigned Numbers Authority).
Note 3 to entry:  The re are two different UPD port numbers: Normal UDP port and Secure UDP port.

3.3.25
UDP range net
defines use for remote access, where a node cannot be accessed directly on the same subnet
as the client
Note 1 to entry:  The IPNetTable holds a NAT Router IP address and access to the node is obtained through this
NAT Router.
Note 2 to entry:  The NAT Router shall hold a table that translates the UDP port number to the actual server node
IP address and UDP port number.
3.3.26
Virtual link-access token
basis for the link-access system
Note 1 to entry:  It is called virtual because the token is not explicitly sent from one normal-class DLE to another,
but implicitly passed as the link is idle.

– 14 – IEC 61158-4-4:2014 © IEC 2014

3.4 Symbols and abbreviations
3.4.1 Constants, variables, counters and queues

3.4.1.1 BNA broadcast node address

3.4.1.2 C(LAC) link access counter

3.4.1.3 C(LIC) link idle counter

3.4.1.4 SNA service node address

3.4.1.5 NCNA no confirm node address

3.4.1.6 Q(UR) user request queue
3.4.1.7 V(ACPDU) acknowledge confirmed PDU
3.4.1.8 V(AUPDU) acknowledge unconfirmed PDU
3.4.1.9 V(BR) bit rate
3.4.1.10 V(DC) device class (simple or normal)
3.4.1.11 V(DMRT) default max retry time
3.4.1.12 V(MID) max indication delay
3.4.1.13 V(NA) node address
3.4.1.14 V(NDLE) number of DLEs
3.4.1.15 V(PNR) permitted number of retries
3.4.1.16 IPNetTable Table to convert IPNetID to IP-addresses
3.4.2 Miscellaneous
3.4.2.1 RCL/ACK response comes later / acknowledge
4 Data Link Protocol Definition
4.1 Overview of the DL-protocol
The DLL provides connectionless data transfer services for limited-size DLSDUs from one
DLS-user to one or more (broadcast) DLS-users.

A DLE is implicitly connected to one PhE and to a single DLSAP. This means, that when a
local DLS-user issues a service primitive at a certain DLSAP, the DLE and hence the Link is
implicitly selected.
A DLE always delivers received DLSDUs at the same DLSAP, and hence to the same DLS-
user.
This concept is illustrated in Figure 1.

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

– 16 – IEC 61158-4-4:2014 © IEC 2014

c) Convert a DLS-user request primitive to a DLPDU, queue it, and send it to a remote DLE

(or all DLEs at the Link if broadcast) at the first opportunity. Possibly wait for an

Acknowledge or Immediate-reply DLPDU from the remote DLE, and (if an Immediate-reply

DLPDU is received) generate a DLS-user indication primitive.

d) Receive an SPDU, and use the associated data to check or gain Link-access

synchronization.
e) Receive a single PhIDU specifying LINK-IDLE, use that to keep Link-access synchronized,

and possibly to initiate sending a DLPDU from the queue if the queue is not empty, or if

the queue is empty, to send an SPDU for Link-access synchronization.

These functions are illustrated in Figure 2 to Figure 4.

4.1.2.1 Acknowledged vs. confirmed
The terms acknowledged and unacknowledged are used to describe whether the receiving
DLE must acknowledge the receipt of a DLPDU or not. The terms confirmed and unconfirmed
are used to describe whether the receiving DLS-user must confirm the receipt of a DLSDU or
not.
The variable V(ACPDU) - Acknowledge Confirmed PDU - defines, whether the DLE must
acknowledge the receipt of Confirmed DLPDUs. The variable V(AUPDU) - Acknowledge
Unconfirmed PDU - defines, whether the DLE must acknowledge the receipt of Unconfirmed
DLPDUs.
A special case is when the first Node-address in a received DLPDU is equal to the Broadcast-
Node-address (BNA). In this case, the receiving DLE shall never acknowledge the receipt of
the DLPDU.
4.1.2.2 Half-duplex and full duplex
Unless otherwise stated, the PhL is assumed to support half-duplex transfer. However, a PhL
supporting full duplex is allowed.
Full duplex systems allow up to 125 DLEs on a Link, all of Normal class. Each DLE is allowed
to transmit immediately, that is, there is no Link Access system. DLEs supporting full duplex
PhEs have separate state machines for receive and transmit, as illustrated in Figure 5 and
Figure 6.
In full duplex systems, Confirmed as well as Unconfirmed DLPDUs are unacknowledged.
PhLs supporting full duplex shall not provide Link-Idle indications.

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

– 18 – IEC 61158-4-4:2014 © IEC 2014

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

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

– 20 – IEC 61158-4-4:2014 © IEC 2014

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

c) Acknowledge - used by DLEs to acknowledge receipt of Confirmed or Unconfirmed

DLPDUs. The receipt of Acknowledge DLPDUs must never be acknowledged.

d) Immediate-reply - used to send responses between DLS-users. The receipt of Immediate-

reply DLPDUs must never be acknowledged.

4.1.2.4 SPDU types
Only one type of SPDU (Support Protocol Data Unit) is defined.

a) Sync - used to send Link access synchronization information between DLEs. An SPDU

holds the Node-address of the DLE holding the Virtual Link-access token. An SPDU can

be "stand-alone" or part of an Acknowledge or Immediate-reply DLPDU.

4.1.2.5 Responder role, receiving a DLPDU from the PhE
This action includes a sequence of steps, as described in the following.
a) Receive a single PhIDU specifying START-OF-ACTIVITY. This PhIDU holds a Node address.
This address is examined to determine, whether its value is equal to the Node-address of
this DLE, or equal to the Broadcast-Node-address (BNA) or the Service-Node-Address
(SNA). If not, ignore this sequence and wait for the next PhIDU specifying START-OF-
ACTIVITY.
b) Receive a sequence of PhIDUs from the PhE, specifying DATA, concatenate them to a
received DLPDU, compute a frame check sequence over the entire sequence of received
data as specified by the value of V(FCM) - FrameCheckMethod, and, if necessary, check
for the proper value. If the value is not correct, ignore the DLPDU and wait for the next
PhIDU specifying START-OF-ACTIVITY.
c) Convert the received DLPDU into its DL-protocol control information and data
components.
d) Generate a DLS-user indication primitive.
e) If the DLPDU received from the remote DLE is of type Confirmed, and the receipt of the
DLPDU must be acknowledged, according to the rules described in 4.1.2.1, wait for a
request or response primitive from the local DLS-user.
If no request or response primitive is issued from the local DLS-user in time (before a
PhIDU specifying "LINK-IDLE for 30 bit periods" is received from the PhE), generate and
immediately send an Acknowledge DLPDU. This DLPDU must specify "Wait" if this DLE is
of Simple class, and "Response Comes Later / Acknowledge" ("RCL/ACK") if this DLE is of
Normal class.
If a response primitive is issued from the local DLS-user in time, generate and
immediately send an Acknowledge DLPDU, specifying "Wait" if this DLE is of Simple
class, and "RCL/ACK" if this DLE is of Normal class.
If a request primitive is issued from the local DLS-user in time, convert it into an
Immediate-reply DLPDU and send it immediately. After sending, wait for the next PhIDU
specifying START-OF-ACTIVITY.
f) If the DLPDU received from the remote DLE is of the Confirmed type, and the receipt of
the DLPDU shall not be acknowledged, wait for the next PhIDU specifying START-OF-
ACTIVITY.
g) If the DLPDU received from the remote DLE is of the Unconfirmed type, and the receipt of
the DLPDU shall be acknowledged, according to the rules described in 4.1.2.1, generate
and immediately send an Acknowledge DLPDU, specifying RCL/ACK. After sending, wait
for the next PhIDU specifying START-OF-ACT
...