IEC 61158-6-21:2010

IEC 61158-6-21 ®
Edition 1.0 2010-08
INTERNATIONAL
STANDARD
Industrial communication networks – Fieldbus specifications –
Part 6-21: Application layer protocol specification – Type 21 elements

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IEC 61158-6-21 ®
Edition 1.0 2010-08
INTERNATIONAL
STANDARD
Industrial communication networks – Fieldbus specifications –
Part 6-21: Application layer protocol specification – Type 21 elements

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
XA
ICS 25.04.40; 35.100.70; 35.110 ISBN 978-2-88912-135-9
– 2 – 61158-6-21 © IEC:2010(E)

CONTENTS
FOREWORD.5

INTRODUCTION.7

1 Scope.8

1.1 General .8

1.2 Overview .8

1.3 Specifications.9

1.4 Conformance.9

2 Normative references .9
3 Terms, definitions, symbols, abbreviations, and conventions .10
3.1 Terms and definitions from other ISO/IEC standards .10
3.2 Other terms and definitions .10
3.3 Abbreviations and symbols.16
3.4 Conventions .17
4 FAL syntax description .19
4.1 General .19
4.2 FAL-AR PDU abstract syntax .19
4.3 Abstract syntax of PDU body.20
4.4 Protocol data units (PDUs) for application service elements (ASEs) .21
5 Transfer Syntax .24
5.1 Overview of encoding .24
5.2 APDU header encoding .25
5.3 APDU body encoding .26
5.4 Encoding of Data types .26
6 FAL protocol state machines .30
7 AP context state machine .32
8 FAL service protocol machine.32
8.1 General .32
8.2 Common parameters of the primitives .32
8.3 AP ASE protocol machine .32
8.4 Service data object ASE protocol machine (SDOM).36
8.5 Process data object ASE protocol machine (PDOM) .40
9 AR protocol machine .41

9.1 General .41
9.2 Point-to-point user-triggered confirmed client/server AREP (PTC-AR) ARPM .42
9.3 Multipoint network-scheduled unconfirmed publisher/subscriber AREP
(MSU-AR) ARPM.44
9.4 Multipoint user-triggered unconfirmed publisher/subscriber AREP (MTU-AR)
ARPM.47
10 DLL mapping protocol machine .49
10.1 Primitive definitions .49
10.2 DMPM state machine .50
Bibliography.51

Figure 1 – Common structure of specific fields.17
Figure 2 – APDU overview .25

61158-6-21 © IEC:2010(E) – 3 –

Figure 3 – Type field.25

Figure 4 – Encoding of Time of Day value.29

Figure 5 – Encoding of Time Difference value.30

Figure 6 – Primitives exchanged between protocol machines.31

Figure 7 – State transition diagram of APAM.34

Figure 8 – State transition diagram of SDOM .37

Figure 9 – State transition diagram of PDOM .40

Figure 10 – State transition diagram of PTC-ARPM .43

Figure 11 – State transition diagram of MSU-ARPM.46
Figure 12 – State transition diagram of MTU-ARPM .48
Figure 13 – State transition diagram of DMPM .50

Table 1 – Conventions used for AE state machine definitions .18
Table 2 – Status code for the confirmed response primitive .21
Table 3 – Encoding of FalArHeader field.25
Table 4 – Transfer Syntax for bit sequences .26
Table 5 – Transfer syntax for data type UNSIGNEDn.27
Table 6 – Transfer syntax for data type INTEGERn.28
Table 7 – Primitives exchanged between FAL-user and APAM.33
Table 8 – Parameters used with primitives exchanged FAL-user and APAM .34
Table 9 – APAM state table – Sender transitions .34
Table 10 – APAM state table – Receiver transitions .35
Table 11 – Functions used by the APAM.35
Table 12 – Primitives exchanged between FAL-user and SDOM .36
Table 13 – Parameters used with primitives exchanged FAL-user and SDOM .37
Table 14 – SDOM state table – Sender transitions .38
Table 15 – SDOM state table – Receiver transitions .39
Table 16 – Functions used by the SDOM .39
Table 17 – Primitives exchanged between FAL-user and PDOM .40
Table 18 – Parameters used with primitives exchanged between FAL-user and PDOM .40
Table 19 – PDOM state table – Sender transitions .41

Table 20 – PDOM state table – Receiver transitions .41
Table 21 – Functions used by the SDOM .41
Table 22 – Primitives issued by user to PTC-ARPM .42
Table 23 – Primitives issued by PTC-ARPM to user .42
Table 24 – PTC-ARPM state table – sender transactions .43
Table 25 – PTC-ARPM state table – receiver transactions .44
Table 26 – Function BuildFAL-PDU.44
Table 27 – Primitives issued by user to ARPM .44
Table 28 – Primitives issued by ARPM to user .44
Table 29 – MSU-ARPM state table – sender transactions .46
Table 30 – MSU-ARPM state table – receiver transactions .46
Table 31 – Function BuildFAL-PDU.46

– 4 – 61158-6-21 © IEC:2010(E)

Table 32 – Primitives issued by user to ARPM .47

Table 33 – Primitives issued by ARPM to user .47

Table 34 – MTU-ARPM state table – sender transactions .48

Table 35 – MTU-ARPM state table – receiver transactions.48

Table 36 – Function BuildFAL-PDU.49

Table 37 – Primitives issued by ARPM to DMPM .49

Table 38 – Primitives issued by DMPM to ARPM .49

Table 39 – Primitives issued by DMPM to DLL .49

Table 40 – Primitives issued by DLL to DMPM .49
Table 41 – DMPM state table – sender transactions .50
Table 42 – DMPM state table – receiver transactions.50

61158-6-21 © IEC:2010(E) – 5 –

INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
INDUSTRIAL COMMUNICATION NETWORKS –

FIELDBUS SPECIFICATIONS –
Part 6-21: Application layer protocol specification –

Type 21 elements
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
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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.
NOTE 1 Use of some of the associated protocol types is restricted by their intellectual-property-right holders. In
all cases, the commitment to limited release of intellectual-property-rights made by the holders of those rights
permits a particular data-link layer protocol type to be used with physical layer and application layer protocols in
type combinations as specified explicitly in the IEC 61784 series. Use of the various protocol types in other
combinations may require permission of their respective intellectual-property-right holders.
International Standard IEC 61158-6-21 has been prepared by subcommittee 65C: Industrial
networks, of IEC technical committee 65: Industrial-process measurement, control and
automation.
This standard cancels and replaces IEC/PAS 62573 published in 2008. This first edition
constitutes a technical revision

– 6 – 61158-6-21 © IEC:2010(E)

The text of this standard is based on the following documents:

FDIS Report on voting
65C/607/FDIS 65C/621/RVD
Full information on the voting for the approval of this standard can be found in the report on

voting indicated in the above table.

This publication has been drafted in accordance with ISO/IEC Directives, Part 2.

A list of all parts of the IEC 61158 series, published under the general title Industrial
communication networks – Fieldbus specifications, can be found on the IEC web site.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be:
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
NOTE 2 The revision of this standard will be synchronized with the other parts of the IEC 61158 series.

61158-6-21 © IEC:2010(E) – 7 –

INTRODUCTION
This part of IEC 61158 is one of a series produced to facilitate the interconnection of

automation system components. It is related to other standards in the set as defined by the

“three-layer” fieldbus reference model described in IEC/TR 61158–1.

The application protocol provides the application service by making use of the services

available from the data-link or other immediately lower 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 application entities (AEs) 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:
• as a guide for implementers and designers;
• for use in the testing and procurement of equipment;
• as part of an agreement for the admission of systems into the open systems environment;
• 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.

– 8 – 61158-6-21 © IEC:2010(E)

INDUSTRIAL COMMUNICATION NETWORKS –

FIELDBUS SPECIFICATIONS –
Part 6-21: Application layer protocol specification –

Type 21 elements
1 Scope
1.1 General
This standard is one of a series produced to facilitate the interconnection of automation
system components. It is related to other standards in the set as defined by the three-layer
fieldbus reference model described in IEC/TR 61158-1:2010.
This standard contains material specific to the Type 21 communication protocol.
1.2 Overview
The Fieldbus Application Layer (FAL) provides user programs with a means to access the
fieldbus communication environment. In this respect, the FAL can be viewed as a window
between corresponding application programs.
This standard provides common elements for basic time-critical and non-time-critical
messaging communications between application programs in an automation environment, as
well as material specific to Type 21. The term “time-critical” is used to represent the presence
of a time-window, within which one or more specified actions must to be completed with some
defined level of certainty. Failure to complete specified actions within the required time risks
the failure of the applications requesting the actions, with attendant risk to equipment, plant,
and possibly human life.
This standard defines interactions between remote applications. It also defines the externally
visible behavior provided by the Type 21 application layer in terms of:
a) the formal abstract syntax defining the application layer protocol data units (APDUs)
conveyed between communicating application entities;
b) the transfer syntax defining encoding rules that are applied to the APDUs;
c) the application context state machine defining the application service behavior visible
between communicating application entities;
d) the application relationship state machines defining the communication behavior
visible between communicating application entities.
The purpose of this standard is to:
a) describe the wire-representation of the service primitives defined in
IEC 61158-5-21:2010;
b) describe the externally visible behavior associated with their transfer.
This standard defines the protocol of the Type 21 application layer in conformance with the
OSI Basic Reference Model (ISO/IEC 7498) and the OSI application layer structure
(ISO/IEC 9545).
61158-6-21 © IEC:2010(E) – 9 –

1.3 Specifications
The principal objective of this standard is to specify the syntax and behavior of the application

layer protocol that conveys the Type 21 application layer services.

A secondary objective is to provide migration paths from previously existing industrial

communications protocols.
1.4 Conformance
This standard does not restrict individual implementations or products, nor does it constrain
the implementations of application layer entities in industrial automation systems.

Conformance is achieved through implementation of this application layer protocol
specification.
2 Normative references
The following referenced documents are essential for the application of this document. For
dated references, only the cited edition applies. For undated references, the latest edition of
the document (including any amendments) applies,.
IEC 61158-3-21:2010 , Industrial communication networks – Fieldbus specifications –
Part 3-21: Data-link layer service definition – Type 21 elements
IEC 61158-4-21:2010 , Industrial communication networks – Fieldbus specifications –
Part 4-21: Data-link layer protocol specification – Type 21 elements
IEC 61158-5-21:2010 , Industrial communication networks – Fieldbus specifications –
Part 5-21: Application layer service definition – Type 21 elements
ISO/IEC 7498-1, Information technology – Open Systems Interconnection – Basic Reference
Model: The Basic Model
ISO/IEC 8822, Information technology – Open Systems Interconnection – Presentation
service definition
ISO/IEC 8824-1, Information technology – Abstract Syntax Notation One (ASN.1):
Specification of basic notation
ISO/IEC 9545, Information technology – Open Systems Interconnection – Application layer

structure
ISO/IEC 10731:1994, Information technology – Open Systems Interconnection – Basic
Reference Model – Conventions for the definition of OSI services
ISO/IEC 9899, Programming Languages – C
IEEE 754-2008, IEEE Standard for Binary Floating-Point Arithmetic
—————————
To be published.
– 10 – 61158-6-21 © IEC:2010(E)

3 Terms, definitions, symbols, abbreviations, and conventions

3.1 Terms and definitions from other ISO/IEC standards

3.1.1 ISO/IEC 7498-1 terms
For the purposes of this document, the following terms as defined in ISO/IEC 7498-1 apply:

a) application entity
b) application process
c) application protocol data unit

d) application service element
e) application entity invocation
f) application process invocation
g) application transaction
h) real open system
i) transfer syntax
3.1.2 ISO/IEC 8822 terms
For the purposes of this document, the following terms as defined in ISO/IEC 8822 apply:
a) abstract syntax
b) presentation context
3.1.3 ISO/IEC 8824-1 terms
For the purposes of this document, the following terms as defined in ISO/IEC 8824-1 apply:
a) object identifier
b) type
3.1.4 ISO/IEC 9545 terms
For the purposes of this document, the following terms as defined in ISO/IEC 9545 apply:
a) application-association
b) application-context
c) application context name
d) application-entity-invocation

e) application-entity-type
f) application-process-invocation
g) application-process-type
h) application-service-element
i) application control service element
3.2 Other terms and definitions
3.2.1
application
function or data structure for which data are consumed or produced

61158-6-21 © IEC:2010(E) – 11 –

3.2.2
application objects
multiple object classes that manage and provide a runtime exchange of messages across the

network and within the network device

3.2.3
application process
part of a distributed application on a network, which is located on one device and addressed

unambiguously
3.2.4
application process identifier
distinguishes multiple application processes used in a device
3.2.5
application process object
component of an application process that is identifiable and accessible through an FAL
application relationship
NOTE Application process object definitions are composed of a set of values for the attributes of their class (see
the definition for “application process object class”). Application process object definitions may be accessed
remotely using the services of the FAL Object Management ASE. FAL Object Management services can be used to
load or update object definitions, to read object definitions, and to create and delete application objects and their
corresponding definitions dynamically.
3.2.6
application process object class
class of application process objects defined in terms of the set of their network-accessible
attributes and services
3.2.7
application relationship
cooperative association between two or more application-entity-invocations for the purpose of
exchange of information and coordination of their joint operation
NOTE This relationship is activated either by the exchange of application-protocol-data-units or as a result of
preconfiguration activities.
3.2.8
application relationship application service element
application-service-element that provides the exclusive means for establishing and
terminating all application relationships
3.2.9
application relationship endpoint
context and behavior of an application relationship as seen and maintained by one of the
application processes involved in the application relationship
NOTE Each application process involved in the application relationship maintains its own application relationship
endpoint.
3.2.10
attribute
description of an externally visible characteristic or feature of an object
NOTE The attributes of an object contain information about variable portions of an object. Typically, they provide
status information or govern the operation of an object. Attributes may also affect the behavior of an object.
Attributes are divided into class attributes and instance attributes.
3.2.11
behavior
indication of how an object responds to particular events

– 12 – 61158-6-21 © IEC:2010(E)

3.2.12
channel
single physical or logical link of an input or output application object of a server to the process

3.2.13
class
set of objects, all of which represent the same type of system component

NOTE A class is a generalization of an object, a template for defining variables and methods. All objects in a
class are identical in form and behavior, but usually contain different data in their attributes.

3.2.14
class attributes
attribute shared by all objects within the same class
3.2.15
class code
unique identifier assigned to each object class
3.2.16
class-specific service
service defined by a particular object class to perform a required function that is not
performed by a common service
NOTE A class-specific object is unique to the object class that defines it.
3.2.17
client
a) object that uses the services of another (server) object to perform a task
b) initiator of a message to which a server reacts
3.2.18
consume
act of receiving data from a producer
3.2.19
consumer
node or sink that receives data from a producer
3.2.20
consuming application
application that consumes data

3.2.21
conveyance path
unidirectional flow of APDUs across an application relationship
3.2.22
cyclic
repetitive in a regular manner
3.2.23
data consistency
means for coherent transmission and access of the input- or output-data object between and
within client and server
3.2.24
device
physical hardware connected to the link

61158-6-21 © IEC:2010(E) – 13 –

NOTE A device may contain more than one node.

3.2.25
device profile
a collection of device-dependent information and functionality providing consistency between

similar devices of the same device type

3.2.26
diagnostic information
all data available at the server for maintenance purposes

3.2.27
end node
producing or consuming node
3.2.28
endpoint
one of the communicating entities involved in a connection
3.2.29
error
discrepancy between a computed, observed, or measured value or condition and the specified
or theoretically correct value or condition
3.2.30
error class
general grouping for related error definitions and corresponding error codes
3.2.31
error code
identification of a specific type of error within an error class
3.2.32
event
instance of a change of conditions
3.2.33
FIFO variable
variable object class composed of a set of homogeneously typed elements, where the first
written element is the first element that can be read
NOTE In a fieldbus system, only one complete element can be transferred as a result of one service invocation.

3.2.34
frame
simplified synonym for data link protocol data unit (DLPDU)
3.2.35
group
a) (General): a general term for a collection of objects
b) (Addressing): when describing an address, an address that identifies more than one
entity
3.2.36
invocation
act of using a service or other resource of an application process
NOTE Each invocation represents a separate thread of control that may be described by its context. Once the
service completes, or use of the resource is released, the invocation ceases to exist. For service invocations, a

– 14 – 61158-6-21 © IEC:2010(E)

service that has been initiated but not yet completed is referred to as an outstanding service invocation. For

service invocations, an Invoke ID may be used to identify the service invocation unambiguously and differentiate it
from other outstanding service invocations.

3.2.37
index
address of an object within an application process

3.2.38
instance
actual physical occurrence of an object within a class that identifies one of many objects in

the same object class
EXAMPLE California is an instance of the object class US-state.
NOTE The terms object, instance, and object instance are used to refer to a specific instance.
3.2.39
instance attributes
attribute that is unique to an object instance and not shared by the object class
3.2.40
instantiated
object that has been created in a device
3.2.41
logical device
specific FAL class that abstracts a software component or a firmware component as an
autonomous self-contained facility of an automation device
3.2.42
manufacturer ID
identification of each product manufacturer by a unique number
3.2.43
management information
network-accessible information that supports management of the operation of the fieldbus
system, including the application layer
NOTE Managing includes functions, such as controlling, monitoring, and diagnosis.
3.2.44
network
set of nodes connected by some type of communication medium, including any intervening

repeaters, bridges, routers, and lower-layer gateways
3.2.45
object
abstract representation of a particular component within a device, usually a collection of
related data in the form of variables, and methods (procedures) for operating on that data that
have clearly defined interface and behavior
3.2.46
object dictionary
collection of definitions, communication-specific attributes and parameters, and application-
dependent data
3.2.47
object-specific service
service unique to the object class that defines it

61158-6-21 © IEC:2010(E) – 15 –

3.2.48
physical device
automation or other network device

3.2.49
point-to-point connection
connection that exists between exactly two application objects

3.2.50
pre-established AR endpoint
AR endpoint placed in an established state during configuration of the AEs that control its

endpoints
3.2.51
process data
object(s) that are already pre-processed and transferred cyclically for the purpose of
information or further processing
3.2.52
produce
act of sending data to be received by a consumer
3.2.53
producer
node that is responsible for sending data
3.2.54
property
general term for descriptive information about an object
3.2.55
provider
source of a data connection
3.2.56
publisher
role of an AR endpoint that transmits APDUs onto the fieldbus for consumption by one or
more subscribers
NOTE A publisher may not be aware of the identity or number of subscribers.
3.2.57
publishing manager
role of an AR endpoint in which it issues one or more confirmed service request application
protocol data units (APDUs) to a publisher to request that a specified object be published.
Two types of publishing managers are defined by this standard, pull publishing managers and
push publishing managers, each of which is defined separately.
3.2.58
push publisher
type of publisher that publishes an object in an unconfirmed service request APDU
3.2.59
push publishing manager
type of publishing manager that requests that a specified object be published using an
unconfirmed service
– 16 – 61158-6-21 © IEC:2010(E)

3.2.60
push subscriber
type of subscriber that recognizes received unconfirmed service request APDUs as published

object data
3.2.61
sending
service user that sends a confirmed primitive or an unconfirmed primitive, or a service

provider that sends a confirmed APDU or an unconfirmed APDU

3.2.62
server
a) role of an application relationship endpoint (AREP) in which it returns a confirmed service
response APDU to the client that initiated the request
b) object that provides services to another (client) object
3.2.63
service
operation or function than an object and/or object class performs upon request from another
object and/or object class
3.2.64
station
host of one AP, identified by a unique data link connection endpoint (DLCEP)-address
3.2.65
subscriber
role of an AREP in which it receives APDUs produced by a publisher
3.2.66
receiving
service user that receives a confirmed primitive or an unconfirmed primitive, or a service
provider that receives a confirmed APDU or an unconfirmed APDU
3.2.67
resource
processing or information capability of a subsystem
3.3 Abbreviations and symbols
AE Application Entity
AL Application Layer
ALME Application Layer Management Entity
ALP Application Layer Protocol
APO Application Object
AP Application Process
APDU Application Protocol Data Unit
AR Application Relationship
AREP Application Relationship End Point
ASCII American Standard Code for Information Interchange
ASE Application Service Element
Cnf Confirmation
DL- (as a prefix) Data Link -
DLCEP Data Link Connection End Point

61158-6-21 © IEC:2010(E) – 17 –

DLL Data Link Layer
DLM Data Link Management
DLSAP Data Link Service Access Point

DLSDU DL-service-data-unit
DNS Domain Name Service
FAL Fieldbus Application Layer

Ind Indication
Req Request
Rsp Response
3.4 Conventions
3.4.1 General conventions
This standard uses the descriptive conventions given in ISO/IEC 10731.
This standard uses the descriptive conventions given in IEC 61158-6-21:2010 for FAL service
definitions.
3.4.2 Convention for the encoding of reserved bits and octets
The term “reserved” may be used to describe bits in octets or whole octets. All bits or octets
that are reserved should be set to zero on the sending side. They will not be tested on the
receiving side except if explicitly stated, or if the reserved bits or octets are checked by a
state machine.
The term “reserved” may also be used to indicate that certain values within the range of a
parameter are reserved for future extensions. In this case the reserved values should not be
used at the sending side. They shall not be tested at the receiving side except if explicitly
stated, or if the reserved values are checked by a state machine.
3.4.3 Conventions for the common coding of specific field octets
APDUs may contain specific fields that carry information in a primitive and condensed way.
These fields shall be coded in the order according to Figure 1.
MSB    LSB
Octet 7 6 5 4 3 2 1 0 Bit Identification

Bit 0
Bit 1
Bit 2
Bit 3
Bit 4
Bit 5
Bit 6
Bit 7
Figure 1 – Common structure of specific fields
Bits may be grouped. Each bit or group of bits shall be addressed by its bit identification (e.g.,
Bit 0, Bits 1–4). The position within the octet shall be as shown in Figure 1. Alias names may
be used for each bit or group of bits, or they may be marked as reserved. The grouping of

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individual bits shall be in ascending order without gaps. The values for a group of bits may be

represented as binary, decimal, or hexadecimal values. This value shall only be valid for the

grouped bits and can only represent the whole octet if all 8 bits are grouped. Decimal or

hexadecimal values shall be transferred in binary values so that the bit with the highest group

number represents the most significant bit (MSB) of the grouped bits.

EXAMPLE: Description and relation for the specific field octet

Bit 0: reserved.
Bits 1–3: Reason_Code. The decimal value 2 for the Reason_Code means general error.

Bits 4–7: Always set to one.
The octet that is constructed according to the description above looks as follows:
(MSB) Bit 7 = 1;
Bit 6 = 1;
Bit 5 = 1;
Bit 4 = 1;
Bit 3 = 0;
Bit 2 = 1;
Bit 1 = 0;
(LSB) Bit 0 = 0.
This bit combination has an octet value representation of 0xf4.
3.4.4 Conventions for APDU abstract syntax definitions
This standard uses the descriptive conventions given in ISO/IEC 8824-2 for APDU definitions.
3.4.5 Conventions for APDU transfer syntax definitions
This standard uses the descriptive conventions given in ISO/IEC 8825-1 for transfer syntax
definitions.
3.4.6 Conventions for AE state machine definitions
The conventions used for AE state machine definitions are described in Table 1.
Table 1 – Conventions used for AE state machine definitions

No. Current state Event/condition => action Next state
Name of this The current Events or conditions that trigger this state The next state
transition state to which transition. after the
this state => actions in this
transition The actions that are taken when the above transition are
applies events or conditions are met. The actions are taken
always indented below events or conditions

The conventions used in the descriptions for the events, conditions and actions are as follows:
:= The value of an item on the left is replaced by the value of an item on the right. If an item
on the right is a parameter, it comes from the primitive shown as an input event.
xxx Parameter name.
Example:
Identifier := Reason
61158-6-21 © IEC:2010(E) – 19 –

means value of the Reason parameter is assigned to the parameter called Identifier.

“xxx” Indicates a fixed value.

Example:
Identifier := “abc”
means value “abc” is assigned to a parameter named “Identifier.”

= A logical condition to indicate an item on the left is equal to an item on the right.

< A logical condition to indicate an item on the left is less than the item on the right.

> A logical condition to indicate an item on the left is greater than the item on the right.

<> A logical condition to indicate an item on the left is not equal to an item on the right.
&& Logical “AND”
|| Logical “OR”
The sequence of actions and the alternative actions can be executed using the following
reserved words.
for
endfor
if
else
elseif
The following shows examples of description using the reserved words.
Example 1:
for (Identifier := start_value to end_value)
actions
endfor
Example 2:
If (condition)
actions
else
actions
endif
4 FAL syntax description
4.1 General
This description of the Type 21 abstract syntax uses formalisms similar to ASN.1, although
the encoding rules differ from that standard.

4.2 FAL-AR PDU abstract syntax
4.2.1 Top level definition
APDU ::= CHOICE {
ConfirmedSend-CommandPDU
ConfirmedSend-ResponsePDU
UnconfirmedSend-CommandPDU
}
4.2.2 Confirmed send service
ConfirmedSend-CommandPDU::=
...