IEC 62056-53:2002

INTERNATIONAL IEC
STANDARD
62056-53
First edition
2002-02
Electricity metering –
Data exchange for meter reading,
tariff and load control –
Part 53:
COSEM application layer
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INTERNATIONAL IEC
STANDARD
62056-53
First edition
2002-02
Electricity metering –
Data exchange for meter reading,
tariff and load control –
Part 53:
COSEM application layer
 IEC 2002  Copyright - all rights reserved
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International Electrotechnical Commission
For price, see current catalogue

– 2 – 62056-53  IEC:2002(E)
CONTENTS
FOREWORD.5

1 Scope.7

2 Normative references .7

3 Terms, definitions and abbreviations .8

4 The COSEM communications framework .10

4.1 Client/server type operation, communication profiles .10

4.2 Connection (association) oriented operation.11

5 Overview : the COSEM application layer .12
5.1 Specification method .12
5.2 Application layer structure .12
5.3 Service specification .13
5.3.1 Services provided for application association establishment and
release .13
5.3.2 Data communication services .14
5.4 Layer management services .15
5.5 Protocol specification .15
6 COSEM application layer – Service specification.15
6.1 Summary of services .15
6.2 Application association establishment and release .16
6.3 Special application associations .17
6.3.1 Mandatory application associations .17
6.3.2 Pre-established application associations .17
6.3.3 Non-confirmed application associations.17
6.4 Data communication.17
6.5 Client COSEM application layer services.18
6.5.1 Application association establishment.18
6.5.2 Application association release.22
6.5.3 Client/server type data communication services .24
6.5.4 Client side services for event notification.33
6.5.5 Client side layer management services.35
6.6 Server COSEM application layer services.37
6.6.1 Application association establishment.37

6.6.2 Application association release.39
6.6.3 Client/server type data communication services .42
7 COSEM application layer protocol specification .53
7.1 State definitions for the client side Control function .54
7.2 State definitions for the server side Control function.55
7.3 Protocol for application association establishment/release .56
7.3.1 Establishment of an application association.56
7.3.2 Establishment of special application associations .58
7.3.3 The AARQ and AARE APDUs.59
7.3.4 Managing the parameters for application association establishment .60
7.3.5 Repeated COSEM-OPEN.request service invocations .61
7.3.6 Releasing an application association .64
7.3.7 Registered COSEM names .66

62056-53  IEC:2002(E) – 3 –
7.4 Protocol for data communications.69

7.4.1 Protocol for the xDLMS services using LN referencing.69

7.4.2 Protocol for the xDLMS services using SN referencing .83

8 Specification of COSEM data types and APDU-s .87

8.1 The COSEM APDUs.87

8.2 The AARQ and AARE APDUs.88

8.3 Useful types .89

8.4 The xDLMS-Initiate.request/response/ConfirmedServiceError PDUs.94

8.5 The conformance block .95

8.6 Definition of APDUs for data communication .96
8.6.1 COSEM APDUs using logical name referencing.96
8.6.2 DLMS APDUs using short name referencing.100
Annex A (normative) The 3-layer, connection-oriented, HDLC based profile.101
A.1 Introduction .101
A.2 The HDLC-based data link layer – Overview.101
A.2.1 Services of the HDLC based data link layer .102
Annex B (normative) The xDLMS application service element .105
B.1 Introduction .105
B.2 DLMS compliance .105
B.3 Extensions to DLMS for COSEM .105
B.3.1 Additional services .105
B.3.2 Additional data types .105
B.3.3 The conformance block.106
B.3.4 DLMS version number .106
B.3.5 Other necessary modifications.106
Annex C (informative) AARQ and AARE encoding examples.107
C.1 Encoding example of the xDLMS-Initiate.request PDU.107
C.2 Encoding example of an AARQ not using the ACSE security mechanism.108
C.3 Encoding example of an AARQ using low level authentication .109
C.4 Encoding example of an AARQ using high-level authentication .110
C.5 Encoding example for the AARE APDU, case of success .111

C.6 Encoding example of the xDLMS-Initiate.response PDU .111
C.7 Encoding of the AARE not using security or using low level security.113
C.8 Encoding of the AARE using high-level security.114
C.9 Encoding example for the AARE-pdu, case of failure 1.115
C.10 Encoding example for the AARE APDU, case of failure 2 .116
Annex D (informative) Data model and protocol .119
Figure 1 – Client/server relationship in COSEM .10
Figure 2 – Exchanging messages via the communications protocol.10
Figure 3 – The COSEM application layer on the top of various lower layer stacks.11
Figure 4 – A complete communications session in the CO environment .12
Figure 5 – The structure of the COSEM application layers .13

– 4 – 62056-53  IEC:2002(E)
Figure 6 – Structure of the COSEM AL when the server is using SN references.15

Figure 7 – Summary of COSEM application layer services .16

Figure 8 – Normal service sequence for the COSEM-OPEN service.16

Figure 9 – Client side services for application association establishment .18

Figure 10 – Client services for releasing an application association .22

Figure 11 – Client side data communication services .24

Figure 12 – Client side services for event notification .34

Figure 13 – Server side services for application association establishment .37

Figure 14 – Server side services for releasing an application association .40
Figure 15 – Server side data communications services using LN referencing.42
Figure 16 – Partial state machine for the client side control function .54
Figure 17 – Partial state machine for the server side control function.55
Figure 18 – MSC for successful application association establishment.57
Figure 19 – Handling non-confirmed COSEM-OPEN.request at the client side .62
Figure 20 – Handling the reception of a non-confirmed AARQ at the server side.63
Figure 21 – Graceful release of an application association.65
Figure 22 – Aborting an application association following a PH-ABORT.indication .66
Figure 23 – MSC for a confirmed GET service in case of success.70
Figure 24 – MSC for a confirmed SET service in case of success .70
Figure 25 – MSC for the SET service in case of failure .71
Figure 26 – MSC for the ACTION service (simplest case) .71
Figure 27 – Example: EventNotificaton triggered by the client.73
Figure 28 – Long data with the GET service in three data blocks .78
Figure 29 – Long data transfer in three data blocks with the SET service.79
Figure 30 – Long data transfer with the ACTION service.82
Figure 31 – MSC for the ReadRequest/Response services .83
Figure A.1 – Data link services used by the client COSEM application layer .102
Figure A.2 – Data link layer services used by the server COSEM application layer .103
Figure D.1 – The three-step approach of COSEM .119

62056-53  IEC:2002(E) – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION

___________
ELECTRICITY METERING – DATA EXCHANGE FOR

METER READING, TARIFF AND LOAD CONTROL –

Part 53: COSEM application layer

FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the 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, the IEC publishes International Standards. Their preparation is
entrusted to technical committees; any IEC National Committee interested in the subject dealt with may
participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. The 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 the IEC on technical matters express, as nearly as possible, an
international consensus of opinion on the relevant subjects since each technical committee has representation
from all interested National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical specifications, technical reports or guides and they are accepted by the National
Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
The International Electrotechnical Commission (IEC) draws attention to the fact that it is claimed that compliance
with this International Standard may involve the use of a maintenance service concerning the stack of protocols on
which the present standard IEC 62056-53 is based.
The IEC takes no position concerning the evidence, validity and scope of this maintenance service.
The provider of the maintenance service has assured the IEC that he is willing to provide services under
reasonable and non-discriminatory terms and conditions for applicants throughout the world. In this respect, the
statement of the provider of the maintenance service is registered with the IEC. Information may be obtained from:
DLMS User Association
Geneva / Switzerland
www.dlms.ch
International Standard IEC 62056-53 has been prepared by IEC technical committee 13:
Equipment for electrical energy measurement and load control.
The text of this standard is based on the following documents:
FDIS Report on voting
13/1268/FDIS 13/1274/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.
———————
Device Language Message Specification.

– 6 – 62056-53  IEC:2002(E)
This publication has been drafted in accordance with the ISO/IEC Directives, Part 3.

Annexes A and B form an integral part of this standard.

Annexes C and D are for information only.

The committee has decided that the contents of this publication will remain unchanged until

2006. At this date, the publication will be

• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
62056-53  IEC:2002(E) – 7 –
ELECTRICITY METERING – DATA EXCHANGE FOR

METER READING, TARIFF AND LOAD CONTROL –

Part 53: COSEM application layer

1 Scope
This part of IEC 62056 specifies the COSEM application layer in terms of structure, services

and protocols, for COSEM clients and servers.
Data communication services with COSEM interface objects, using Logical name (LN)
referencing and Short name (SN) referencing, are specified. COSEM servers use either LN or
SN referencing during a given association: this is negotiated during the Application
Association establishment. The COSEM client always uses LN referencing. If the client
communicates with a server using SN referencing, the LN services are mapped to SN
services.
Annex C includes encoding examples for APDUs. Annex D gives an explanation of the role of
data models and protocols in electricity meter data exchange.
2 Normative references
The following referenced documents are indispensable for the application 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.
IEC 60050-300:2001, International Electrotechnical Vocabulary – Electrical and electronic
measurements and measuring instruments – Part 311: General terms relating to
measurements – Part 312: General terms relating to electrical measurements – Part 313:
Types of electrical measuring instruments – Part 314: Specific terms according to the type of
instrument
IEC 61334-4-41:1996, Distribution automation using distribution line carrier systems – Part 4:
Data communication protocols – Section 41: Application protocols – Distribution line message
specification
IEC 61334-6:2000, Distribution automation using distribution line carrier systems – Part 6:
A-XDR encoding rule
IEC/TR2 62051:1999, Electricity metering – Glossary of terms
IEC 62056-21, Electricity metering – Data exchange for meter reading, tariff and load control
– Part 21: Direct local data exchange
IEC 62056-42:2001, Electricity metering – Data exchange for meter reading, tariff and load
control – Part 42: Physical layer services and procedures for connection-oriented
asynchronous data exchange
IEC 62056-46, Electricity metering – Data exchange for meter reading, tariff and load control
– Part 46: Data link layer using HDLC protocol
———————
To be published.
– 8 – 62056-53  IEC:2002(E)
IEC 62056-61, Electricity metering – Data exchange for meter reading, tariff and load control

– Part 61: OBIS Object identification system

IEC 62056-62, Electricity metering – Data exchange for meter reading, tariff and load control

– Part 62: Interface objects
ISO/IEC 8649:1996, Information technology – Open Systems Interconnection – Service definition

for the Association Control Service Element

ISO/IEC/TR2 8650-1:1996, Information technology – Open systems interconnection – Connection-

oriented protocol for the association control service element: Protocol specification

ISO/IEC 8824:1990, Information technology – Open Systems Interconnection – Specification
of Abstract Syntax Notation One (ASN.1)
ISO/IEC 8825:1990, Information technology – Open Systems Interconnection – Specification
of Basic Encoding Rules for Abstract Syntax Notation One (ASN.1)
ISO/IEC 13239:2000, Information technology – Telecommunications and information exchange
between systems – High-level data link control (HDLC) procedures
3 Terms, definitions and abbreviations
3.1 Terms and definitions
For the purpose of this part of IEC 62056, the definitions in IEC 60050-300 and IEC/TR
62051, as well as the following, apply.
3.1.1
base_name
the short_name corresponding to the first attribute (“logical_name”) of a COSEM interface
object
3.1.2
class_id
interface class identification code
3.1.3
client
a station, asking for services

3.1.4
COSEM interface object
an instance of a COSEM interface class
3.1.5
server
a station, delivering services. The tariff device (metering equipment) is normally the server,
delivering the requested data or executing the requested tasks.

62056-53  IEC:2002(E) – 9 –
3.2 Abbreviations
AA Application Association
AARE Application Association REsponse

AARQ Application Association ReQuest

ACSE Application Control Service Element

AE Application Entity
AP Application Process
APDU Application layer Protocol Data Unit
API Application Programming Interface
ASE Application Service Element
ASO Application Service Object
A-XDR Adapted eXtended Data Representation
BER Basic Encoding Rules
CF Control function
.cnf confirm service primitive
CO Connection Oriented
COSEM COmpanion Specification for Energy Metering
DLMS Distribution Line Message Specification
DSAP Data link Service Access Point
GMT Greenwich Mean Time
HDLC High-level Data Link Control
HLS High-Level Security
IC Interface Class
LLC Logical Link Control (sub-layer)
LLS Low Level Security
LPDU LLC Protocol Data Unit
LSB Least Significant Bit
LSAP LLC sub-layer Service Access Point
m mandatory, used in conjunction with attribute and method
definitions
MSB Most Significant Bit
MSC Message Sequence Chart
o optional, used in conjunction with attribute and method definitions
OBIS OBject Identification System
PDU Protocol Data Unit
.req .request service primitive
.res .response service primitive
SAP Service Access Point
xDLMS-ASE extended DLMS Application Service Element

– 10 – 62056-53  IEC:2002(E)
4 The COSEM communications framework

4.1 Client/server type operation, communication profiles

Communication with electricity metering equipment using the COSEM interface classes is
based on the client/server paradigm, where metering equipment plays the server role. In

this environment, communication takes place always between a client and a server

application process: in other words, the server application process provides remote services
to the client application process. These services are provided via exchanging messages

(SERVICE.requests/.responses) between the client and the server application processes, as it

is shown in Figure 1.
Server application
Client application (COSEM device)
SERVICE.request
SERVICE.response
IEC  268/02
Figure 1 – Client/server relationship in COSEM
In general, the client and the server application processes are located in separate devices,
exchanging messages is done with the help of the communications protocol.
.request
Client Server
.response
.response
.request
Application
layer
Protocol
Intermediate
protocol layers
Physical layer
Physical channel
IEC  269/02
Figure 2 – Exchanging messages via the communications protocol
———————
The metering equipment is an abstraction; consequently the equipment playing the role of a server may be any
type of equipment for which this abstraction is suitable.

62056-53  IEC:2002(E) – 11 –
In general, communication protocols are structured in layers. The client and server COSEM
applications use services of the highest protocol layer, that of the application layer:

consequently, this is the only protocol layer which shall contain COSEM specific element(s).

This is called the xDLMS_ASE. All COSEM interface object related services – the xDLMS

application protocol – are provided by this xDLMS_ASE.

Other protocol layers are independent from the COSEM model, consequently the COSEM

application layer can be placed on the top of a wide variety of lower protocol layer stacks, as

it is shown in Figure 3.
Profile 2
Profile 1 Profile M
Application layer
ACSE
xDLMS_ASE
N layer
N layer
N layer
N-1 layer
Physical layer Physical layer
Physical layer
IEC  270/02
Figure 3 – The COSEM application layer on the top of various lower layer stacks
A complete protocol stack – including the application layer, a physical layer and all protocol
layers between these extreme layers – is called a communications profile.
A communications profile is characterized by the protocol layers included, their parameters,
and by the type – connection-oriented or connectionless – of the ACSE included in the
application layer.
4.2 Connection (association) oriented operation
The xDLMS application protocol is a connection-oriented protocol. It means, that the client

and server application processes can use the services of the xDLMS_ASE only when these
application processes are associated . Therefore, in this environment a communication
session consists of three phases, as it is shown on Figure 4.
———————
ACSE = Association Control Service Element
Application associations can be considered as application level connections.

– 12 – 62056-53  IEC:2002(E)
Client application Server application

Phase 1.
Connection establishment
Phase 2.
Data communication
Phase 3.
t
Connection release
IEC  271/02
Figure 4 – A complete communications session in the CO environment
In the COSEM environment, application association establishment is normally done by using
the association request/response services of the standard association control service
element. On the other hand, for the purposes of very simple devices, one-way communicating
devices and for multicasting and broadcasting, pre-established application associations are
also allowed; see 6.3.2. For these associations, there is no need to use the services of the
ACSE: a full communication session may include only the data communication phase. (It can
be considered that the connection establishment phase has been already done somewhere in
the past.)
5 Overview : the COSEM application layer
5.1 Specification method
The COSEM application layer is specified in terms of structure, services and protocols.
5.2 Application layer structure
The main component of the client and server COSEM application layers is the COSEM ASO,
which provides services to the COSEM application process, and uses services provided by
the supporting lower layer.
Both the client and server side COSEM ASO contains three mandatory components:
• the ACSE. The task of this element is to establish, maintain and release application
associations. For the purposes of connection-oriented profiles, the connection-oriented
ACSE, specified in ISO/IEC 8649 and ISO/IEC/TR2 8650-1 is used;

• the Extended DLMS application service element (xDLMS_ASE). The task of this element is
to provide data communication services between COSEM equipment. See also Annex B;
• the Control function (CF). This element specifies how the ASO services invoke the
appropriate service primitives of the ACSE and the xDLMS ASE and the services of the
supporting layer.
NOTE Both the client and the server COSEM ASO may contain other, optional application protocol components.
Figure 5 shows ‘minimal’ COSEM ASOs, containing only the three mandatory components.

62056-53  IEC:2002(E) – 13 –
COSEM client
COSEM server
application process
application process
Referencing by Logical
COSEM client ASO services
COSEM server ASO services
Name or by Short Name
Referencing by Logical Name
COSEM client application COSEM server application
L L
COSEM client ASO COSEM server ASO

Client control function
Server control
Ft(iServer CF)
(Client CF)
Server Server
Client Client
xDLMS_ASE ACSE xDLMS_ASE ACSE
Supporting layer services Supporting layer services
Supporting layer (data link) and other
Supporting layer (data link) and other
protocol layers protocol layers
WAN, ex. PSTN
IEC  272/02
Figure 5 – The structure of the COSEM application layers
5.3 Service specification
Service specifications cover the services required of, or by the COSEM client and server
application processes at the logical interfaces with the respective COSEM application layer,
using connection-oriented procedures.
Services provided by the COSEM ASO fall into three categories:
• application association establishment and release;
• data communication;
• layer management.
The client and server application layer services are specified in clause 6.
5.3.1 Services provided for application association establishment and release
These services are the following:
• COSEM-OPEN;
• COSEM-RELEASE;
• COSEM-ABORT.
The COSEM-OPEN service is used during application association establishment phase and
relies on the association request/response services of the ACSE. In the case of pre-
established application associations (6.3.2) these services are not used.
As in any COSEM communications profile, there is a one-to-one relationship between an
application association and a supporting protocol layer connection, the COSEM-RELEASE
and COSEM-ABORT services – used during the connection release phase – do not rely on
the ACSE. Application associations are released or aborted simply by disconnecting the
corresponding supporting layer connection.
Applications
Protocol
(interface objects)
(communications)
– 14 – 62056-53  IEC:2002(E)
5.3.2 Data communication services

IEC 62056-62 specifies two referencing methods for COSEM servers: referencing by Logical

Names (LN) and referencing by Short Names (SN). Therefore, two distinct service sets are

specified for the server side xDLMS_ASE. One set uses exclusively LN references, the other

set uses exclusively SN references. Thus, these services are the following:

• COSEM interface object attribute-related services: GET, SET for LN referencing and

Read, Write, Unconfirmed Write for SN referencing;

• COSEM interface object method-related services: ACTION (LN), Write (SN);

• the EventNotification (LN), InformationReport (SN) services.

The services listed above rely on the services of the xDLMS_ASE. Most of these services
contain references to attributes or methods of COSEM interface objects.
The service set to be used on the server side during the data communications phase is
negotiated during the association establishment phase, using the conformance block, see 8.5.
It shall not change during the lifetime of the established association. Using LN or SN services
within a given application association is exclusive. Therefore, it can be considered that there
are two, different server xDLMS_ASE-s: one providing services with Logical name references
and another providing services with Short name references. The server application layer shall
include one of these xDLMS_ASE-s.
NOTE A server could use both LN and SN referencing in different application associations.
On the client side, in order to handle the different referencing schemes transparently for the
COSEM client application process, the COSEM client application layer provides only one
service set, using Logical name referencing. This has two major consequences:
• using a unique, standardized service set between COSEM client applications and the
communications protocol – hiding the particularities of different COSEM servers – allows
to specify an Application Programming Interface (API). This is an explicitly specified
interface corresponding to this service set for applications running in a given computing
environment (e.g. Windows98, UNIX, etc.) Using this – public – API specification, client
applications can be developed without knowledge about particularities of a given server;
• when the COSEM server device does not use Logical name referencing, the client
application layer shall include an additional component. The purpose of this component is
to map the LN service set, used by the client application process into/from the service set,
used by the server application process. Figure 6 shows the COSEM client application
layer when the server is using Short name references. The additional component is called
SN_MAPPER_ASE. See also 6.5.5.2.

62056-53  IEC:2002(E) – 15 –
COSEM client
COSEM server
application process
application process
COSEM client ASO services
COSEM server ASO services SN referencing (RD/WR)
Referencing by Logical Name
COSEM client application COSEM server application

L L
COSEM client ASO
COSEM server ASO
Client control function
Server control
Client
Ft(iServer CF)
xDLMS_ASE
Client
Server Server
ACSE
Client xDLMS_ASE ACSE
SN_MAPPER
Supporting layer services Supporting layer services
Supporting layar (data link) and other
Supporting layer (data link) and other
protocol layers
protocol layers
PSTN
IEC  273/02
Figure 6 – Structure of the COSEM AL when the server is using SN references
5.4 Layer management services
Layer management services have local importance only. Therefore, specification of these
services is not within the scope of this standard. The specific SetMapperTables service is
defined in 6.5.5.1.
5.5 Protocol specification
The COSEM application layer protocols specify the procedures for the transfer of information
for application association control, authentication (ACSE procedures) and for data exchange
between COSEM clients and servers (xDLMS procedures). These procedures are defined in
terms of:
• the interactions between peer ACSE and xDLMS protocol machines through the use of
services of the supporting protocol layer;
• the interactions between the ACSE and xDLMS protocol machines and their service user;
• the abstract syntax (ASN.1, ISO/IEC 8824) representation of Application Protocol Data

Units (APDUs) is also specified with the application protocols; see clause 8.
NOTE All COSEM services are operating on an already established physical connection. Establishment of this
physical connection is done outside of the COSEM protocol, therefore, it is not within the scope of this standard.
6 COSEM application layer – Service specification
6.1 Summary of services
A summary of the services available at the top of the COSEM application layer is shown in
Figure 7.
Applications
Protocol
(interface objects)
(communications)
– 16 – 62056-53  IEC:2002(E)
COSEM client
COSEM server
application process
application process
Application layer
ZZ.request
ZZ.response
EventNotification
IEC  274/02
Figure 7 – Summary of COSEM application layer services
NOTE In the figure, above XX and ZZ refers to client/server type data communication services. These services
may be different on the client side and the server side, if the server does not use LN referencing. See 6.4.
6.2 Application association establishment and release
The COSEM-OPEN, COSEM-RELEASE and COSEM-ABORT services are used for the
establishment and release of application associations.
The COSEM-OPEN.request service is invoked by the COSEM client application process to
open an application association to a COSEM server application process. Invoking this service
implies – after connecting the lower layers – to generate a COSEM-OPEN.indication service
primitive at the server side. The server shall respond to this request by invoking the COSEM-
OPEN.response service, which is transferred to the client application process as a remote

confirmation (COSEM-OPEN.confirm). This normal opening sequence is shown in Figure 8.
Server
Client
application layer
application layer
COSEM-
COSEM-
OPEN.indication
OPEN.request
COSEM-
OPEN.confirm COSEM-
OPEN.response
time
IEC  275/02
Figure 8 – Normal service sequence for the COSEM-OPEN service
———————
Except for the physical layer, which should be already connected.
COSEM-OPEN.req
COSEM-OPEN.cnf
COSEM-RELEASE.req
COSEM-RELEASE.cnf
COSEM-ABORT.ind
XX.req
XX.cnf
Trigg_EventNotif.req
EventNotification.ind
COSEM-OPEN.ind
COSEM-OPEN.res
COSEM-RELEASE.ind
COSEM-RELEASE.res
COSEM-ABORT.ind
ZZ.ind
ZZ.res
EventNotification.req or
InformationReport.req
62056-53  IEC:2002(E) – 17 –
NOTE The COSEM-OPEN.request may also be locally confirmed, for example when the connection of a lower

layer is not successful.
The COSEM-RELEASE service is provided for graceful disconnection of an existing

application association. As COSEM server application processes are not allowed to request a

graceful disconnection, the COSEM-RELEASE.request service is available only for the

COSEM client. The nominal service sequence for the COSEM-RELEASE service is the same

as is shown in Figure 8. for the COSEM-OPEN service, replacing the word ‘OPEN’ with the

word ‘RELEASE’.
The ABORT service is used to indicate the disconnection of the physical connection. This

service is the same at both sides.

6.3 Special application associations
6.3.1 Mandatory application associations
As specified in 4.6 of IEC 62056-62, each physical device shall contain a management logical
device. The mandatory contents of the management logical device are defined in 4.6.4 of
IEC 62056-62. The management logical device must support an application association to a
public client, with the lowest security level. The client address 0x10 is reserved for the public
client.
6.3.2 Pre-established application associations
A pre-established application association does not need to be established using the COSEM-
OPEN service. It can be considered, that this OPEN has already been done (it is of no importance
how). Consequently, pre-established application associations should be considered to be existing
from the moment of the establishment of the physical connection between the client and the
server devices. A pre-established application association can be either confirmed or non-
confirmed (depending on the way it is pre-established), but in any case it cannot be released. The
purpose of this type of association is to simplify data exchange with simple devices, (e.g.
supporting one-way communication only). The pre-established application association eliminates
the need of connection establishment and release (phases 1 and 3 on Figure 4) and only data
communication services are used. These must use connectionless services of the supporting
lower protocol layers.
6.3.3 Non-confirmed application associations
A client application may invoke the COSEM-OPEN.request service in two different ways:
confirmed or non-confirmed. A non-confirmed COSEM-OPEN.request invocation shall result in
the establishment of a non-confirmed application association. Within this application
association the client COSEM application layer shall accept only non-confirmed xDLMS
service requests (GET, SET, ACTION). The purpose of having this type of association is to

allow multicasting and broadcasting.
6.4 Data communication
For data communication purposes, the client application layer provides the following set of
services (referred to as XX on Figure 7):
• GET service (.request, .confirm);
• SET service (.request, .confirm);
• ACTION service (.request, .confirm).
All these services refer to attributes or methods of COSEM interface objects via logical
names.
———————
Pre-established associations cannot be supported by a lower protocol layer not providing non-connected data
communication services.
– 18 – 62056-53  IEC:2002(E)
There are also non-client/server type services to support receiving information like alarms

from a COSEM server without first requesting it by the client. These are:

• EventNotification service (.indicate);

• Trigger_EventNotification_Sending (.request).

The client application layer obtains knowledge during the application association establish-

ment phase about the referencing method used by the server. When the client application

process invokes the data communication services, the COSEM client application layer shall

send the APDU corresponding to the appropriate service invocation to the server (referred to
as ZZ in Figure 7).
When the server is also using LN references, the server side service set is the complementary
of the client side service set (the same service set, but .request services shall be transferred
as .indication services, and the .confirm services are originated as .response services).
When the server is using SN references, the service set is as follows:
• READ service (.indication, . response);
• WRITE service (.indication, .response);
• UNCONFIRMED WRITE service (.indication);
• InformationReport service (.request).
As explained in 5.3.2, in order to able to ‘map’ between the different service sets, the client
application layer shall include an additional protocol component, called ‘Client SN_MAPPER’.
The corresponding server application layer shall signal the reception of this (LN or SN
referencing) APDU to the server application process. In most cases, the server application
process responds to the received .request service by invoking the corresponding .response
service. Upo
...