Meter data exchange – standardisation for interoperability
The European utility and metering industry recognised the needs of the liberalised market for meter data exchange. Based on the work of the DLMS User Association, new international standards are being developed by IEC TC13 WG14 and will be ready for publication in 2001.
In the past, technical solutions for remote meter reading systems were to a large extent defined in bilateral agreements between a supplier and a user. This was a quite workable approach as long as automatic meter reading was limited to small groups of utility customers or to special applications only. The outcome was the creation of a variety of closed systems and proprietary solutions to meet specific customer needs.
When meter communication started to spread, attempts were made to create a quasi standard. This included the adaptation of existing protocols for applications they were never intended for, or extension of protocol definitions. Most of these adaptations continued to be operable only in closed context, as different suppliers had diverse views about the possibilities. As a result, some limitations and risks concerning flexibility, robustness and data security had to be accepted. The integration of meters to utility IT systems remained a difficult task.
With the growing number of market participants and resulting complexity of trading and data management, bilateral agreements are no longer workable. To meet the requirements of the liberalised energy market, metering systems need to support the trading mechanism and market operation rules. Metering data must be modelled, identified and made available for authorised parties in a manufacturer and media independent way in various utility metering and communication structure environments. Fierce competition – in the utility industry and outside – necessitates higher levels of data security as metering information becomes a valuable source of competitive information.
The elements of the specification
The COSEM specification – COmpanion Specification for Energy Metering – uses object-modelling techniques to provide a view of the functionality of the metering equipment, as it is available at its interface(s). Draft IEC 62056-62 defines the metering-domain interface classes, like registers, profiles, clocks and sche-dules, and other classes’ modelling application associations (associated partners and their rights) and media set-ups. Each class has its own specific list of attributes holding data, and methods of executing tasks.
Instances of the interface classes, called COSEM objects, are uniquely identified with a name called the logical name. The Object Identification System (OBIS) is defined in draft IEC 62056-61, originally based on the German Energy Data Identification System.
The functions of the metering equipment and access to data will be determined by the set of objects selected and their parameters. This is left entirely to the manufacturer and the user.
Attributes and methods of COSEM objects can be accessed either via the object name, using logical name referencing, or directly using short name referencing. For this purpose, a general set of data communication services is available, like GET/READ, SET/WRITE and ACTION. These services are not object-specific; they are common for all current and future objects. The services are provided by the messaging service element of the application layer, draft IEC 62056-53, which is the only mandatory part in any protocol stack designed to access COSEM objects. The COSEM messaging service element is based on the IEC 61334-4-41 DLMS standard – developed earlier by IEC TC57 – with a few extensions added.
TC13 has also defined a protocol stack based on a simplified, three-layer OSI model and the client-server paradigm. Application association is controlled by the connection-oriented Association Control Service Element (ACSE, ISO/IEC 8649) of the application layer. The lower protocol layers package and transport the information. The data link layer is based on the ISO/IEC 13239 HDLC standard, defined in draft IEC 62056-46, while the physical layer is defined in draft IEC 62056-42. The same protocol stack can also be used for local data exchange as defined in draft IEC 62056-21. The protocol work consisted essentially of selecting functions and options from the basic standards appropriate for the metering environment.
Features and advantages
- Meter interface object model supports meter installation, billing, tariff and contract management, power quality, network monitoring and data exchange functions.
- Object identification system suitable for electricity, gas, water and heat metering.
- Special functions can be met using manufacturer-specific objects and new functions by defining new, standard interface classes, identified and accessible in a standardised way.
- Suitable from simple residential to complex industrial and distribution meters, through free selection of objects and messaging services.
- The current protocol stack supports point-to-point and point-to-multipoint configurations on dedicated and switched data transmission facilities, with half-duplex and full-duplex connections like the PSTN, GSM or optical port. The protocol stack is negotiable when the connection is built.
- Support of unsolicited event reporting, multi-casting and broadcasting.
- Handling multiple client-server associations with defined access rights while providing improved security through mutual authentication of the client and the server. Data encryption is possible.
- Easy system integration – only one device driver for any meter type from any manufacturer.
IEC TC13 WG14 has received strong input from the DLMS UA. When the project was launched, good drafts were already available for circulation. During the work and as real implementations have progressed, further useful inputs have been received from national committees and from the DLMS UA.
The specification consists of six documents, all in the Committee Draft for Vote (CDV) stage. From the feedback received so far, TC13 hopes that the result will be positive. The target publishing date is mid-2001. At its recent meeting, CEN TC294 – responsible for meter data exchange for gas, water and heat meters – has also decided to adapt the COSEM specification.
Several providers have started implementation or have already brought meters and systems to the market. This illustrates the maturity of the specification.
With new standards, the issue of migration is always raised. There are probably a few hundred thousand commercial and industrial meters on the wall. A large majority – except in North America and markets following ANSI standards – talk the IEC 61107 protocol. These meters are integrated into data collection systems through specific device drivers – essentially one for each manufacturer’s type. This solution undoubtedly solves the problem of integrating a variety of meters into common systems. As long as these systems remain functionally adequate, there is no reason to replace them.
Draft IEC 62056-21 defines how a meter can support both existing IEC 61107 modes and the new, transparent binary mode, able to transport the COSEM objects. With this, existing systems can still be used. When the COSEM driver is added, new and improved functionality from all COSEM meters becomes available.
Meeting diverse needs
There is a potential conflict between the need for meeting diverse needs and the need for standardised systems. Competition has also to be maintained and even encouraged.
The COSEM specification addresses this problem. Special and new needs can be met by using manufacturer-specific objects and by defining new interface classes compliant to the agreed rules. These objects are also identified and accessible in a standardised way. Competition by functionality is made possible through free selection of the objects offered and services supported, within the context of the standard.
Maintenance and implementation compatibility
Standards also need management and maintenance. There are specific identifiers to be allocated and questions need to be answered. Experience with the use of the specification needs to be gathered and kept until it can be brought into the standardisation process. Similar activities are being carried out for IEC 61107 by the FLAG Association and for IEC 61142 by the EURIDIS association. The DLMS UA will fulfil this role in the case of the COSEM specification.
In order to prove that with COSEM the declared objective – interoperability – can be reached, the DLMS UA started to develop a conformance test specification and tool and is preparing to run a certification scheme. The experience from conformance testing will be brought back to TC13 and in the future, the specification could be completed with interoperability sections.
Relationship with other standards
Compared to earlier TC13 standards like IEC 61107 and IEC 61142, and to standards developed by other bodies for meter data exchange, the key merits of the new specification are the existence of an interface object model and the clear separation of the model and the protocol.
This, together with the built-in flexibility, promises to meet the needs of the deregulated market for interoperable systems. To converge European and North-American approaches, a special interface class has been defined for carrying the ANSI C12.19/IEEE 1377 Utility Industry End Device Data Tables.
Speed of standardisation
Communication is probably the fastest-developing industry, while standardisation – always seeking international consensus and sometimes struggling with limited resources – is a slower process. In the case of the COSEM specification the development time, thanks to the industry support, was relatively short. The project was launched in 1998 and the standards will be published in 2001.
Conclusion and next steps
The COSEM specification, developed by the DLMS UA and standardised by IEC TC13, has a good chance to meet the needs of liberalised energy markets for interoperable metering systems. It supports a wide range of applications, functionality and communication environments and both the model and the protocol are open to future evolution. Next steps will most probably address value-added applications like home automation, and the definition of protocols for other communication architectures and media, as market priorities dictate.
As history teaches, the real market success now is in the hands of providers and users. IEC TC13 hopes that its work will prove to be useful, and that industry players will adopt it to their mutual benefit.