DLMS User Association
Device Language Message Specification
Newsletter No. 1998/4, July '98
from: DLMS UA Office, PO Box 89, CH-1211 Geneva 16: dlms@dlms.com
The User Association of the Device Language Message Specification: Meter Data Exchange for Electricity, Gas, Heat and Water Utilities.
Content:
Editorial
The "COSEM Interface Objects"
The first product, as announced in the last Newsletter, led to comments which will slightly alter the direction. Comments were direct and indirect. Let us take the indirect comments first. In a plenary meeting of an IEC Technical Committee, which standardises electricity meters, there have been interventions to sort out the abbreviation jungle. COSEM was mentioned, even if there were no activities started towards standardisation before the meeting! The confusion came mainly from the fact, that DLMS in standardisation means "Distribution Line Message Specification", whereas the logo of the DLMS UA contains "Device Language Message Specification". The glossary of this Technical Committee contained both abbreviations. The compromise found is the following: The official abbreviation means "Distribution Line Message Specification", whereas the name "DLMS User Association" contains the trademarked expression "Device Language Message Specification".
The direct comment came from the creators of the COSEM documents. DLMS is too much interleaved with the meter objects. In order to strictly separate the different functions, the objects will be described in the body of the document, and the mapping to DLMS will be in the annex. The document covers still the same functionality as before.
The "COSEM Information Models for Energy Meters"
A next consequence of this restructuring is the renaming of COSEM. "Companion Specification" is no longer true after the separation. The abbreviation has now a new meaning: Common Object Specification for Energy Metering. COSEM is now clearly reserved for the information model object definitions, and DLMS for the mapping and messaging. The DLMS User Association covers both aspects and more, e.g. the link to lower layers.
COSEM: Common Object Specification for Energy Metering
is a strong element for interoperability. It is covering the kind of interoperability which was most lacking in the past. The coverage will certainly be enlarged in the future.
One activity of the DLMS UA is aiming in this direction: A Working Group VAS (value added services) will define COSEM objects for value added services.
Best regards
Paul Fuchs, DLMS User Association, Editor
COSEM, Communication Profile
1. Introduction
The DLMS UA Newsletter 3 introduced the COSEM Interface Objects. Interface Classes are generic descriptions. Interface Objects are instantiations of Interface Classes. E.g. the class "Register" is formed by combining the features which are necessary to model the behaviour of a generic measuring register as seen from the client (central unit, hand held terminal). Defining a specific meter means defining several specific registers, e.g. two specific objects of the class "register" may be instantiated. This means that specific values are assigned to the different attributes. Through the instanciation one register becomes a "positive, active energy register" whereas the other becomes a "total, positive, reactive energy register".
- COSEM is a complete set of specifications defining
- a library of metering objects,
- how the objects are mapped to DLMS data units,
- how the DLMS data units are transported over a specific channel (the first complete set of specifications uses PSTN channels, ... more channels will follow).
- COSEM does not define new standards.
- COSEM defines which standards are used and how they are used.
The second book (COSEM Communication Profile) is subject of this DLMS UA Newsletter. It covers the 3 Layer Connection Oriented Profile, its HDLC based Data Link Layer and the Physical Layer Interface of the Connection Oriented Profile.
2. 3-Layer Connection oriented Profile
The scope of this document is to specify a 3-layer connection-oriented communications reference model which should be applied in any COSEM communications environment when services of higher layers are not required. Although this reference model includes communications profiles as well as for connection oriented than connectionless communications environments, this document specifies only the connection-oriented profile. This profile should be applied for point-to-point and for point-to-multipoint communications to metering equipment through local or remote direct connection. Examples for this type of communications are communications to metering equipment through the Public Switched Telephone Network ( PSTN ) or through a local communications link, e.g. through an optical port.
COSEM communication is based on the Client/Server paradigm, where metering equipment plays the server role. Note that the metering equipment is an abstraction, consequently the equipment playing the server role may be any type of equipment for which this abstraction is suitable. Figure 1. shows the communications architecture covered by this profile.
[Figure 1 not found]
The modem - if present - may be incorporated in the server and/or in the client. Direct connection (null modem) between the Client and the Server may also be used.
At the server side special configurations, where more than one servers are grouped to use the same communications link, may exist. These configurations are called multi-drop configuration.
Various considerations and implications result from using a 3-layer reference model, instead of a 7-layer one.
Figure 2 gives an overview for the application association establishment.
[Figure 2 not found]
- ASO, Application Service Object: An active element within (or equivalent to the whole of) the application-entity embodying a set of capabilities defined for the Application Layer that corresponds to a specific ASO-type. An ASO that provides the functions of the establishment and data transfer phases is considered a complete protocol.
- ASE, Application Service Element: A set of application functions that provide a capability for the inter-working of application-entity-invocations for a specific purpose; ASEs are a component of application service objects. An ASE can be considered to be a protocol module that is combined with others to form a complete protocol.
- ACSE: The Association Control Service Element is the common mechanism in the ALS for establishing and releasing ASO-associations.
- CF, Control Function: The component of an ASO that controls the interactions among the ASEs and/or ASOs and the service provided by the containing ASO. The CF defines how the service primitive of the Service Definition are mapped to the primitives of the component ASEs and ASOs.
- LLC: Logical Link Control
- MAC: Medium Access Control
In order to be able to access a COSEM Object, a COSEM Client must establish an association with the COSEM Logical Device, which includes that object. In any case, authentication takes place during this association-establishment. Associations are established ( and released normally or abnormally ) in using the standard connection-oriented Association Control Service Element (ACSE).
Authentication may be established with no security, with low level, password based authentication security or with high level, four-pass authentication security.
3. HDLC based Data Link Layer for 3-Layer connection oriented Profile
This document gives only an overview of the HDLC protocol. The complete HDLC protocol is defined in ISO/IEC 13239. Enhancements of HDLC are used as defined in several amendments of ISO/IEC 13239.. The relevant chapters are referenced within this document.
This document contains the precise definitions for:
- the subset of the HDLC protocol used in the COSEM environment,
- the HDLC options used in the COSEM environment,
- the values assigned to the relevant HDLC parameters (e.g. time-outs).
Examples are given for:
- the typical exchange of HDLC frames,
- the negotiation procedure,
- implementation of the FCS.
This document describes the data link layer based on HDLC within the communications architecture used in the COSEM three-layer connection oriented profile.
The data link layer is divided into two sublayers: the Logical Link Control (LLC) sublayer and the Medium Access Control (MAC) sublayer. This division is artificial: the only role of the LLC sublayer is to ensure consistent data link addressing - it is used as a sort of protocol selection.
The LLC sublayer is based on LLC type 1 as defined in ISO 8802-2.
The MAC sublayer is based on HDLC as defined in ISO/IEC 13239. Enhancements of HDLC are used as defined in several amendments of ISO/IEC 13239.
The two sublayers are defined in terms of:
- services provided by the layer to the next upper layer (services),
- services used by the layer (mapping to the services of the next below layer).
- what the layer is doing and how it is accomplished (protocol).
LLC and MAC state transition definition tables are given, as well for the server as for the client side.
4. Physical Layer Interface (Connection Oriented Profile)
The standards groups and the computer industry have developed many specifications defining the interfaces of Data Communication Equipment (DCE) such as modems and Data Terminal Equipment (DTE), such as computers, terminal or other communicating devices. Acceptance of these Specifications has made it possible to interface equipment from different vendors.
Physical Level interfaces are so named because DTE and DCE are physically connected by either wires, cables or wave signals.
The physical layer provides the data transfer interface between DTE and DCE, the control signals e.g. data flow handshaking, clocking signals, the electrical ground and mechanical connectors.
In order to ensure maximum flexibility, COSEM specify rather a physical interface than the physical layer itself. The following assumptions are taken in consideration:
- the communication is point to point or point to multipoint
- half-duplex or duplex connections are both possible
- asynchronous transmission with 1 start bit, 8 data bits, no parity and 1 stop bit
For data communications under the above conditions the interfaces described in this document are recommended.
This Document proposes a set of Physical Layer Interfaces which are appropriate for the COSEM 3-layer connection oriented profile. COSEM does not impose constraints by allowing only a limited number of physical layer interfaces. It is a good idea, that when ever a new interface has to be added, it should be documented here.
Lots of the metering devices in the commercial an industrial environment are equipped with the IEC 1107 optical interface. Depending on its configuration a meter may be capable to communicate with either the IEC 1107 protocol or the COSEM protocol stack.
Therefore a special selection mechanism has been agreed, to allow the protocol selection during the connection establishing procedure as defined in IEC 1107.
DA/DSM '98 London, 27 - 29 Oct. 1998
The CIFACES 98 Congress and Exhibition was a success
The "blue book", the COSEM Interface Objects, and the "green book", the COSEM Communication Profile, have been presented at CIFACES in Strasbourg/France during the 6th International Congress on Electricity Billing and Metering, held on 14 and 15 May 1998. The booth of the DLMS User Association was built for discussions and presentations on a large monitor of the demo stand. The logos of all member companies were displayed on the wall, already 14 flags of important organisations were shown.
The interest on the two presented books was quite remarkable. The books have the "look and feel" of standards, but they are still reserved for "members only", and as such, they were symbolically chained to the booth of the DLMS User Association. A strong wish was expressed to "go public", to open the content, e.g. to standards bodies.
The next step towards reality: DA/DSM '98 in London, 27-29 Oct.
Deregulation, liberalisation and the increasing competition forces utilities to reorganise in order to meet the changing customer demands. DA/DSM DistribuTECH Europe is developed by the European utility distribution industry to serve as a meeting place for those involved in European utility distribution activities and who would like to hear, discuss and see the solutions that will help to go through the changes more smoothly. DA/DSM DistribuTECH Europe is part of a series of global events (Asia and Americas) and organised for the fifth time in Europe.
The booth of the DLMS User Association will be double the size it had on previous exhibitions. The presentation is now in the planning phase. Some members have reacted to the call for contribution. There will be meters on the wall, either pre-released final products or prototypes in a final stage. And there will be master stations, accessing the devices and presenting DLMS and COSEM object features.
The DLMS User Association will also actively participate by contributing papers, as well to the DA/DSM DistribuTECH Europe as also to the pre-conference full day seminar on 26 Oct 1998, called "Metering: A deregulation survival kit".
2nd General Meeting
The General Meeting of the DLMS UA will take place
Change! On 29 October (earlier announced: on 28 October), 1998, of course in the close neighbourhood of the DA/DSM in London. Main points of discussion will be the elections (Management Committee and auditor), acceptance of the annual report and accounts, decisions on the budget and membership fees for 1999.
(Archive: Newsletter No. 1998/3, March '98)
(Archive: Newsletter No. 1997/2, December '97)