DLMS/COSEM (IEC 62056, AINSI C12, EN13757-1) is the global standard for energy & water smart management, advanced control and innovative metering.

It specifies an object-oriented data model, an application layer protocol and media-specific communication profiles.

DLMS/COSEM comprises three key components: 

  • COSEM - Companion Specification for Energy Metering - the object model capable of describing virtually any application;
  • OBIS - Object Identification System, the naming system of the objects; and DLMS - Device Language Message Specification - the application layer protocol that turns the information held by the objects into messages.
  • DLMS/COSEM can be used for all utilities / energy kinds, all market segments, all applications and over virtually any communication media.


COSEM stands for Companion Specification for Energy Management

The COSEM object model describes the semantics of the language.

 COSEM interface classes and their instantiations (objects) can be readily used for modelling energy management use cases including metering, yet general enough to model any application.

Object modelling is a powerful tool to formally represent simple or complex data. Each aspect of the data is modelled with an attribute. Objects may have several attributes and also methods to perform operations on the attributes. 

Objects can be used in combinations, to model simple use cases such as register reading or more complex ones such as tariff and billing schemes or load management. 

Today there are 89 interface classes specified, but up to 65 535 are possible.


OBIS stands for Object Identification System

OBIS is the naming system of COSEM objects.

OBIS codes are specified for electricity, gas, water, heat cost allocators (HCAs) and thermal energy metering, as well as for abstract data that are not related to the energy kind measured.

The hierarchical structure of OBIS allows classifying the characteristics of the data e.g. electrical energy – active power – integration – tariff – billing period;

There are 281 474 billion OBIS codes available of which 4 398 billion are reserved for standardization purposes. The rest can be used for manufacturer, country and consortia specific purposes.

DLMS /COSEM application layer services

DLMS stands for Device Language Message Specification

The syntax of the language is specified by the DLMS services.

DLMS/COSEM uses a client-server paradigm where the end devices, typically meters are the servers and the Head End Systems or concentrators are the clients.

The DLMS/COSEM application layer provides:

  • the ACSE services to connect the clients and the servers; and
  • the xDLMS services to access the data held by the COSEM objects. The xDLMS services are the same for each object; this allows new objects to be added to the model without affecting the application layer.

The application layer also builds the messages (APDUs, Application Protocol Data Units), applies, check and removes cryptographic protection as needed and manages transferring long messages in blocks.

The messages can be then transported over virtually any communication media.

There are various built-in mechanisms available for optimizing the traffic to the characteristics of the media.


The application messages can be transported over virtually any communication media

The DLMS/COSEM communication profiles specify, for each communication the protocol stack and the binding of the lower protocol layers to the DLMS/COSEM application layer.

Communication profiles are available for:

  • Local ports, PSTN/GSM: with HDLC data link layer RS232 / RS485;
  • GPRS;
  • IPv6, IPv4, TCP and UDP;
  • S-FSK PLC;
  • G3-PLC with UDP/ IPv6;
  • Prime PLC without IP, with IPv6, IPv4, TCP and UDP;
  • Wired and wireless M-Bus;
  • Mesh networks with IPv6 and 6LowPAN;
  • Wi-SUN, LoRaWAN, NB IoT and CoAP.

DLMS/COSEM specification

The DLMS/COSEM specification is developed and maintained by the DLMS User Association:

- COSEM and OBIS are specified in the Blue Book;

- the DLMS/COSEM application layer, the lower layers and the communication profiles are specified in the Green Book.

The contents of these Books are internationally standardized by IEC TC13 WG14 and CEN TC294.