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A Python library for DLMS/COSEM
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A Python library for DLMS/COSEM.


DLMS/COSEM (IEC 62056, EN13757-1) is the global standard for smart energy metering, control and management. It specifies an object-oriented data model, an application layer protocol and media-specific communication profiles.

DLMS/COSEM comprises three key components:

Companion Specification for Energy Metering - the object model capable of describing virtually any application.
Object Identification System, the naming system of the objects
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 (Companion Specification for Energy Metering)

The COSEM object model describes the semantics of the language.

COSEM interface classes and their instantiations (objects) can be readily used for modelling metering use cases, 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.

OBIS (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.

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 model where the end devices, typically meters are the servers and the Head End Systems are the clients.

The DLMS/COSEM application layer provides:

  • the ACSE services to connect the clients and the servers.
  • 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 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;
  • Coming soon: Wi-SUN and NB IoT.

Development of this library

We are developing this library as an ongoing project to support DLMS/COSEM in our AMR (Automatic Meter Reading) system Utilitarian.

We are focusing our efforts on supporting DLMS over IP-based transports.

As of now we support:

  • Parsing DataNotification via UDP.

Future Work:

  • GET, SET, ACTION over pre-established associations.
  • Interface classes implementation.
  • DLMS Client to handle communication.
  • Establish Connections.
  • More Security options.

Tested with Italian Gas meters that are using a companion standard to DLMS. If you notice an error using the library please raise an issue.

This library is developed by Palmlund Wahlgren Innovative Technology AB. We are based in Sweden and are members of the DLMS User Association. We are currently developing a Head End System for Multi Utility Automatic Meter Readings.


We only support Python 3.6+

pip install dlms-cosem

Example Usage

To parse a message you need to use the XDlmsAPDUFactory

from dlms_cosem.dlms import apdu_factory

message = 'xxx'
apdu = adpu_factory.apdu_from_bytes(message)
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