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IEC 62056 is a set of standards for electricity metering data exchange by the International Electrotechnical Commission.

The IEC 62056 standards are the international standard versions of the DLMS/COSEM specification.

DLMS or Device Language Message Specification (originally Distribution Line Message Specification),[1] is the suite of standards developed and maintained by the DLMS User Association (DLMS UA) and has been adopted by the IEC TC13 WG14 into the IEC 62056 series of standards. The DLMS User Association maintains a D Type liaison with IEC TC13 WG14 responsible for international standards for meter data exchange and establishing the IEC 62056 series. In this role, the DLMS UA provides maintenance, registration and compliance certification services for IEC 62056 DLMS/COSEM.

COSEM or Companion Specification for Energy Metering, includes a set of specifications that defines the transport and application layers of the DLMS protocol. The DLMS User Association defines the protocols into a set of four specification documents namely Green Book, Yellow Book, Blue Book and White Book. The Blue Book describes the COSEM meter object model and the OBIS object identification system, the Green Book describes the architecture and protocols, the Yellow Book treats all the questions concerning conformance testing, and the White Book contains the glossary of terms. If a product passes the conformance test specified in the Yellow Book, then a certification of DLMS/COSEM compliance is issued by the DLMS UA.

The IEC TC13 WG14 groups the DLMS specifications under the common heading: "Electricity metering data exchange - The DLMS/COSEM suite". DLMS/COSEM protocol is not specific to electricity metering, it is also used for gas, water and heat metering.


DLMS Master


DLMS (Device Language Message Specification) is a suite of standards developed and maintained by the DLMS User Association. COSEM (Companion Specification for Energy Metering) includes a set of specifications that define the transport and application layers of the DLMS protocol.

In DLMS/COSEM all the data in electronic utility meters and devices are represented using mapping them to appropriate classes and related attribute values.

Objects are identified with the help of OBIS (Object Identification System) codes (as per IEC 62056-61).

The DLMS driver allows only for readout and displaying only numeric values of DLMS object data fields. Connection via TCP (HDLC or WRAPPER) or serial (RS232/RS485) ports are supported.

The setup of the DLMS driver consists of communication and tag configuration. Protocol-specific parameters (except for DLMS/IEC handshake mode) apply for both serial and IP connections.


Devices section

serial_number, physical_address and logical_address define the meter addressing parameters. Either serial_number (meter serial number) or a combination of physical_address and logical_address is used. If a serial number is provided, physical and logical server addresses are ignored.

Before configuring the Device section it is best to first check the connection parameters with a 3rd party DLMS utility.

client_address is defined in hex and usually depends on the authentication used. Most meters support hex 11 for no authentication.

type defines the object referencing. SN should be used for short name referencing and LN for logical name referencing.

mode defines the communications mode. If IEC is used along with comms settings for serial readout, the connection is initiated as per IEC 62056-21, at the default initial baud rate (300 7E1). DLMS-HDLC shall be used for HDLC connections via IP. DLMS-WRAPPER is also supported for IP connections. The default setting is DLMS-HDLC.

timeout_ms defines the reply timeout for telegrams both via serial and TCP.

auth and password define the authentication mode and password. This can be set to None, or other authentication variant (see table below), depending on the mode configured and supported by the particular meter.
ip and port define the IP address and TCP port for DLMS communication via IP.

Connection parameters are device-specific and can differ between makes, models and utility companies. For initial connection settings please refer to the configuration of the particular meter.

When ip and port are configured, any serial port settings are ignored and the connection is initiated only via IP.

Device configuration parameters for DLMS meters acquisition:





Default Value

(when not specified)





User-­friendly name for a device

Yes Yes

description string

Description of a device

No No

device_alias string

Alphanumeric string to identify a device

Yes Yes

enable boolean

Enabling/disabling of a device

No No 1 0 1
protocol string

Protocol to be used

Yes Yes
serial_number integer

Meter serial number

No No 0

physical_address integer

Meter's physical server address

No No 1600

logical_address integer

Meter logical server address

No No 0

address_size integer

Meter address size in bytes

No No 1 1 4



Client address

Yes Yes

type string

Meter object referencing: SN - short referencing, LN - logical referencing

mode string

Initial handshake mode.

timeout_ms integer

Timeout in milliseconds

No No 2500

auth string


No No None None, Low, High, HighMd5, HighSha1, HighSha256, HighGmac, HighEcdsa
password string

Password for authentication

No (when auth is None) No (when auth is None)

ip string

IP address

Yes -

port integer

TCP port

Yes -


Communication port

- Yes
baudrate integer

Communication speed (bauds/s)

- No 9600 300, 600, 1200, 2400, 4800, 9600, 19200, 38400, 57600, 115200
databits integer

Data bit count for communication

- No 8 6 9
stopbits integer

Stop bit count for communication

- No 1 1 2
parity string

Communication parity option

- No none none, even,  odd
flowcontrol string

Communication device flow control option.

- No none none
retry_counter integer

Number of requests, before the link is considered lost (device status signals are changed) and reconnect attempt will be issued

No No 3

scan_rate_ms integer

If provided and positive all reads and writes will be executed within the timeframe in milliseconds

No No 10000

reconnect_time integer

Defines how often (in milliseconds) the client will try to reestablish communication with the meter after an unsuccessful attempt.

No No 1000

Signals section

DLMS configuration parameters creating signals:





Default Value

(when not specified)




User-­friendly signal name

Yes Yes



Device alias from a Devices tab

Yes Yes



Unique alphanumeric name of the signal to be used

Yes Yes



Enabling/disabling of an individual signal

No No 1





Enable logging in the event log

No No 0





Address of value to read (Short name).

No No 0



OBIS codes can be accompanied by an attribute index, eg.: Objects of register and extended register types do not require indexes and the scalers are applied to values automatically (though they can still be used if attributes other than the value need to be read out).

Yes Yes

Debugging the DLMS service

If the configuration for DLMS devices is set up, the handler for the protocol will start automatically. If the configuration is missing or contains errors, the protocol will not start. It is done intentionally to decrease unnecessary memory usage.

If DLMS does not work properly (e.g. no communication between devices, data is corrupted, etc.), a user can launch a debug session from the command-line interface and find out why the link is not functioning properly. To launch a debugging session, a user should stop the dlms process and run the dlms command with respective flags as in the table shown below.

Procedure for DLMS protocol service debugging:

  • Step 1: Service must be stopped by entering the following command into the WCC Lite:
    /etc/init.d/dlms stop
  • Step 2: After service is stopped it must be started with the preferred configuration file (JSON files found in /etc/dlms folder) and a debug level 7: dlms ­-c /etc/dlms/dlms.json ­-d7 --dlms                                                                                      Additional output forming options described in the table below.
  • Step 3: Once the problem is diagnosed normal operations can be resumed with the following command: /etc/init.d/dlms start

DLMS command line debugging options

Option  Description
­-h [ –-help ]  Display help information
­-V [ –-version ]  Show version
-p [ -–port ] ­Show output for one port only
­-d <debug level> Set debugging level
-­c [ –-config ]  Config path