DLMS or Device Language Message Specification is a commonly used protocol that facilitates communication between utility control centers, data concentrators and smart meters. Also known as IEC 62056, it is an international standard that was created by the International Electrotechnical Commission (IEC).
DLMS protocol is a versatile communication standard created for utility metering and control systems. Its purpose is to facilitate information exchange between devices regardless of their brand or the communication technology they use. This protocol is adaptable across various physical mediums like power line carriers, RF, infrared, cellular and optical communication.
This article aims to make DLMS easier to understand by breaking down its functionality and showcasing its potential uses.
Table of Contents
What is DLMS?
DLMS is a universally adopted protocol standard utilized in electricity, water and gas meters worldwide. This standard is essential for accessing data from various meter types and manufacturers. It enables clients to communicate with meters effectively ensuring they understand and use the same communication “language”.
This presents a significant issue. When you have meters from various manufacturers that don’t communicate using the same protocols it necessitates multiple data collection systems resulting in increased costs and complexity. Managing multiple reading systems and converting gathered data into a uniform format for comparison adds further complexity. Additionally, being restricted to a specific meter manufacturer can prevent the possibility of switching to a different model.
To enhance compatibility, a standardized approach is essential along with mandatory certification for meters. Without proper certification, meters lack full compatibility. Minor meter differences can hinder their seamless cooperation leading to ongoing issues.
DLMS is a standard that draws from various IEC standards:
- IEC 62056-21: Direct local data exchange
- IEC 62056-42: Physical Layer Services and Procedures for Connection-Oriented Asynchronous Data Exchange
- IEC 62056-46: Data link layer using HDLC protocol
- IEC 62056-47: COSEM transport layers for IPv4 networks
- IEC 62056-53: COSEM application layer
- IEC 62056-61: OBIS Object identification system
- IEC 62056-62: Interface objects
Additionally, there exist nationalized sub-standards based on DLMS. These sub-standards aim to eliminate unnecessary functionalities simplifying meter implementation and enhancing their durability.
- India Standard 15959 (Part-1) 2011: Specifies data exchange protocols for electricity meter reading, tariff information and load control.
- India Standard 15959 (Part-2) 2016: Provides companion specifications for data exchange related to electricity meter reading, tariff and load control specifically designed for smart meters.
- Italy Standard UNI/TS 11291-11-2: Refers to a specific standard from Italy.
- Chinese Standard DL/T698.45: Refers to a standard from China related to a particular subject.
DLMS is extensively documented yet it’s not as simple a protocol as M-BUS, MeterBus, Profibus or other field buses.
Drawing a comparison between DLMS and field buses isn’t quite fitting given their distinct purposes yet this misconception occurs frequently.
Fieldbuses are more familiar to most readers, hence we’ll use them here as an illustration.
The primary difference between those protocols and DLMS lies in the volume of data they handle. Fieldbuses typically deal with reading register values with limited data size. For example, the read payload might only encompass a 16-bit register address.
Modbus RTU request to read 2 registers:
Request: 01 03 02 58 00 02 44 60
DLMS request to read 2 registers:
Request: 7E A0 24 03 21 5A 5C F0 E6 E6 00 C0 03 C1 02 00 03 01 01 15 19 00 FF 02 00 00 05 01 00 1F 04 00 FF 02 00 31 8E 7E
Authentication Levels Enable Different Access Rights
Different authentication levels exist in DLMS but are missing from field buses. Each level gives different degrees of control over the meter.
The client can view the amount of electricity used by using authentication levels. However, they are not permitted to shut off the meter. On the other hand, “What steps can I take to adjust the scaler to decrease electricity consumption?” is a question.
Without proper authentication, clients can usually read meter values. With low-level authentication, clients can adjust the time while high-level authentication grants them full control enabling actions like firmware updates, meter resets and more.
In a closed system or within fieldbuses authentication levels might seem unnecessary. However, in DLMS establishing communication with the meter is essential before accessing any data from it.
There are pre-established connections that don’t need authentication allowing clients to simply read values from the meter. However, it’s important to note that not all meters support these pre-established connections.
Secured Connections with Ciphering
Securing connections in fieldbuses may not be important but it becomes mandatory when transmitting data Over The Air via LoRa or other Mesh networks. DLMS supports three different ways of securing the data.
- Authentication
- Encryption
- Authentication and Encryption
Logical Name and Interfaces
In Fieldbus protocols, it is important to know the registered address for retrieving a meter’s value. When the register value is accurate the meter responds with the corresponding data. However, if you switch the meter type or model the register address changes and needs to be updated accordingly.
It won’t take much work to update this data if you have ten meters. If you have 100 meters or more, updating this will be completely different.
Within DLMS, there exist interfaces that specify the type of data you want from the meter. The concept revolves around ensuring that all meter manufacturers adhere to standardized interfaces and logical names.
You can replace a meter with a new one if different meters use the same interfaces and logical names. This allows for changing the meter model and manufacturer while still using the old data collection system.
Client Address
Every authentication level corresponds to its client address. Therefore, when the authentication level changes the client address changes as well. The DLMS standard defines a client address only when the connection is established without authentication.
In an ideal scenario, all meter manufacturers would use the same client addresses. However, these addresses aren’t defined in the DLMS standard resulting in different meters using varying values.
If the client’s address is wrong the meter won’t respond. Only the meter manufacturer knows the correct client address to use. Therefore, it’s important to have this value documented. While it can be determined through trial and error it’s more efficient to retrieve it from the document.
Server Address
Each meter needs to have its unique server address. This address allows the meter to determine which messages it should receive. Additionally, it allows the client to identify the sender of the messages.
If you’re establishing a connection using a Point-to-Point connection (like TCP/IP or a Serial port) you can use the default server address 1.
The meter serial number commonly serves as the server address enabling multiple meters to operate within the same network (UDP, radio, RS-485).
PDU and Frame Size
The size of the Protocol Data Unit (PDU) is determined by the meter it originates from. If a meter has limited memory the PDU size will be smaller. The frame size, on the other hand, is contingent upon the communication channel used. For example, in a communication channel like TCP/IP the frame size could be 1024 bytes. Conversely, in a wireless communication environment like Over The Air, the frame size might typically be around 100 bytes.
For example:
The data size is 1MB but the meter has only 2KB (PDU) of memory available to store the data. Consequently, the entirety of the data cannot be read all at once. The size of the PDU (2 KB) is read into the memory in portions. Once the PDU reaches its capacity it’s transmitted over a communication channel. The size of the frame depends on the specific communication channel which might result in the PDU being split into 20 frames. Each of these frames needs to be delivered before the next PDU can be requested.
Many meters use a default frame size of 128 bytes which isn’t a problem in most cases. However, it could become an issue if the communication channel shifts from GPRS to Lora.
Why DLMS?
The need for a standardized communication protocol for smart meters arose with the increasing adoption of these devices in the energy sector. DLMS emerged as a solution due to its key features:
- Openness and Flexibility
DLMS is not tied to any specific vendor or technology allowing for interoperable communication between devices from different manufacturers. This flexibility is crucial for creating a diverse and competitive smart grid ecosystem.
- Scalability and Extensibility
DLMS is designed to scale to accommodate large networks of smart meters. It also provides mechanisms for extending functionality to support future applications and technologies.
- Object-oriented Data Model
DLMS utilizes an object-oriented data model that represents real-world entities like meters, sensors and tariffs. This model facilitates easy access and manipulation of data by applications simplifying integration and interfacing.
- Security and Authentication
DLMS incorporates robust security features to protect data integrity and prevent unauthorized access to metering devices. This ensures the reliability of the information shared.
Applications Across Various Sectors
The DLMS (Device Language Message Specification) protocol is exceptionally versatile finding applications across various sectors. Below is a summary of its main applications:
- Electricity Metering
DLMS is used in electricity metering systems. It allows for gathering consumption data, simplifies remote meter reading and accommodates different billing methods.
- Gas Metering
The procedure is used in gas metering to manage and control gas usage. DLMS enables precise measurement and remote transmission of gas consumption data.
- Water Metering
DLMS plays an important part in water metering as it allows for the tracking and reporting of water usage. It helps monitor patterns of consumption and detects any leaks or irregularities.
- Heat Metering
DLMS expands its capabilities to include heat metering applications enabling the measurement and oversight of heat consumption in heating systems thereby ensuring their efficient utilization.
DLMS’s Strengths
DLMS distinguishes itself in the smart metering market with a unique blend of advantages:
- Standardized Object Models
DLMS uses standardized object models allowing structured data access in smart meters and utility devices. These models are adaptable and customizable to suit specific requirements.
- Security and Reliability
DLMS offers robust security features ensuring secure communication between utilities and consumers. It maintains data confidentiality and integrity improving reliability.
- Open Standardization
DLMS’s open standard promotes interoperability among devices from different manufacturers. This compatibility enables seamless operation within a unified system regardless of device origins.
- Flexibility
The adaptable nature of the protocol enables the creation of personalized objects to meet the changing requirements within utility metering systems.
- Global Adoption
DLMS’s strengths have contributed to its widespread adoption making it an important component in modern utility metering systems worldwide.
In the context of IoT gateways, DLMS plays an important role in enabling connectivity & data exchange between smart devices and centralized systems. IoT gateways act as intermediaries collecting data from various sensors & devices, processing it and transmitting it to the cloud or other centralized systems for analysis and decision-making.
A DLMS-enabled IoT gateway acts as a bridge allowing seamless integration of diverse devices and ensuring streamlined communication using DLMS protocol. These gateways can aggregate data from different devices such as smart meters, sensors and actuators and communicate with utility management systems or IoT platforms.
Conclusion
DLMS is a communication protocol that breaks down barriers between devices ensuring seamless communication, security, and adaptability. As our world becomes more interconnected, DLMS stands as the cornerstone enabling efficient resource management and innovation in utility systems globally.
Manvendra Kunwar 
Gulshan Kumar