Protocols & Standards · June 14, 2026 · 2 min read

DLMS/COSEM Explained: The Global Standard for Smart Meter Communication

DLMS/COSEM is the world’s most widely deployed standard for smart meter data exchange. If your electricity meter can talk to a head-end system (HES), there is a high probability it speaks DLMS — or will soon.

What is DLMS/COSEM?

DLMS (Device Language Message Specification) is the application layer messaging protocol. COSEM (Companion Specification for Energy Metering) defines the object model — how meter data is structured, named, and accessed. Together they form a complete end-to-end standard maintained by the DLMS User Association.

The standard is published as the IEC 62056 series by the International Electrotechnical Commission.

Key Concepts

The Object Model

Every piece of data in a DLMS meter is represented as a COSEM object. Each object has:

  • A class ID (e.g., Class 3 = Register, Class 7 = Profile Generic)
  • An OBIS code (Object Identification System) — a 6-byte address like 1.0.1.8.0.255 for active energy import
  • Attributes (readable values) and Methods (callable actions)

Communication Profiles

DLMS can run over virtually any transport:

  • HDLC — serial/optical port (the classic IEC 62056-21 Mode E)
  • TCP/IP — direct Ethernet or GPRS/3G/4G
  • PLC — powerline carrier (PRIME, G3-PLC, Meters & More)
  • NB-IoT / LwM2M — via the DLMS Water Smart Meter Generic Companion Profile

Security

DLMS/COSEM supports strong authenticated encryption (AES-128 GCM) at the application layer, independent of the transport — a major advantage over protocol-level-only security.

OBIS Codes: The Address Book of a Meter

Every meter value has a globally standardized OBIS code. Common electricity examples:

  • 1.0.1.8.0.255 — Active energy import (kWh), total
  • 1.0.2.8.0.255 — Active energy export (kWh), total
  • 1.0.31.7.0.255 — Instantaneous current, L1
  • 1.0.32.7.0.255 — Instantaneous voltage, L1
  • 0.0.96.1.0.255 — Meter serial number

Why DLMS Dominates

  • Interoperability — a certified DLMS meter from any vendor should work with any certified HES
  • Completeness — covers everything from billing data to firmware updates (image transfer, Class 18)
  • Extensibility — vendor-specific objects can be added without breaking compliance
  • Legal backing — MID-certified meters in the EU almost universally use DLMS

Further Reading

  • DLMS User Association Blue Book (object model): dlms.com
  • DLMS User Association Green Book (architecture): dlms.com
  • IEC 62056-7-5: DLMS/COSEM transport layers
  • IEC 62056-6-2: COSEM interface classes