DLMS or Device Language Message Specification a generalized concept for abstract modelling of communication entities for Automatic Meter Reading and Smart Metering systems. COSEM (COmpanion Specification for Energy Metering) sets the rules, based on existing standards, for data exchange with energy meters. DLMS is a language or communication protocol used for to carry the information between the metering equipment and the data collection systems.

Automatic meter reading (AMR) is the technology of automatically collecting consumption, diagnostic, and status data from water meter or energy metering devices (gas, electric) and transferring that data to a central database for billing, troubleshooting, and analyzing. This technology mainly saves utility providers the expense of periodic trips to each physical location to read a meter. Another advantage is that billing can be based on near real-time consumption rather than on estimates based on past or predicted consumption. This timely information coupled with analysis can help both utility providers and customers better control the use and production of electric energy, gas usage, or water consumption.

Automatic meter reading technologies include handheld, mobile and network technologies based on telephony platforms (wired and wireless), radio frequency (RF), or powerline transmission. Protocols are standarized between manufacturers by such as DLMS or IEC 62056.

Device Language Message Specification (DLMS) is the suite of standards developed and maintained by the DLMS User Association and has been co-opted by the IEC TC13 WG14 into the IEC 62056 series of standards. 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 three specification documents namely Green Book, Yellow Book and Blue Book.
The IEC TC13 WG 14 defines the DLMS specifications under the common heading: “Electricity metering – Data exchange for meter reading, tariff and load control.” IEC 61107 or currently IEC 62056-21, was an international standard for a computer protocol to read utility meters.