What is BS EN 62056-42 – COSEM three-layer connection profile for data exchange about? 
DLMS/COSEM is the global standard for energy & water smart management, advanced control and innovative utility meter data exchange. It specifies an object-oriented data model, an application layer protocol and media-specific communication profiles.
BS EN 62056 is a European Standard series that discusses electricity metering and data exchange for meter reading, tariff and load control.
BS EN 62056-42 is the 42nd part of the BS EN 62056 series that specifies the physical layer services and protocols within the Companion Specification for Energy Metering (COSEM) three-layer connection oriented profile for asynchronous data communication.
In annex A of BS EN 62056-42, an example of how this physical layer can be used for data exchange through the Public Switched Telephone Network (PSTN) using intelligent Hayes modems is given.
Annex B of BS EN 62056-42 gives an explanation of the role of data models and protocols in electricity meter data exchange.
Note 1: BS EN 62056-42 does not specify physical layer signals and mechanical aspects.
Note 2: Local, implementation-specific issues are also not specified in BS EN 62056-42.
Who is BS EN 62056-42 - COSEM three-layer connection profile for data exchange for? 
BS EN 62056-42 on COSEM three-layer connection profile for data exchange is relevant to: 
- Electric supply meter device manufacturers
- Power distribution and transmission companies
- Utility companies
- Local authorities
- Regulatory bodies
- Quality control and testing personnel
- Engineers
Why should you use BS EN 62056-42 - COSEM three-layer connection profile for data exchange?
COSEM includes a set of specifications that defines the transport and application layers of the DLMS protocol that are of significance to the successful large-scale roll outs of systems such as smart metering systems that contain a large number of end-devices. The COSEM objects provide several mechanisms, like selective access, compact data types, and compact encoding to ensure high efficiency.
BS EN 62056-42 walks you through service and protocol specifications required for secure data exchange within smart utility meters and similar devices as messages between the end devices / meters may need to be transported to the applications of utilities, energy service providers and
similar organizations through a number of devices and the communication links between them. Therefore, BS EN 62056-42 can contribute to providing application level, end-to-end security that ensures confidentiality, authenticity, and proof of origin between the end points.
Thus, by complying with BS EN 62056-42 guidelines, you can ensure safe interoprability and system integration with efficient data exchange between devices.
