IEC 62056-3-1:2021 describes two sets of profiles: the first set of profiles allows a bidirectional communication between a client and a server. This set of profiles is made of three profiles allowing local bus data exchange with stations either energized or not. For non-energized stations, the bus supplies energy for data exchange. Three different profiles are supported: • base profile: this three-layer profile provides remote communication services; NOTE 1 This first profile was published in IEC 61142:1993 and became known as the Euridis standard. • profile with DLMS: this profile allows using DLMS services as specified in IEC 61334-4-41; NOTE 2 This second profile was published in IEC 62056-31:1999. • profile with DLMS/COSEM: this profile allows using the DLMS/COSEM Application layer and the COSEM object model as specified in IEC 62056-5-3 and in IEC 62056-6-2 respectively. The three profiles use the same physical layer and they are fully compatible, meaning that devices implementing any of these profiles can be operated on the same bus. The transmission medium is twisted pair using carrier signalling and it is known as the Euridis Bus. The second set of profiles allows unidirectional communication between a given Energy Metering device and a Customer Energy Management System. This second set is made up of three profiles. Subclause 4.2.1 to Clause 8 included specify the bidirectional communication using twisted pair signalling and Clause 9 to 9.5 the unidirectional communication using twisted pair signalling. This second edition cancels and replaces the first edition of IEC 62056-3-1, issued in 2013, and constitutes a technical revision. The main technical changes with regard to the previous edition are as follows: • addition of a profile which makes use of the IEC 62056 DLMS/COSEM Application layer and COSEM object model; • review of the data link layer which is split into two parts: – a pure Data Link layer; – a "Support Manager" entity managing the communication media; • ability to negotiate the communication speed, bringing baud rate up to 9 600 bauds.