A communications system in the stricter sense of the term is a system that enables information and data to be transmitted. To this end, connections are established between multiple communication subscribers. Open communications systems allow all connected subscribers to communicate freely and require standardisation of interfaces and logical functions. In data networks, this is realised in hierarchical models with several standardised levels.
Information and data are typically exchanged between devices via application-specific bus systems that employ a strict protocol. An example of a standardised data protocol is VDMA standard sheet 24223 – Device Profile for Liquid and Vacuum Pumps.