The logical design of a star network comprises a number of point to point connections which communicate via a central processing unit. Short haul modems are used to extend the distance between the units and to provide galvanic isolation. Different interfaces and cable types (e.g. 4-wire and fiber optic cables) can be combined in an asynchronous star network. Since each unit communicates with the central processing unit via a separate line, all other communication is not interrupted in the event of a single cable failure. Westermoís star network, which is a polling network, requires intelligent units which recognise their own addresses.