Locally controlled telecommunications switching system, in particular PBX system

A locally controlled telecommunications switching system, which can be used as both a PBX system and an in-house telephone system, has a plurality of functional units (subscriber circuits, push-button dialling receiver, ringing tone generator and, if necessary, exchange line connection set) as well as a data bus via which switching data are transmitted, and a message bus via which connections are switched through. To enable the telecommunications switching system to be extended in simple stages, a control circuit (1, 2, 3, 4, 5) is allocated to each functional unit (TS1, TSn, TWE, RTG, AVS) to which it is physically connected to form a module. The control circuits of all the functional units have an identical structure and are provided with an input/output circuit (6, 7, 8, 9, 10), a control processor (16, 17, 18, 19, 20), a bus control (21, 22, 23, 24, 25) and a switching network (11, 12, 13, 14, 15).