Abstract: A modular telecommunication system comprises a plurality of switching blocks connected in parallel by interconnecting lines. Each of the switching blocks includes a multiplicity of line terminators each adapted to be connected to a data terminal. In each switching block there are provided (1) a central processing system for establishing communication links associated with a respective call, (2) a communications controller for controlling local data exchange between pairs of line terminators connected thereto across real channels, (3) a virtual channel controller for controlling remote data exchange across virtual channels to different switching blocks and (4) interface units arranged between the virtual channel controller and a respective one of the interconnecting lines.