Abstract: A digital information switching system features modular design with dispersed processing in which data is switched locally in one of a plurality of remote switching units for connection between local terminals, and data to be exchanged between terminals connected to different remote switching units is switched in a central switching unit, which is connected to the remote switching units by way of interswitch links. Both the central switching unit and the remote switching units are of the same general configuration being individually processor controlled. Reliability of each unit in the system is enhanced by diagnostic and maintenance features including provision of redundant devices in each unit, detection of device failures, automatic replacement of failed devices with redundant devices and communication of the failure to a remote service center.