To ensure quality service, a toll switching system must be able to meet very stringent dependability and maintainability requirements. To meet these requirements a large package of maintenance software has been developed. This software consists of four functional areas. The first area deals with the detection and recovery from software malfunctions. These malfunctions include failing defensive program checks, scheduling irregularities, and mutilated data. The second area is concerned with the recovery from hardware faults. Hardware fault recovery is stimulated by a failing hardware check and is completed when the system has been reconfigured around the faulty unit. The third area is concerned with the diagnostic programs that aid the craftsperson in the identification and repair of the faulty unit. The fourth area provides for overall coordinated system recovery from multiple or very severe hardware and software malfunctions.