Abstract: A security system for an exchange having distributed control. Exchange control is distributed among a plurality of microprocessors and in microprocessor terminal units connected to a time-division switching network. The security system is organized on three levels: (I) a first level comprising security means in each microprocessor for detecting faults and for taking decisions concerning current processing; (II) a second level comprising means for managing said security blocks and for switching over from one block to another and re-configuring the links affected by the switchover; and (III) a third level comprising means for managing the microprocessors of the exchange control means and the two point-to-point links, said third level means comprising two identical peripheral control units controlling respective mass memories each containing a copy of the software needed to run the exchange.

Abstract: Subscribers (Ab1 to Ab8) in a telecommunications system are normally connected via respective subscriber lines (L1 to L8) to respective subscriber terminals (T1 to T8). Automatic subscriber line test means are connected via a subscriber line test bus (BL) and various relay contacts (r1 to r8 and re1 to re8) to the subscriber lines for testing purposes. Eight subscriber terminals (T1 to T8) populate a single circuit card, thereby constituting a terminal unit (TU1 to TUp). A group of terminal units is associated with a spare terminal unit (TUS). When a faulty terminal unit is detected, it is taken out of service and the spare terminal unit takes over. This is done by switching the subscriber lines connected to the faulty terminal unit over to the test bus. The spare terminal unit is likewise connected to the test bus. To enable the test means to continue testing the remainder of the telecommunications system without being interrupted by the emergency connection via the test bus, isolator means (I) are provided.

Abstract: Traffic simulator for tandem exchange testing. The simulator comprises a calling side module (CAM) to simulate a calling exchange, with facilities for the selection of dialling information, type of test operation and signalling code and connected to the tandem exchange (CT) at an i/c circuit terminating equipment (JA) of a type suited to the selected signalling code; answering side module (CAV) to simulate a called exchange, connected to the tandem exchange at an o/g circuit terminating equipment (JD) and comprising means for selection of the signalling code for communication with said terminating equipment, said two modules being independent and signal flows between them passing exclusively through the tandem exchange.