Private telephone system - has priority and group facilities allowing change of priority through local instrument addressing central control memory

摘要

The system is used to increase the versatility of priority call selection and group connections. The former can be particularly useful if the telephone system is also used for emergency communications, for e.g in process or power plants. Certain, or, if necessary, all instruments (TS1,TSN) on the system are provided with controls for selecting a range of priorities (KN11....KM1X;KMN1...KMNY). A call and associated selected priority is put into a working store (MU) in the central processor (CC) where it is checked. If the priority has changed then the store is updated. If the called extension is engaged then by exercising a higher priority the existing call can be interrupted. Also priorities can be established even if the system is already fully occupied at the moment at which a new priority call is entered. As a precaution against conflicting instructions, only one extension can exercise top priority at any one time.