Internal telephone control system - uses individual telephone set each having four functional buttons and three status indicator lights

摘要

The circuit provides a functional button (Tp) which enables the free accessibility to be terminated and a conversation to be limited to already connected stations. In that state, the additional lamp (Lp) lights up at the 'protected' conversing stations. If thereafter another station tries to reach a protected station, the caller will get no audible engaged signal. If the protected conversation circle decides that other stations may be admitted, the functional button (Tp) must be actuated once more. Thereafter, a connection storage unit (VZS) in the central control unit (ZE) which holds the uncompleted calls, now renews automatically the internal call attempts of the still waiting stations, and these now join the no longer protected station group. Members of a protected conversation are aware of other stations calling through the light of specific colour illuminated on the button belonging to that station. A non-participating station can be called by a member of a protected group to join it.