Telephone call restrictor

Details Telephone call restrictor Telephone call restrictor

1974-08-08

1976-10-12

Cooper, William C.

H04M 166

Patent

active

039859720

ABSTRACT:
A telephone call restrictor is described for restricting telephone calls from one or more trunk or extension lines to a select group of telephone numbers. The restrictor comprises a digit coupler for detecting a predetermined number of the digits of the number called -- e.g., three, six or nine. One or more of the detected digits is individually decoded for providing a first output corresponding to the numerical value of the digit decoded. The detected digits not decoded are used to address a programmable read only memory (PROM). The memory is prearranged to contain code words corresponding to acceptable telephone numbers. The outputs of the decoder and memory are compared. If the digits decoded and the digits used to address the memory are from an acceptable telephone number, a predetermined correspondence exists between the output of the decoder and the output of the memory indicating an acceptable number has been dialed. If the correspondence does not exist, a memory abort signal is generated for causing a dial tone to reappear on the lines, restricting the call.

REFERENCES:
patent: 3736383 (1973-05-01), LeBaron
patent: 3851109 (1974-11-01), Downs

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