Inhibiting trunk calls from private branch exchanges
阅读：158发布：2021-03-23
专利汇可以提供Inhibiting trunk calls from private branch exchanges专利检索，专利查询，专利分析的服务。并且To prevent the unauthorized initiation of toll calls from a local telephone station served by a private branch exchange (PBX), the latter is equipped with monitoring circuitry working into a binary/decimal counter which is activated during the dialing of an initial digit (or combination of digits) and, in response to one or more predetermined values thereof, trips a flip-flop to disconnect the station from the line. The flip-flop is also tripped if dialing is commenced before reception of a dial tone from the central office, or if dialing is continued after the arrival of a second a-c signal (line free or busy) from that office. To forestall the generation of a spurious dial tone by voice frequencies. the a-c path from the local station to the PBX is opened during dialing.，下面是Inhibiting trunk calls from private branch exchanges专利的具体信息内容。
1. A device for preventing the initiation of certain outgoing calls, characterized by a predetermined numerical value of at least one specified call-number digit, from a local station served by a private branch exchange connected via an outgoing line to a central office of a telecommunication system, comprising: pulsing means at said branch exchange responsive to a call selector at said station for periodically opening and closing a line loop between said branch exchange and said central office to transmit successive digits over said line; monitoring circuitry at said branch exchange controlled by said pulsing means and including pulse-repeating means for generating trains of stepping pulses in the rhythm of dial pulses emitted by said call selector and integrating means connected to said pulse-repeating means for deriving an individual digital pulse from any such train of stepping pulses; electronic pulse-counting means connected to said pulserepeating means for receiving said stepping pulses therefrom, said pulse-counting means having an output circuit with at least one output lead electrically marked in response to a predetermined number of consecutive stepping pulses; digit-counting means connected to said integrating means for receiving said digital pulses therefrom and ascertaining the numerical order of a transmitted digit represented by any train of stepping pulses; evaluation means connected to both said pulse-counting means and said digit-counting means for emitting an inhibition signal upon establishing a prohibited correlation between said predetermined number and the numerical order of the transmitted digit, said evaluation means being further connected to said monitoring circuitry for actuation by a reading pulse generated at the end of each digital pulse, said pulse-counting means being connected to said monitoring means for resetting by a zero-setting pulse following said reading pulse with a predetermined delay; and switch means controlled by said evaluation means for effectively decoupling said station from said line in response to said inhibition signal.
2. A device as defined in claim 1 wherein said evaluation means comprises a first and a second gating circuit each provided with input connections to both said pulse-counting means and said digit-counting means, sAid first gating circuit having an output connection to said switch means, further comprising blocking means controlled by said second gating circuit for deactivating said pulse-counting means upon ascertainment of a relationship inconsistent with said prohibited correlation between said predetermined number and the numerical order of the selected digit.
3. A device as defined in claim 2 wherein said monitoring circuitry comprises differentiation means connected to said pulse-repeating means for generating a variety of pulses upon substantial variations in the average potential of said line, including a seizure pulse upon initial closure of the line loop and a release pulse upon final opening thereof, said switch means comprising a first flip-flop settable by said output connection and coupled to said differentiation means for resetting by said seizure pulse, said blocking means comprising a second flip-flop settable by said second gating circuit and coupled to said integrating means for resetting in the absence of a digital pulse.
4. A device as defined in claim 3 wherein said digit-counting means comprises a plurality of decoding stages and wherein said second gating circuit comprises a like plurality of coincidence gates connected on the one hand to the output circuit of said pulse-counting means and on the other hand to respective decoding stages for successive enablement thereby upon the occurrence of consecutive digits in an initial portion of a call number, said first gating circuit including at least one coincidence gate connected to said output circuit and one of said decoding stages for enablement thereby upon the occurrence of the last digit of said initial portion.
5. A device as defined in claim 4 wherein said output circuit comprises ten output leads connected to be individually energized in conformity with the number of stepping pulses in a train identifying a selected digit, certain of said output leads being connected to the coincidence gates of said second gating circuit for ascertaining said inconsistent relationship upon selection af any digit of said initial portion, at least one of said output leads being connected to the coincidence gate of said first gating circuit for establishing said prohibited correlation upon selection of said last digit.
6. A device as defined in claim 3 wherein said monitoring circuitry further includes a detector for alternating-current signals from said central office and discriminating means controlled by said detector and by said pulse-repeating means for determining the presence of a line signal from said central office prior to generation of the first stepping pulse and, in the absence of such line signal, for operating said switch means independently of said evaluation means.
7. A device as defined in claim 6 wherein said pulse-repeating means, said differentiation means and said detector are provided with respective protective circuits for suppressing transients in the inputs thereof.
8. A device as defined in claim 6 wherein said monitoring circuitry further comprises bistable means coupled to said differentiation means for setting by said seizure and reading pulses and coupled to said detector for resetting in the presence of a line signal, further comprising signal-counting means connected to said bistable means for advancement by any line signal preceded by an open-loop condition, said detector controlling said discriminatory means through said bistable means and signal-counting means.
9. A device as defined in claim 8, further comprising circuit-breaker means controlled by said bistable means in the set state thereof for effectively decoupling said station from said central office.
10. A device as defined in claim 7, further comprising gate means inserted between said bistable means and said detector and provided with an input connection to said integrating means for preventing any resetting of said bistable means by a line signal in the presence of a digital pulse, said second flip-flop beiNg connected to said integrating means by way of said gate means.
11. A device as defined in claim 7 wherein said signal-counting means includes a decoder connected to said differentiation means for receiving said reading pulse therefrom, said decoder being effective with a count of line signals greater than one to operate said switch means upon generation of a further stepping pulse subsequently to a recurring line signal, said signal-counting means being connected to said differentiation means for restoration to zero by said seizure pulse.
12. A device as defined in claim 7 wherein said pulse-counting means is connected to said differentiation means for restoration to a starting condition by said zero-setting pulse.
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