WO1998033308A2

WO1998033308A2 - Validation-checking device for public telephones

Info

Publication number: WO1998033308A2
Application number: PCT/EP1998/000353
Authority: WO
Inventors: Massimo Mondardini
Original assignee: Urmet Sud Costruzioni Elettro-Telefoniche S.P.A.
Priority date: 1997-01-27
Filing date: 1998-01-23
Publication date: 1998-07-30
Also published as: ITTO970057A1; WO1998033308A3; AU6212298A; IT1291472B1

Abstract

A validation-checking device (10) comprising selective detectors (11-12) for the charge frequency signal (12 kHz) and for the checking signal (16 kHz) emitted respectively by the exchange (CT) and by the telephone set (TP), and a microcontroller (15) which is operatively connected to a line disconnector (17) and is suitable to check for the presence of the checking signal sent by the telephone set upon each charge signal sent by the exchange and to disconnect the line, by opening the disconnector (17), in the absence of the checking signal. The checking signal is defined by specific timings and recurrence frequencies which are caused to be dependent on the data of the phonecard used to enable the public telephone (TP).

Description

VALIDATION-CHECKING DEVICE FOR PUBLIC TELEPHONES Technical field

The present invention relates to a validation-checking device which can be installed at a telephone exchange and can be connected to a telephone line with which a public telephone is associated and has the dual function of checking the correct line connection of the public telephone and to boost the line voltage in order to transfer to the public telephone more power than can be tapped by the user outlet. Disclosure of the Invention

More precisely, and with reference to the first function, the present invention has the aim of providing a device which, inserted between the exchange and the public telephone, is capable of promptly detecting any undue intrusion of a telephone terminal which is connected in parallel to, or in replacement of, the public telephone with the fraudulent aim of making the call without paying the charge.

With reference to the second function, the present invention has the object of providing a device having a booster circuit which is capable, when required by the operating conditions, to force the line current and therefore the power transfer in order to raise to positive values the energy balance of the public telephone terminal during its use and in any condition, also allowing to implement additional signals and/or services on said terminal.

An object of the present invention is to provide a device whose circuits have a high impedance, so as to avoid interfering with the normal periodic line tests performed by the exchange.

According to the invention, this aim, these important objects and others which will become apparent hereinafter are achieved with a validation-checking device having the specific characteristics stated in the appended claims.

Substantially, and for the purposes of the first function, the device operates as a consequence of the fact that a periodic signal having a preset frequency, typically 12 kHz, is emitted by the exchange on the telephone line associated with any public telephone. This signal indicates the charge and is matched by a signal having a preset frequency, typically 16 kHz, which is generated and emitted by the telephone set. The device according to the invention is substantially provided with detectors which are selective for said charge and checking frequency signals and with a microcontroller which is operatively connected to a line disconnector, which checks that on each charge pulse that arrives from the exchange a timed checking pulse having specific recurrence frequencies is produced which originates from the telephone set. If the checking pulse is not present, the microcontroller disconnects the line to the exchange and breaks off the call. Advantageously, according to the invention, the signature of the checking signal is caused to be dependent on the data that are transferred beforehand on the same telephone line during the validation of the cards used for the call and/or during dialing. For this purpose, a preset algorithm is used which resides in the logic controller of the check pulse generator associated with the telephone set. The algorithm, by receiving the data of the card and/or the dialing data, generates a charge checking criterion by acting on the duration and recurrence frequency of the pulse emitted by the telephone set. The same algorithm is implemented in the microcontroller of the checking device in order to recognize the check signal.

Another characteristic of the device according to the invention is the fact that it comprises a controlled current source, or booster, which is arranged in series to the transmission bridge of the exchange, is sensitive to the absorption of the telephone set and is suitable to constantly force on the line a current which is sufficient to meet the energy demand of the telephone set and to compensate for the losses cause by line resistances. A guard circuit is provided in order to limit the boosting function of the source when the total line voltage approaches safety limit values. Brief description of the drawings

Further characteristics and advantages of the validation-checking device according to the present invention will become apparent from the following detailed description and with reference to the accompanying drawings, provided by way of non-limitative example, wherein: figure 1 is a block diagram of the device; figure 1A is an enlarged-scale view of a detail of figure 1; figure 2 is an elevation view of the device of figure 1 in its preferred constructive embodiment. Ways of carrying out the invention In the drawings, the letters a and b designate the wires of a telephone line which is connected, at one end, with a conventional distribution frame P interposed to a telephone exchange CT and, at the other end, to a public telephone set TP which is provided with a reader L for debit cards, credit cards and optionally chip-cards.

The reference numeral 10 generally designates the device according to the present invention, which is installed at the exchange CT and is inserted as a four- terminal element between the exchange and the telephone set TP.

In a per se known manner, the exchange CT sends to the telephone set TP, over the telephone line a-b, charge signals in the form of a frequency, typically 12 kHz, for a preset period. Correspondingly, the telephone set TP sends to the exchange, over the telephone line a-b, charge checking signals in the form of a frequency, typically 16 kHz, which has a preset period and recurrence frequency.

The device 10 according to the invention has the purpose of checking that each 12-kHz pulse coming from the exchange CT is matched by a 16-kHz checking pulse that arrives from the telephone set TP and of disconnecting the telephone line if the checking pulse does not occur.

For this purpose, the device comprises a detector 11 which is selective for the 12-kHz signals and a detector 12 which is selective for the 16-kHz frequency signals. These detectors are arranged in a bridge-like configuration on the line wires a-b. The detectors 11 and 12, arranged in parallel to a receiver 13 for DTMF dialing, form a unit 14 for detecting the signals that flow through the line wires a-b which is operatively connected to a microcontroller 15. The microcontroller, activated by the seizure signal that arrives from a corresponding seizure probe 16 inserted on the line wire a controls, by means of an output "u", a disconnector 17 which is inserted on the other line wire b. The microcontroller 15 checks the match between the charge signals and the checking signals and, if the checking signals are not present, opens the disconnector 17 and disconnects the line. Advantageously, according to the present invention, the charge checking signal is defined by a preset period and recurrence frequency which are caused to be dependent on the data transferred beforehand over the telephone line a-b during validation of the phonecard being used and during dialing.

For this purpose, the telephone set TP comprises a source 18 for the 16-kHz checking frequencies, which is controlled by a logic controller 19 containing a specific algorithm, generally designated by the reference numeral 20. The algorithm, by receiving in input the card data and the dialing data, generates a specific charge checking criterion, acting both on the duration and on the period of said 16-kHz frequency signal. A corresponding algorithm 21 is implemented in the microcontroller 15 of the device 10 to recognize the checking signal.

An alarm and signaling section 22 is also associated with the microcontroller 15, and the entire device 10 is provided with a power supply circuit 23 which allows to supply a backup battery (not shown) even in on-hook conditions. Advantageously, the alarm section 22, in addition to activating local and/or remote signals S, activates, by means of a dedicated output 22a, an electronic breaker circuit 26 which is inserted as a bridge on a line wire and is suitable to connect the wire to the ground (figure 1A) in order to provide a fault signal which can be detected immediately during normal and periodic line tests performed by the exchange .

According to the invention, the device 10 is also provided with a controlled current source or booster which is arranged in series to the transmission bridge of the exchange (not shown) and is suitable to constantly force on the line a current which is sufficient to meet any energy demand of the telephone set TP. The source, generally designated by the reference numeral 24, comprises a current- generating section 24a and a control section 24b which is controlled by the control signal that is emitted by a voltage detector 25 arranged as a bridge on the line wires a-b. The detector 25 also acts as a limiter for the boosting function of the source 24, acting so as to deactivate it when the line voltage approaches safety limit values.

From the construction point of view, the device 10 is accommodated in a casing 30 which reproduces, as shown in figure 2, the structure of the conventional module of the "quick strip" of the distribution frame so as to allow immediate installability on said distribution frame by means of the multiple connector K.

Without altering the concept of the invention, the details of execution and the embodiments may of course be altered extensively with respect to what has been described and illustrated by way of non-limitative example without thereby abandoning the scope of the invention defined by the appended claims.

Claims

1. A validation checking device (10) for public telephones (TP), characterized in that it comprises selective detectors (11-12) for a charge frequency signal (12 kHz) and for a checking signal (16 kHz) emitted respectively by an exchange (CT) and by a telephone set (TP), and a microcontroller (15) which is operatively connected to a line disconnector (17) and is suitable to check for the presence of the checking signal sent by the telephone set on each charge signal sent by the exchange and to disconnect the line, by opening said disconnector (17), in the absence of said checking signal.

2. A device (10) according to claim 1, characterized in that said checking signal is determined by specific timings and recurrence frequencies which are caused to be dependent on the data of a phonecard used to enable said public telephone (TP) .

3. A device (10) according to claim 1, characterized in that the checking frequency signal is produced by a source (18) of the telephone set (TP) which is controlled by a logic controller (19) containing an algorithm (20) which, by receiving the data of the telephone card, generates a specific charge checking criterion by acting both on the duration and on the period of the frequency signal, a corresponding algorithm (21) being implemented on the microcontroller (15) of the device (10) to recognize the checking signal.

4. A device according to claim 1, characterized in that it further comprises a controlled current source (24) which is arranged in series to a transmission bridge of the exchange (CT) and is suitable to constantly force on the telephone line (a-b) a current which is sufficient to meet any energy demand of the telephone set (TP).

5. A device (10) according to claim 4, characterized in that said source (24) comprises a current generating section (24a) and a control section (24b), and in that the control section is controlled by the control signal emitted by a voltage detector (25) which is arranged as a bridge on the line wires (a-b) and also acts as a limiter for the boosting function of said generator (24).

6. A device (10) according to claim 1, characterized in that said selective detectors (11-12) and said microcontroller (15) are inserted in a bridge configuration on the line wires (a-b) and in that the microcontroller (15) is controlled by an activation signal of a seizing probe (16) which is inserted on one of the wires of the telephone line.

7. A device according to claim 1, characterized in that it comprises an alarm section (22) which is operatively connected to an electronic breaker (26) inserted in a bridge-like configuration on a line wire (b) of the telephone line and suitable to connect, in case of malfunction, said wire to the ground in order to provide a fault signal which can be detected during ordinary periodic line tests.

8. A device (10) according claim 1, characterized in that it is accommodated in a casing (30) provided with a multiple connector (K) that reproduces the structure of the conventional module of the "quick strip" of the exchange distribution frame so as to allow immediate installability by simple insertion of said device (10) in said exchange distribution frame.