TELEPHONE TRUNK BARRING DEVICE

Abstract: Telephone trunk barring device, characterised in that it is to be associated with a telephone and interposed between a dialling means (16) and a signal generator means (18) arranged to send signals corresponding to dialled digits on an output (30, 32) of the telephone which is arranged to be connected to a telephone line, the telephone trunk barring device comprising a decoder means (12) connected to an output of the dialling means (16) of the telephone to analyse the signals corresponding to the dialled digits transmitted by the dialling means (16), the signal generator means (18) connected to the decoder means (12) for transmission of a line signal to the telephone line which is a signal corresponding to the dialled digits and a control means (12) arranged between the decoder means (12) and the signal generator means (18) to selectively block the transmission of some signals corresponding to the dialled digits.

Description: TITLE TELEPHONE TRUNK BARRING DEVICE DESCRIPTION The present invention relates to a telephone trunk barring device particularly envisaged for use within a telephone instrument. FIELD OF THE INVENTION In general, telephone trunk barring devices are located in an exchange to which one or more telephones may be connected. These prior art devices are arranged to restrict the dialing of STD (subscriber trunk dialling) and ISD (international subscriber dialing) numbers from any prescribed telephone or telephones connected to the exchange. These prior art devices have a disadvantage in that the barring action is not left to the control of the sub¬ scriber or owner of any one telephone connected to the exchange. It is also known to provide a key lock means to restrict access to use of a telephone. Such means bars all use of the telephone including non toll calls, such as local area calls, information calls, emergency calls and the like. Some other prior art devices are intended for location within a telephone instrument and monitor an output of the telephone. If a barred number or code is dialled the barring device open circuits the telephone output and terminates the call. It has been found that monitoring such an output for a telephone employing DTMF (dual tone modulated frequency) dialling is particularly difficult. SUMMARY OF THE INVENTION The present invention provides a telephone trunk barring device for use within a telephone and located between a call means and a signal generator means and a line driver means of the telephone. In accordance with one aspect of the present invention there is provided a telephone trunk barring device, characterised in that it is to be associated with a telephone and interposed between a dialling means and a signal generator means arranged to send signals corresponding to dialled digits to an output of the telephone which is arranged to be connected to a teleph¬ one line, the telephone trunk barring device comprising a decoder means connected to an output of the dialling means of the telephone to analyse the signals corresponding to the dialled digits transmitted by the dialing means, the signal generator means connected to the decoder means for transmission of a line signal to the telephone line which is a signal corresponding to the dialled digits and a control means arranged between the decoder means and the signal generator means to selectively block the transmission of some signals corresponding to the dialled digits. In accordance with a further aspect of the present invention there is provided a telephone characterised in that it comprises a trunk barring device interposed OMPI between a dialling means and a signal generator means, th telephone being arranged to accept dialled digits from the dialling means, and interrogate the dialled digits if a control means of the telephone is enabled to intercept 5 such dialled digits and block the transmission of signals corresponding to restricted numbers. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described, by way of 0 example, with reference to the accompanying drawings, in which:- Figure 1 is a circuit diagram of a telephone trunk barring device of the present invention shown in connection in a portion of a typical telephone circuit;- and 5 Figure 2 is a circuit diagram of a typical line driver means of the telephone circuit of Figure 1. DESCRIPTION OF THE INVENTION In Figure 1 there is shown a telephone circuit 0 comprising a telephone trunk barring device in accordance with the present invention comprising a computer means 10. The computer means 10 comprises a microprocessor integrated circuit 12 and a non volatile random access memory (RAM) integrated circuit 14. 5 For the purposes of this example the microprocessor 12 is a CMOS type microprocessor such as a National Semi¬ conductor one chip microprocessor given the serai number COP 402. However, it is understood that other micro¬ processors could be used. Q A CMOS type microprocessor has been found to be of GMPI particular suitability to the present device as it has low power consumption and does not require a well reg¬ ulated power supply. The RAM 14 is connected to the microprocessor 12 by a serial input SI and a serial output SO which allow serial passage of data therebetween. An output Y7 of the microprocessor 12 is connected to an enabling input EN to allow the microprocessor 12 to enable the RAM 14 as required. There is also a clock CLK connection between the micro¬ processor 12 and the RAM 14. The clock CLK connection is provided to synchronise bi-directional flow of data between the RAM 14 and the microprocessor 12. It is intended that, in * use, the RAM 14 will be used to store subscriber data such as an access code, described hereinafter, and/or some extra restricted call codes or the like. The extra restricted call codes are telephone numbers and/or area codes which may be entered by the subscriber and to which access is restricted. The microprocessor 12 is connected to a call means such as a keypad 16, as shown in Figure 1. The connection is made from outputs KBO0 to KBO 3 and from inputs KBI(J to KBI3, which, under control of the microprocessor 12, to the keypad 16 and are arranged to scan the keypad 16 for a key closure. A keypad 16 key closure is represented by an 8 bit number at the inputs and outputs KBI and KBO. It is understood that the call means could be a rotary action dialler which sends a number of pulses corresponding to the number to be called. In this case it is envisaged that the dialler be connected to an interrupt input of the microprocessor 12, although some other inputs could be used. The microprocessor 12 comprises a store of numbers which correspond to STD and ISD prefix codes that represent geographical locations to which telephone calls may not be made unless authorised, as described hereinafter. It has been found that, in Australia, all the STD and ISD prefix codes to be barred may be represented by a relatively small group of numbers, such as about 20 numbers. Thus, it is not usually necessary in the device of the present invention, to have a store of all STD and ISD codes to be barred. The relatively small store of numbers are usually chosen so that emergency telephone numbers and/or local area telephone numbers that have leading digits which correspond to STD or ISD area codes, but are allowable toll free telephone numbers, may be dialled by any person using the telephone. The microprocessor 12 is further connected to a signal generator means 18. The connection is made from outputs Y0 to Y4 of the microprocessor 12 to inputs R0 to R3 of the signal generator means 18. In a telephone comprising a keypad 16 the signal generator means 18 is a tone generator, as shown in Figure 1, whereas in a telephone comprising a rotary action dialler the signal generator means 18 is a pulse generator. In either case the connection is identical, and only the tone generator integrated circuit need be removed and a pulse generator integrated circuit inserted, for example. In conventional telephones having call means of keypad 16 type a tone generator, similar to the tone generator, is connected directly to the keypad 16. This usually leads to unrestricted use of the telephone. The connection from the outputs Y0 and Y4 to the inputs R0 to R3 is arranged to carry a signal, corresponding to a dialled number, to the signal generator means 18. The signal generator means 18 then generates, at its outputs A, B and C, signals to be sent to the remainder of the telephone circuit in order to effect a dialled number. In Figure 2 theie is shown a typical line driver means of the telephone circuit to which the signal generator means 18 is connected at the outputs A, B and C shown in Figure 1. The circuit of Figure 2 is commonly found in conventional telephone instruments and is shown here as an example of a possible arrangement of the device of the present invention within a telephone. The output A is arranged to provide an output signal that corresponds to a dialled digit. In the case of a rotary type dialler the output A would have a signal comprising a number of pulses corresponding to a dialled digit. In the case of a keypad 16 the output A would have DTMF signals corresponding to a dialled digit. The output B is arranged to provide an output signal to mute sound in an earpiece RX as a telephone number is dialled out to exchange or extension lines to which the telephone is connected. The output C is arranged to provide a transmit enable signal to a microphone TX once a telephone number has been completely dialled out, that is, while the telephone number is dialling out to the exchange or extension lines any sound entering the microphone TX will be ignored. The typical line driver means is connected to a telephone exchange line or telephone extension line at connections 30 and 32. The connections 30 and 32 provide input from the exchange or extension lines, to a full wave bridge rectifier 33. The bridge rectifier 33 provides a signal between connections 34 and 36 that has a direct current component of between about 40 volts to about 50 volts which is used to power the device of the present invention. There is also provided a voltage regulator 38 comprising a voltage dropping resistor Rl and a zener diode Dl as shown in Figure 1. The voltage regulator 38 is configured to produce a voltage at node 40 of about 5 volts when there is a potential difference between connections 34 and 36 of greater than about 10 volts. During dialling the line voltage between connections 30 and 32 may drop to about 10 volts, in some situations. The voltage regulator 38 is configured to supply power, at about 5 volts, to the microprocessor 12, the RAM 14 and the signal generator means 18 when the telephone handpiece is on-hook and off-hook and when a telephone number is being dialled. In short, the microprocessor 12 is always active and awaiting some form of key closure or number dial or the like. The typical line driver means also comprises relay contacts 42 and 44 which are actuated by the handpiece of the telephone. -a-ϋRE O .PI In Figure 2, the relay contacts 42 and 44 are shown in a closed condition corresponding to the handpiece being off-hook. In this case power is also supplied to the remainder of the line driver means. There is provided a connection 46 connected from the line driver means to a sense input SENA of the micro¬ processor 12 via a voltage divider network 48. The connection 46 provides an indication to the sense input SENA whether the handpiece is on-hook or off-hook. The voltage divider network 48 comprises resistors R2 and R3 and zener diode D2 arranged to produce a signal of less than about 20 volts, such as about 5 volts, at the sense input SENA when the handpiece is off-hook. In use, the telephone trunk barring device of the present invention is connected in a telephone circuit between a call means, such as a keypad 16, a signal generator means 18 and a line driver means. The device allows a telephone to be barred so that restricted telephone calls, such as STD and ISD calls, may only be made by authorised people. The device also allows unauthorised people to make toll free calls, local calls and emergency calls. An authorised person may remove the barring restriction by entering an access code. The access code signals the microprocessor 12 to remove the bar restriction and allow all following numbers to be dialled. During installation of a telephone comprising the device of the present invention, after the telephone is connected to an exchange line or an extension line and with the handpiece on-hook, a link 50, shown in Figure 1, is provided to short an input SENB of the microprocessor 12 to a ground connection 52. The existence of the link 50 signals the microprocessor 12 to accept an access code, such as a 4 digit access code, typed in the keypad 16 by the subscriber. The access code is then stored in the RAM 14, in known manner. Although a 4 digit access code is referred to herein it is understood that an access code comprising more or less digits could be used. At this time the subscriber may also add extra restricted call codes to be barred, that are not covered by the store of codes in the microprocessor 12. The extra restricted call codes are also stored in the RAM 14. Once the access code and any extra restricted call codes are entered the link 50 is removed and telephone is ready for use. The device of the present invention allows a telephone two modes of operation. In the first mode of operation, the handpiece of the telephone is left on-hook. This allows use of telephone functions other than dialling a telephone number to make a telephone call. In particular, an authorised person, such as. the sub¬ scriber, may enter his access code, while the handpiece is on-hook, in order to remove the bar restriction. Once the access code is entered, fay pressing the relevant buttons of the keypad 16, the microprocessor 12 compares the access code with the access code stored in the RAM 16. If the dialled access code is identical to the stored access code the bar restriction will be removed. If the OMW_ dialled access code is not identical to the stored access code the bar restriction is maintained. It is intended that the access code be entered after first dialling a set up code or number such as for example the number 9 or a code 11 or a function such as #. With the bar restriction removed any person may dial any telephone number whether or not it corresponds to a restricted telephone number or code. Still in the first mode, the bar restriction may be reinstated by pressing a predetermined number or code such as for example the number 9 or a code 11 or a function such as #. It is realised that it is not essential for the set up code to be identical to the code used to reinstate the bar restriction. In a second mode of operation, the handpiece is off-hook. This allows the use of telephone number dialling facilities, subject .to the barring restrictions. With the handpiece off-hook and the bar restrictions active, a person may dial any desired number. As the number is dialled the microprocessor 12 temporarily stores the first three digits of the number to be checked with the store of numbers corresponding to restricted numbers. It has been found that, in Australia, only the first three digits of the dialled number need he checked in order to establish if the number corresponds to a restricted STD or ISD code. In Australia, if the first dialled digit is a zero and the bar restriction is active, the microprocessor 12 is alerted that the following numbers may constitute a restricted code or number. The microprocessor 12 then compares the next two dialled digits with the store of codes corresponding to restricted STD and ISD codes to check if the dialled number does correspond to a restricted code or number. If there are any extra restricted call codes stored in the RAM 14, the micro¬ processor 12 operates similarly to compare the dialled number to them. If the dialled number does correspond to a restricted code or number then the three dialled digits and all subsequent digits are ignored. This condition is reset when the handpiece is replaced, after which dialling procedures may be recommenced. If the dialled digits do not correspond to a restricted code or number then the first three digits and all subsequent digits are accepted. Then signals corresponding to the dialled numbers are output by the microprocessor 12 at the outputs Y0 to Y3 and sent to the inputs R0 to R3 of the signal generator means 18. Then, in known manner, the signal generator means 18 sends signals to the connections 30 and 32, and thus to the exchange lines or extension lines to which the telephone is connected, corresponding to the dialled digits. If the bar restriction is made inactive as described hereinabove, any person may make any telephone call be it restricted or not. In this case the microprocessor 12 scans the keyboard 12 and detects each- dialled digit in turn. For each digit received a set of output signals are sent at the outputs Y0 to Y4 to direct the signal generator means 18 to transmit a code corresponding to the dialled digit, to the connections 30 and 32. That is, none of the dialled digits are interrogated before sending corresponding signals to the exchange or extension lines to which the outputs 30 and 32 are connected.. After a telephone call is completed the handpiece is replaced, as is conventional practice. The replaced handpiece opens the contacts 42 and 44 which sets a low condition at the input SENA. A low condition at the input SENA signals the microprocessor 12 that the telephone is no longer communicating over the exchange or extension lines and directs the microprocessor 12 to continue to scan the keyboard 16. It is envisaged that the device of the present invention could also comprise other features. Such features could include; an LCD display to display the time of the day, a number dialled and other information ι extra RAM to accommodate a store of frequently used telephone numbers; means to calculate STD and ISD charges^ a last number redial facility; or the like. All but the latter of these features would be accessible while the handpiece is on-hook. It is also envisaged that the device of the present invention could be arranged so that an authorised person may change his access code. It is envisaged that this would be accomplished by first entering an access code set-up code, entering the old access code and then entering a new access code. It is further envisaged that the device of the present invention could be integrated in slice form and mounted and interconnected onto a single substrate to produce a single integrated circuit from the three integrated circuits described hereinabove. In this case only a few external components would be required. These components may include a power supply filter capacitor 60, as shown in Figure 1 and if a clock facility is provided, a resistor and capacitor to connect in parallel with a resistor 62 and a capacitor 64 used to derive the microprocessor timing and the clock output CLK. It is still further envisaged that the microprocessor 12 could be arranged to be able to store, say, one complete telephone number in the RAM 14 in a manner similar to that used to store extra restricted call codes. Once stored, it is envisaged that the telephone could be barred such that only the stored complete telephone number may be dialled. That is, any number dialled, except an emergency police number (i.e. 000 in Australia) , will cause the telephone to dial the stored complete telephone number. In this manner any unauthorised use of the telephone could be used to alert the subscriber and/or foil the unathorised user. It is also envisaged that, in countries where a telephone may not draw any power when the telephone handpiece is on-hook, means may be provided to ensure no current is drawn in the on-hook condition but arranged so that, under control of a user, the telephone instrument may be switched on whilst in the on-hook condition to allow use of the on-hook features described hereinabove. Other modifications and variations such as would be O *.»M_rιP_»I apparent to a skilled addressee are deemed within the scope of the present invention. For example, a tone generator producing signals other ' than DTMF signals could be used.

Claims: CLAIMS 1. A telephone trunk barring device, characterised in that it is to be associated with a telephone and inter¬ posed between a dialling means and a signal generator means arranged to send signals corresponding to dialled digits to an output of the telephone which is arranged to be connected to a telephone line, the telephone trunk barring device comprising a decoder means connected to an output of the dialing means of the telephone to analyse the signals corresponding to the dialled digits transmitted by the dialing means, the signal generator means connected to the decoder means for transmission of a line signal to the telephone line which is a signal corresponding to the dialled digits and a control means arranged between the decoder means and the signal generator means to selectively block the transmission of some signals corresponding to the dialled digits. 2. A telephone trunk barring device according to Claim 1, characterised in that the control means is arranged to intercept the dialled digits and further arranged to interrogate at least the first two dialled digits and selectively block the transmission of some signals corresponding to the dialled digits. 3. A telephone trunk barring device according to Claim 1 or 2, characterised in that the control means is arranged to interrogate at least the first two dialled digits intercepted by comparing them to a store of numbers corresponding to restricted telephone call numbers and further arranged to block the transmission of any signals corresponding to restricted numbers. 4. A telephone trunk barring device according to any one of the preceding claims, characterised in that an access code, dialled into the dialling means is used to disable the control means so that dialled digits are not interrogated. 5. A telephone trunk barring device according to any one of the preceding claims, characterised in that the dialling means is a keypad dialler arranged to be scanned by the control means and the signal generation means is a tone generator. 6. A telephone trunk barring device according to any one of claims 1 to 4, characterised in that the dialling means is a rotary type dialler arranged to send pulses corresponding to the dialled digits to the control means and the signal generation means is a pulse generator. 7. A telephone characterised in that it comprises a trunk barring device interposed between a dialling means and a signal generator means, the telephone being arranged to accept dialled digits from the dialling means, and interrogate the dialled digits if a control means of the telephone is enabled to intercept such dialled digits and block the transmission of signals corresponding to restricted numbers- 8. A telephone trunk barring device according to any _ - >-- MP one of the preceding claims, characterised in that it comprises a sense means arranged to indicate to the control means whether a handpiece of the telephone is on-hook or off-hook. OMPI

Inventors: GRANATH LARS ROLAND, GRANATH, LARS, ROLAND
Applicants: MALCA PTY LTD, MALCA PTY. LTD.
Application year: 1984
Main classification: H04M1
IPC codes: H04M1