GB2200516A

GB2200516A - Call barring apparatus

Info

Publication number: GB2200516A
Application number: GB08801741A
Authority: GB
Inventors: Richard Drewnicki; Mark George Rainer; John Philip Cracknell; David Christopher Cracknell
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-01-27
Filing date: 1988-01-27
Publication date: 1988-08-03
Also published as: GB8701723D0; GB8801741D0

Abstract

Apparatus for barring unauthorized outgoing calls on telephone lines comprises electrical circuit means 1 which is adapted to be connected in parallel into a telephone line and including means for selecting the kind of calls to be barred 9, means for sensing the telephone line conditions when a call is being made 8, means for blocking transmission of the unauthorized call to the telephone exchange 6 and means 7 for generating a tone, such as an unobtainable or like tone, which prompts the unauthorized user to abort the call, thereby releasing the telephone line with a minimum of delay. Suitably the apparatus is adapted to be directly pluggable into a line jack plug socket. <IMAGE>

Description

CALL BARRING APPARATUS The present invention relates to apparatus for barring or preventing unauthorized calls on telephone lines, more particularly but not exclusively for use with telephones having dials of the "push button" type.

Unauthorized- telephone calls, in particular home and overseas long distance calls with the advent of direct dialling have always been a problem since they raise the cost of telephone bills without the knowledge of the authorized user. This is not only the case with companies and firms whose personnel during the day and night staff and say cleaners may use the telephones for personal calls without authorization, but also with owner occupied homes when the owners are away on holiday and leave their keys with the cleaner forexample. The increasing use of PABX extensions with which the telephone switch board operation can be bypassed by dialling a digit, sucfl as the number 9, compounds the problem. A serious example of abuse is the unauthorized reverse charge call particularly a toll call from abroad.

Whilst there are various mechanical apparatus available on the market for preventing unauthorized telephone calls on telephones of the "rotary dial" type, not only do such apparatus not meet with British Telecom and British Standards Institute Approval as they can can prevent the use of the telephone for emergency calls but they are not suitable for push-button dial telephones. This is because the mechanical devices work by locking into the rotary dial to prevent rotation and thus dialling of a call. Although, such devices have the advantages of being inexpensive for an individual to buy, simple to operate and are readily visible to act as a deterrant, it is still possible for unauthorized users to by-pass such devices by dextrous misuse of the telephone hook switch or receiver rest.

The disadvantages of mechanical call barring apparatus and the need for an electrical call barring apparatus which could be used not only with rotary dial telephones but also with push-button telephones has already resulted in the availability of apparatus which is series connected into the existing telephone system. Thus the British Standards Institute in its draft standard No. 6789, Part 7 recognizes two modes of operation for such apparatus, referred to as "Store and Forward" and "Monitor and Release" respectively. In the Store and Forward mode, as digits are dialled on a telephone connected with the apparatus, the digits are monitored by a device which, having validated the called number will then re-dial the digits to the telephone exchange.

If the number is invalid, e.g. for a long distance call, the dial locking device does not re-dial the digits and the line to the telephone exchange is released, if it was already seized.

In the Monitor and Release mode, the digits are dialled direct to the telephone exchange and the call barring apparatus forces a line release (disconnection) in the event of unauthorized digits being dialled.

The disadvantages of call barring apparatus in either of these two modes are high costs of installation which are. well outside the range of the domestic user, it is essential that the call barring apparatus disconnects or releases the line from the telephone exchange, the requirement for series connection means that inexpensive plug-in versions for the domestic user cannot be produced and because the unauthorized user has no way of knowing that the call has been barred, he or she may hold on for a while or make repeated attempts to obtain number which ties up the telephone network selection equipment which can produce line overload preventing authorized users from using the telephone and ultimately resuiting in the need for the telephone company to invest further monies in selector equipment to increase capacity on a false basis.Another problem which occurs is with operator calls as the operator may have no way of knowing that the call is being made by an unauthorized user.

Accordingly, the main object of the present invention is to provide a call barring apparatus which avoids or substantially reduces the aforerbentioned problems and disadvantages.

To this end, the present invention consists in apparatus for barring unauthorized outgoing calls on telephone lines, said apparatus comprising electrical circuit means which is adapted to be connected in parallel into a telephone line and including means for selecting the kind of calls to be barred, means for sensing the telephone line conditions when a call is being made, means for blocking transmission of the unauthorized call to the telephone exchange and means for generating a tone, such as an unobtainable or like tone, which prompts the unauthorized user to abort the call, thereby releasing the telephone line with a minimum of delay.

The means for blocking transmission of the unauthorized call may be a pulse blocking circuit where the telephone operates on a pulse sending basis or in the case when tone sending is employed the blocking means may be incorporated in the tone generating means such that the tone generated by the tone generating means also blocks unauthorized call transmission.

By means of the invention, a simple and inexpensive call barring apparatus can be constructed which can be incorporated into the telephone line at any location from the telephone to the telephone exchange, which, if required, can be adapted to be plugged into an existing telephone jack plug socket or into the lead frame in the telephone exchange, which can be used for any kind of telephone currently available on the market and which will permit selected calls such as emergency calls (e.g. 999 calls in the U.K.) and specially designated free calls such as Link line/Toll free (0800 in the U.K. and 800 in the U.S.A.). Furthermore, the use of a prompting tone such as another "unobtainable" tone or similar tone prompts the unauthorized user to hang up in a reasonably short time which avoids increasing telephone network selector demand which increases the cost of equipment.

Advantages of the invention are that the connection of the apparatus is in parallel so that the connection to the telephone line can be made independently of other attachments or telephones and call barring (dial blocking) will apply to any instrument on that line, the apparatus can sense all line conditions such as telephone "on" or "off" hook and dialling but will ignore incoming ringing signals.

Preferably, the call barring apparatus will be line powered and draw no rebore electrical current than is normally permitted for attachments although the electric current may increase within the permitted levels when the tel-ephone is in use.

In a preferred embodiment of the invention the connections to the telephone line comprises a plug connector for plugging into an existing wall socket in the authorized users premises or in the lead frame in a telephone exchange.

In cases where the plggable-in apparatus is for sale to an authorized ser, such apparatus ideally includes a socket for engagement by a corresponding jack-plug on the telephone lead and releasable locking means for preventing removal of the apparatus from the wall socket. The lock may be a mechanical lock which is released in any suitable way for example by means of a key. The apparatus may include a facility which would allow it to be enabled or disabled either by application of a signal to the line which could be acoustically generated either electronically, pneumatically or mechanically directed into the telephone mouthpiece and which is conveniently pocket sized or by a switch which is hidden behind a locked cover plate for example.

The mechanical lock may be of any suitable kind but a moulded plastics lock which is integral with a surrounding plastics casing may be preferred.

In order to adapt the call barring apparatus for use with PABX extensions, it may include a facility for ignoring the initial dialling-out digit (e.g. digit 9) for a telephone line.

The selecting means are preferably adapted for various levels of barring which can be authorized user or manufacturer selectable according to marketing requirements. Thus, for example, the selecting means may bar long distance or toll calls and permit local telephone calls as well as emergency calls and "free calls" or bar all calls other than emergency and authorized free calls. For this purpose, the sensing means which is preferably a programmable electric circuit, may be provided with connectors such as pin connectors for engaging with complementary sockets in different positions to obtain the different levels of call barring or being connected to suitable switches for achieving the same results, or be soldered connections.

Alternatively, separate models may be marketed, each with a different ievel of call-barring decided by the manufacturer to suit the particular requirements.

The selection process may involve the barring of local calls at certain times of day, e.g. at peak rate times, yet allow local calls at other times.

In order to avoid the possibility of an unauthorized user making calls through the operator by dialling accepted digits,and it is not desired to exclude access to the operator, e.g. for emergency calls should that be necessary, the tone generating means preferably includes a facility to provide an indenti-ier tone on calls made to the operator dialling te specified digits (100 in the U.K.).

Thus, identifier tone will indicate to the operator that the call is unauthorized or may indicate to the operator that the call is one which requires money to be inserted like in pay phones in which case the unauthorized user will be thwarted from making a chargeable call. Such an identifier tone can also be used to warn the operator that an unauthorized reverse charge call is being made when the unauthorized user responds to the call from the operator by lifting the phone off the hook.

It wiffli b-e appreciated that call barring apparatus onstructed in accordance with the invention ray be included anywhere in the telephone line between the telephone and the telephone exchange. Thus, it may be in the form of a plug-in device as already discussed which is particularly suitable for small companies or domestic users, in the case of firms or companies having telephone switchboards it. may be connected in the lines upstream of the switchboard and be made to bar calls on one or several or all the telephone lines, or in each telephone. For PABX applications the apparatus may be used in multiples in a permanently wired format.

In a preferred embodiment of apparatus constructed in accordance with the invention, the electrical circuit means further includes a line interface circuit which is connected to the line sensing means and to tone signal generating and tone blocking means, a dial pulse blocking circuit connected to said line interface circuit and to a control logic circuit,thecontrol logic circuitbeing connectedto said selecting means and to said tone signal generating and tone blocking means, said line sensing means and said dial blocking circuit, and a power supply circuit for said control logic circuit connected between the line interface circuit and said control logic circuit.

In order that the invention may be more readily understood, reference will now be made, by way of example, to the accompanying drawings, in which : - Fig. 1 is a block diagram of an electrical circuit forming one embodiment of call barring apparatus constructed according to the invention, Fig. 2 is a rear perspective view of a plugin adaptor, containing the apparatus of Fig. 1 and showing one way in which the call barring apparatus maybe connected into a telephone line, Fig. 3 is a front perspective view of the adaptor of Fig. 2, and Fig. 4 is a schematic view of a further embodiment of dual plug in adaptor and wall socket.

Referring to Fig. 1 of the drawings, the call barring apparatus comprises an electrical circuit of which the portions within the dashed lines are constructed in the form of a chip 1 whereas the portions outside the dashed lines are formed of discrete components. The circuit has telephone line connections 2, which connect the apparatus in parallel with the telephone line and which are bridged by a line interface circuit 3 which is connected in turn to a power supply circuit 4 for a control logic circuit 5, a dial pulse circuit 6, a tone signal generator and tone blocking circuit 7 and a line sensing circuit 8. Circuits 4, 6, 7 and 8 are all connected to the control logic circuit 5, which receives the output of a programming interface circuit 9 for selecting the level of the calls to be barred, e.g. toll calls.The line conditions sensed by the sensing circuit include "On-hook" , "off-hook" in speech mode, "Off-hook" in signalling (dialling) mode and"on-hook in ringing (incoming call) mode.

When the line connections 2 are connected into a telephone line, the apparatus operates in the following manner. With the telephone (not shown) "on-hook" the apparatus is at rest with there being negligible electric current drawn from the telephone network. When the phone is taken off-hook circuit 8 detects a drop in voltage and emits an informing signal down line-lO to circuit 5. At this point circuit 5 may or may not modify the characteristics of the power supply circuit 4 in order to increase the available power supply to the chip 1. There is a time delay whilst circuit 5, waits to see what digits are being dialled, if any. For example, there may be an off-hook condition due to answering an incoming call. If no digits are dialled and/or the phone is hung up, the circuit 5 does. nothing.

If digits are dialled then circuit 8 emits an updating signal to circuit 5 on the line condition.

Circuit 5 is able to tell what digits are dialled bv counting. the voltage pulses. This action loads a register in the circuit 5 with information according to the digits dialled and examines that register for legality according to information received from the selecting circuit 9 along line 11.

In the event that the call is not one which is selected by circuit 9 to be barred, then the call is allowed to proceed normally and circuit 5 resets itself in normal manner when the phone is hung up.

However, if an illegal combination of digits is dialled, i.e. a combination which has. been selected by circuit 9 as barred, then circuits 6 and 7 come into operation. The dial pulse blocking circuit 6 is a switchable amplified capacitor which is non-linear and has the characteristics of:- high impedance at low A/C voltage, e.g. speech signals, low impedance to high rate voltage rises in order to block signal pulses but enabling circuit 8 to detect when phone hang-up has occurred. After the barred call has been dialled, circuit 5 then emits a simultaneous signal to circuit 7 so that the latter will prevent any tone signals being sent to the telephone exchange.

Having blocked any dial pulse tones from being sent to the telephone exchange, circuit 7 generates pulses or tones, for example by applying A/C current to the line, to cause a tone to be heard in the telephone earpiece and which is recognized by the unauthorized user as being an unobtainable or like tone, thereby prompting the user to hang-up.

All necessary timing requirements are handled by timing circuitry 12 which is connected to the control logic circuit 5 and which is partly incorporated in the chip 1.

The call barring apparatus illustrated in Fig. 1 may be adapted to be plugged into an existing wall mounted jack plug-socket by means of the adaptor 20 illustrated in Figs. 2 and 3. The circuit of Fig. 1 is housed within a casing 21, which is preferably of moulded plastics, with the line connections 2 being connected to a connecting pin 22 which plugs into the socket. The casing has a rear access plate 23 secured as by screws 24 so that the circuit in the casing is inaccessible once the adaptor is plugged in. A securing latch is indicated at 25 and incorporates a pair of notches 26 which mate with existing tabs in the socket. The latch 25 is such that once the adaptor is plugged in, it cannot normally be withdrawn from the socket except by the use of a releasing key which is inserted into a key hole 27 on the front of the adaptor.The telephone jack plug on the lead to the telephone is plugged into the front socket 28.

Although particular embodiments have been described, it should be appreciated that various modifications may be made without departing from the invention. For example, whilst the invention has been described as relating to telephone calls, the invention is equally applicable to calls made on other kinds of apparatus which make use of telephone lines, for example telex and telecopier machines.

Furthermore, the call barring apparatus may be incorporated into a telephone or oter telecommunications instrument and may share part of the dial encoder circuit (chips and share part of the control logic. Also, the key pad (push button dial) could be used as the programming input with a special code number or numbers to enable reprogramming or disabling.

In the embodiment of Figure 4 a magnetically operated reed switch 30 is fitted with the appropriate circuitry into a telephone wall socket 31 and is biassed on into a barring mode by a magnet 32 suitably positioned in the same casing In order to disable the barring mode it is necessary to counter the magnetic field of the biasing magnet by a substantially equal and opposite field. To this end a key 33 is provided, suitably comprising a dual outlet adaptor housing containing a second similar magnet 34 arranged such that on plugging the adaptor into the wall socket 31 the magnet 34 is critically positioned at a similar distance from the reed switch 30 and is arranged to present a substantially equal and opposite magnetic field to that of magnet 32. Thus the magnetic field at the reed switch 30 is neutralised and the switch 30 is unbiased and switches open to an unbarring condition.

In the embodiment of Figure 4 two variants are possible by reversing the relative positions of the magnets 32 and 34 and this gives a limited degree of security. It will be understood that an excessive external field strength will reclose the switch 30 and restore the barring mode so that anyone using an improper adaptor with too strong a magnet will be barred.

Claims

1. Apparatus for barring unauthorized outgoing calls on telephone lines, said apparatus comprising electrical circuit means which is adapted to be connected in parallel into a telephone line and.including means for selecting the kind of calls to be barred, means for sensing the telephone line conditions when a call is being made, means for blocking transmission of the unauthorized call to the telephone exchange and means for generating a tone, such as an unobtainable or like tone, which prompts the unauthorized user to abort the call, thereby releasing the telephone line with a minimum of delay.

2. Apparatus as claimed in claim 1, in which the means for blocking transmission of the unauthorized call is a pulse blocking circuit where the telephone operates on a pulse sending basis.

3. Apparatus as claimed in claim 1, when tone sending is employed in which the blocking means is incorporated in the tone generating means such that the tone generated by the tone generating means also blocks unauthorized call transmission.

4. Apparatus as claimed in any preceding claim adapted to be plugged into an existing telephone jack plug socket.

5. Apparatus according to any of claims 1-3 which is adapted into the lead frame in the telephone exchange.

6. Apparatus as claimed in any preceding claim which will permit selected calls such as emergency calls (e.g. 999 calls in the U.K.) and specially designated free calls such as Link Line/Toll free (0800 in the U.K. and 800 in the U.S.A.).

7. Apparatus as claimed in any preceding claim which is line powered and draws no more electrical current than is normally permitted for attachments.

8. Apparatus as claimed in any preceding claim which comprises a plug connector for plugging into an existing wall socket in the authorized users premises or in the lead frame in a telephone exchange.

9. Apparatus as claimed in any preceding claim which includes a socket for engagement by a correspondmg jack-plug on a telephone lead and releasable locking means for preventing removal of the apparatus from the wall socket.

10. Apparatus as claimed in claim 9 in which the lock is a mechanical lock which is released by means of a key.

11. Apparatus as claimed in any preceding claim which includes a facility adapted to allow it to be enabled or disabled either by application of a signal to the line, which could be acoustically generated either electronically, pneumatically or mechanically directed into the telephone mouthpiece and which is conveniently pocket sized or by a switch which is hidden behind a locked cover plate for example.

12. Apparatus as claimed in claim 11, in which the facility is provided by an acoustically generated signal.

13. Apparatus as claimed in any preceding claim adapted for use with PABX extensions, including a facility for ignoring the initial dialling-cut digit (e.g. digit 9) for a telephone line.

14. Apparatus as claimed in claim 1, in which the electrical circuit means further includes a line interface circuit which is connected to the line sensing means and to tone signal generating and tone blocking -means, a dial pulse blocking circuit connected to said line interface circuit and to control logic circuit, the control logic circuit being connected to said selecting means and to said tone signal generating and tone blocking means, said line sensing means and said dial blocking circuit, and a power supply circuit for said control logic circuit connected between the line interface ricuit and said control logic circuit.

15. Apparatus arranged and adapted to operate substantially as described with reference to the accompanying drawings.