GB2366686A

GB2366686A - Method and device for detecting the unauthorized use of a telephone line

Info

Publication number: GB2366686A
Application number: GB0130157A
Authority: GB
Inventors: Jacques Labie
Original assignee: IPM INTERNAT SA
Current assignee: IPM INTERNAT SA
Priority date: 1999-05-17
Filing date: 2000-05-10
Publication date: 2002-03-13
Also published as: EP1179257A1; WO2000070850A1; MXPA01011765A; AU4140000A

Abstract

The inventive method for protecting a telephone line consists of establishing an electrical signature using the parameters of the line when it is being used by the authorized telephone, and comparing this signature each time the line is used. If the two signatures differ, the line is subjected to a certain measure: either the line is interrupted or a noise is produced, making any use impossible. The surveillance module (3) for carrying out this method is connected to a telephone line (4) in order to prevent the telephone line from being used by an unauthorized telephone. This module is provided with means for measuring the electrical parameters of the line during a communication and with means for comparing this signature with a reference signature. The module generates a signal on the line or interrupts the line if the signatures are different.

Description

2366686 PROCEDURE AND DETECTION DEVICE OF NON-AUTHORISED TELEPHONE LINE

USE The present invention concerns telephony, more particularly a procedure and a 5 device to fight against the non-authorised use of a telephone line linking a telephone centre and an authorised telephone.

By authorised telephone we understand either a subscriber telephone intended for private use or a public telephone by pre-payment. These apparatus are 10 called pre-payment because previous to their use it is necessary t o introduce a means of payment. The known means at present are tokens, coins and more recently credit cards, mostly of optical, magnetic, or smart card type.

Since the installation of these telephones the fraudsters have tried by diverse 15 means, sometimes successfully, to surmount the security systems of these apparatus in order to make telephone calls without paying,. The coin recognition techniques on the one hand and the implementation of optical and smart cards on the other hand have made the task of the fraudsters very difficult, even impossible.

This is why these fraudsters have changed the focus of their attention from the telephone apparatus to the telephone line. It has to be known that in many countries the lines are not underground, and thus are much more vulnerable.

25 We have also seen flourish, on the open-wire lines, I deviation pincers connected.to an ordinary telephone violating the rights of the line owner.

This practice has been fought against by the telecommunications operators, who in general are the owners of the line and of the public telephone, with 30 electronic counter-measures placed onboth sides of the telephone line, either in the centre or in the telephone.

With the liberalisation of the telecommunications the operators have diversified and it often occurs that the owner of the telephone centre is not the same as the owner of the public telephone. In this way the task of tracking the abuse involves only the latter, the owner of the centre not becoming involved with the problem.

5 The document PCT/DE95/00838 describes a counter-measure device using two modules, one on the side of the telephone and the other on the side of the centre. When the telephone is unhung the module "telephone" identifies itself to the module "centre" and the latter authorises the connection of said centre. If the "centre" module detects an unhanging and the identification does not take place then the connection with the centre is forbidden. This identification process between the two modules can be done during all the length of the conversation at regular intervals.

Although this solution offers a security to the access of the telephone service, it implies a modification in the centre, which sometimes is not possible. It needs the installation of two modules previously initialised to work together.

i7urthermore, the identification signals can disturb the communication.

Another device is described in the document EP 0 571 291 also intended for the protection of the portion of line between a telephone and the centre. When the telephone is unhung the authorised subscriber has to introduce a code to obtain access to the centre. If the code is not correct the line is cut- and the subscriber is not authorised to use it.

This device has the advantage of simplicity and the disadvantage of the definition of a constant code for the user. The imagination of the fraudsters has no limit and it has to be known that there are cheap apparatus available, in the shops that connect directly to the line showing the codes emitted on them. It is then easy to memorise the code and to reproduce it when using fraudulently -the line.

The document FIR 2 765 061 describes a module placed in series on the line and comparing the activities upstream of the module (towards the telephone) and downstream of the module (towards the centre). If these activities are different, the circuit is interrupted and a signal is generated by this module. This signal can also be injected on the line in order to dissuade the fraudsters.

With this approach it is considered that the portion of line upstream is secure 5 and that it does not matter which telephone can be connected there. This solution does not respond to the risk of fraud on the portion of line upstream of said module. Furthermore, for the well functioning of this invention the presence of the series commuter on the line is necessary. This is often difficult to obtain on an existing installation and implies the duplication of the detection 10 equipment (detector upstream and detector downstream).

Procedures using taxation impulses have been proposed, for example imposing on the telephone the re-sending of the taxation impulse emitted by the centre in a given time, either on the same frequency or on a different one. The absence 15 of the re-sending means that the telephone using the line is not authorised and the control module placed on the centre side cuts the line. This solution needs the presence of a module on both sides of the line to be protected.

The objective of the present invention is to prevent any non-authorised use of 20 the telephone line without modification on the telephone side.

To this end.this objective is wholly achieved by a procedure according to the invention characterised in that Jt consists, in an initialisation phase, in establishing and memorising an electric signature of representative reference of 25 the whole of electric parameters of the line when it is used by the apparatus authorised to telephone, in a surveillahce phase, in measuring the elec tric parameters composing the electric signature of the line being used by a telephone, comparing this signature with the memorised reference signature and, in case the two signatures are different, making the use of the line 30 impossible.

By electric signature we understand a group of electric parameters of the telephone that are representative of all.the operation phases, notably engaging a line, the numeration, the end of the communication, the reception of a call.

These parameters, amongst others, consist in the measure of tension of the line, the line's current, the level of DTMF modulation, the duration of the numeration impulses, the current of the rings and the intervals of time between 5 the different stages of a phone call.

According to the invention this procedure is advantageously installed by a surveillance module comprising measuring means for the establishment of the signature as well as the c&nparison of this signature with the reference 10 signature. This module also -comprises means to prevent the use of the line if the two signatures are different. It can be installed in any place of the line to be protected as the electric parameters are measurable wherever the authorised telephone, and hence the fraudster telephone, may be placed. Nevertheless, it is desirable to place it as near as possible to the centre so that the fraudster 15 cannot neutralise the protection 'by interrupting, even provisionally, the line downstream of the fraudster telephone.

In the case ihat a non-authorised telephone trying to communicate is detected, several measures can be taken. -The surveillance module can open the line 20 even though it is placed upstream of the fraudster or inject a signal making any dialogue on the line impossible.

The -invention is not limited to a series module on the telephone line, it extends also to a module connected in parallel on the line. In fact, it is often difficult on 25 an existing installation to insert the device in the line. On the contrary, it is always possible to connect in parallel on the connecting bars to this effect this module at the entrance of the line in a building for example. In this case, it is not possible to cut the line, and the detection of the intruder will be fought against with the generation of a noise in order to dissuade him from using it.

30, This noise can be of several kinds, for example DTMF impulses, fixed or variable frequencies, or white noise.

The procedure according to the invention takes place in two stages. The first consists in acquiring the signature of the telephone to be protected. In the case where the telephone is known, for example manufactured by the same manufacturer of the surveillance module, the parameters of the signature can be directly charged in the module!s memory. In the case where the telephone -is of any other type, an initialisation phase of the telephone's parameters is 5 necessary. The module is placed in a learning mode in which it analyses the electric parameters of the telephone at the end of the line and constructs its electric signature. This mode is started manually and can be finished manually or automatically after a certain delay.

10 When a new telephone is instafled on the protected line it is possible to command the initialisation phase at a distance. To this effect the installer has an initialisation module that informs the surveillance module of the installation of this new telephone. The dialogue between these two modules is based on cryptographic communications, that is, using an encrypting algorithm offering a 15 very, high identification security. A few uses with the new telephone are enough for the main parameters composing the signature to be determined; the complementary parameters, for example when this telephone receives a call, are established during the predetermined period of the learning phase.

20 The invention will be better understood with the help of the following detailed description referring to the annexed figures in which:

- Figure 1 represents the configuration according to the state of the art; - Figure 2 represents the installation according to the invention that 25. implements a surveillance module of the parallel type for the protection 'of the line.

In Figure I the telephone 1 has a security module 11 as near to it as possible tha ' t when unhangihg the phone will identify itself to the. -module of the -telephone 30 centre 21 connected as near as possible to the centre 2. The portion of line 4 between these two modules is secured andthe intrusion in this line will be detected by the centre module 21 as the intruder's telephone will not have emitted the identification signals that the telephone module 11 em.its.

The portion of line between the telephone 1 and the telephone module 11 is no longer secured as this module does not know which telephone it is and when the latter engages the line the telephone module 11 will emit towards the centre module 21 -the identification message whichever the telephone is connected 5. downstream. This is why, ideally, the telephone module 11 is integrated in the telephone 1.

In Figure 2 the surveillance module 3 is placed in parallel on the line 4 and analyses the electric signals. The identification module 5 is connected on the 10 line, at whichever place, and informs the surveillance module 3 of the change of the telephone to be protected.

This invention is not limited to public telephones and this principle can be also applied to private telephones. In fact, the owners of the latter can be very 15 interested in not allowring the use of their lines by the fraudsters. In this case, it is possible to memorise in the surveillance module several signatures if the private owner has more than one telephone. Nevertheless, it will be necessary not to use telephones that are cheap and easily available. To this effect, the invention extends also to private telephones where 'we can programme a 20 variation of, the electric parameters taken into account for determining the signature. This variation is the function of a key that can be introduced mechanically (code wheel selector, for example) or numerically (by means of the numbers on the phone). The private owner will thus be assured that h is telephone is identified. in a single way although using a telephone bought in a 25 local shop. Although the fraudster has the same telephone he will not be accepted by the surveillance module because the electric parameters defining the signature will not have the same values as those of the authorised user.

Thanks to this principle, the user can use several telephones on the line even 30 though the same key is introduced in each telephone.

The surveillance modules advantageously have an alarm exit indicating that a fraud attempt has been detected. We can connect this exit to an acoustic generator or direct it to a surveillance board.

In one embodiment of the invention several surveillance modules can be assembled to protect several lines. These modules can be advantageously set not only mechanically but also electrically, that is, they have a connector on 5 either part on which electric signals are transmitted by means of an intermodule bus. Each module is linked to the two adjacent modules. A module called master is placed at the end of the series of modules. In the case where the telephones connected on these lines are of the same, type it is possible to carry out the acquisition phase by one single module and to transfer these 10 parameters composing the signature of this telephone to the.l.other modules. The inter-module bus comprises a link of the series type to this effect connecting the modules to the master module. In this configuration the master module. receives the messages of the state of the different modules composing the chain of modules to which it is connected by means of the se ries link and 15 transmits them to the alarm exit. In this way an acoustic signal is generated if one of the mod-ules detects a fraud attempt.

In-the same way, the master module can have a modem (modulatordemodulator) allowing the transmission or. reception of information to or from all 20 the modules, for example the state of the module, the counter of number of fraud attempts, the re-programming of the parameters or of the software.

These modules are preferably powered by means of a lowering tension transformer delivering an alternative tension. In the chain configuration of the 25 modules this powering is connected to each module by means of the intermodule bus. This tension is isolated galvanically in each module and then sent again and filtered for the use of the module itself.

In one embodiment, the surveillance module is equipped with a DOV (Data 30 Over Voice) interface allowing the transmission of data between said module and the telephone to be protected. This allows, for the telephones that have this possibility, to reinforce the security by a dialogue between these two elements, for example receiving the tax impulsations.

Claims

1. A procedure of surveillance of non-authorised access to a telephone line characterised in that it consists, in an initialisation phase, in establishing and 5 memonsing an electric signature of reference, representative of at least one part of the electric parameters of the line when it is used by the authorised apparatus, in a surveillance phase, in measuring the electric parameters composing the electric signature of the line being used by a telephone, comparing this signature with the memorised reference signature and, in the 10 case where the two signatures are different, making the use of the line impossible.

2. A procedure according,to Claim 1, characterised in that it consists in making the use of the line impossible by injecting a noise on said line.

3. A procedure according to Claim 1, characterised in that it consists in making 15 the use of the line impossible by interrupting said line.

4. A procedure according to Claim 1, characterised in that the establishment and memorisation of the reference signature is done by an analysis of the electric parameters of the apparatus authorised to telephone.

5. A procedure according to Claim 4, characterised in that the state of 20 establishment and memorisation-of the reference signature is commanded at a distance by an initialisation module connected to the line.

6. A procedure according to Claim 1, choracterised in that the establishment and memorisation of the reference signature is done'by programming predefined values.

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7. A procedure according to Claim 1, characterised in that the establishment and memorisation of the reference signature is done by transfer of the parameters of the electric signature established in a similar module.

8. A surveillance module (3) of non-authorised access to a telephone line (4) connected to said line for an installation comprising a telephone line (4) , a 30 telephone centre (2), and at least one telephone (1), for the implementation of the procedure according to Claim 1, characterised in that it comprises measuring means to measure the electric parameters of the telephone line (4) being used by a telephone (1), comparison means to compare these parameters with the reference parameters of the authorised telephones (1) and intervention means to prevent the use of said line.

9. A module according to Claim 8, characterised in that these intervention means comprise a noise generator connected to the telephone line (4),.

5

10. A module according to Claim 8, characterised in that these intervention means comprise a relay in series on the telephone line (4).

11. A module according to Claims 8 to 10, characterised in that it comprises at least one memory to memorise representative information of the functioning of said module.

10

12. A module according to Claims 8 to 11, characterised in that it comprises a memory to memorise a management programme of said.module.

13. A module according to any of the Claims 8 to 12, characterised in that it comprises an exit indicating that the intervention means to prevent the use of the telephone line (4) have been activated.

15

14. A module according to Claims 8 to 1 3, characterised in that it comprises an inter-module bus that can link two adjadent similar modules.

15.. A module according,to Claim 14, characteris6d in that the iritermodule bus comprises connections for the powering of said modules.

16. A module according to any of the Claims 8 to 15, characterised in that it 20 comprises a modem for the transmission of representative information of the functioning and for the updating of the management programme of said module.

17. A module according to any of the Claims 8 to 16, characterised in that it comprises a mod ulator-demodulato,r of the Data Over Voice type.

25

18. A telephone characterised in that it comprises means to vary the electric parameters of functioning according to a key defined by the user.