EP1410616A2

EP1410616A2 - Secure public telephony system

Info

Publication number: EP1410616A2
Application number: EP02700507A
Authority: EP
Inventors: Jean-Paul Mengus
Original assignee: Schlumberger Systemes SA; Schlumberger Malco Inc
Current assignee: SPT PUBLICOM; Axalto Inc
Priority date: 2001-02-22
Filing date: 2002-02-20
Publication date: 2004-04-21
Also published as: FR2821227A1; WO2002067564A3; CA2437586A1; WO2002067564A2; FR2821227B1

Abstract

The invention relates to a secure public telephony system comprising at least one public telephone (10) which is connected to a telecommunication network (1) and a securement device that can monitor the exchanges of information between said public telephone and at least one part of the numbers called. The inventive system is characterised in that the securement device comprises a remote server (20). Said server (20) can be connected to the public telephone by means of the telecommunication network (1) and is adapted to transfer the information exchanged between said telephone and the numbers called.

Description

SECURE PUBLIC TELEPHONY SYSTEM

The present invention relates to the field of telecommunications and in particular that of public telephone networks. The present invention relates more specifically to a secure public telephone system.

The present invention therefore relates to a telephone installation for the transmission of information over a telephone line comprising a telephone set of the type without subscription and connectable to said telephone line and a security server associated with said telephone set.

Public telephone sets allow users, by payment (by coins, tokens or cards), to communicate information, such as voice or data, through a telephone line. Telephone charging is done by counting charging pulses sent to a telephone exchange or even directly by the electronic circuits of the telephone set, the latter then having its own table for charging telephone communications.

Like all self-service devices that deliver valuable goods and services, public phones are under attack from fraudsters. Among the most frequent frauds concerning the telephone installation itself, one can quote the diversion of the telephone line connecting the public telephone set to the telephone exchange by directly connecting to this one a traditional telephone set or even by modifying the transmitted data on this line as the charging data when these pass on the line. To respond to such attacks, the applicant has developed line security tools consisting of establishing authentication between a telephone set and an associated module mounted on the transmission line connecting the telephone set to the telephone exchange and interrupting communication by attempted fraud.

These tools are based on the installation on the telephone line of a control module associated with each telephone set to be secured. The telephone set has a particular structure and circuits which allow the exchange between the control module and the telephone set of authentication information which is compared to verify that the telephone set is authorized to be used.

The present invention proposes to perfect such tools by using a securing device which is at the same time particularly efficient, simple and inexpensive to implement.

The secure public telephone system according to the invention is therefore of the type comprising at least one public telephone connected to a telecommunications network and a security device capable of supervising the exchange of information between this public telephone and at least part of the numbers called.

According to the invention, the secure public telephone system is characterized in that the security device is formed by a remote server, this server being able to be connected to said public telephone by means of said telecommunications network and being adapted to transit the information exchanged between the public telephone and the numbers called. According to another characteristic of the secure public telephone system which is the subject of the present invention, the public telephone comprises means for transmitting communications to the server in the form of coded digital data. According to another characteristic of the secure public telephone system which is the subject of the present invention, the public telephone is equipped with the IP communication protocol and in that the information exchange sessions between the public telephone and the server use this IP protocol, the voice being coded in VoIP. According to another characteristic of the secure public telephone system which is the subject of the present invention, the telephone comprises selection means capable of directing part of the calls to the server, the calls directed to the server being selected according to predetermined criteria. According to another characteristic of the secure public telephone system which is the subject of the present invention, the criteria for selecting calls directed to said server include the cost of communications.

According to another characteristic of the secure public telephone system which is the subject of the present invention, the public telephone is connected to the telecommunications network by means of a telephone exchange and this exchange includes means capable of refusing any direct communication with a telephone number. call meeting the predetermined selection criteria according to which this communication must pass through the server.

According to another characteristic of the secure public telephone system object of the present invention, the public telephone addresses calls that do not meet the criteria predetermined selection, without any particular processing and in particular without digital coding of the channel.

According to another characteristic of the secure public telephone system which is the subject of the present invention, the server comprises means capable of synchronizing and regulating the sessions for exchanging information between the public telephone and the numbers called passing through the server.

According to another characteristic of the secure public telephone system which is the subject of the present invention, the server comprises means capable of authenticating the sessions for exchanging information between the public telephone and the numbers called passing through the server.

According to another characteristic of the secure public telephone system which is the subject of the present invention, the server comprises appropriate means for transferring data to the public telephone in parallel with the information exchange sessions between said telephone and the numbers called passing through the server, these data concerning in particular the taxation of sessions and information related to the operation of said telephone

Other characteristics and advantages of the present invention will appear better on reading the following description of an embodiment of the invention given by way of non-limiting example. The description refers to the appended figures in which:

- Figure 1 is a simplified view showing the secure public telephone system according to the invention; - Figure 2 is a block diagram detailing the operation of the secure public telephone system according to the invention.

In Figure 1 appears shown a telephone referenced 10 which belongs to a public telephone network.

Such a network generally comprises between several tens to several thousand telephones, or even several tens of thousands, depending on its territorial coverage.

The telephone 10 is conventionally intended to be used in self-service by users, who, for a fee, can make telephone communications to subscriber stations 5, consult Audiotel-type services 3, or even access the Web and the Internet or information servers residing on private networks. The telephone set 10 comprises, in known manner, a box 101 provided with a keyboard 102 for dialing a call number, a display device 103, for example with liquid crystal, and a telephone handset 104. The telephone set 10 further comprises a memory card reading / writing device, the insertion slot 105 of which can be seen. Of course, the telephone set can be equipped with a coin cashing system in addition to or in replacement of the card reading / writing device payment.

The telephone 10 is connected to a communication network 1 which, in the example illustrated in FIG. 1, is the public switched telephone network PSTN or PSTN (acronym for Public Switching Telephone Network).

The connection of the telephone 10 to the PSTN network 1 is carried out by means of a wired link 2 (with two wires) which leads into a telephone exchange 4 which is either a local exchange center CLR or a center with autonomous routing CAA.

This network 1 could also be constituted by a network of digital type ISDN (Integrated Services Digital Network). Furthermore, the public telephone 10 includes hardware and software resources allowing its operation and in particular to debit the users of the amounts corresponding to the costs of the communications or services used, the users being able to pay either by means of payment cards, telephone or bank cards. , or by means of coins.

These hardware and software resources are now well known and therefore do not require further description.

However, it will be specified that the telephone 10 includes an electronic command and control unit formed by a microprocessor or microcontroller, not shown, conventionally comprising a central unit (UC) of the input / output interfaces (I / O) and of various types of memories. (RAM, ROM, EPROM, ...). This microcontroller is therefore able to control and supervise the operation of the telephone apparatus 10 according to appropriate programs.

Thus, the slot 105 cooperates with non-illustrated guide means which brings the card into a processing position where the external electrical contact pads of the card are connected to the connection elements of the read / write head also not shown. A processing circuit controlled by the microcontroller controls the reading or writing of new information in the memory of the card.

Indeed, in the case of prepaid telephone cards, a first memory area contains identification information and a second memory area contains the successive balances of the card. In the case where the card memory is PROM type, the card contains a certain number of memory points which are initially blank (state 0). Each memory point corresponds to a unit amount. The balance is modified by irreversibly passing from state 0 to state 1 an integer number of points corresponding to the amount to be debited associated with the charging pulse sent by the microcontroller. The transition from state 0 to state 1 is obtained by applying a write voltage to the memory points considered.

In addition, the telephone 10 is equipped with the IP communication protocol (Internet Protocol) as well as TCP or UDP protocols in accordance with the technical recommendations of the IETF ("internet Engineering Task Force"). Finally, the physical layer of the telephone 10 is produced by analog (or digital depending on the nature of the network 1) modems.

The connection of the telephone 10 to the PSTN network 1 is subject to restrictions of use defined with the operator of this network. These restrictions will be specified below. These restrictions are implemented in the central office 4 of the PSTN network 1 using appropriate programs controlling the various materials used. These materials and this type of program are known and therefore do not require further details.

The server 20 is arranged in a location which is not accessible to users, for example on the premises of the operator of the public telephone network. The connection of the server 20 to the PSTN network 1 is carried out by means of an appropriate secure link, allowing including handling multiple communications simultaneously.

This server 20 is responsible, as will be detailed below, for establishing reliable and authenticated information exchange sessions which consists, for example, in certain identification of the telephones 10 during an information exchange or even in encrypt data to secure communication when needed.

This server 20 is formed by a computer, for example of the PC type operating under Windows NT (registered trademark). Any call arrives at an input port of the server which is not shown, which is listened to continuously, then analyzed by an appropriate software application for example in Java language (registered trademark) and then routed to the requested recipient: subscriber or server delivering a service.

Referring to FIG. 2, the method for securing calls according to the invention will now be described.

To secure the use of the telephone 10 and avoid fraud to the detriment of the public telephone operator, it is therefore important to prohibit unauthorized use of the telephone

10 and the telephone line which connects it to the PSTN network, that is to say to the CLR or the CAA.

This ban can relate to all calls made by telephone 10 or even relate only to part of the calls.

In accordance with the present invention, the security method therefore consists in differentiating the calls into two groups, that of the calls to be secured and that of the calls for which security is not necessary and to apply appropriate treatment to each type of call.

The criteria for securing a call can be diverse and varied and adapted in particular by the operator of the public telephone network to his specific needs. A criterion can for example be the cost of the communication, as soon as the cost of the communication to a subscriber or to a server exceeds a certain amount then the communication is secure.

As specified above, the telephone 10 is suitable for paying access to subscribers or to services. The price paid by the user for these services is obviously defined by the public telephone operator according to their cost price. Thus, the price of a local call will not be the same as that of a national call or international, the same for services.

In accordance with international rules, the numbering plan for services and telephone subscribers follows a set of rules established by the standardization bodies ETSI, ECTRA and ITU (cf. recommendations E.164, E.213 and X.121).

The differentiation between the calls to be protected and the others can therefore be easily established from only the telephone numbers.

The first step of the method therefore consists in detecting the line seizure when the handset 104 is lifted and the numbering which follows. When a user picks up the handset

104, the off-hook signal is perceived by appropriate means which inform the microprocessor thereof by sending a signal characteristic, it then initiates the progress of the line securing program according to the invention.

During the entry by the user of the telephone number called, the system for implementing the method according to the invention records this number formed, in the case of a voice frequency telephone set, by a series of DTMF signals according to the recommendation F.23 from FUIT (International Telecommunication Union) and converts them into binary code to be processed by the microcontroller. ₍ The microcontroller then operates the analysis of the called number and determines, from appropriate tables stored in an appropriate memory (EPROM or non-volatile RAM), it is a call to be secured because it belongs for example to the group high cost communications (national or international calls, servers ...) or if it is a call that may not be secure because of low cost (local call, emergency number, etc.) .

If it is a call number that does not require security (local call, etc.), then the telephone number entered by the user on the keypad of the telephone set is sent to the CLR / CAA telephone exchange. so that the latter establishes through its switches, a line with the telephone number called and sends the latter a ring signal.

The microcontroller supervises the line to determine whether the called party has picked up and that communication has been established. If this is the case, then price pulses are regularly sent to the collection system, whether it is to the card reader to toast the corresponding units of a prepaid telephone card or to the coin selector of change to cash coins. These tariff pulses are produced by the microcontroller from tariff tables stored in an appropriate memory of the telephone or even by the telephone exchange 4 and received on the line parallel to the communication in progress.

The call having been identified as having to be secured (national or international call, Audiotel server, etc.), the microcontroller then triggers appropriate processing of the call.

This processing consists in passing the exchange of information with the telephone number, whether voice or data, through the GATEWAY 20 server.

To do this, the information transmitted by the user in non-digital form such as voice, is digitized by an appropriate signal processing algorithm of the CODEC type, then coded and compressed according to the recommendations G.723.1 (linked to H.323) in MP-MLQ / ACELP at 5.3 and 6.3 kbit / s or G.728 in LD-CELP at 16 kbit / s or G.729 in CS-ACELP at 8 kbit / s. Obviously, these ITU standards are for reference only. The information thus coded is sent in packets to the server 20 via a modem and the PSTN network, through a session using the IP and UDP protocols, with the responsibility for this server of directing them to the number called by the user.

This voice processing is called VoIP. Obviously any other available method can also be used such as VoFR (Voice over Frame Relay) or VToA (Voice Telephony over ATM).

When the GATEWAY server 20 receives the call from the telephone 10 it processes the request by an appropriate application allowing the control and the establishment of a session in the protocol sense of the term. A standard interface ("socket") is then opened and the request is re-sent to the number called after processing adapted to it. In particular, if the station called is a subscriber number with only a conventional telephone station, the server proceeds via conversion cards to the reverse processing of that operated by the telephone and sends a signal to this station. decoded voice.

The information originating from the number called also passes through the server 20 and is therefore the subject of a processing symmetrical to that of the data received by this number, they are coded by the server 20 and on their arrival decoded by the public telephone 10 .

In the context of the present invention, the server 20 therefore has a certain number of functions provided by appropriate hardware and software means. A first function consists in directing the information received from the telephone 10 towards the requested call number, this is a call re-routing function. The server 20 can choose to operate the most suitable telecommunication network for re-routing, this may be the PSTN network 1 or even any other network to which the server 20 may have access, such as the Internet network for example.

Another function consists, when necessary, in translating the data transmitted in the format of the subscriber stations or servers called. Another function is to synchronize and regulate the information exchange sessions between the public telephone and the numbers called. Another function is still to establish reliable information exchange sessions and authenticated or to encrypt all or part of the data exchanged.

In addition to processing the information exchanged between the public telephone 10 and the telephone number called, the telephone 10 and the server 20 send security data which can be encrypted by appropriate algorithms such as SSL (Socket Secure Layer) and which guarantee that the session processed by the GATEWAY server 20 is well established with the public telephone 10 and not with a telephone connected directly to the connection line 2.

The server 20 can also provide information useful for the operation of the telephone 10 such as for example the charging pulses for the call in progress, thus the telephone 10 no longer has to manage rate tables for all secure calls.

Indeed, in parallel with the transfer of data between the telephone 10 and the station called via the server 20, the microcontroller of the telephone proceeds as previously with respect to a local call, namely that it supervises the communication and addresses regularly tariff pulses to the card or coin cashing system and this, depending on the cost of the communication determined from a tariff table suitable for the call, tariff table stored in an appropriate memory of the public telephone or else from the tariff information provided by the server 20 and communicated to the telephone 10.

To further strengthen the security of the public telephone system according to the invention, the connection of the telephone 10 to the PSTN network 1 is subject to restrictions of use defined with the operator of this network. An example of restriction is that that all calls that must be secured and therefore must pass through the server 20, cannot be taken into account and therefore routed by the exchange 4. Thus if a fraudster accesses the connection line 2, he can only access one limited number of telephone numbers. Another example of restriction consists in redirecting any call received by the central office from line 2 and concerning a number to be secured to the server 20, which if it detects a call not coming from the telephone 10 is then able to trigger an appropriate alert. Obviously the present invention is not limited to the single embodiment illustrated, which has been given only by way of example.

Claims

1. Secure public telephone system comprising at least one public telephone (10) connected to a telecommunications network (1) and a security device capable of supervising the exchange of information between said public telephone and at least part of the numbers called , characterized in that said security device is formed by a remote server (20), said server (20) being able to be connected to said public telephone via said telecommunication network (1) and being adapted to transmit information exchanged between said telephone and the numbers called.

2. Secure public telephone system according to claim 1, characterized in that said telephone (10) comprises means for transmitting communications to said server (20) in the form of coded digitized data.

3. Secure public telephone system according to claim 2, characterized in that said telephone (10) is equipped with the Internet communication IP protocol and in that the information exchange sessions between said telephone (10) and said server (20) use said IP protocol, the voice being encoded in VoIP.

4. Secure public telephone system according to any one of the preceding claims, characterized in that said telephone (10) comprises selection means capable of directing part of the calls to said server (20), calls directed to said server (20) being selected according to predetermined criteria.

5. Secure public telephone system according to claim 4, characterized in that the selection criteria for calls directed to said server include the cost of communications.

6. Secure public telephone system according to any one of the preceding claims, characterized in that said telephone (10) is connected to the telecommunications network (1) via a telephone exchange (4) and in that said central (4) comprises means capable of refusing any direct communication with a telephone number meeting said predetermined selection criteria.

7. Secure public telephone system according to any one of the preceding claims, characterized in that said telephone (10) addresses calls that do not meet said predetermined selection criteria, without special processing and in particular without digital coding of the channel.

8. Secure public telephone system according to any one of the preceding claims, characterized in that said server (20) comprises means capable of synchronizing and regulating information exchange sessions between said telephone (10) and the called numbers transiting through said server (20).

9. Secure public telephone system according to any one of the preceding claims, characterized in that said server (20) comprises means capable of authenticating information exchange sessions between said telephone (10) and the numbers called passing through. by said server (20).

10. Secure public telephone system according to any one of the preceding claims, characterized in that said server (20) includes means suitable for transferring data to said telephone (10) parallel to the information exchange sessions between said telephone and the numbers called passing through said server (20), said data relating in particular to the charging of said sessions.