Abstract:
The invention relates to a process of restriction the access of a terminal to a telecommunication network. The invention includes using the current user authentication procedure usually implemented in telecommunications systems for authenicating users, so as to verify the users&#39;s rights of access in relation to certain criterions, such as, the destination of the call, its time, and its duration.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a process of restricting access to a telecommunications network of a first unit of a telecommunications system, said access being managed by a second unit of said telecommunications system, and said telecommunications system including an authentication procedure of said first unit by said second unit. 
     The invention likewise relates to a telecommunications system comprising at least a first and a second unit, said second unit notably including means for managing the access of said first unit to a telecommunications network, and authentication means of said first unit. 
     The invention finally relates to a central unit of a telecommunications system comprising at least one other unit said central unit having managing means for managing the access of said other unit to a telecommunications network, and authentication means for authenticating said other unit. 
     The invention has highly significant applications in the field of telecommunications, notably within the scope of the DECT standard for professional or private PABX applications. 
     The abstract of Japanese Patent Application JP-A-05 014 489 describes a circuit which permits of restricting the access for incoming or outgoing calls as a function of the respective time range. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is an object of the present invention to propose a simple procedure permitting the restriction of the access as a function of a large variety of criterions without the necessity of the use of specific means. By way of example, the invention permits of restricting the access to a telecommunications network as a function of time, destination of the call; its duration . . . . 
     Therefore, a process according to the invention of restricting access to a telecommunications network and as defined in the opening paragraph is characterized in that it comprises the implementation of said authentication procedure. 
     The invention is thus particularly advantageous in notably all the mobile telecommunications systems in which user authentication procedures are defined. 
     For restricting said access as a function of at least one predefined criterion, in a particularly advantageous embodiment the process according to the invention notably-comprises assigning a code called access code to each of these criterions and it uses said access code as a key which, applied to said authentication procedure, permits of determining the rights of said first unit in relation to said criterion. 
     By way of example, a process according to the invention notably comprises: 
     transmitting an authentication request from said second unit to said first unit, 
     calculating a first and a second authentication result at the level of said respective first and second units, by utilizing said access code as a key, said access code previously being entered by a user at the level of said first unit, 
     transmitting said first result from said first unit to said second unit, 
     comparing said first and second results at the level of said second unit to determine whether said first unit has right of access in relation to said criterion. 
     The process according to the invention is applied notably in an advantageous manner to the DECT standard defined by ETSI (European Telecommunications Standard Institute). In this case, it advantageously implements the procedure called “user authentication” defined in the part GAP (Generic Access Profile; ETSI 300444) of this standard. 
     A standardized use of such a process within the scope of a mobile telephony standard offers the additional advantage of permitting an interoperability between mobile units and base units from different manufacturers. 
     These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 represents an example of a telecommunications system according to the invention, 
     FIG. 2 represents a simplified diagram explaining the operation of the “user authentication” procedure of the DECT standard, and 
     FIG. 3 represents an example of an access restriction process according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the following of the description, a process and a system according to the invention will be described within the scope of the DECT mobile telephony standard defined by ETSI. However, the invention is applicable to any other telecommunications system having a user authentication procedure (CT 2 , GSM, ETACS, TETRA . . . ). 
     According to FIG. 1, a telecommunications system according to the invention comprises, installed inside a dwelling  0  or an office, for example, a base unit  1  linked to the public telecommunications network  2  by a cable  3 , and a plurality of mobile terminal units  4  inside the building  0  and communicating with the base unit by radio. Such systems are notably described in the article entitled “The complete solution for cordless access”, published in “Philips Telecommunication Review”, Vol. 52, No. 3 January 1995. 
     The invention notably relates to the restriction of access of units  4  to the telecommunications network  2  as a function of predefined criterions. By way of example, these criterions are notably the time of the call, its destination, its duration . . . . For example, for professional applications, the access to the network is likely to be restricted to certain time ranges corresponding to the normal hours in which staff is present. It is also likely to be restricted to certain countries. For domestic applications, for example, the process according to the invention notably permits of checking the duration of calls. 
     In this example, the base unit  1  plays the role of second unit and the mobile units  4  play the role of first units. 
     In FIG. 2 is described in a diagram the authentication procedure provided in the part GAP of the DECT standard (ETSI 300444). This authentication procedure is provided in the standard to permit the authentication of a user for, for example, bank applications. The user has a personal code called UPI (User Personal Identifier). When a base unit wishes to obtain a signature from the user of a mobile unit, it transmits thereto a request “authentication request” whose format is described in the standard cited above. 
     On its part, said mobile unit receives the request “authentication request”. 
     It calculates a first authentication result RES 1  based on the UPI code entered by the user via the keypad of the unit. Then the mobile unit sends a reply “authentication reply” containing said first result to the base unit. 
     The base unit then calculates a second authentication result XRES 1  based on the UPI code assigned to said mobile unit, after which the base unit compares said first and second results RES 1  and XRES 1 . The user is correctly authenticated when they are the same. 
     The authentication results RES 1  and XRES 1  are calculated in accordance with Recommendation ETS 300175-7: The UPI code is combined with a key hidden to the user and stored in a memory before being applied, together with other data generated at random and transmitted to the other unit in the request or reply messages, to a calculating unit for calculating an authentication algorithm called DSAA (DECT Standard Authentication Algorithm). 
     The invention notably has for its object to apply this procedure to the access restriction for mobile units to the telecommunications network. 
     Therefore, a certain number of access criterions are defined and an access code is assigned to each of these criterions. The users which have rights of access in relation to said criterions are in possession of the corresponding access codes. 
     The process according to the invention will now be described with reference to FIG. 3 for a first embodiment. 
     In step  10 , a user dials a telephone number NT on the keypad of his unit  4 . The unit  4  then starts the communication by emitting a message “call request” to the base unit  1 . 
     In step  11 , the base unit receives this message. It then analyzes the called number contained in this message in step  12  to determine whether it is an emergency number. Indeed, in an advantageous embodiment of the invention, certain emergency numbers are defined for which the procedure of network access restriction and access control is not implemented. They are, for example, the telephone numbers of the fire brigade, the police . . . . Thus, if the number of the called unit is an emergency number, the base unit directly goes over to step  30  where the call is processed. In the opposite case, the process according to the invention continues with step  13 . 
     In step  13 , the base unit runs through a list of defined criterions by verifying whether they can be applied. And for each criterion C that can be applied, it performs the operations corresponding to steps  113  to  120 . When the list has been completed, this means that the access has been given for all the defined criterions, and the operation carries on with step  30 . 
     By way of example, verifying whether a criterion is applicable comprises: 
     for a criterion relating to the destination of the call, verifying whether the formed number is likely to be forbidden (for example, if one seeks to check the international access code, one verifies whether the compound number starts with  19  and if this is not the case, the access is authorized and the operation carries on directly to box  30 ), 
     for a criterion relating to the time of call, verifying the time given by the clock of the base unit (if one is in a time range during which the access is not checked, the operation directly proceeds to box  30 ). 
     In step  113 , the base unit sends an authentication request “authentication request” to the calling user. In another advantageous embodiment, an audio signal and/or an advice is sent to the base unit beforehand to warn the user and ask him to enter the access code that corresponds to said criterion. In practice, this audio signal and this advice are transmitted in messages CC-INFO whose INFORMATION ELEMENT field is equal to &lt;&lt;SIGNAL&gt;&gt; for the audio signal and to &lt;&lt;MULTIDISPLAY&gt;&gt; for the advice, respectively. 
     In step  114 , the mobile unit receives this request. In step  115 , the user enters said access code CA and, in step  116 , the mobile unit calculates a first authentication result RES 1  by utilizing this code as a key instead of the identification code UPI. In step  117 , this result RES 1  is sent to the base station in a message “authentication reply”. 
     This reply is received by the base unit in step  118 . In step  119 , it calculates a second authentication result XRES 1  based on the access code that corresponds to the selected criterion. Then, in step  120 , it compares the two authentication results RES 1  and XRES 1 . If these results are the same, the access to the telecommunications network is authorized for the criterion C. The operation is thus resumed at step  13  to verify whether the access is also authorized as a function of other criterions. On the other hand, if the two results are different, the access is denied to the base unit and the communication is terminated in step  40 . 
     In this embodiment, the access code corresponding to a criterion is asked from the user for the start of the communication. 
     In another embodiment, another type of criterion is defined for which the is cyclically asked for the access code. Such a criterion notably permits of checking the duration of the communications. An elementary duration is defined beyond which the user is to enter the access code that corresponds to this criterion. If the code entered is correct, the communication is continued, the user thus being conscious of the elapsed time. On the other hand, if the code is not correct, this means that the user is not authorized to carry on with this communication beyond this elementary duration, and the communication is shut off. 
     Although the invention has been described within the scope of the DECT standard, it is not restricted thereto. It may notably be used in any telecommunications system in which a user authentication procedure is provided. 
     Furthermore, the invention is not restricted to the embodiments which have just been described by way of example. Variants may be provided notably by substituting equivalent technical means.