Abstract:
A method of storing subscriber data in a mobile-communication system includes the steps of providing a high-priority-subscriber-storage area in addition to an ordinary-subscriber-storage area, and storing subscriber data of a relevant subscriber in the high-priority-subscriber-storage area if priority of the relevant subscriber exceeds a predetermined threshold and if the ordinary-subscriber-storage area is full.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a method and a device for controlling subscriber data of mobile stations in a mobile-communication system, and particularly relates to a method and a device for controlling subscriber data which store or delete subscriber data of mobile stations in or from a visitor location register of a cellular-mobile-communication system. 
     2. Description of the Related Art 
     FIG. 16 is an illustrative drawing showing a configuration of a cellular-mobile-communication system. A cellular-mobile-communication system includes a home-location register HLR, a visitor-location register VLR, a mobile-service-switching center MSC, base stations BSS, and mobile stations MS. 
     The home-location register HLR stores subscriber data (mobile customer data) such as an identification number, a location, and an identification key with respect to each of the mobile stations MS covered by a home network. The home-location register HLR transmits subscriber data to a visitor-location register VLR of a given area when a mobile station MS moves to this area. 
     The visitor-location register VLR receives and stores the subscriber data of each mobile station MS residing in its area of control when the home-location register HLR of each mobile station MS transmits the subscriber data. 
     The mobile-service-switching center MSC receives a location-update request from the mobile stations MS via the base stations BSS, and requests the visitor-location register VLR to attend to location-update processing. Further, the mobile-service-switching center MSC attends to switch control of receipt and transmission of calls with respect to the location-registered mobile stations MS via the base stations BSS. 
     FIG. 17 is a flowchart of a process of registering a location. FIGS. 18A through 18E are illustrative drawings showing data structures of messages and data which are exchanged during the process of registering a location. 
     When a mobile station MS moves from a wireless service area to another wireless service area, or when a power switch of a mobile station MS is turned on, the mobile station MS receives information on the wireless service area sent from the base station BSS. When the mobile station MS detects that the received information is different from information stored in the mobile station MS, the mobile station MS transmits a signal requesting updating of a location. 
     Upon receiving the signal for requesting location update, the base station BSS transmits a location-update-request message  13 - 1  to the mobile-service-switching center MSC (step S 12 - 1  in FIG.  17 ). 
     Upon receiving the location-update-request message  13 - 1 , the mobile-service-switching center MSC transmits an authentication-request message to the visitor-location register VLR in order to check if the mobile station MS that requested location update is a legitimate registered station (step S 12 - 2 ). 
     Upon receiving the authentication-request message, the visitor-location register VLR searches for a home-location register HLR that is home to the relevant mobile station MS. This search is made based on a mobile identification number of the mobile station MS. Then, the visitor-location register VLR sends the authentication-request message to the home-location register HLR that is found in the search (step S 12 - 3 ). 
     In response to the authentication-request message, the home-location register HLR refers to the subscriber data of the mobile station MS by using the mobile identification number, and notifies the visitor-location register VLR of an authentication-request acknowledgement (step S 12 - 4 ). 
     The visitor-location register VLR forwards the authentication-request acknowledgement to the mobile-service-switching center MSC (step S 12 - 5 ). 
     In accordance with the authentication-request acknowledgement, the mobile-service-switching center MSC transmits a registration-notification message  13 - 2  to the visitor-location register VLR (step S 12 - 6 ). 
     Upon receiving the registration-notification message  13 - 2  from the mobile-service-switching center MSC, the visitor-location register VLR forwards the registration-notification message  13 - 2  to the home-location register HLR (step S 12 - 7 ). 
     In response to the registration-notification message  13 - 2  sent from the visitor-location register VLR, the home-location register HLR reads subscriber data of the relevant mobile station MS from a subscriber-data-storage area  13 - 3 , and sends a subscriber-data message  13 - 4  to the visitor-location register VLR (step S 12 - 8 ). 
     The visitor-location register VLR stores the subscriber data of the relevant mobile station MS sent from the home-location register HLR, and notifies the mobile-service-switching center MSC of a registration-notification acknowledgement (step S 12 - 9 ). 
     Upon receiving the registration-notification acknowledgement from the visitor-location register VLR, the mobile-service-switching center MSC informs the base station BSS of a result of the location update (step S 12 - 10 ). 
     With reference to FIG. 18A, the location-update-request message  13 - 1  includes a mobile identification number and a mobile-station electronic serial number of the relevant mobile station MS as well as a base-station ID of a wireless service area where the mobile station MS is currently located. The location-update-request message  13 - 1  is sent from the base station BSS to the mobile-service-switching center MSC. 
     With reference to FIG. 18B, the registration-notification message  13 - 2  includes the mobile identification number and the mobile-station electronic serial number of the relevant mobile station MS as well as a mobile-service-switching-center ID of the wireless service area where the mobile station MS is currently located. The registration-notification message  13 - 2  is sent from the mobile-service-switching center MSC to the visitor-location register VLR and from the visitor-location register VLR to the home-location register HLR. 
     With reference to FIG. 18D, the subscriber-data-storage area  13 - 3  of the home-location register HLR stores a mobile identification number, a mobile directory number, location information including a mobile-service-switching-center ID of an area of a current location, a priority parameter, etc., with respect to each mobile station MS that belongs to the home network. 
     The priority parameter indicates priority that is given to a subscriber service class of a relevant mobile station MS. The priority parameter may range from 0 to 15, for example, as shown in FIG.  18 E. 
     With reference to FIG. 18C, the subscriber-data message  13 - 4  includes the mobile identification number, the mobile-service-switching-center ID, the mobile directory number, and the priority parameter. The subscriber-data message  13 - 4  is sent from the home-location register HLR to the visitor-location register VLR as a response to the registration notification, and is stored in the visitor-location register VLR. 
     The subscriber data stored in the visitor-location register VLR is generally deleted when the mobile station MS moves to another wireless service area. The deletion of the subscriber data is prompted by a notice sent from the home-location register HLR when a visitor-location register VLR of the new wireless service area receives and stores the subscriber data in response to a location-update request. 
     FIG. 19 is a flowchart of a process of deleting a location update. Here, a new visitor-location register VLR is one that is provided in an area into which the mobile station MS moves, and an old visitor-location register VLR is one that is provided in an area from which the mobile stations MS moves out. The old visitor-location register VLR has subscriber data of the mobile station MS stored therein. 
     From steps S 14 - 1  to S 14 - 7 , a process of updating a location is performed with respect to the new visitor-location register VLR in the same manner as in the steps S 12 - 1  through S 12 - 7  of FIG.  17 . 
     Upon receiving the registration-notification message from the new visitor-location register VLR, the home-location register HLR searches for the old visitor-location register VLR by referring to the information on the visitor location stored in the subscriber-data-storage area. Then, the home-location register HLR transmits a registration-cancellation message to the old visitor-location register VLR (step S 14 - 8 ). 
     Having received the registration-cancellation message, the old visitor-location register VLR deletes the subscriber data of the relevant mobile station MS, and transmits a registration-cancellation acknowledgement (step S 14 - 9 ). 
     The home-location register HLR receives the registration-cancellation acknowledgement from the old visitor-location register VLR, and, then, sends the subscriber data to the new visitor-location register VLR (step S 14 - 10 ). 
     Steps S 14 - 10  through S 14 - 12  of FIG. 19 are the same as the steps S 12 - 8  through S 12 - 10  of the location-update process shown in FIG. 17, and a duplicate description thereof will be omitted. 
     As described above, each time a mobile station MS moves from a wireless service area to another wireless service area, a process of registering subscriber data needs to be performed with respect to a visitor-location register VLR of the new wireless service area. Further, the subscriber data of the relevant mobile station MS needs to be deleted from a visitor-location register VLR of the old wireless service area. 
     A visitor-location register VLR has only a limited memory area for storing subscriber data. since the number of mobile stations MS residing in a given area is a matter of random occurrence, a given visitor-location register VLR may receive an excessively large number of location-update requests issued from mobile stations MS. In this case, the visitor-location register VLR may have the subscriber-data-storage area thereof completely full of data, and cannot store new subscriber data. Such a visitor-location register VLR simply rejects new requests for location update in excess of the number of mobile stations MS that can be accommodated therein. A mobile station MS, which is rejected after issuing a request for location update, cannot receive a communication service. 
     Accordingly, there is a need for a scheme which can improve a success rate of location update when a location update is requested by a mobile station MS that belongs to a service class having high priority. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a general object of the present invention to provide a scheme which can achieve the need described above. 
     It is another and more specific object of the present invention to provide a scheme which can improve a success rate of location update when a location update is requested by a mobile station MS that belongs to a service class having high priority. 
     In order to achieve the above objects according to the present invention, a method of storing subscriber data in a mobile-communication system includes the steps of providing a high-priority-subscriber-storage area in addition to an ordinary-subscriber-storage area, and storing subscriber data of a relevant subscriber in the high-priority-subscriber-storage area if priority of the relevant subscriber exceeds a predetermined threshold and if the ordinary-subscriber-storage area is full. 
     The method described above utilizes information about priority of subscribers, and gives precedence to subscribers having priority exceeding the predetermined threshold so as to secure a place for storing the subscriber data of such subscribers in the high-priority-subscriber-storage area. This improves a success rate of location update (i.e., success rate of storing subscriber data) when a location update is requested by a subscriber using a mobile station MS that belongs to a service class having high priority. 
     According to another aspect of the present invention, a method of deleting subscriber data of a mobile station in a mobile-communication system includes the steps of checking priority of a mobile station when receiving a message indicating either a power down of the mobile station or a completion of a call by the mobile station, keeping subscriber data of the mobile station if the priority of the mobile station exceeds a predetermined threshold, and deleting the subscriber data of the mobile station if the priority of the mobile station does not exceed the predetermined threshold. 
     The method described above utilizes information about priority of mobile stations, and determines whether to delete subscriber data based on whether the priority of a relevant mobile station exceeds the predetermined threshold. Therefore, a mobile station having priority exceeding the threshold can keep its subscriber data registered in the system even when the mobile station is switched off or a call is completed. 
     According to another aspect of the present invention, a method of storing subscriber data in a mobile-communication system includes the steps of storing subscriber data of a relevant subscriber in a data-storage area if there is a space therein, and replacing subscriber data of another subscriber in the data-storage area with the subscriber data of the relevant subscriber if the data-storage area is full and if priority of the relevant subscriber exceeds a predetermined threshold, said another subscriber having lower priority than the relevant subscriber and being currently not on phone. 
     The method described above utilizes information about priority of subscribers, and gives precedence to subscribers having priority exceeding the predetermined threshold when registering the subscriber data of the subscribers in the data-storage area. This improves a success rate of location update (i.e., success rate of storing subscriber data) for subscribers using mobile stations MS that belong to service classes having high priority. 
     Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a flowchart of a process of registering a location according to a first embodiment of the present invention; 
     FIG. 2 is a block diagram of a device for controlling storage of subscriber data according to the first embodiment of the present invention; 
     FIG. 3 is a flowchart of a process of registering a location according to a second embodiment of the present invention; 
     FIG. 4 is a block diagram of a device for controlling storage of subscriber data according to the second embodiment of the present invention; 
     FIG. 5 is a flowchart of a process of registering a location according to a third embodiment of the present invention; 
     FIG. 6 is a block diagram of a device for controlling storage of subscriber data according to the third embodiment of the present invention; 
     FIG. 7 is a flowchart of a process of registering a location according to a fourth embodiment of the present invention; 
     FIG. 8 is a block diagram of a device for controlling storage of subscriber data according to the fourth embodiment of the present invention; 
     FIG. 9 is a flowchart of a process of deleting registered data according to a fifth embodiment of the present invention; 
     FIG. 10 is a flowchart of a process of deleting registered data according to a sixth embodiment of the present invention; 
     FIG. 11 is a block diagram of a device for controlling storage of subscriber data according to the fifth and sixth embodiments of the present invention; 
     FIG. 12 is a flowchart of a process of deleting registered data according to a seventh embodiment of the present invention; 
     FIG. 13 is a flowchart of a process of controlling a timer; 
     FIG. 14 is a flowchart of a process of deleting registered data according to an eighth embodiment of the present invention; 
     FIG. 15 is a flowchart of a process of controlling a timer; 
     FIG. 16 is an illustrative drawing showing a configuration of a cellular-mobile-communication system; 
     FIG. 17 is a flowchart of a process of registering a location; 
     FIGS. 18A through 18E are illustrative drawings showing data structures of messages and data which are exchanged during the process of registering a location; and 
     FIG. 19 is a flowchart of a process of deleting a location update. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following, embodiments of the present invention will be described with reference to the accompanying drawings. 
     FIG. 1 is a flowchart of a process of registering a location according to a first embodiment of the present invention. FIG. 2 is a block diagram of a device for controlling storage of subscriber data according to the first embodiment of the present invention. 
     In the first embodiment, a subscriber-data-storage area of a visitor-location register VLR is divided into two areas. One is a high-priority-subscriber-storage area PA for storing subscriber data of mobile stations MS which have priority greater than a predetermined threshold, and the other is an ordinary-subscriber-storage area NA for storing subscriber data of other mobile stations MS. 
     At a step S 1 - 1 , the visitor-location register VLR receives subscriber data of a subscriber from the home-location register HLR during a process of location update for this mobile-station subscriber. 
     At a step S 1 - 2 , a check is made as to whether there is an available space in the ordinary-subscriber-storage area NA. 
     If there is an available space in the ordinary-subscriber-storage area NA, the subscriber data is stored in the ordinary-subscriber-storage area NA at a step S 1 - 3 , and a notice is transmitted at a step S 1 - 4  in order to indicate a completion of the process. 
     If there is not an available space in the ordinary-subscriber-storage area NA, a check is made at a step S 1 - 5  as to whether priority of the mobile-station subscriber exceeds a predetermined threshold. 
     If the priority exceeds the predetermined threshold, at a step S 1 - 6 , a check is made as to whether there is an available space in the high-priority-subscriber-storage area PA. 
     If there is an available space in the high-priority-subscriber-storage area PA, at a step S 1 - 7 , the subscriber data is stored in the high-priority-subscriber-storage area PA. At a step S 1 - 8 , a notice is transmitted in order to indicate a completion of the process. 
     If there is no available space in the high-priority-subscriber-storage area PA, at a step S 1 - 9 , a notice is transmitted in order to indicate a failure to store the data. Further, if the priority does not exceed the threshold at the step S 1 - 5 , at a step S 1 - 10 , a notice is transmitted in order to indicate a failure to store the data. 
     With reference to FIG. 2, a device  10  for controlling storage of subscriber data according to the first embodiment of the present invention includes a data receiving unit  11 , a priority-check unit  12 , a data-storage-control unit  13 , and a notifying unit  14 . The device  10  stores subscriber data in a subscriber data-storage unit  20 . As previously described, the subscriber-data-storage unit  20  of the first embodiment is divided into the ordinary-subscriber-storage area NA and the high-priority-subscriber-storage area PA. 
     The data receiving unit  11  receives subscriber data which is requested to be registered. The priority-check unit  12  checks priority of the subscriber of the subscriber data, and informs the data-storage-control unit  13  whether the priority exceeds a predetermined threshold. The data-storage-control unit  13  stores the subscriber data in the ordinary-subscriber-storage area NA if there is a space. Alternatively, the data-storage-control unit  13  stores the subscriber data in the high-priority-subscriber-storage area PA if there is a space and if the priority of the subscriber exceeds the predetermined threshold. Depending on whether the data-storage-control unit  13  succeeds in storing the subscriber data, the notifying unit  14  transmits a notice indicating a success or a failure in storing (registering) the subscriber data in the subscriber-data-storage unit  20 . 
     FIG. 3 is a flowchart of a process of registering a location according to a second embodiment of the present invention. FIG. 4 is a block diagram of a device for controlling storage of subscriber data according to the second embodiment of the present invention. 
     In the second embodiment, a subscriber-data-storage area of a visitor-location register VLR is divided into two areas. One is a high-priority-subscriber-storage area PA for storing subscriber data of mobile stations MS which have priority greater than a predetermined threshold, and the other is an ordinary-subscriber-storage area NA for storing subscriber data of other mobile stations MS. 
     At a step S 2 - 1 , the visitor-location register VLR receives subscriber data of a subscriber S 1  from the home-location register HLR during a process of location update for this mobile-station subscriber. 
     At a step S 2 - 2 , a check is made as to whether there is an available space in the ordinary-subscriber-storage area NA. 
     If there is an available space in the ordinary-subscriber-storage area NA, the subscriber data is stored in the ordinary-subscriber-storage area NA at a step S 2 - 3 , and a notice is transmitted at a step S 2 - 4  in order to indicate a completion of the process. 
     If there is not an available space in the ordinary-subscriber-storage area NA, a check is made at a step S 2 - 5  as to whether priority of the mobile-station subscriber S 1  exceeds a predetermined threshold. 
     If the priority exceeds the predetermined threshold, at a step S 2 - 6 , a check is made as to whether there is an available space in the high-priority-subscriber-storage area PA. 
     If there is an available space in the high-priority-subscriber-storage area PA, at a step S 2 - 7 , the subscriber data is stored in the high-priority-subscriber-storage area PA. At a step S 2 - 8 , a notice is transmitted in order to indicate a completion of the process. 
     If there is no available space in the high-priority-subscriber-storage area PA, at a step S 2 - 9 , a check is made as to whether there is a subscriber S 2  registered in the high-priority-subscriber-storage area PA who has lower priority than the subscriber S 1 , and is not on the phone. 
     If there is such a lower-priority subscriber S 2 , at a step S 2 - 10 , subscriber data of the lower-priority subscriber S 2  is replaced by the subscriber data of the subscriber S 1 , and a notice is transmitted at a step S 2 - 11  in order to indicate a completion of the process. 
     When the subscriber data of the lower-priority subscriber S 2  is replaced by the subscriber data of the subscriber S 1 , the subscriber data of the lower-priority subscriber S 2  is moved to the ordinary-subscriber-storage area NA by replacing subscriber data of another subscriber who is not on the phone. This insures that the subscriber data of the lower-priority subscriber S 2  is stored in the ordinary-subscriber-storage area NA. 
     If it turns out at the step S 2 - 9  that there is no such a lower-priority subscriber, a notice is transmitted at a step S 2 - 12  in order to indicate a failure to store the subscriber data. Further, if the priority does not exceed the threshold at the step S 2 - 5 , at a step S 2 - 13 , a notice is transmitted in order to indicate a failure to store the subscriber data. 
     With reference to FIG. 4, a device  10 A for controlling storage of subscriber data according to the second embodiment of the present invention includes the data receiving unit  11 , the priority-check unit. 12 , a data-storage-control unit  13 A, the notifying unit  14 , and a data-search unit  15 A. In FIG. 4, the same elements as those of FIG. 2 are referred to by the same numerals, and a description thereof will be omitted. 
     The data-storage-control unit  13 A stores the subscriber data in the ordinary-subscriber-storage area NA if there is a space. Alternatively, the data-storage-control unit  13 A stores the subscriber data in the high-priority-subscriber-storage area PA if there is a space and if the priority of the subscriber exceeds the predetermined threshold. Even if there is no space in the high-priority-subscriber-storage area PA, the data-search unit  15 A searches for a subscriber in the high-priority-subscriber-storage area PA who has lower priority than the relevant subscriber and is not on the phone. If such a subscriber having lower priority is found, the data-storage-control unit  13 A replaces the subscriber having lower priority with the relevant subscriber. Further, the data-storage-control unit  13 A moves the subscriber having lower priority from the high-priority-subscriber-storage area PA to the ordinary-subscriber-storage area NA by replacing another subscriber in the ordinary-subscriber-storage area NA who is not on the phone. 
     FIG. 5 is a flowchart of a process of registering a location according to a third embodiment of the present invention. FIG. 6 is a block diagram of a device for controlling storage of subscriber data according to the third embodiment of the present invention. 
     In the third embodiment, a subscriber-data-storage area of a visitor-location register VLR has only an ordinary-subscriber-storage area NA. 
     At a step S 3 - 1 , the visitor-location register VLR receives subscriber data of a subscriber S 1  from the home-location register HLR during a process of location update for this mobile-station subscriber. 
     At a step S 3 - 2 , a check is made as to whether there is an available space in the ordinary-subscriber-storage area NA. 
     If there is an available space in the ordinary-subscriber-storage area NA, the subscriber data is stored in the ordinary-subscriber-storage area NA at a step S 3 - 3 , and a notice is transmitted at a step S 3 - 4  in order to indicate a completion of the 
     If there is not an available space in the ordinary-subscriber-storage area NA, a check is made at a step S 3 - 5  as to whether priority of the mobile-station subscriber S 1  exceeds a predetermined threshold. 
     If the priority exceeds the predetermined threshold, at a step S 3 - 6 , a check is made as to whether there is a subscriber S 2  in the ordinary-subscriber-storage area NA who is not on the phone. 
     If there is a subscriber S 2  who is not on the phone, at a step S 3 - 7 , a check is made as to whether priority of the mobile-station subscriber S 2  is lower than the priority of the subscriber S 1 . 
     If the priority of the subscriber S 2  is lower than the priority of the subscriber S 1 , at a step S 3 - 8 , subscriber data of the subscriber S 2  is replaced by the subscriber data of the subscriber S 1 , and a notice is transmitted at a step S 3 - 9  in order to indicate a completion of the process. 
     If the check at the step S 3 - 7  finds that the priority of the subscriber S 2  is not lower than the priority of the subscriber S 1 , at a step S 3 - 10 , a check is made as to whether there is another subscriber who is not on the phone. 
     If there is no such a subscriber who is not on the phone, at a step S 3 - 11 , a notice is transmitted in order to indicate a failure to store the subscriber data. 
     If there is such a subscriber who is not on the phone, the procedure goes back to the step S 3 - 7 , and repeats the following steps. 
     If it turns out at the step S 3 - 6  that there is no such a subscriber who is not on the phone, a notice is transmitted at a step S 3 - 12  in order to indicate a failure to store the subscriber data. Further, if the priority does not exceed the threshold at the step S 3 - 5 , at a step S 3 - 13 , a notice is transmitted in order to indicate a failure to store the subscriber data. 
     With reference to FIG. 6, a device  10 B for controlling storage of subscriber data according to the third embodiment of the present invention includes the data receiving unit  11 , the priority-check unit  12 , a data-storage-control unit  13 B, the notifying unit  14 , and a data-search unit  15 B. The subscriber-data-storage unit  20  has only the ordinary-subscriber storage area NA. In FIG. 6, the same elements as those of FIG. 4 are referred to by the same numerals, and a description thereof will be omitted. 
     The data-storage-control unit  13 B stores the subscriber data in the ordinary-subscriber-storage area NA if there is a space. Even when there is no space in the ordinary-subscriber-storage area NA, an attempt is made to create room in the ordinary-subscriber-storage area NA if the subscriber has priority higher than a predetermined threshold. Namely, the data-search unit  15 B searches for a subscriber in the ordinary-subscriber-storage area NA who has lower priority than the relevant subscriber and is not on the phone. If such a subscriber having lower priority is found, the data-storage-control unit  13 B replaces the subscriber having lower priority with the relevant subscriber. 
     FIG. 7 is a flowchart of a process of registering a location according to a fourth embodiment of the present invention. FIG. 8 is a block diagram of a device for controlling storage of subscriber data according to the fourth embodiment of the present invention. 
     In the fourth embodiment, a subscriber-data-storage area of a visitor-location register VLR has only an ordinary-subscriber-storage area NA. 
     At a step S 4 - 1 , the visitor-location register VLR receives subscriber data of a subscriber S 1  from the home-location register HLR during a process of location update for this mobile-station subscriber. 
     At a step S 4 - 2 , a check is made as to whether there is an available space in the ordinary-subscriber-storage area NA. 
     If there is an available space in the ordinary-subscriber-storage area NA, the subscriber data is stored in the ordinary-subscriber-storage area NA at a step S 4 - 3 , and a notice is transmitted at a step S 4 - 4  in order to indicate a completion of the process. 
     If there is not an available space in the ordinary-subscriber-storage area NA, a check is made at a step S 4 - 5  as to whether priority of the mobile-station subscriber S 1  exceeds a predetermined threshold. 
     If the priority exceeds the predetermined threshold, at a step S 4 - 6 , a check is made as to whether a subscriber S 2  having the lowest priority in the ordinary-subscriber-storage area NA has lower priority than the subscriber S 1 . If the answer is affirmative, the procedure goes to a step S 4 - 7 . 
     At the step S 4 - 7 , a check is made as to whether the subscriber S 2  is currently on the phone. 
     If the subscriber S 2  is not on the phone, at a step S 4 - 8 , subscriber data of the subscriber S 2  is replaced by the subscriber data of the subscriber S 1 , and a notice is transmitted at a step S 4 - 9  in order to indicate a completion of the process. 
     If the check at the step S 4 - 7  finds that the subscriber S 2  is on the phone, at a step S 4 - 10 , a check is made as to whether another subscriber having the next lowest priority (next to the subscriber S 2 ) has lower priority than the subscriber S 2 . 
     If the check at the step S 4 - 10  finds that there is not such a subscriber, at a step S 4 - 11 , a notice is transmitted in order to indicate a failure to store the subscriber data. 
     If the check at the step S 4 - 10  finds that there is such a subscriber, the procedure goes back to the step S 4 - 7  to check if this subscriber is on the phone, and repeats the steps following thereto. 
     If it turns out at the step S 4 - 6  that the subscriber S 2  having the lowest priority in the ordinary-subscriber-storage area NA does not have lower priority than the subscriber S 1 , a notice is transmitted at a step S 4 - 12  in order to indicate a failure to store the subscriber data. 
     Further, if the priority of the subscriber S 1  does not exceed the threshold at the step S 4 - 5 , at a step S 4 - 13 , a notice is transmitted in order to indicate a failure to store the subscriber data. 
     With reference to FIG. 8, a device  10 C for controlling storage of subscriber data according to the fourth embodiment of the present invention includes the data receiving unit  11 , the priority-check unit  12 , a data-storage-control unit  13 C, the notifying unit  14 , and a data-search unit  15 C. The subscriber-data-storage unit  20  has only the ordinary-subscriber-storage area NA. In FIG. 8, the same elements as those of FIG. 4 are referred to by the same numerals, and a description thereof will be omitted. 
     The data-storage-control unit  13 C stores the subscriber data in the ordinary-subscriber-storage area NA if there is a space. Even when there is no space in the ordinary-subscriber-storage area NA, an attempt is made to create room in the ordinary-subscriber-storage area NA if the subscriber has priority higher than a predetermined threshold. Namely, the data-search unit  15 C searches for a subscriber in the ordinary-subscriber-storage area NA who has the lowest priority lower than that of the relevant subscriber among subscribers who are not on the phone. If such a subscriber having the lowest priority is found, the data-storage-control unit  13 C replaces the subscriber having the lowest priority with the relevant subscriber. 
     FIG. 9 is a flowchart of a process of deleting registered data according to a fifth embodiment of the present invention. 
     At a step S 5 - 1 , the visitor-location register VLR receives a power-down message, which indicates a power-down of a mobile station MS, and is sent via the base stations BSS and the mobile-service-switching center MSC. Here, subscriber data of this mobile station MS is kept in a subscriber-data-storage area as registered data. 
     At a step S 5 - 2 , a check is made as to whether priority of a subscriber service class of the mobile station MS exceeds a predetermined threshold. 
     If the priority of a subscriber service class of the mobile station MS does not exceeds the predetermined threshold, at a step of S 5 - 3 , the subscriber data of the mobile stations MS is removed from the subscriber-data-storage area of the visitor-location register VLR. 
     FIG. 10 is a flowchart of a process of deleting registered data according to a sixth embodiment of the present invention. 
     At a step S 6 - 1 , the visitor-location register VLR receives a call-completion message, which indicates a completion of a call by a mobile station MS, and is sent via the base stations BSS and the mobile-service-switching center MSC. Here, subscriber data of this mobile station MS is kept in a subscriber-data-storage area as registered data. 
     At a step S 6 - 2 , a check is made as to whether priority of a subscriber service class of the mobile station MS exceeds a predetermined threshold. 
     If the priority of a subscriber service class of the mobile station MS does not exceeds the predetermined threshold, at a step S 6 - 3 , the subscriber data of the mobile stations MS is removed from the subscriber-data-storage area of the visitor-location register VLR. 
     FIG. 11 is a block diagram of a device for controlling storage of subscriber data according to the fifth and sixth embodiments of the present invention. 
     A device  10 D for controlling storage of subscriber data according to the fifth and sixth embodiments of the present invention includes a data-storage-control unit  13 D, a message receiving unit  16 , and a priority-check unit  17 . The configuration of FIG. 11 may be used along with any one of the configurations of the first through fourth embodiments previously described. 
     In FIG. 11, the message receiving unit  16  receives either a power-down message or a call-completion message. The priority-check unit  17  refers to the subscriber-data-storage unit  20  to check priority of a mobile station MS that issued the message received by the message receiving unit  16 , and determines whether the priority exceeds a predetermined threshold. The data-storage-control unit  13 D deletes the subscriber data of the mobile station MS from the subscriber-data-storage unit  20  if the priority does not exceeds the predetermined threshold. 
     A timer unit  18  of FIG. 11 is used in the following embodiments in which subscriber data will be deleted a certain time period after receiving a relevant message. 
     FIG. 12 is a flowchart of a process of deleting registered data according to a seventh embodiment of the present invention. In the seventh embodiment, subscriber data is deleted only a certain time period after a power-down message is received. 
     FIG. 13 is a flowchart of a process of controlling a timer. This process is performed as part of the process of FIG.  12 . 
     At a step S 7 - 1 , the message receiving unit  16  of the visitor-location register VLR receives a power-down message via a base station BSS and a mobile-service-switching center MSC. The power-down message indicates a power down of a mobile station MS. 
     At a step S 7 - 2 , the priority-check unit  17  of the visitor-location register VLR checks priority of a subscriber-service class of the mobile station MS, and determines whether the priority exceeds a predetermined threshold. If the priority exceeds the predetermined threshold, the procedure ends without deleting subscriber data. 
     If the priority does not exceed the predetermined threshold, at a step S 7 - 3 , a deletion flag is set to an active status. 
     At a step S 7 - 4 , a request to start a deletion-countdown timer is sent to the timer unit  18 . 
     AT a step S 8 - 1  of FIG. 13, the timer unit  18  receives the request for start of the deletion-countdown timer. At a step S 8 - 2 , a selection is made among different timers having different expiration time periods in accordance with the priority of the mobile station MS. For example, the lower the priority, the shorter the expiration time of the selected timer may be. At a step S 8 - 3 , the selected timer is started. 
     In FIG. 12, the data-storage-control unit  13 D waits for an event to occur. Here, the event is either reception of a notice from the timer unit  18  indicating an expiration of the timer or reception of a request for location update issued in association with switching on of the mobile station MS. 
     At a step S 7 - 6 , a check is made as to whether the event is a reception of a request for location update associated with switching on of the mobile station MS. If it is, the deletion flag is set to inactive status at a step S 7 - 7 , and a request to stop the deletion-countdown timer is transmitted to the timer unit  18  at a step S 7 - 8 . 
     If it turns out at the step S 7 - 6  that the event is a reception of a notice from the timer unit  18  indicating an expiration of the timer, at a step S 7 - 9 , subscriber data of the mobile station MS is deleted. This ends the procedure. 
     In FIG. 13, at a step S 8 - 4 , the timer unit  18  waits for an event to occur. Here, the event is either expiration of the timer or reception of a request from the data-storage-control unit  13 D requesting a stop of the deletion-countdown timer. 
     At a step S 8 - 5 , a check is made as to whether the event is an expiration of the deletion-countdown timer. If it is, the expiration of the timer is reported to the data-storage-control unit  13 D at a step S 8 - 6 . If the check at the step S 8 - 5  finds that the event is a reception of a request for stop of the deletion-countdown timer sent from the data-storage-control unit  13 D, the deletion-countdown timer is stopped at a step S 8 - 7 . The procedure thereafter goes back to the step S 8 - 1 . 
     FIG. 14 is a flowchart of a process of deleting registered data according to an eighth embodiment of the present invention. In the eighth embodiment, subscriber data is deleted only a certain time period after a call-completion message is received. 
     FIG. 15 is a flowchart of a process of controlling a timer. This process is performed as part of the process of FIG.  14 . 
     At a step S 9 - 1 , the message receiving unit  16  of the visitor-location register VLR receives a call-completion message via a base station BSS and a mobile-service-switching center MSC. The call-completion message indicates a completion of a call by a mobile station MS. 
     At a step S 9 - 2 , the priority-check unit  17  of the visitor-location register VLR checks priority of a subscriber-service class of the mobile station MS, and determines whether the priority exceeds a predetermined threshold. If the priority exceeds the predetermined threshold, the procedure ends without deleting subscriber data. 
     If the priority does not exceed the predetermined threshold, at a step S 9 - 3 , a deletion flag is set to an active status. 
     At a step S 9 - 4 , a request to start a deletion-countdown timer is sent to the timer unit  18 . 
     AT a step S 10 - 1  of FIG. 15, the timer unit  18  receives the request for start of the deletion-countdown timer. At a step S 10 - 2 , a selection is made among different timers having different expiration time periods in accordance with the priority of the mobile station MS. For example, the lower the priority, the shorter the expiration time of the selected timer may be. At a step S 10 - 3 , the selected timer is started. 
     In FIG. 14, the data-storage-control unit  13 D waits for an event to occur. Here, the event is either reception of a notice from the timer unit  18  indicating an expiration of the timer or reception of a request for transmission or receipt of a call issued by the mobile station MS. 
     At a step S 9 - 6 , a check is made as to whether the event is a reception of a request for transmission or reception of a call by the mobile station MS. If it is, the deletion flag is set to inactive status at a step S 9 - 7 , and a request to stop the deletion-countdown timer is transmitted to the timer unit  18  at a step S 98 . 
     If it turns out at the step S 9 - 6  that the event is a reception of a notice from the timer unit  18  indicating an expiration of the timer, at a step S 9 - 9 , subscriber data of the mobile station MS is deleted. This ends the procedure. 
     In FIG. 15, at a step S 10 - 4 , the timer unit  18  waits for an event to occur. Here, the event is either expiration of the timer or reception of a request from the data-storage-control unit  13 D requesting a stop of the deletion-countdown timer. 
     At a step S 10 - 5 , a check is made as to whether the event is an expiration of the deletion-countdown timer. If it is, the expiration of the timer is reported to the data-storage-control unit  13 D at a step S 10 - 6 . If the check at the step S 10 - 5  finds that the event is a reception of a request for stop of the deletion-countdown timer sent from the data-storage-control unit  13 D, the deletion-countdown timer is stopped at a step S 10 - 7 . The procedure thereafter goes back to the step S 10 - 1 . 
     As described above, the present invention utilizes a priority parameter that is set for a subscriber service class of a mobile station MS, and stores subscriber data in the subscriber-data-storage area of the visitor-location register according to the priority of the subscriber. This improves a success rate of registering a location for a subscriber having high priority. In this manner, the present invention can provide a diligent communication service that is in accordance with priority of each subscriber-service class. 
     Further, the present invention is not limited to these embodiments, but various variations and modifications may be made without departing from the scope of the present invention. 
     The present application is based on Japanese priority application No. 10-358733 filed on Dec. 17, 1998, with the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.