EP1243157A1

EP1243157A1 - Managing subscriber information in a mobile communication network

Info

Publication number: EP1243157A1
Application number: EP00988845A
Authority: EP
Inventors: Jukka Heino
Original assignee: Nokia Oyj; Nokia Inc
Current assignee: Airbus Defence and Space Oy
Priority date: 1999-12-29
Filing date: 2000-12-28
Publication date: 2002-09-25
Also published as: AU2520201A; WO2001050801A1; FI19992806L; FI19992806A7

Abstract

A method of registering subscribers in a mobile communication system comprising a home location register for at least partly storing static subscriber information and dynamic subscriber information on the subscribers in the mobile communication system and at least a first visitor location register communicating with the home location register for storing the static subscriber information and the dynamic subscriber information on the subscribers registered in said visitor location register. When a registration of the subscriber is removed from the visitor location register, the visitor location register is arranged to retain the stored static subscriber information on the subscriber and to update the removal of the registration in the dynamic subscriber information on the subscriber. When the subscriber is registered, the visitor location register receives a registration message of the subscriber, checks whether the static subscriber information on the subscriber is found in the visitor location register, asks the home location register for the static subscriber information on the subscriber if the static subscriber information is found in the first visitor location register, and registers the subscriber in the visitor location register if the static subscriber information on the subscriber does not prevent the registration.

Description

MANAGING SUBSCRIBER INFORMATION IN A MOBILE COMMUNICATION

NETWORK

BACKGROUND OF THE INVENTION

The invention relates to managing subscriber information in mobile communication networks, and particularly to optimizing data transfer between databases comprising subscriber information.

In mobile communication networks, enabling mobile subscribers to move freely in the coverage area of a network and in visited networks as well requires various subscriber-specific information to be updated in the data- bases of the networks when a subscriber moves from one area to another. Updates of the subscriber-specific information are required by connection setup when the subscriber communicates with the mobile communication network through different network elements and connection maintenance when the subscriber moves from one area to another of the network element. According to Figure 1 , mobile communication networks typically comprise at least one Home Location Register HLR and several Visitor Location Registers VLR. The home location register HLR typically comprises static subscriber information on all subscribers registered in the network, such as information on different services the subscriber is authorized to use and, in addition, subscriber location information with the accuracy of at least a visitor location register. The network elements through which a mobile station establishes a connection to the mobile communication network, typically partly over a radio connection, communicate with one visitor location register VLR. Figure 1 shows a simplified structure of a mobile communication network wherein a Mobile Station MS establishes a radio connection to one Base Transceiver Station BTS wherefrom a direct connection to the visitor location register VLR is shown in Figure 1. In practice, at least a Mobile Switching Centre MSC is typically provided between the base transceiver station BTS and the visitor location register VLR, which is usually arranged in connection with the mobile switching centre MSC, and, depending on the structure of the network, possibly a Base Station Controller BSC. The operation of these network elements is not, however, relevant to the present invention, so they are not described in closer detail. It is also to be noted that although the names of the network elements set forth above are terms typically used in a Global System for Mo- bile Communication GSM network, they are herein intended as generic terms that can be applied to any mobile communication network comprising similar network elements.

The visitor location register VLR comprises information on each mobile station registered in the visitor location register; location information on the mobile station with the accuracy of at least a base transceiver station and static subscriber information on the subscriber located in the home location register HLR. Said information is produced in the visitor location register VLR when the subscriber registers in that visitor register e.g. in connection with switching on the mobile station or when the mobile station moves from the base transceiver station in the area of another visitor location register to a base transceiver station in the area of the visitor location register at issue, either without a call connection between the mobile station and the base transceiver station or with the call connection remaining unbroken (handover). The visitor location register VLR of the new base transceiver station then retrieves the static information on the subscriber from the home location register HLR and at the same time informs the home location register HLR of the new location of the subscriber. The static information and the location information on the subscriber are stored in the visitor location register VLR.

The mobile station MS changes the base transceiver station BTS by registering in the new base transceiver station either controlled by the system or by selecting the base transceiver station itself, depending on the implementation. If the base transceiver station is changed within the area of the same VLR (the old and the new BTS being connected to the same visitor location register), the new location is updated only in said VLR; there is no need to update the information in the home location register HLR. If the base transceiver station is changed between two base transceiver stations which belong to different visitor location registers, the visitor location register of the new base transceiver station retrieves the static subscriber information from the HLR and stores it and the location information as described above. At the same time, the information on the subscriber is removed from the visitor location register of the old base transceiver station.

If subscriber A is now to establish a call to subscriber B, the current visitor location register VLR of subscriber B can be read from the home location register HLR, in which case the call can be routed to a correct visitor loca- tion register VLR, which knows the location of subscriber B accurately, and subscriber B can then be paged through a correct base transceiver station BTS. The subscriber rights of subscriber A, in turn, can be checked directly from the visitor location register of subscriber A.

A problem with the arrangement described above is the great data transmission need between the home location register HLR and the visitor lo- cation register VLR. The large increase in the number of subscribers in the mobile communication networks considerably increases the need to update the static subscriber information in the visitor location registers taking place between the home location register HLR and the visitor location register VLR and, correspondingly, the need to update the new visitor location registers of the subscribers in the home location register. Attempts have been made to remove drawbacks of the problem by building data transmission connections with a sufficiently high capacity between the home location register HLR and different visitor location registers VLR, which, however, simultaneously adds to the building and operating costs of the network. Another problem with the arrangement described above is the large number of storing operations taking place in the visitor location register VLR. In order for the numerous storing operations to be carried out quickly enough, the subscriber information in the databases of the visitor location registers is no longer always provided with disk backup wherein the static subscriber in- formation is typically stored in several different parts of the database. When the number of storing operations then increase, it becomes impossible to store them on a disk simultaneously. Due to the performance of the system, at least some of the subscriber information must be stored in a Random Access Memory RAM which allows information to be quickly entered therein and read therefrom. On the other hand, the visitor location registers VLR also comprise information which is not to be lost e.g. during electricity cut off, i.e. information which requires disk backup, such as e.g. base transceiver station configurations. Consequently, the structure of the databases in the visitor location registers VLR is complex and only partly backuped, preventing a typical relation model in the databases from being used and requiring a complex interrogation and registration process in order to recover from an error situation.

BRIEF DESCRIPTION OF THE INVENTION

An object of the invention is thus to provide a method and an apparatus implementing the method such that the above-mentioned problems can be alleviated. The objects of the invention are achieved by a method and a system which are characterized by what is set forth in the independent claims. Preferred embodiments of the invention are disclosed in the dependent claims. The idea underlying the invention is that when a subscriber exits the area of a visitor location register, the subscriber information on the subscriber is not removed from the visitor location register but the subscriber is only registered as exited. When the subscriber then later returns to the area of the visitor location register, the information necessary for registering the subscriber is likely to be found in said visitor location register and thus needs not be retrieved from the home location register; it will suffice that the correctness of the information is checked by a simple verification process. The visitor location register is preferably dimensioned to accommodate the subscriber information on substantially more subscribers than can typically be simultaneously registered in the area of the visitor location register.

An advantage of the method and system of the invention is that the data transmission need between the home location register HLR and the visitor location register VLR decreases considerably. Since the static subscriber information on the subscriber is likely to be found already in the visitor location register when the subscriber starts registering, the subscriber information needs to be asked from the home location register far more seldom than in the prior art solution. The load on the network thus decreases significantly and more advantageous data transmission connections can be used between the home location register and the visitor location register. A further advantage is that the number of storing operations diminishes considerably particularly in the visitor location register, which reduces the storage load and makes error situations less likely. A still further advantage is that according to a preferred embodiment of the invention, the information on subscribers who have not registered in said visitor location register for a long time is periodically removed from the visitor location register, which means that there is always room in the visitor location register for the registration of new subscribers and the visitor location register will not be loaded with single removals of the old subscribers.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described in closer detail in connection with the accompanying drawings, in which Figure 1 is a block diagram showing parts of a simplified structure of a mobile communication network relevant to the invention, and

Figure 2 is a flow diagram showing a subscriber registration procedure according to a preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows the structure of a mobile communication network simplified as described above. To illustrate the invention, the network of Figure 1 comprises only one home location register HLR and three visitor location registers VLR1 , VLR2 and VLR3. The arrangement of the invention does not, however, by no means restrict the number of home location registers or visitor location registers nor the number of other network elements either. A connection is established in a simplified manner as described in Figure 1 from the visitor location register VLR1 to base transceiver stations BTS11 and BTS12 wherefrom a direct connection is shown in Figure 1 to the visitor location reg- ister VLR without describing network elements therebetween. Similarly, a connection is established from the visitor location register VLR2 to base transceiver stations BTS21 and BTS22 and from the visitor location register VLR3 to base transceiver stations BTS31 and BTS32. A subscriber establishes a connection to the mobile communication network by establishing a radio con- nection to a base transceiver station by a mobile station MS.

Now, according to a preferred embodiment of the invention, when the subscriber exits the area of the visitor location register, the information on the subscriber is not, however, removed from said visitor location register but the subscriber is only registered as exited from the area of the visitor location register. If the subscriber e.g. moves from the base transceiver station BTS12 to the base transceiver station BTS21 , in which case the visitor location register of the subscriber is changed from the VLR1 to VLR2, the static subscriber information stored in the visitor location register VLR1 remains in the database of the visitor location register VLR1 and in the location information on the sub- scriber, the subscriber is registered as exited from the area of the visitor location register VLR1. If the subscriber later returns to the area of the visitor location register VLR1 , there is no need to retrieve the static subscriber information from the home location register HLR but it is already stored in the visitor location register VLR. Switching off the mobile station MS also represents a situation where the subscriber exits the area of the visitor location register. Neither in such a case is the static subscriber information removed from said visitor location register.

As far as a conventional mobile communication network is concerned, particularly straining are subscribers who frequently move in the area of two visitor location registers, e.g. frequently move from the base transceiver station BTS12 to the base transceiver station BTS 21 and vice versa, in which case the visitor location register also changes from the VLR1 to VLR2 or vice versa. The static subscriber information is abundant and it is typically located in different parts of the database. If the static subscriber information must be retrieved from the home location register HLR each time the visitor location register changes, the telecommunication connections between the home location register and the visitor location register become extremely loaded. In addition, the relation and directory structures of the databases of the visitor location registers cause several slight changes in the different parts of the data- base, which is particularly straining particularly as far as the disk backup process is concerned.

In the system of the invention, the need to retrieve information from the home location register HLR to the visitor location register VLR is substantially reduced. If the static subscriber information is found in the visitor location register when the subscriber registers in its area, it will suffice that the correctness of the static information is checked from the home location register by a simple interrogation. Typically, the static subscriber information is changed extremely seldom, so the static subscriber information stored in the visitor location register is usually correct. This applies particularly to subscribers who move frequently on the border between two visitor location registers. After the correctness has been verified, only the location and registration information on the subscriber is updated in the database of the visitor location register VLR.

The static subscriber information HS on all subscribers in the network is stored in the database of the home location register HLR, the informa- tion comprising e.g. a subscriber right profile of the subscriber. A time stamp HST is also stored in connection with each subscriber record to indicate the point of time when the information HS was generated or last modified. In addition, the home location register comprises subscriber-specific dynamic information HD indicating whether the subscriber is registered in the system and in the area of which visitor location register VLR. Also the dynamic information HD is provided with a time stamp HDT; this, however, is not utilized in the present invention.

The static information VS on the subscribers visiting the database of the visitor location register VLR is stored therein and read from the home location register HLR when the subscriber is registered in the visitor location register. The information VS correspond with the information HS in the home location register, provided that it has not been changed after being read. In connection with the static information VS, also a time stamp VST is stored which is copied simultaneously with the static information from the home loca- tion register HLR, whereby immediately after the copying procedure the time stamp VST corresponds with the time stamp HST. Furthermore, dynamic information VD is stored in the visitor register VLR to indicate whether the subscriber is registered in the area of said visitor location register VLR and in the area of which base transceiver station. In order to enable connection setup to the mobile communication system in the first place, the subscriber must first be added to the databases of the mobile communication system. The static subscriber information HS and the time stamp HST are then entered into the home location register HLR, whereby the time stamp HST is then the time of addition. When the static sub- scriber information is changed, e.g. in connection with an update of the subscriber profile, the new information HS and the time stamp HST corresponding with the time of the change are updated in the databases of the home location register HLR. Furthermore, the home location register HLR examines the dynamic information HD to find out whether the subscriber is registered in the system, and in response to a registration, the home location register HLR transmits the updated information HS and HST to a corresponding visitor location register VLR, which updates the static information VS and the time stamp VST to correspond with the information transmitted by the HLR. When the subscriber registered in the visitor location register VLR moves in the area of base transceiver stations in the area of the visitor location register, the subscriber-specific dynamic information VD in the visitor location register VLR and the time stamp VDT are updated each time when the subscriber registers in a new base transceiver station.

According to a preferred embodiment of the invention, the database of the visitor location register VLR is designed large enough to be able to comprise subscriber information on substantially more subscribers than can typically be located in the area of the visitor location register VLR. A maximum value of the number of simultaneously registered subscribers can then be set in the visitor location register VLR and the visitor location register VLR can be dimensioned substantially larger than necessary for storing the subscriber in- formation on the subscribers determined by said maximum value. Said maximum value of simultaneous registrations in the visitor location register VLR can preferably be dimensioned to represent a typical maximum number of subscribers in the area of one visitor location register. A visitor location register then typically comprises subscriber information both on subscribers currently registered in the visitor location register and on subscribers who have once been registered in the visitor location register but have now left the area of the visitor location register.

Since the subscriber information is not removed from the visitor location register when the subscriber exits the area thereof but the subscriber is only registered as exited, mainly two problems follow: the subscriber information on the subscribers who have visited the area of the visitor location register VLR gradually fills up the database of the VLR and the change in the static subscriber information VS on the subscriber while the subscriber is located in the area of another visitor location register will not be updated in the old visitor location register, which means that when the subscriber returns to the area of the old visitor location register, the static information VS is incorrect.

According to a preferred embodiment of the invention, in order to eliminate said problems the information included in the verification information, such as time stamps, can be utilized. When the subscriber then exits the area of the visitor location register VLR, the point of time when the subscriber exited the area of said visitor location register VLR is stored in the visitor location register as the time stamp VDT. Furthermore, a visitor-location-register- specific maximum storage time T_max is determined for the subscriber information to determine how long the subscriber information will be stored in said visitor location register. It is now possible to preferably prevent the database of the visitor location register VLR from filling up with subscriber information by removing periodically at predetermined intervals the subscriber information on those subscribers whose time stamp VDT has been stored longer than the maximum storage time T_max. The maximum storage time T_max can preferably be adjusted with respect to a typical number of subscribers in the visitor location register VLR and the size of the database of the VLR. Alternatively, if a new subscriber tries to register in the visitor location register VLR and the database of the VLR is full, the information on the subscriber having the oldest time stamp VDT can be removed from the database regardless of whether the maximum storage time T_max has elapsed or not. The time stamps, preferably the time stamp VST of the static information, may also be utilized in examining the update of the static subscriber information VS. The time stamp VST stored in the visitor location register VLR indicates when the static subscriber information was last updated. When the subscriber, after having exited the area of the visitor location register VLR, re- turns to the same area, the visitor location register asks for the time stamp HST of the static information HS stored in the home location register HLR. If the time stamp VST in the visitor location register VLR matches with the time stamp HST in the home location register HLR (VST = HST), the static subscriber information VS stored in the visitor location register is correct. If, on the other hand, the time stamp VST in the visitor location register VLR does not match with the time stamp HST in the home location register HLR (VST ≠ HST), the visitor location register VLR requests new static subscriber information HS from the home location register and stores it in its database as information VS. The examination of the update described above can of course be implemented e.g. by utilizing check sums or other such verification information.

In the following, a subscriber registration procedure of a preferred embodiment of the invention will be described by means of the flow diagram of

Figure 2. At the outset (block 200), it is assumed that the subscriber switches on his or her mobile station while being located in the area of the base trans- ceiver station BTS12, in which case the subscriber tries to register in the visitor location register VLR1. The visitor location register VLR1 receives a registration message of the subscriber (202), on the basis of which it is examined whether the static subscriber information VS can be found in the database of the VLR1 (204). If so, the home location register HLR is asked for the time stamp HST of the static subscriber information (206), which is compared with the time stamp VST of the static information in the visitor location register VLR1 (208). If they match, the acceptability of the registration of the subscriber is checked (210) on the basis of the static information VS. If the registration of the subscriber can be accepted, the subscriber is registered and updated in the dynamic subscriber information VD as registered in the base transceiver station BTS12, and the time stamp VDT is updated to correspond with the registration time (212). In addition, an acknowledgement of the registration is transmitted to the subscriber. Next, the visitor location register VLR1 informs the home location register HLR that the subscriber has registered in the area of the VLR1 , whereby the registration time VDT is transmitted simultaneously (214).

If the static subscriber information VS is not found in the database of the VLR1 in the procedure described above (204) or the time stamp HST does not correspond with the time stamp VST (208), the visitor location register VLR1 requests the static subscriber information HS and the time stamp HST from the home location register HLR on the basis of which the acceptability of the registration of the subscriber is checked (218). If the registration of the subscriber is acceptable, it is checked whether there is room in the database of the visitor location register VLR1 for the registration of the new subscriber (220). If not, the information on a subscriber who is not registered in the visitor location register VLR1 is removed from the database (222). The selection of such a subscriber can be based e.g. on which one of the subscribers has been away from the area of the visitor location register VLR1 for the longest time. Naturally, the information on any other subscriber can also be removed. It is to be noted that according to a preferred embodiment of the invention, the storing capacity of the database of the visitor location register VLR1 is dimensioned large enough so that all information on the subscribers in the area of the VLR1 can be stored therein. If, then, there is no room left in the database, it means that subscribers who are not registered in the visitor location register VLR1 must also be stored therein who, when necessary, can be removed therefrom. When the storage level of the subscriber information has been checked from the database, the information HS and HST received from the home location register HLR are stored to correspond with the information VS and VST (224). Next, the subscriber is registered and updated in the dynamic subscriber information VD as registered in the base transceiver station BTS12, and the time stamp VDT is updated to correspond with the registration time (226), as in step 212 above. In addition, an acknowledgement of the registration is transmitted to the subscriber. Next, the process returns to step 214.

If the registration of the subscriber cannot be accepted (210 or 218) e.g. because of subscriber profile specifications, the visitor location register VLR1 refuses to register the subscriber (228) and the subscriber will not be able to establish a connection to the network.

After the home location register HLR has been informed of the registration of the subscriber (214), the home location register HLR checks from its own database whether the registration information on the subscriber has been transmitted earlier from another visitor location register (230). If, according to this information, the subscriber is registered in another visitor location register, the home location register HLR transmits a command to remove the registration of the subscriber to said visitor location register and to store the time stamp VDT as the exit time (232). Finally, the home location register HLR updates its own dynamic information HD and HDT in its database on the basis of the dynamic information VD and VDT received from the visitor location register VLR1 (234).

According to a preferred embodiment of the invention, the proce- dure described above is carried out also when the subscriber moves from the area of a first visitor location register to the area of a second visitor location register, e.g. in connection with handover. The subscriber can then at the outset (block 200) e.g. move from the area of the base transceiver station BTS21 (connected to the visitor location register VLR2) to the area of the base trans- ceiver station BTS12 (connected to the visitor location register VLR1 ). The procedures described above for registering the subscriber are substantially the same. Particularly the checking and removal of the subscriber registration information from the another visitor location register carried out by the home location register HLR take place in the visitor location register VLR2. According to a preferred embodiment of the invention, the removal of the registration from the visitor location register when the subscriber switches off his or her mobile station MS is carried out such that the mobile station MS connected e.g. to the base transceiver station BTS12 transmits a registration removal message to the visitor location register VLR1 through the base transceiver station BTS12. The VLR 1 then registers in the dynamic subscriber information VD that the subscriber is not registered in the area of the visitor location register VLR1. The time stamp VDT is simultaneously updated to correspond with the registration removal time. The home location register HLR is informed of both the registration removal and the exit time VDT, and the HLR updates in its information HD that the subscriber is no longer regis- tered in the visitor location register VLR1. A value of the exit time VDT is copied as the exit time HDT.

According to a preferred embodiment of the invention, the information on subscribers who have not been registered in said visitor location reg- ister for a long time can be removed periodically from the visitor location register. Each visitor location register then searches its database for subscribers who are not registered in said visitor location register. The time stamp VDT of these subscribers is compared with the predetermined maximum storage time T_max, and when the time stamp VDT of the subscriber is older than the point of time determined by the maximum storage time T_max, the subscriber information VS, VST, VD, VDT on said subscriber is removed from the visitor location register. When appropriately parametrized, this procedure is extremely useful since when the databases of the visitor location register fill up without the periodic removal of information, the removal of old subscribers described above each time when a new subscriber is being registered (block 222) causes incessant strain on the system. Such a cleaning procedure can be carried out e.g. once in every 24 hours, preferably at night when the load in the network is low.

According to a preferred embodiment of the invention, a default visitor location register, or a "home VLR", in the area of which the subscriber most often establishes a connection to the mobile communication system can be determined for the subscriber. In this default visitor location register, a subscriber-specific maximum storage time T_max, which is preferably longer than that of a subscriber to whom said visitor location register is not a "home VLR", can be determined for the subscriber. It is thus preferably more likely that the information on the subscriber in the area of the visitor location register will be found in said visitor location register.

According to still another preferred embodiment of the invention, the removal of the information on the subscribers who are not registered in the visitor location register can be determined as a function of distance of the subscriber with respect to the area included in the visitor location register. The information on all subscribers who have exited the area of the visitor location register far enough is then removed from the visitor location register. This embodiment of the invention can be applied to mobile communication systems comprising mechanisms for determining distances of subscribers from the area of the visitor location register. The invention has been described above in a simplified mobile communication system comprising only one home location register HLR. The invention can, however, also be applied to mobile communication systems which comprise several home location registers HLR and in which a single network element may be provided with the functionalities of both the home location register and the visitor location register. If the system comprises several home location registers HLR, the visitor location registers VLR must know the home location register of each subscriber. This can be implemented e.g. by number analysis or, alternatively, such that each visitor location register VLR always informs a particular home location register HLR which is able to route a message further to a correct home location register.

The invention can be implemented in any mobile communication system wherein similar functions as described above have been determined for the home location register and the visitor location register. The procedure of the invention is most preferably implemented in a Trans European Trunked Radio or Terrestrial Trunked Radio TETRA system, which is a digital Private Mobile Radio or Professional Mobile Radio PMR type private network, typically a company or official network, wherein all channels are used by one or more companies or official organizations. In the TETRA system, the distribution of speech items between terminals and base transceiver stations is controlled by a Switching and Management Infrastructure SwMI, the base transceiver stations being connected to Digital Exchanges DXT therein. A visitor location register VLR is typically connected in connection with each exchange, and the system usually com- prises only one home location register HLR. Companies and official organizations may reserve channels for their use from the TETRA infrastructure, in which case the allocation of the channels in the area is typically restricted to the operation area of an organization, and the number subscribers is not particularly high. The simpler structure and the relatively low number of subscrib- ers of the TETRA system compared e.g. to common mobile communication networks thus make the TETRA system suitable for the procedure of the invention.

It is obvious to one skilled in the art that as technology advances, the basic idea of the invention can be implemented in many different ways. The invention and its embodiments are thus not restricted to the examples described above but they can vary within the scope of the claims.

Claims

1. A method of registering subscribers in a mobile communication system comprising a home location register for at least partly storing static subscriber information and dynamic subscriber information on the subscribers in the mobile communication system and at least a first visitor location register communicating with the home location register for storing the static subscriber information and the dynamic subscriber information on the subscribers registered in said visitor location register, in which method a registration message of the subscriber is received by the first visitor location register, c h a r a c - t e r i z e d by checking the first visitor location register in order to find the static subscriber information on the subscriber, asking the home location register for the static subscriber information on the subscriber in response to the fact that the static subscriber infor- mation is not found in the first visitor location register, registering the subscriber in the first visitor location register in response to the fact that the static subscriber information on the subscriber does not prevent the registration.

2. A method as claimed in claim 1 , c h a r a c t e r i z e d by checking, before said subscriber registration and in response to the fact that the static subscriber information is not found in the visitor location register, whether there is room in the visitor location register for the subscriber information on a new subscriber, and removing from the visitor location register the subscriber information on a second subscriber whose dynamic subscriber information indicate that said second subscriber is no longer registered in said visitor location register.

3. A method as claimed in claim 2, c h a r a c t e r i z e d by removing from the visitor location register the subscriber information on the second subscriber who, according to the dynamic subscriber informa- tion, has been unregistered in said visitor location register for the longest time.

4. A method as claimed in any one of the preceding claims, c h a r a c t e r i z e d in that the static subscriber information on the subscriber comprises a static time stamp to indicate the point of time when the subscriber information was last changed, and the dynamic subscriber information comprises a dy- namic time stamp to indicate the point of time when the dynamic subscriber information was last changed.

5. A method as claimed in claim 4, c h a r a c t e r i z e d by checking the correspondence between the static subscriber infor- mation on the subscriber in the visitor location register and the static subscriber information on the subscriber in the home location register by comparing said static time stamps, and updating the static subscriber information on the subscriber in the visitor location register to correspond with the static subscriber information on the subscriber in the home location register in response to the fact that the static time stamp in the visitor location register is different from the static time stamp in the home location register.

6. A method as claimed in any one of the preceding claims, c h a r a c t e r i z e d by, in response to the registration of said subscriber in the first visitor location register, checking from the home location register whether the registration information on the subscriber has been transmitted earlier from a second visitor location register, transmitting a command to remove the registration of the subscriber to said second visitor location register in response to finding said registration information, and updating the dynamic subscriber information on the subscriber in the home location register to correspond with the dynamic subscriber information on the subscriber in the visitor location register.

7. A method as claimed in any one of the preceding claims, c h a r a c t e r i z e d by determining a maximum storage time for storing in the visitor location register the subscriber information on the subscriber who is not registered in the visitor location register, and removing periodically from the visitor location register the subscriber information on the subscriber who, according to the dynamic subscriber information on the subscriber, has been unregistered in the visitor location register longer than said maximum storage time.

8. A mobile communication system comprising a home location register for at least partly storing static subscriber information and dynamic subscriber information on the subscribers in the mobile communication system and at least one visitor location register communicating with the home location register for storing the static subscriber information and the dynamic subscriber information on the subscribers registered in said visitor location register, characterized in that the visitor location register, when the registration of the subscriber is removed from said visitor location register, is arranged to retain the stored static subscriber information on the subscriber and to update the removal of the registration in the dynamic subscriber information on the subscriber.

9. A mobile communication system as claimed in claim 8, char- acterized in that the visitor location register is arranged to inform the home location register of said registration removal, and the home location register is arranged to update said registration removal in the dynamic subscriber information on the subscriber.

10. A mobile communication system as claimed in claims 8 or 9, characterized in that the static subscriber information on the subscriber comprises a static time stamp to indicate the point of time when the static subscriber information was last changed, and the dynamic subscriber information comprises a dynamic time stamp to indicate the point of time when the dynamic subscriber information was last changed.

11. A mobile communication system as claimed in claim 10, characterized in that the visitor location register is arranged to check the stored static subscriber information on the subscriber in response to a registration request presented by the subscriber in order to find the static information on said subscriber, ask the home location register for the static subscriber information on said subscriber in response to the fact that the static subscriber information is not found in the visitor location register, and register said subscriber in the visitor location register in response to the fact the static information on the subscriber does not prevent the registration.

12. A mobile communication system as claimed in claim 11, characterized in that the visitor location register is arranged to check, before said subscriber registration and in response to the fact that the static subscriber information is not found in the visitor location register, whether there is room in the visitor location register for the subscriber information on a new subscriber, and remove from the visitor location register the subscriber information on a second subscriber whose dynamic subscriber information indicate that said second subscriber is no longer registered in said visitor location register.

13. A mobile communication system as claimed in claim 12, c h a r a c t e r i z e d in that the visitor location register is arranged to remove from the visitor location register the subscriber information on the second subscriber who, ac- cording to the dynamic subscriber information, has been unregistered in said visitor location register for the longest time.

14. A mobile communication system as claimed in any one of claims 11 to 13, c h a r a c t e r i z e d in that the visitor location register is arranged to check the correspondence between the static subscriber information on the subscriber in the visitor location register and the static subscriber information on the subscriber in the home location register by comparing said static time stamps, and update the static subscriber information on the subscriber in the visitor location register to correspond with the static subscriber information on the subscriber in the home location register in response to the fact that the static time stamp in the visitor location register.

15. A mobile communication system as claimed in any one of claims 11 to 14, c h a r a c t e r i z e d in that in response to the registration of said subscriber in the first visitor location register, the home location register is arranged to check whether the registration information on the subscriber has been transmitted earlier from a second visitor location register, transmit a command to remove the registration of the subscriber to said second visitor location register in response to finding said registration information, and update the dynamic subscriber information on the subscriber in the home location register to correspond with the dynamic subscriber information on the subscriber in the visitor location register.

16. A mobile communication system as claimed in any one of claims 8 to 15, characterized in that the visitor location register is arranged to determine a maximum storage time for storing in the visitor location register the subscriber information on the subscriber who is not registered in the visitor location register, and remove periodically from the visitor location register the subscriber information on the subscriber who, according to the dynamic subscriber information on the subscriber, has been unregistered in the visitor location register longer than said maximum storage time.

17. A mobile communication system as claimed in any one of claims 8 to 16, characterized in that said mobile communication system is a TETRA system.

AMENDED CLAIMS

[received by the International Bureau on 25 April 2001 (25.04.01); original claims 1-17 replaced by new claims 1-7 (3 pages)]

1. A method of registering subscribers in a mobile communication system comprising a home location register for at least partly storing static subscriber information and dynamic subscriber information on the subscribers in the mobile communication system, which the static subscriber information on the subscriber comprises a static verification information to indicate the last change of the subscriber information, and at least a first visitor location register communicating with the home location register for storing the static subscriber information and the dynamic subscriber information on the subscri- bers registered in said visitor location register, in which method a registration message of the subscriber is received by the first visitor location register, c h a r a c t e r i z e d by checking the static subscriber information on the subscriber in the first visitor location register, checking the correspondence between the static subscriber information on the subscriber in the visitor location register and the static subscriber information on the subscriber in the home location register by comparing said static verification informations, and updating the static subscriber information on the subscriber in the visitor location register to correspond with the static subscriber information on the subscriber in the home location register in response to the fact that the static verification information in the visitor location register is different from the static verification information in the home location register.

2. A method as claimed in claim 1 , c h a r a c t e r i z e d by, in res- ponse to the registration of said subscriber in the first visitor location register, checking from the home location register whether the registration information on the subscriber has been transmitted earlier from a second visitor location register, transmitting a command to remove the registration of the subscriber to said second visitor location register in response to finding said registration information, and updating the dynamic subscriber information on the subscriber in the home location register to correspond with the dynamic subscriber information on the subscriber in the visitor location register. 3. A method as claimed in claims 1 or 2, c h a r a c t e r i z e d by 20

determining a maximum storage time for storing in the visitor location register the subscriber information on the subscriber who is not registered in the visitor location register, and removing periodically from the visitor location register the subscriber information on the subscriber who, according to the dynamic subscriber information on the subscriber, has been unregistered in the visitor location register longer than said maximum storage time.

4. A mobile communication system comprising a home location register for at least partly storing static subscriber information and dynamic subscriber information on the subscribers in the mobile communication system, which the static subscriber information on the subscriber comprises a static verification information to indicate the last change of the subscriber information, and at least one visitor location register communicating with the home location register for storing the static subscriber information and the dy- namic subscriber information on the subscribers registered in said visitor location register, which visitor location register, when the registration of the subscriber is removed from said visitor location register, is arranged to retain the stored static subscriber information on the subscriber and to update the removal of the registration in the dynamic subscriber information on the subscriber, c h a r a c t e r i z e d in that the visitor location register is arranged to check the stored static subscriber information on the subscriber in response to a registration request presented by the subscriber, check the correspondence between the static subscriber informati- on on the subscriber in the visitor location register and the static subscriber information on the subscriber in the home location register by comparing said static verification informations, and update the static subscriber information on the subscriber in the visitor location register to correspond with the static subscriber information on the subscriber in the home location register in response to the fact that the static verification information in the visitor location register is different from the static verification information in the home location register.

5. A mobile communication system as claimed in claim 4, c h a r a c t e r i z e d in that in response to the registration of said subscriber in the first visitor location register, the home location register is arranged to check whether the registration information on the subscriber has been transmitted earlier from a second visitor location register, transmit a command to remove the registration of the subscriber to said second visitor location register in response to finding said registration in- formation, and update the dynamic subscriber information on the subscriber in the home location register to correspond with the dynamic subscriber information on the subscriber in the visitor location register.

6. A mobile communication system as claimed in claims 4 or 5, c h a r a c t e r i z e d in that the visitor location register is arranged to determine a maximum storage time for storing in the visitor location register the subscriber information on the subscriber who is not registered in the visitor location register, and remove periodically from the visitor location register the subscriber information on the subscriber who, according to the dynamic subscriber information on the subscriber, has been unregistered in the visitor location register longer than said maximum storage time.

7. A mobile communication system as claimed in any one of claims 4 to 6, c h a r a c t e r i z e d in that said mobile communication system is a TETRA system.