Abstract:
A method and apparatus for home location register fault recovery in a system which uses a gateway location register to reduce signaling between visitor location registers and home location registers. When a home location register is recovering from a fault, the home location register sends a reset message to the gateway location registers which are serving mobile subscribers associated with the home location register. The gateway location register sends a reset message to visitor location registers which are serving mobile subscribers associated with the home location register. The gateway location register can determine which mobile subscribers are associated with the home location register by comparing mobile subscriber identification information stored in the gateway location register with information contained in the reset message from the home location register.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Referenced-applications 
     This application claims priority under 35 U.S.C. §§119 and/or 365 to U.S. Provisional Application No. 60/128,786 filed on Apr. 12, 1999, the entire content of which is hereby incorporated by reference. This application is also related to the following applications filed on Apr. 12, 2000: U.S. patent application Ser. No. 09/453,907 “Gateway Location Register Fault Recovery”; U.S. patent application Ser. No. 09/453,908 “Support For Features Associated With A Subscriber In Networks With A Gateway Location Register And A Visitor Location Register”; and U.S. patent application Ser. No. 09/547,991 “Gateway Location Registers In A UMTS Systerm”, all of which are herein expressly incorporated by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not Applicable 
     REFERENCE TO A MICROFICHE APPENDIX 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Description of Related Art 
     Not Applicable 
     2. Field of the Invention 
     The present invention relates to mobile communications systems, and more specifically, to recovery of a home location register from a fault in a system where a gateway location register serves a visitor location register. 
     FIG. 1 illustrates a wireless communication system in accordance with the Global System for Mobile communication (GSM) standard. The GSM standard is designed to provide a uniform interface which allows mobile communication subscribers of various countries to operate their mobile devices regardless of the current location of the mobile subscriber. A mobile subscriber typically has a subscription with a network which is designated as the mobile subscriber&#39;s home public land mobile network  110  (HPLMN). The HPLMN  110  has a home location register (HLR)  115  which contains, among other things, various information regarding the services provided to the mobile subscriber. When a mobile subscriber roams into a different network, which is referred to as a visited public land mobile network  120  (VPLMN), the VPLMN requires certain data regarding the mobile subscriber&#39;s subscription. The data regarding the mobile subscriber&#39;s subscription is also known as the mobile subscriber&#39;s profile. The mobile subscriber&#39;s profile is transferred from the HLR to a visitor location register (VLR) in the VPLMN  120 . 
     In a GSM system mobile subscriber data is stored within the VLR that is associated with the mobile services switching center (MSC) that currently serves the mobile subscriber in order to reduce internetwork signaling between VLRs and HLRs. The decentralization of the VLRs within a GSM system (i.e., each MSC being equipped with a VLR) reduces intranetwork signaling as well. So, for example, if the mobile subscriber is roaming in an area of the VPLMN  120  which is controlled by the MSCNVLR  130 , the HLR  115  will transfer the mobile subscriber&#39;s profile to MSC/VLR  130 . Similarly, if the mobile subscriber is roaming in an area controlled by MSC/VLR  135 , the HLR  115  will transfer the mobile subscribers profile to MSCNVLR  135 . 
     Although FIG. 1 illustrates the MSCNVLR as a single network node, one skilled in the art will recognize that the MSC and VLR can be implemented as separate network elements. 
     To increase the compatibility of GSM with other types of systems, it is anticipated that future versions of the GSM standard, also called Universal Mobile Telecommunications System (UMTS), will incorporate elements of other mobile communications systems. For example, the Japanese Personal Digital Cellular (PDC) system includes a network node which is used to reduce internetwork signaling known as a gateway location register (GLR). FIG. 2 illustrates an exemplary mobile communications system in accordance with the PDC system. Like a GSM system, a home network  210  includes an HLR  215  which contains the mobile subscriber&#39;s profile. When a mobile subscriber roams into a visited network  220  the mobile subscriber&#39;s profile is transferred to GLR  225 . In GSM terms, the GLR can be described as a VLR for all mobile subscribers roaming from other networks. Hence, only one GLR is needed for each network. 
     FIG. 3 illustrates an exemplary UMTS system which incorporates the GLR of the PDC system. When a mobile subscriber of HPLMN  310  roams into VPLMN  320 , the HLR  315  will transfer the mobile subscriber&#39;s profile to GLR  325 . Then, depending upon which area within the VPLMN  320  the mobile subscriber is roaming, the GLR  325  will transfer the mobile subscriber&#39;s profile to the respective MSCNVLR  330 ,  335  or  340 . The introduction of the GLR  325  into a GSM system reduces internetwork signaling because once the mobile subscriber roams into VPLMN  320 , the HLR will only need to transfer the mobile subscriber&#39;s profile to GLR  325 . GLR  325  will be responsible for transferring the mobile subscriber&#39;s profile to the proper MSC/VLR within VPLMN  320  as the mobile subscriber travels around the VPLMN  320 . 
     The protocol used by GSM/UMTS systems for transferring data between VLRs and HLRs is the mobile application part (MAP). FIG. 4 illustrates a conventional method using the MAP protocols in a GSM system when an HLR is recovering from a fault. In step  405  the HLR loads the contents of its non-volatile backup memory into its dynamic memory. Next the HLR sends a MAP_RESET message to the VLRs to which the HLR&#39;s mobile subscribers are currently associated as indicated by the information in the backup memory in accordance with step  410 . The MAP_RESET request message includes the HLR number, which is the E. 164  number of the HLR, and, optionally, an HLR identity (Id) list. The HLR Id list is a list of the possible combinations of leading digits of the IMSIs that belongto the concerned HLR, including Country Code (CC), network code and the leading digits of the National Destination Code (NDC). In step  415 , the VLR determines which of the mobile stations that are currently served by the VLR are associated with the HLR which sent the MAP_RESET message. In conventional GSM systems there are two different ways for the VLR to determine which mobile stations are associated with a particular HLR. If the HLR Id list parameter is present in the MAP_RESET message the affected mobile subscribers can be identified as those mobile stations whose leading digits of their IMSI matches the digits of either of the HLR identities in the HLR Id list parameter. If the HLR Id list parameter is not present in the MAP_RESET message the affected mobile subscribers are derived using the HLR number in the MAP_RESET message, i.e., the affected mobile subscribers are those for which the HLR number stored in the mobile subscriber record in the VLR matches the HLR number received in the MAP_RESET message. 
     In step  420  the VLR sets the “Location Information Confirmed In HLR” flag for all of the affected mobile stations to “Not Confirmed”. Setting this flag will force the VLR to perform a MAP_UPDATE_LOCATION service to update the HLR at the next authenticated radio contact with each affected mobile station. In step  425  the VLR waits for an authenticated radio contact from the concerned mobile subscriber. In step  430  the VLR determines whether it has received an authenticated radio contact from the concerned mobile subscriber. If the VLR has not received an authenticated radio contact from the concerned mobile subscriber, in accordance with the “No” path out of decision step  430 , the VLR continues to wait in accordance with step  425 . If the VLR receives an authenticated radio contact from the concerned mobile subscriber the VLR sends a MAP_UPDATE_LOCATION message to the HLR indicating that the VLR is serving the concerned mobile subscriber in accordance with step  435 . The location updates sent from the VLRs to the HLR will gradually restore and confirm the mobile subscriber data of the restarted HLR. 
     Since GLRs are optional elements within the UMTS system, MAP procedures must be completely independent of the presence or absence of GLRs in a network. Accordingly, by using an HLR interface towards the VLRs and a VLR interface towards the HLRs, the GLR should be completely transparent. However, because of the dual nature of the GLR in the network it may be difficult for the GLR to behave in a way which simultaneously will be perceived as VLR behavior by the HLRs, and as HLR behavior by the VLRs. One such case is the fault recovery behavior of the HLR. 
     In a conventional GSM UMTS system, if a GLR were added to a VPLMN containing a VLR, the HLR would send the MAP_RESET message to the GLR instead of the VLR. However, since the GSM MAP protocols do not account for a GLR in the network, and the PDC MAP protocols do not account for a VLR in the network, there are no procedures defining how an HLR should recover from a fault when some of its affected mobile subscribers are located in areas where a gateway location register serves a visitor location register. 
     Accordingly, it would be desirable to provide methods and apparatus for HLR fault recovery in a UMTS system including a gateway location register and a visitor location register. Further, it would be desirable for the HLR fault recovery to be performed without violating the GSM MAP protocol, i.e. using the specified message formats and not violating any specified message sequences. 
     BRIEF SUMMARY OF THE INVENTION 
     According to exemplary embodiments of the present invention, methods and apparatus are provided for home location register fault recovery. A gateway location register receives a reset message from the home location register. The reset message contains a home location register number for the home location register. The gateway location register sends another reset message to a visitor location register. The another reset message includes a gateway location register number for the gateway location register. Alternatively, the another reset message includes a home location register number for the home location register and the home location register identity list. 
     In accordance with this aspect of the present invention the reset message and the another reset message can be MAP_RESET messages. In addition, the gateway location register can determine a mobile subscriber associated with the home location register, and the gateway location register determines that the visitor location register serves the mobile subscriber. Further, the reset message and the another reset message can include a home location register identity list. In addition, the visitor location register can identify affected mobile subscribers using either the gateway location register number or the home location identity list. 
     In accordance with another aspect of the present invention a gateway location register receives a reset message from the home location register, wherein the reset message includes a home location register number. A mobile subscriber associated with the home location register is determined by comparing a country code and national destination code of a mobile subscriber identity stored in a record associated with the mobile subscriber with a country code and national destination code of the home location register number. Alternatively, a mobile subscriber associated with the home location register can be determined by comparing the home location register number received in the reset message with a home location register number stored in a mobile subscriber record in the gateway location register. 
     In accordance with this aspect of the present invention the gateway location register determines a visitor location register which is currently serving the mobile subscriber. Another reset message is sent to a visitor location register which has been determined to be currently serving the mobile subscriber. Further, the another reset message is received by the visitor location register and it is determined whether there is a home location register identity list in the another reset message. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     The present invention will now be described with reference to the accompanying drawings in which: 
     FIG. 1 illustrates a conventional GSM system; 
     FIG. 2 illustrates a conventional PDC system; 
     FIG. 3 illustrates the relationship of UMTS system elements in a system which includes a GLR; 
     FIG. 4 illustrates a conventional method in a GSM system when an HLR is recovering from a fault; 
     FIG. 5 illustrates an exemplary method for the behavior of a GLR in a UMTS system where an HLR is recovering from a fault in accordance with one embodiment of the present invention; 
     FIGS. 6A and 6B illustrate an exemplary method for the behavior of a GLR in a UMTS system where an HLR is recovering from a fault in accordance with another embodiment of the present invention; 
     FIGS. 7A and 7B illustrate an exemplary method for the behavior of a GLR in a UMTS system where an HLR is recovering from a fault in accordance with yet another embodiment of the present invention; 
     FIG. 8 illustrates an exemplary method for the behavior of a VLR in a UMTS system where an HLR is recovering from a fault in accordance with one embodiment of the present invention; 
     FIG. 9 illustrates an exemplary method for the behavior of a VLR in a UMTS system where an HLR is recovering from a fault in accordance with another embodiment of the present invention; and 
     FIG. 10 illustrates an exemplary method for the behavior of a VLR in a UMTS system where an HLR is recovering from a fault in accordance with yet another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following description, for purposes of explanation and not limitation, specific details are set forth, such as particular sequences of inter and intra network signaling, types of messages, etc. in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known methods, devices, and network elements are omitted so as not to obscure the description of the present invention. 
     The exemplary radio communication systems discussed herein are described as operating in accordance with the UMTS system, however, one skilled in the art will recognize that the present invention can be implemented in other mobile communications systems where a gateway is used to reduce internetwork signaling. 
     FIG. 5 illustrates an exemplary method for the behavior of a GLR in a UMTS system where an HLR is recovering from a fault in accordance with one embodiment of the present invention. In step  505  the GLR receives a MAP_RESET message from the HLR. In step  510  the GLR determines whether the HLR Id list is present in the MAP_RESET message. If the HLR Id list is not present in the MAP_RESET message, in accordance with the “No” path out of decision step  510 , the GLR uses the received HLR number to determine which mobile subscribers are associated with the HLR which sent the MAP_RESET message in accordance with step  515 . The GLR can determine which mobile subscribers are associated with the HLR by either comparing the received number with the number stored in the HLR Number record element in the mobile subscriber records stored in the GLR or by matching the Country Code and National Destination Code (CC+NDC) derived from the International Mobile Subscriber Identity (IMSI) with the CC+NDC of the received HLR number. 
     If the HLR Id list is present in the MAP_RESET message, in accordance with the “Yes” path put of decision step  510 , the GLR uses the HLR Id list to determine which mobile subscribers are associated with the HLR which sent the MAP_RESET message in accordance with step  520 . Once the GLR has determined the mobile subscribers associated with the HLR which sent the MAP_RESET message, in accordance with either step  515  or step  520 , the GLR sends a MAP_UPDATE_LOCATION message to the HLR for each affected mobile subscriber, i.e., each mobile subscriber associated with the HLR recovering from a fault, in accordance with step  525 . 
     FIGS. 6A and 6B illustrate an exemplary method for the behavior of a GLR in a UMTS system where an HLR is recovering from a fault in accordance with another embodiment of the present invention. In step  605  the GLR receives a MAP_RESET message from an HLR. In step  610  the GLR determines whether the HLR Id list is present in the MAP_RESET message. If the HLR Id list is not present in the MAP_RESET message, in accordance with the “No” path out of decision step  610 , the GLR uses the received HLR number to determine which mobile subscribers are associated with the HLR which sent the MAP_RESET message in accordance with step  615 . The GLR can determine which mobile subscribers are associated with the HLR by either comparing the received number with the number stored in the HLR Number record element in the mobile subscriber records stored in the GLR or by matching the CC+NDC derived from the IMSI with the CC+NDC of the received HLR number. 
     If the HLR Id list is present in the MAP_RESET message, in accordance with the “Yes” path out of decision step  610 , the GLR uses the HLR Id list to determine which mobile subscribers are associated with the HLR which sent the MAP_RESET message in accordance with step  620 . Once the GLR has determined the mobile subscribers associated with the HLR which sent the MAP_RESET message, in accordance with either step  615  or step  620 , the GLR sets the “Location Information Confirmed In HLR” flag to “Not Confirmed” for each mobile subscriber served by the GLR which is associated with the HLR in accordance with step  625 . In step  630  the GLR sends a MAP_RESET message, including the GLR number instead of the HLR number, to each VLR where at least one of the mobile subscribers associated with the HLR is located. 
     The MAP_RESET message will cause the VLRs to begin the location updating procedure with the GLR upon the next authenticated radio contact with one of the affected mobile subscribers. Accordingly, in step  635  the GLR receives a MAP_UPDATE_LOCATION message from a VLR which has received the MAP_RESET message. In step  640  the GLR determines whether the “Location Information Confirmed In HLR” flag is set to “Not Confirmed” for the mobile subscriber identified in the MAP_UPDATE_LOCATION message. If “Location Information Confirm In HLR” flag is set to “Confirmed” for the mobile subscriber, i.e., the flag is not set to “Not Confirmed”, in accordance with the “No” path out of decision step  640 , the GLR follows the normal location update procedure in accordance with step  645 , i.e., the GLR will respond with a MAP_UPDATE_LOCATION response message after sending subscription information from mobile subscriber records stored in the GLR using the MAP_INSERT_SUBSCRIBER_DATA procedure. 
     If the “Location Information Confirmed In HLR” flag is set to “Not Confirmed” for the mobile subscriber, in accordance with the “Yes” path out of decision step  640 , the GLR sends a MAP_UPDATE_LOCATION message to the HLR for the mobile subscriber identified in the MAP_UPDATE_LOCATION message received from the VLR in accordance with step  650 . When the location updating procedure between the GLR and HLR is completed and a successful outcome has been confirmed, the GLR sets the “Location Information Confirmed In HLR” flag to “Confirmed” for the mobile subscriber in accordance with step  655 . Also, in this case the GLR will send mobile subscriber data and a MAP_UPDATE_LOCATION response message to the VLR. 
     FIGS. 7A and 7B illustrate an exemplary method for the behavior of a GLR in a UMTS system where an HLR is recovering from a fault in accordance with yet another embodiment of the present invention. The method illustrated in FIGS. 7A and 7B is similar to the method described above in connection with FIGS. 6A and 6B. Accordingly, it will be understood that the steps in FIGS. 7A and 7B which have the same numbers as the steps described above with respect to FIGS. 6A and 6B perform the same functions as those described above with regard to FIGS. 6A and 6B. The difference between the method described above in connection with FIGS. 6A and 6B and the method described in FIGS. 7A and 7B, is in step  730 . In step  730  the GLR sends a MAP_RESET message, without replacing the HLR number, to each VLR where at least one of the mobile subscribers associated with the HLR which sent the MAP_RESET message is located. In contrast, in step  630 , the GLR replaces the HLR number with the GLR number in the MAP_RESET message sent to the VLRs. As can be seen by comparing FIGS. 6A and 6B with FIGS. 7A and 7B, whether the HLR number or the GLR number is placed in the MAP_RESET messages sent to the VLRs does not further effect the behavior of the GLR. However, as will be described in more detail below, the behavior of the VLR will depend upon whether the GLR number or the HLR number is present in the MAP_RESET message. 
     In the case of a MAP_RESET indication, indicating a restart in an HLR in a foreign network, in a system where a GLR serves a VLR, the VLR must be able to address the fact that there is both a (foreign) HLR and a GLR in the system. In other words, the VLR must be able to identify all the mobile subscribers belonging to the restarted HLR, but when the MAP_UPDATE_LOCATION procedures are executed, they should be directed towards the GLR, just as any MAP_UPDATE_LOCATION procedure. 
     Since, in a UMTS system where a GLR serves VLRs the MAP_RESET message from the HLR will be delivered to the VLRs via the GLR, the VLR should preferably determine whether the MAP_RESET message is originating from the HLR or the GLR, i.e., whether the HLR or the GLR is recovering from a fault. In addition, the VLR, in a UMTS system, should be able to handle MAP_RESET messages sent directly from an HLR in a foreign PLMN, i.e., if the PLMN with which the VLR is associated does not have a GLR. Further, the VLR should be able to handle MAP_RESET messages sent from an HLR in the VLR&#39;s own PLMN. Accordingly, FIGS. 8-10 illustrate exemplary behavior of a VLR in the UMTS system for handling MAP_RESET messages in which the VLR can, among other things, address the different situations discussed above. 
     FIG. 8 illustrates an exemplary method for the behavior of a VLR in a UMTS system where an HLR is recovering from a fault in accordance with one embodiment of the present invention. In step  805  the VLR receives a MAP_RESET message from a GLR. In step  810  the VLR determines whether an HLR Id list is included in the MAP_RESET message. If the HLR Id list is present in the MAP_RESET message, in accordance with the “Yes” path out of decision step  810 , the VLR uses the HLR Id list to derive the affected mobile subscribers in accordance with step  815 . The VLR then sets the “Location Information Confirmed In HLR” flag to “Not Confirmed” for each affected mobile subscriber in accordance with step  835 . In step  840  the VLR follows normal VLR behavior as specified in Technical Standard GSM 09.02 which is herein expressly incorporated by reference. Generally, the VLR behavior specified by Technical Standard GSM 09.02 is for the VLR to wait for an authenticated radio contact with the affected mobile subscriber and then initiate a location updating procedure with the HLR, via the GLR in the case of a UMTS system including a GLR in the mobile subscriber&#39;s current VPLMN. 
     If the HLR Id list is not present in the MAP_RESET message, in accordance with the “No” path out of decision step  810 , the VLR determines whether the number in the received HLR Number parameter matches the number of the GLR in the VLR&#39;s own network in accordance with step  820 . The number received in the HLR number parameter of a MAP_RESET message will match the GLR number when the GLR is recovering from a fault. According to exemplary embodiments of the present invention the VLRs which are served by a GLR can have the GLR&#39;s number programmed as configuration data in the VLR. When the GLR has sent the MAP_RESET message, because the GLR is recovering from a fault, all of the mobile subscribers served by the VLR, which is served by the GLR, will be affected. Accordingly, if the number in the received HLR Number parameter matches the number of the GLR in the VLR&#39;s own network, in accordance with the “Yes” path out of decision step  820 , the VLR sets the “Location Confirmed In HLR” flag to “Not Confirmed” for all mobile subscribers visiting from other networks in accordance with step  825 . In step  840  the VLR follows normal VLR behavior as specified in Technical Standard GSM 09.02. 
     If the number in the received HLR Number parameter does not match the number of the GLR in the VLR&#39;s own network, in accordance with the “No” path out of decision step  820 , the VLR uses the HLR number to derive the affected mobile subscribers by matching the CC+NDC derived from the IMSIs stored in the VLR&#39;s mobile subscriber records with the CC+NDC of the received HLR number in accordance with step  830 . 
     In a PLMN where a VLR is supported by a GLR, messages which would be addressed to the HLR associated with the mobile subscriber in a network without a GLR, are addressed to the GLR. The GLR then forwards the messages to the particular HLR when necessary, e.g., MAP_UPDATE_LOCATION messages would not be forwarded to the HLR if the concern mobile subscriber was already registered in the GLR. Accordingly, in a system where a VLR is served by a GLR the GLR&#39;s address is stored in the VLR&#39;s mobile subscriber records instead of the address of the HLR associated with the particular mobile subscriber. Hence, the VLR will not be able to derive the mobile subscribers associated with a particular HLR using a stored HLR number. Instead, the VLR derives the mobile subscriber associated with the VLR using the CC+NDC of the mobile subscriber&#39;s IMSI with the CC+NDC of the HLR number in the received MAP_RESET message. 
     In step  835  the VLR sets the “Location Confirmed In HLR” flag to “Not Confirmed” for each affected mobile subscriber. In step  840  the VLR follows normal VLR behavior as specified in Technical Standard GSM 09.02. 
     FIG. 9 illustrates an exemplary method for the behavior of a VLR in a UMTS system where an HLR is recovering from a fault in accordance with another embodiment of the present invention. In accordance with this embodiment of the present invention, the GLR could include a dummy HLR Id list parameter which would be easily recognizable by the VLR to indicate that the MAP_RESET message is originating from the GLR, i.e., to indicate that the GLR is recovering from a fault. For example, the dummy HLR Id list parameter could contain only zeroes, or some other dummy pattern which, like zeroes, could be programed by the manufacturer of the VLRs, i.e., not requiring network specific configuration. 
     Accordingly, in step  905  the VLR receives a MAP_RESET message from a GLR. In step  910  the VLR determines whether the HLR Id list is included in the MAP_RESET message. If the HLR Id list is not included in the MAP_RESET message, in accordance with the “No” path out of decision step  910 , the VLR uses the HLR number to derive the affected mobile subscribers by matching the CC+NDC derived from the IMSIs stored in the VLR&#39;s mobile subscriber records with the CC+NDC of the received HLR number in accordance with step  915 . The VLR sets the “Location Confirmed In HLR” flag to “Not Confirmed” for each affected mobile subscriber in accordance with step  935 . In step  940  the VLR follows normal VLR behavior as specified in Technical Standard GSM 09.02. 
     If the VLR determines that the HLR Id list is included in the MAP_RESET message, in accordance with the “Yes” path out of decision step  910 , the VLR determines whether the HLR Id list is a dummy HLR Id list in accordance with step  920 . Since the dummy HLR Id list indicates that the MAP_RESET message is originating from a GLR which is recovering from a fault, all of the mobile subscribers served by the VLR will be affected subscribers. Accordingly, if the VLR determines that the HLR Id list is a dummy HLR Id list, in accordance with the “Yes” path out of decision step  920 , the VLR sets the “Location Confirmed In HLR” flag to “Not Confirmed” for all mobile subscribers visiting from other networks in accordance with step  930 . In step  940  the VLR follows normal VLR behavior as specified in Technical Standard GSM 09.02. 
     If the VLR determines that the HLR Id list is not a dummy HLR Id list, in accordance with the “No” path out of decision step  920 , the VLR uses the HLR Id list to derive the affected mobile subscribers in accordance with step  925 . In step  935  the VLR sets the “Location Confirmed In HLR” flag to “Not Confirmed” for each affected mobile subscriber. In step  940  the VLR follows normal VLR behavior as specified in Technical Standard GSM 09.02. 
     FIG. 10 illustrates an exemplary method for the behavior of a VLR in a UMTS system where an HLR is recovering from a fault in accordance with yet another embodiment of the present invention. In step  1005  the VLR receives a MAP_RESET message from a GLR. In step  1010  the VLR determines whether an HLR Id list is included in the MAP_RESET message. If the HLR Id list is present in the MAP_RESET message, in accordance with the “Yes” path out of decision step  1010 , then the VLR uses the HLR Id list to derive the affected mobile subscribers in accordance with step  1015 . In step  1035  the VLR sets the “Location Confirmed In HLR” flag to “Not Confirmed” for each affected mobile subscriber. In step  1040  the VLR follows normal VLR behavior as specified in Technical Standard GSM 09.02. 
     If the HLR Id list is not present in the MAP_RESET message, in accordance with the “No” path out of decision step  1010 , the VLR uses the number received in the HLR Number parameter to derive the affected mobile subscribers by matching the received number with the number stored in the HLR Number record element in the mobile subscriber records stored in the VLR in accordance with step  1020 . In step  1025  the VLR determines whether there was a match found between the HLR Number parameter in the MAP_RESET message and the HLR Number record stored in the mobile subscriber records in the VLR. If the VLR determines that there is a match between the HLR Number parameter in the MAP_RESET message and the HLR Number record stored in at least one of the mobile subscriber records in the VLR, in accordance with the “Yes” path out of decision step  1025 , the VLR sets the “Location Confirmed In HLR” flag to “Not Confirmed” for each affected mobile subscriber in accordance with step  1035 . In step  1040  the VLR follows normal VLR behavior as specified in Technical Standard GSM 09.02. 
     If the VLR determines that there is not a match between the HLR Number parameter in the MAP_RESET message and the HLR Number record stored in any one of the mobile subscriber records in the VLR, in accordance with the “No” path out of decision step  1025 , the VLR uses the number received in the HLR Number parameter to derive the affected mobile subscribers by matching the CC+NDC derived from the IMSIs with the CC+NDC of the received HLR Number parameter in accordance with step  1030 . In step  1035  the VLR sets the “Location Confirmed In HLR” flag to “Not Confirmed” for each affected mobile subscriber. In step  1040  the VLR follows normal VLR behavior as specified in Technical Standard GSM 09.02. 
     The exemplary embodiments of the present invention described above allow a system including a GLR and VLRs to handle HLR fault recovery situations without violating the GSM MAP specification. The message formats are unchanged and no message sequence is violated. 
     The present invention has been described by way of exemplary embodiments to which the invention is not limited. Other embodiments are of course possible. For example, in one embodiment the VLR behavior could be to exactly follow the VLR behavior specified in Technical Standard GSM 09.02. Further, one skilled in the art will recognize that the methods disclosed herein are also applicable in a UMTS system including generic packet radio service (GPRS) nodes for serving GPRS mobile subscribers. Other modifications and changes will occur to those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.