A METHOD IN CONJUNCTION WITH UPDATING ONE OR MORE HLR-DATABASES INCLUDED IN A MOBILE TELEPHONE SYSTEM

Abstract: A method in conjunction with updating one or more HLR-databases included in a GSM-type mobile telephone system. Updating of an HLR (HRL1) is requested by sending a so-called Reset-message, which identifies the HLR-database concerned, to a number of VLR-databases (11). The losses in process capacity of the VLR-bases will be relatively small, because of the following: the time points (t:HLR1) at which Reset-messages and the time points (t:MS1) at which radio contacts were made with different mobile stations (MS1) are registered in each VLR. For each radio contact made between a VLR and a mobile station, a search is made in VLR to ascertain whether the mobile station belongs to an HLR which has been requested updating. If such is the case, the time point of the earliest preceding radio contact between VLR and the mobile station is compared in VLR with the time point at which the Reset-message was received, wherein HLR is updated with data from VLR when the preceding radio contact occurred before the Reset-message was received.

Description: A METHOD IN CONJUNCTION WITH UPDATING ONE OR MORE HLR-DATABASES INCLUDED IN A MOBILE TELEPHONE SYSTEM TECHNICAL FIELD The present invention relates to a method in conjunction with updating of one or more HLR-databaεes which are included in a GSM- type mobile telephone system, wherein updating of such a database is requested by transmitting to a number of VLR-databases a special signal which identifies the HLR-database concerned. BACKGROUND ART A GSM-network includes two types of net databases, HLR (Home Location Register) and VLR (Visitor Location Register) . A network will normally include several HLRs and several VLRs. Among other things, each HLR-database has stored therein all permanent data for those subscribers, i.e. those mobile stations, which belong to this particular HLR. The telephone number of the mobile stations and information concerning additional services which are included in the subscription are examples of such data. The active status of the additional services and information which discloses in which VLR-database a respective mobile station is registered at that particular moment are also stored in HLR. The permanent data stored in HLR is secured by also storing the data in an external medium with the aid of "backup" . Among other things, there is stored in each VLR-database infor¬ mation which discloses the whereabouts of respective mobile stations that are registered in a particular VLR at that par¬ ticular time. Each VLR also contains a copy of the subset of all subscriber data that is contained in HLR and is relevant to this VLR. This subset is obtained from HLR in conjunction with a new mobile station entering the area covered by a VLR, whereupon data is signalled from HLR to VLR with the aid of CCITT 7-signalling. The described structure is highly vulnerable to errors and fault in the network, caused for instance by restarts in HLR or VLR an also by signalling associated errors. Consequently, there hav been defined within GSM standardized work procedures for restorin data in these so-called node types in the most robust way pos sible, so as to avoid an error spreading to several nodes an resulting in breakdowns in the network. When a VLR-database has lost its data for some reason or another, the VLR will update its data autonomously, by signalling backward and forwards between itself and those mobile stations which ar located within the area covered by this particular VLR. This mean that those HLR-databases to which the mobile stations belong will not be affected immediately by a restart in a VLR. Data i collected from each individual HLR upon the next radio contac with a mobile station which belongs to this HLR. On the other hand, if an HLR has been restarted, which means tha the data therein may be corrupted, it is necessary for this HLR t request the assistance of different VLR in recreating parts of th data that was stored in HLR. This primarily concerns informatio as to which VLR mobile stations are registered at that time. According to GSM-standards, this is carried out by the HLR- database concerned informing all VLR-databases that this par¬ ticular HLR has been restarted and needs to be updated with ne data. This is effected with the aid of a "Reset" operation, which is signalled over the CCITT 7-network. According to GSM-standards, when a "Reset-message" is received, those mobile stations which are registered in this VLR and which, at the same time, belong to the HLR which needs to be updated are marked in each VLR-database in a special way. This marking is effected by allocating a flag, referred to as a "HLR confirmation flag" to each such mobile station. The intention with this procedure is to update HLR with data rom VLR on the next occasion on which VLR has radio contact with a mobile station that has been marked with this flag. In this way, HLR receives information which discloses in which VLR respective mobile stations are registered at that particular time. Certain other data is updated at the same time, although this data is less important than the data which discloses to which VLR the mobile stations belong. It can also be mentioned that when updating HLR, a certain amount of data is transmitted from HLR to VLR, for instance subscriber data which applies to the mobile station. Known methods for updating VLR-databases and HLR-databases are described in: ETSI TC GSM, Recommendation GSM 03.07, Restoration Procedures, Version: 3.2.0, Date: October 1990. The known method of updating an HLR-database, however, is difficult to apply in practice, since a Reset-message does not contain information which discloses those mobile stations which belong to the HLR to be updated nor yet those VLR-databases which contain any data whatsoever required for the relevant updating procedure. Consequently, it is necessary to derive such infor- mation from the VLR-databases, by searching each and every one of said VLR-databases for the information obtained in conjunction with the entry of different mobile stations into the area covered by this VLR . Accordingly, it is necessary for each individual VLR to search through the whole of its subscriber register in order to find the HLR to which respective mobile stations belong. This search results in process capacity losses on the part of the VLR- databases, and these losses will, of course, be much greater on those occasions when * a HLR is restarted several times within a short period of time or when several HLRs are restarted shortly after one another and several Reset-messages are therefore transmitted in sequence. Each VLR will therewith search through its subscriber register for each Reset-message received. DISCLOSURE OF THE INVENTION The object of the present invention is to provide a method of procedure in conjunction with updating one or more HLR-databases, so that the losses in the process capacity of the VLR-databases will be smaller than they would otherwise be when practicing the aforesaid known method. In brief, this is achieved in the fol lowing way: The time points at which Reset-messages are received and also t time points when radio contact is made with different mobil stations are registered in VLR. With each radio contact between VLR and a mobile station, a search is made in VLR with th intention of learning whether or not the mobile station belongs t a HLR that has requested updating. If such is the case, the tim point of the preceding radio contact between VLR and the mobil station is compared in VLR with the time at which the Reset message was received, wherein HLR is updated with data from V when the preceding radio contact took place earlier than the tim at which the Reset-message was received. This obviates the necessity of searching in VLR to establish thos mobile stations which are of interest for the updating procedur immediately after receiving the Reset-message. Instead, thi search is spread-out over time and is effected for each individua mobile station in conjunction with the next radio contact wit said station. The invention is characterized by the features set forth in th following Claims. - BRIEF DESCRIPTION OF»THE DRAWING The invention will now be described in more detail with referenc to the accompanying drawing, in which Figure 1 illustrates tw tables which contain certain information which is stored in a VLR database in accordance with the invention? and Figure 2 il lustrates an example of a course of events that occur whe signalling to and from a VLR-database. BEST MODE OF CARRYING OUT THE INVENTION Figure 1 shows two tables, 12 and 13, which are enclosed by rectangle 11 which represents a VLR-database. The table 1 contains certain subscriber data which is stored in the VLR- database, in accordance with the invention. The time at which a new radio contact occurs between the VLR-database and any mobile station that is located within the area covered by this VLR is registered and stored in VLR. This is symbolized in the Figure by the identity of the mobile station having been written into the left column of table 12, and by the time having been written into the right column of said table. The left column of the table includes the references MSI, ... ,MSn, ... , which thus represent the identity , of different mobile stations. The right column of the table includes the references t:MSl, ... ,t:Msn, ... , which repre¬ sent the times at which radio contacts were made with the mobile stations in the left column. Upon renewed radio contact with a mobile station, for instance MSI, the time, t:MSl, is updated in the VLR-database, so that the stored time information will always correspond to the latest radio contact between the VLR-database and the mobile station in question. The times at which any Reset-messages were received and the HLR- databases from which these signals derive are registered and stored in the VLR-database. This has been symbolized in the Figure by writing the identity of the HLR-database into the left column in table 13, and by writing the time points into the right column of the table. The left column of table 13 includes references HLR1, ... ,HLRn, ... , which thus represent the identity of different HLR-databases. The right column of table 13 includes references t:HLRl, ... ,t:HLRn, ... , which represent the times at which Reset- messages were received from the HLR-databases in the left column. When a new Reset-message is received from a HLR, for instance HLR1, the time point, t:HLRl, is updated so that the time infor¬ mation stored in the VLR-database will always relate to the last received Reset-message from the HLR-database in question. With each radio contact between a VLR and a mobile station which is located within the area covered by this VLR at that particular time, a search is made in VLR in order to ascertain whether or no the mobile station belongs to a HLR which has requested updating i.e. belongs to a HLR which has transmitted a Reset-message. I such is the case, the time point stored in VLR, according to tabl 12, of the earliest preceding registered radio contact between VL and this mobile station is compared with the stored time point a which the Reset-message was received, in accordance with table 13 When the Reset-message was received at a later time than the tim of the earliest preceding radio contact, the HLR-database i updated with data from the VLR-database concerned. In other cases this updating has already taken place. If, when comparing time points, it is established that no earlie radio contact between VLR and the mobile station concerned ha been registered, the HLR-database is updated in the same manner a though an earliest preceding radio contact had been registered a a time earlier than the time of receiving the Reset-message. Figure 2 illustrates an example of a course of events concernin a reciprocal signalling process, to and from a VLR-database. Th Figure includes a time axis on which five time points, tl-t5, hav been marked. At time point tl, radio contact takes place betwee VLR and a mobile station MSI, which is symbolized with th reference sign MSI above the time axis at time point tl. MSI i assumed to belong to the HLR-database HLR1. A search is then mad in the VLR-database in order to ascertain whether or not a Reset message has been received from HLR1. In this example, it has bee assumed that this is not the case, and HLR1 is therefore no updated. At t2, VJ R receives a Reset-message from HLR1, which i symbolized with the reference sign HLR1. At t3 , a new radi contact is made between VLR and MSI. A search is again made in VLR in order to ascertain whether or not a Reset-message has bee received from HLR1, which this time is established to be the case The time point tl of the earliest preceding radio contact with MS is then compared-with the time point t2 at which the Reset-messag was received. Since tl is earlier than t2, updating is carried ou in this particular case. At t4, a radio contact is made with mobile station MS2, which is assumed not to belong to a HLR whic has requested updating. Consequently, no updating is carried out. At t5, a new radio contact is made with MSI. It is established tha a Reset-message has been received from HLR1 at t2 and that th earliest preceding radio contact with MSI took place at t3 ' , whic is later than t2. Consequently, no updating is carried out in thi case either. As before mentioned, the losses in the processor capacity of th VLR-database will be relatively small when practicing th inventive method. This is because the search effected in eac individual VLR to establish which mobile stations are of interes with respect to the updating of a HLR-database is spread-out ove time, instead of requiring each VLR to search through its sub scriber register with each received Reset-message.

Claims: CLAIMS 1. A method in conjunction with updating one or more HLR-dat bases which are included in a G≤M-type mobile telephone syste wherein updating of such a database is requested by transmitti 5 to a number of VLR-data-bases a special message which identifi the HLR-database concerned, cha r a c t e r i z ed by regist ring, storing and updating in each individual VLR-database (1 the time point (e.g. t:HLRl; t2) at which said message w received from each individual HLR-database (e.g. HLR1) ; regist 10 ring, storing and updating in each individual VLR-database (1 the time points (e.g. t:MSl; tl, t3-t5) of each radio conta between this VLR-database and each individual mobile station (e. MSI, MS2) which is located within the area covered by the VL database at that particular time; searching the VLR-database 15 ascertain whether or not a mobile station belongs to a HL database (e.g. HLR1) which has requested updating, with each rad contact between a VLR-database (11) and said mobile station (e. MSI, MS2) ; when the mobile station (e.g. MSI) belongs to a HL database (e.g. HLR1) which has requested updating, comparing a 20 registered time point (e.g. t:MSl; tl, t3) of an earliest prec ding radio contact between the VLR-database (11) concerned and t mobile station concerned in the VLR-database with the register time point (e.g. -t:HLRl; t2) at which said message was receiv from the HLR-database to which the mobile station belongs; a 25. updating a HLR-database (e.g. HLR1) which has requested updati with data from the VLR-database (11) when the earliest precedi radio contact occurred earlier than the time at which said messa was received. 2 . A method according to Claim 1 , c h a r a c t e r i z e d 30 updating a HLR-database which has requested updating even when is established that no time point was registered for an imm diately preceding radio contact between the VLR-database and t mobile station.

Inventors: LANTTO JOERGEN, MOBERG JOERGEN, LANTTO, JOERGEN, MOBERG, JOERGEN
Applicants: ERICSSON TELEFON AB L M, TELEFONAKTIEBOLAGET LM ERICSSON
Application year: 1993
Main classification: H04Q7
IPC codes: H04W8, H04W24