LOCATION UPDATE IN A SUPER-CHARGED ENVIRONMENT

Abstract: The present invention relates to a method and network entity for performing a location update in a Super-Charged environment of a mobile network, wherein a release message is transmitted from the mobile network to an old network entity having served a mobile terminal, in response to a location update request message received from a new network entity (31) serving the mobile terminal (1). A subscriber identity allocated to the mobile terminal (1) at the old network entity (30) is released or de-allocated in response to the receipt of the release message. Thus, even in a Super-Charged environment, the old network entity is informed of the fact that the mobile terminal (1) has left its service area, and may re-allocate the subscriber identity which has been allocated to the mobile terminal (1).

Description: LOCATION UPDATE IN A SUPER-CHARGED ENVIRONMENT FIELD OF THE INVENTION The present invention relates to a method and network entity for performing a location update in a Super-Charged network, i.e. a mobile network in which a Super-Charger concept is used to optimize mobility management signaling. BACKGROUND OF THE INVENTION The continued growth of international travel for business and leisure leads to a significant increase in the number of subscribers roaming in mobile networks, such as UMTS (Universal Mobile Telecommunications System) or GSM (Global System for Mobile Communications) networks. Every time a subscriber moves to a location area served by a different VLR (Visitor Location Register) or SGSN (Serving GPRS Support Node) , the subscriber data must be downloaded from the HLR (Home Location Register) in the Home-PLMN (Public Land Mobile Network) to the new network entity serving the user, and deleted in the old VLR or SGSN. In this respect, the term "network entity" is used to designate any network element which may serve a mobile user and which may comprise a data base for storing subscriber data. The term "subscriber data" is used to designate all kind of information associated with a subscription which is required for service provisions, identification, authentication, routing, call handling, charging, subscriber tracing, operation and maintenance purposes. Some subscriber data is referred to as permanent subscriber data, i.e. it can only be changed by administration means. Other data is temporary subscriber data which may change as a result of normal operation of the system. The HLR contains all permanent subscriber data and all relevant temporary subscriber data for all mobile subscribers permanently registered in the HLR. The VLR contains all subscriber data required for call handling and other purposes for mobile subscribers currently located in the area controlled by the VLR. However, if the location areas associated with the network entities are small or a subscriber frequently moves between location areas, the subscriber movements will lead to a large signaling load. This is equally applicable to subscribers moving within their home network and to roaming subscribers for which additional international signaling costs are incurred. The Super-Charger concept is used to modify subscriber data handling to reduce the signaling load associated with roaming. The reduction in signaling load is achieved without introducing a new network node, but requires new functionality within the network. The aim of the Super-Charger concept is to reduce the mobility management costs associated with inter-VLR and SGSN location updates. Instead of canceling the subscriber data at the old VLR or SGSN when the subscriber moves to a location area served by a different VLR or SGSN, the Super-Charger concept suggests maintaining the subscriber data at the old VLR or SGSN so as to remove the need to use a cancel location procedure. The HLR then performs the normal insertion procedure of the subscriber data at the new VLR or SGSN, and maintains the subscriber data at the old VLR or SGSN. Therefore, no additional signaling is required. The mobile network benefits from this Super-Charger concept when the subscriber roams to a previously visited VLR or SGSN, since the user's subscription data is already present. In this case, provided that the subscription data is still valid, the need to perform the insert subscriber data procedure is removed. Consequently, the Super-Charger concept reduces mobility management costs by reducing the volume of location update signaling. This is of most benefit in metropolitan areas where the density of VLRs is high to cope with the large number of subscribers, and where subscribers regularly commute between location areas served by different VLRs. Assuming that the subscriber data has not changed since the last attach of the subscriber in the location area, the VLR has the option to use the subscriber data previously downloaded. As an example, during the morning commute in a Super-Charged network, the user's subscription data is retained by the VLR despite the move of the subscriber to another VLR. During the subsequent evening commute, the subscription data is retained by the VLR upon leaving the travel location, and an insert subscriber data procedure is not necessary at the home location, since the user's subscription data is already present at the VLR serving the home location. Thus, in a Super-Charged network, the subscriber information is no longer deleted from the VLR or SGSN data base when a mobile station leaves the area served by the VLR or SGSN. This results in a continuous growth of the VLR or SGSN data base size. Consequently, a new data management system is required so that the serving network entity can handle newly arrived mobile stations. Such a new data management system may be based on two options, i.e. the old subscriber data may either be deleted periodically using an audit system or may be deleted dynamically to make room for newly arrived subscribers. As already mentioned, the Super-Charger concept modifies the location update procedures to reduce the cost of inter- VLR and SGSN mobility management. In particular, a new pa- ra eter is added to the MAP UPDATE LOCATION and MAP UPDATE GPRS LOCATION messages, which indicates whether the VLR or SGSN requires subscriber data. The MAP MS PURGE message is no longer sent when inactive subscription data is removed from the VLR or SGSN data bases during data base management procedures. The subscriber's IMSI (International Mobile Subscriber Identity) is retrieved from the mobile station instead of the old VLR, wherein the authentication triplets are already available in the data base serving the mobile station. Thus, a communication of the authentication trip- lets from the old VLR is not required. In order to support the subscriber identity confidentiality service, the VLRs allocate a unique TMSI (Temporary Mobile Subscriber Identity) to visiting mobile subscribers. There- fore, the VLR is capable of correlating the IMSI of a mobile station and the current TMSI for that mobile station. Similarly, in GPRS (General Packet Radio Service) networks, a packet TMSI (P-TMSI) is used for identifying a mobile station. If old and new location areas are managed by dif- ferent VLRs or SGSNs, the old VLR or SGSN is not made aware of the fact that the subscriber has left its service area in a Super-Charged environment. Thus, the efficiency of the TMSI management in the VLR or the SGSN is decreased, since the TMSI or P-TMSI value range is a limited resource. According to a proposed solution in Super-Charged networks, the above problem is alleviated by a timer approach, according to which the TMSI or P-TMSI is only valid for a certain specified period of time after the last contact be- tween the mobile station and the network. However, this so- lution leads to the drawback of an enormous binding of network resources. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method and network entity for performing a location update in a Super-Charged environment, by means of which the management efficiency of the subscriber identity can be increased while requiring less network resources. This object is achieved by a method for performing a location update in a Super-Charged environment of a mobile net- work, said method comprising the steps of: transmitting a location update request message from a new network entity serving a mobile terminal to said mobile network; transmitting a release message from the mobile network to an old network entity having served the mobile terminal before, in response to the receipt of the location update request message; and releasing a subscriber identity allocated to the mobile terminal at the old network entity in response to the re- ceipt of the release message. Additionally, the above object is achieved by a network entity for performing a location update procedure for a mobile terminal in a Super-Charged environment of a mobile network, said network entity comprising: detecting means for detecting a location update request message received from the mobile network; message generation means for generating a release message in response to the detection result of the detection means, the release message being a request to release a subscriber identity allocated to the mobile terminal; and transmitting means for transmitting the release message to an old network entity having served the mobile terminal. Furthermore, the above object is achieved by a network entity for performing a location update procedure for a mobile terminal in a Super-Charged environment of a mobile network, said network entity comprising: receiving means for receiving a release message from the mobile network; release means for releasing a subscriber identity allocated to the mobile terminal in response to the receipt of the release message; and memory control means for maintaining subscriber data corresponding to the subscriber identity, irrespective of the release of the subscriber identity. Accordingly, subscriber identity numbers are released or de-allocated while still maintaining the corresponding subscriber data in the old network entity. Thus, although subscription data of the subscribers are still available to reduce the signaling load in the networks due to location update procedures, the subscriber identities are released and can be re-allocated when the subscriber moves to a new location area managed by a different network entity. Thus, the efficiency of the subscriber identity management in the network entities can be increased without requiring additional timer functions or audit systems. Preferably, the release message is transmitted from a home location register. The subscriber identity may be a TMSI or a P-TMSI. The network entity may be a VLR or a SGSN. Furthermore, the release message may be a cancel location operation. BRIEF DESCRIPTION OF THE DRAWINGS In the following, the present invention will be described in greater detail on the basis of a preferred embodiment with reference to the accompanying drawings, in which: Fig. 1 shows a basic block diagram indicating network components participating at a location update procedure, Fig. 2 shows a transmission diagram indicating message flows for an inter-VLR location update in a Super-Charged GSM network according to the preferred embodiment of the present invention, Fig. 3 shows a basic block diagram of a network entity for performing a location update procedure according to the preferred embodiment of the present invention, and Fig. 4 shows a basic block diagram of another network en- tity for performing a location update procedure according to the preferred embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENT The preferred embodiment will now be described on the basis of a GSM system as shown in Fig. 1. According to Fig. 1, the Super-Charged GSM network com- prises a HLR 4 arranged at the home PLMN of a mobile terminal or mobile station (MS) 1. In the HLR 4, the subscription data of the MS 1 is permanently stored. In the present case shown in Fig. 1, the MS 1 is moving from a location area served by an old VLR 30 to a new location area served by a new VLR 31. The connection between the MS 1 and the old VLR 30 or the new VLR 31 is established via an old Base Station Subsystem (BSS) 20 and a new BSS 21, respectively. In particular, the BSS is a sub-system of the Base Station equipment, i.e. transceivers, controllers, etc., which is viewed by the network through a single interface. The HLR 4 is a data base in charge of the management of the MS 1 and other mobile subscribers. The PLMN may contain one or several HLRs, depending on the number of mobile subscribers, the capacity of the equipment and the organization of the network. The main subscription information stored in the HLR 4 concerns the location of the MS 1 in order to be able to route calls to the MS 1. All management interventions occur on this data base. When the MS 1 is roaming in a location area of the network, it is controlled by a VLR in charge of this area. When the MS 1 appears in the location area of the new VLR 31, it starts a location updating procedure. A Mobile Switching Center (MSC, not shown) in charge of that area notices this registration and transfers the identity of the location area where the MS 1 is situated to the new VLR 31. According to the preferred embodiment, the new VLR 31 transmits a location update request to the HLR 4 in response to the receipt of a location update request from the MS 1. Then, the HLR 4 transmits a release command to the old VLR 30, which may be acknowledged by the old VLR 30. Then, the HLR 4 transmits a location update acknowledgment to the new VLR 31 to thereby terminate the location update procedure. Having received the release command, the old VLR 30 may release the allocation of the TMSI to the MS 1. Thus, even in the Super-Charged environment, the old VLR 30 is aware of the fact that the MS 1 has left its location area. In the above-described case shown in Fig. 1, the subscription data of the MS 1 is already available at the new VLR 31, since the location area of the new VLR 31 has been pre- viously visited by the MS 1, as in the case of the described evening commute. In case the MS 1 roams to a new location area not previously visited, the HLR 4 performs the normal insert subscriber data procedure at the new VLR 31, wherein the subscriber data is maintained at the old VLR 30. Fig. 2 shows a transmission diagram of the message flow in the above-described case of Fig. 1. As already mentioned, it is assumed in this example that the MS 1 has previously visited the location area served by the VLR 31. According to Fig. 2, the MS 1 transmits a location update request to the new VLR 31, wherein the location update request contains a LAI (Location Area Identity) of the location area served by the old VLR 30. Then, the new VLR 31 transmits an Identity Request to the MS 1 in order to request the mobile station to provide its IMSI transmitted with a subsequent Identity Response from the MS 1 to the new VLR 31. Then, an authentication signaling is performed. Provided that the authentication signaling was successful, the new VLR 31 transmits an Update Location Request indicating that no subscription data is required to the HLR 4. In response to the receipt of the Update Location Request from the new VLR 31, the HLR 4 performs a check of the subscriber data as regards any change requiring an update procedure of the subscription data. Thereafter, the HLR 4 transmits a release command to the old VLR 30 in order to trigger the release of the TMSI at the old VLR 30. This release command may be a modified MAP-operation Cancel Location. In the following, an example of an ASN.l (Abstract Syntax Notation One) description of such a Cancel Location Modification is given: CancelLoca tionArg ;;= [3] SEQUENCE { Iden ti ty Iden ti ty, Cancella tionType Cancella tionType OPTIONAL, ExtensionContainer ExtensionCon tainer OPTIONAL, temporarylden ti tyManagemen t Temporarylden ti tyManagemen t Temporarylden ti tyManagemen t : : = ENUMERATED { Release TMSI (0) , Release P-TMSI (1) , ) The release command may be acknowledged by the old VLR 30 using a Release Acknowledgment message. Then, the HLR 4 transmits an Update Location Acknowledgment message to the new VLR 31 to thereby indicate the successful completion of the location update procedure. Thus, the above-described location update procedure according to the preferred embodiment of the present invention leads to the advantage that the old VLR 30 releases the TMSI allocated to the MS 1, such that the TMSI is now again available for new MSs entering the location area of the old VLR 30. Fig. 3 shows a basic block diagram of a network entity such as a VLR or an SGSN serving a predetermined location area. According to Fig. 3, the network entity comprises a transceiver (TRX) 301 arranged for transmitting and receiving subscriber data or messages to or from a mobile network. In case a new MS having not previously entered the location area requests a location update, a location update procedure is performed, wherein subscription data is received by the TRX 301 from the HLR 4 and stored into a data base 303 via a memory control unit 302 arranged for controlling reading and writing into the database 303. Furthermore, a TMSI release unit 304 is provided and connected to the reception output of the TRX 301. The TMSI release unit 304 is arranged to detect a release command re- ceived from the HLR 4 and to control the memory control unit 302 so as to release the respective TMSI allocated to a subscriber indicated in the release message. In response thereto, the memory control unit 302 releases or deallocates the TMSI which may then be allocated to a new subscriber. Fig. 4 shows a basic block diagram of the HLR 4 or any other network entity provided as a data base in charge of the management of mobile subscribers. According to Fig. 4, the network entity comprises a transceiver (TRX) 41, arranged for transmitting and receiving subscriber data or messages from or to the mobile network. Furthermore, a message detection unit 42 is provided, which is arranged to detect a location update request message received from the mobile network and to output a corresponding indication to a message generation unit 43. Based on the subscriber information included in the location update request message and supplied from the message detection unit 42, the message generation unit 43 generates a release message indi- eating the IMSI of the respective subscriber requesting the location update. The release message is supplied to the TRX 41 in order to be transmitted via the mobile network to the old VLR or SGSN having served the mobile subscriber. It is to be noted that the basic block diagrams shown in Figs. 3 and 4 only comprise those components essential for performing the functions required for the present invention. Any other components of the shown network entities have been omitted for reasons of simplicity. Furthermore, it is noted that the functions of the respective blocks shown in Figs. 3 and 4 may be achieved by corresponding sub-routines of a control program controlling a processing unit, e.g. CPU, arranged in the respective network entity. In summary, the present invention relates to a method and network entity for performing a location update in a Super- Charged environment of a mobile network, wherein a release message is transmitted from the mobile network to an old network entity having served a mobile terminal, in response to a location update request message received from a new network entity 31 serving the mobile terminal 1. A subscriber identity allocated to the mobile terminal 1 at the old network entity 30 is released or de-allocated in re- sponse to the receipt of the release message. Thus, even in a Super-Charged environment, the old network entity is informed of the fact that the mobile terminal 1 has left its service area, and may re-allocate the subscriber identity which has been allocated to the mobile terminal 1. It is pointed out that the present invention is not limited to the preferred embodiment described above. It can be applied in any mobile network where a location update is performed in respective network entities. Thus, the above de- scription of the preferred embodiment and the accompanying drawings are only intended to illustrate the present invention. The preferred embodiment of the invention may thus vary within the scope of the attached claims.

Claims: Claims 1. A method for performing a location update in a Super- Charged environment of a mobile network, said method com- prising the steps of: a) transmitting a location update request message from a new network entity (31) serving a mobile terminal (1) to said mobile network; b) transmitting a release message from said mobile network to an old network entity (30) having served said mobile terminal (1) before, in response to the receipt of said location update request message; and c) releasing a subscriber identity allocated to said mobile terminal (1) at said old network entity (30) in response to the receipt of said release message. 2. A method according to claim 1, wherein said release message is transmitted from a home location register (4) . 3. A method according to claim 1 or 2, wherein said subscriber identity is TMSI or a P-TMSI. 4. A method according to any one of the preceding claims, wherein said old and new network entities are visitor loca- tion registers (30, 31) . 5. A method according to any one of the preceding claims, wherein said old and new network entities are Serving GPRS Support Nodes. 6. A method according to any one of the preceding claims, wherein subscriber data corresponding to said released subscriber identity are maintained in said old network entity (30) . 7. A method according to any one of the preceding claims, wherein said release message is a cancel location operation. 8. A network entity for performing a location update procedure for a mobile terminal (1) in a Super-Charged environment of a mobile network, said network entity comprising: a) detecting means (42) for detecting a location update re- quest message received from said mobile network; b) message generation means (43) for generating a release message in response to the detection result of said detection means (42) , said release message being a request to release a subscriber identity allocated to said mobile ter- minal (1) ; and c) transmitting means (41) for transmitting said release message to an old network entity (30) having served said mobile terminal (1) . 9. A network entity according to claim 8, wherein said network entity is a home location register (4) . 10. A network entity according to any one of claims 8 to 9, wherein said old network entity is a visitor location reg- ister (30) or an SGSN. 11. A network entity according to any one of claims 8 to 10, wherein said subscriber identity is a TMSI or a P-TMSI. 12. A network entity according to any one of claims 8 to 11, wherein said release message is a cancel location operation. 13. A network entity for performing a location update pro- cedure for a mobile terminal (1) in a Super-Charged envi- ronment of a mobile network, said network entity comprising: a) receiving means (301) for receiving a release message from said mobile network; b) release means (304) for releasing a subscriber identity allocated to said mobile terminal (1) in response to the receipt of said release message; and c) memory control means (302) for maintaining subscriber data corresponding to said subscriber identity, irrespec- tive of said release of said subscriber identity. 14. A network entity according to claim 13, wherein said subscriber identity is a TMSI or a P-TMSI. 15. A network entity according to claim 13 or 14, wherein said network entity is a visitor location register (30) or a SGSN. 16. A network entity according to any one of claims 13 to 15, wherein said release message is a cancel location operation.

Inventors: MAEKINEN TEEMU, MUHONEN AHTI, MAEKINEN, TEEMU, MUHONEN, AHTI
Applicants: MAEKINEN TEEMU, MUHONEN AHTI, NOKIA NETWORKS OY, MAEKINEN, TEEMU, MUHONEN, AHTI
Application year: 1999
Main classification: H04Q7
IPC codes: H04W8, H04W60