Title of Invention	METHOD AND SYSTEM FOR DETERMINING THE LOCATION OF A MOBILE SUBSCRIBER REGISTERED IN A CELLULAR MOBILE RADIO NETWORK
Abstract	Method and system for determining the location of a mobile subscriber registered in a cellular mobile radio network A lower signalling load and shorter connecting delay compared with the known two-stage location interro-gation is achieved in the case of optimal routing due to the fact that the home location register (HLRB) itself, when receiving the message (SRIL) for location interroga-tion, checks the feasibility of setting up the direct connection between gateway mobile switching centre (GMSCA) of a first network (IPLMN) and visited mobile switching centre (VMSCB) of another network (VPLMN) for reasons of charging for the call and, if the result of the check is positive, sends a modified message which additionally contains a code (PRN) for requesting a temporary mobile subscriber roaming number (MSRN) to the visitor location egister (VLRB). As a result, the home location register can carry out the feasibility check of setting up the connection for reasons of charging for the call already after the first reception of a location interrogation and call up immediately i.e. without waiting for another location interrogation by the gateway mobile switching centre the mobile subscriber roaming number from the responsible visitor location register and send it to the requesting gateway mobile switching centre.

Title of Invention

METHOD AND SYSTEM FOR DETERMINING THE LOCATION OF A MOBILE SUBSCRIBER REGISTERED IN A CELLULAR MOBILE RADIO NETWORK

Abstract

Method and system for determining the location of a mobile subscriber registered in a cellular mobile radio network A lower signalling load and shorter connecting delay compared with the known two-stage location interro-gation is achieved in the case of optimal routing due to the fact that the home location register (HLRB) itself, when receiving the message (SRIL) for location interroga-tion, checks the feasibility of setting up the direct connection between gateway mobile switching centre (GMSCA) of a first network (IPLMN) and visited mobile switching centre (VMSCB) of another network (VPLMN) for reasons of charging for the call and, if the result of the check is positive, sends a modified message which additionally contains a code (PRN) for requesting a temporary mobile subscriber roaming number (MSRN) to the visitor location egister (VLRB). As a result, the home location register can carry out the feasibility check of setting up the connection for reasons of charging for the call already after the first reception of a location interrogation and call up immediately i.e. without waiting for another location interrogation by the gateway mobile switching centre the mobile subscriber roaming number from the responsible visitor location register and send it to the requesting gateway mobile switching centre.

Full Text	2A Description The invention relates to a method and a system for determining the location of a mobile subscriber registered in a cellular mobile radio network, for optimized routing in the case of an incoming call directed to the mobile subscriber. A cellular mobile radio network such as, for example the "digital'ladio communication system defined in accordance with the GSM standard-(Global System for Mobile Communication) is built up of a large number of"radio cells and provides a mobile subscriber with a maximum degree of mobility in the context of radio communication. The cross-border international mobileradio network according to the GSM standard has a base station for setting up and clearing down and maintaining radio links between mobile subscriber stations and base stations, a switching system for setting up, administering and releasing connections taking into consideration mobility-specific functions and an operating and maintenance system for monitoring operating conditions and for controlling the network components arranged distributed in the mobile radio network. The tasks of the switching system include the administration of the subscriber data of the mobile subscribers, finding the location of a called mobile subscriber or, respectively, of his mobile subscriber station anywhere in the GSM coverage area, setting up the connection and registering the call-charge data for outgoing calls from the mobile subscriber for incoming calls at the mobile subscriber. To carry out its tasks, the switching system has mobile switching centres which handle especially the mobility-related methods and functions during the setting up and clearing down of connections and during the processing of a connection within the mobile radio network and at the interfaces to other communication networks, and has visitor location registers and home location registers, the visitor location register of which temporarily contains the subscriber data of the mobile subscribers currently located within the coverage area of an associated mobile switching centre whilst in the home location register the subscriber data of the mobile subscribers are permanently administered. The subscriber data specify the subscriber profile, i.e. the services and authorizations booked by the mobile subscriber. In addition, the home location register stores information on the identification of the visitor location register in which the mobile subscriber is currently being administered because he is located there. As a rule, this is the address of the visitor location register or of the mobile switching centre so that the location of the mobile subscriber can be determined by a location request directed from the mobile switching centre to the home location register. The home location register can use the address of the currently responsible visitor location register for interrogating a mobile subscriber roaming number which is needed for being able to set up a connection from a gateway mobile switching centre to a visited mobile switching centre. To support optimal routing in the GSM mobile radio network, the gateway mobile switching centre of a first network can send an internetwork message for location interrogation to the home location register of another network in which the called mobile subscriber is permanently registered with his subscriber data according to GSM Recommendation 03.79, version 0.9.0 of 31.07.1996. The purpose of the location interrogation lies in a provision of information by means of which the gateway mobile switching centre can set up a direct connection to a visited mobile switching centre of another network in which the called mobile subscriber is currently regis- tered due to him being located there. According to the above-mentioned GSM Recommenda-t ion 03.79, support of optimal routing requires a two-Ht-^p. initially the gateway mobile switching centre only calls up information on the location of the called mobile subscriber, e.g. in the form of the address of the responsible visited mobile switching centre, by means of a first interrogation {send location info) directed to the home location register of the other network. For this purpose, the home location register sends a message for interrogating subscriber information (provide subscriber info) to the visitor location register currently responsible for the mobile subscriber and receives a message (provide subscriber info acknowledge) as acknowledgement. Following this, the home location register sends information for identifying the visited mobile switching centre in a message (send location info acknowledge), by means of which the first interrogation is acknowledged, back to the gateway mobile switching centre. After that, the gateway mobile switching centre checks whether there are any impediments, for charging reasons, to a direct connection to the visited mobile switching centre. The requirements for the charging of the call when supporting optimal routing are described in Chapter 9.1 on page 24 in GSM Recommendation 03.7 9._ If the result of the check is positive, the gateway mobile switching centre directs a second location request (send routing info) to the home location register in order to request the mobile subscriber roaming number from the visitor location register. The advantage of the two-stage location interrogation which must be initiated in each case by the gateway mobile switching centre lies in the fact that the mobile subscriber roaming number is only requested by the visitor location register if, after the charging requirements have been checked, the utilization of a mobile subscriber roaming number for setting up the connection is ensured and thus the issuing of mobile subscriber roaming numbers which remain unused because -4- the charging requirements have not been met is avoided. It is; tiie object of the invention to specify a method and a system of the type initially mentioned by means of which the location interrogation can be improved with respect to signalling toad and connecting delay for optimal routing. According to the invention, this object of improving the location interrogation with respect to a lower signalling bad and shorter connecting delay compared with the known two-stage location interrogation is achieved by the fact that the home location register itself, when it receives the message for location interrogation, checks the feasibility of setting up the direct connection between the gateway mobile switching centre and the visited mobile switching centre and, with a positive result of the check, sends a modified message, which additionally contains a code for requesting a temporary mobile subscriber roaming number, to the visitor location register. As a result, the home location register can carry out the feasibility check of setting up the connection for reasons of charging for the call already after the first reception of a location interrogation and call up immediately i.e. without waiting for another location interrogation according to the known method described - the mobile subscriber roaming number from the responsible visitor location register and send it to the requesting gateway mobile switching centre. The advantage of the known solution of ensuring that only those temporary mobile subscriber roaming numbers which are actually needed are assigned and occupied is retained in the method according to the invention. The additional advantages of the invention consist in a lower signalling load due to the omission of a number of signalling messages which are required between the components for supporting the optimal routing in the two-stage location interrogation, and in a faster -5- setting up of the connection in the case of a direct connection between mobile switching centres of a first and second network. ""~~~""3£cc0r"ding to a further development of the invention, the visitor location register checks the message provided for interrogating subscriber information for the presence of the code and, if the result of the check is positive, issues a mobile subscriber roaming number which is sent back additionally to the home location register in a message by means of which the interrogation is acknowledged. The visitor location_ register advantageously carries out the check of the message for_ interrogating subscriber information only in the case where the mobile subscriber can be reached. According to a further development of the invention, the home location register sends a message back to the gateway mobile switching centre, by means of which the location interrogation is acknowledged and additionally the mobile subscriber roaming number issued by the visitor location register on request is transmitted. It is of advantage if the gateway mobile switching centre checks the incoming message for the existence of a mobile subscriber roaming number so that, in the case of a positive result of the check, the mobile subscriber roaming number is used for setting up the direct connection to the visited mobile switching centre or, if the result of the check i s nagative a second message for location interrogation is sent to the home location register . Thus both the known method and the novel and inventive method can exist independently of one another and side by side. In the case where a temporary mobile subscriber roaming number has already been transmitted after the first location interrogation from the home location register, the second location interrogation according to the two-stage known method is skipped and the direct connection for the optimal routing can already be set up early directly by means of the temporary mobile subscriber roaming number already available. - 6 - The invention will be explained with reference to an illustrative embodiment shown in, in which, in detail, Figure 1 shows in a block diagram the flow of messages between the network facilities affected by the location interrogation for internetwork optimal routing, and Figure 2 shows in a flow chart the processing of the location interrogation by the home location register in the home network of the called mobile subscriber. Using as an example the international cellular mobile radio network according to the GSM standard, the block diagram in Figure 1 shows the sequence for deter- mining the location of a mobile subscriber registered in the cellular mobile radio network. _ In this process, optimal routing for the mobile terminated call is supported. In the clinical present example, it shall be assumed that this is a call which is initiated by a mobile subscriber A and is directed to the mobile subscriber B (mobile-to-mobile call). Mobile subscriber A is located within the coverage area of a first network IPLMN whilst mobile subscriber B is permanently registered with his subscriber data in another network HPLMN and is temporarily registered in another network VPLMN due to his current location. For the called mobile subscriber B, the HPLMN network represents his home PLMN and the VPLMN network represents his visited PLMN. For the sake of simplicity, it will also be assumed that the networks IPLMN, HPLMN, and VPLMN have an identical network structure corresponding to the international GSM mobile radio network,. but are operated by corresponding network operators in different countries. Thus, it will be assumed, for example, that mobile subscriber A is calling from a mobile radio network in Germany and mobile subscriber B has his home in the mobile radio network of Switzerland but is registered as visitor in the mobile radio network of Austria due to his current location. The block diagram shows a visited mobile switch- - 7 - ing centre VMSCA and a gateway mobile switching centre GMSCA in the IPLMN network, a home location register HLRB in a HPLMN network and a visitor location register VLRB and a visited mobile switching centre VMSCB in the VPLMN network. In the present example, the incoming call directed to mobile subscriber B is initiated by a mobile subscriber A which is located in the coverage area of the visited mobile switching centre VMSCA when the call is initiated. Naturally, it is also possible that the call is started by a line-connected party A - for example from the public switched telephone network (PSTN). Both alternatives have in common that the call is forwarded to the gateway mobile switching centre GMSCA which is arranged at the interface to other networks in the IPLMN network. In addition, visited mobile switching centre VMSCA and gatway mobile swiching centre GMSCA can also be collocated. On the basis of the subscriber call number of mobile subscriber B, dialled by mobile subscriber A by entering it in a mobile subscriber station, the visited mobile switching centre VMSCA receives a (call setup) message via the corresponding base station system in the IPLMN network for setting up a signalling connection (1). The visited mobile switching centre VMSCA sends a request for processing an outgoing call to a visitor location register (not shown), which signals to the visited mobile switching centre VMSCA the permission for setting up the signalling connection. The visited mobile switching centre VMSCA thereupon sends a message IAM (initial address message according to the ISDN user part (ISUP) which is used on the connecting lines between the mobile (switching centres, to the gateway mobile switching centre GMSCA (2). For the present case where the gateway mobile switching centre GMSCA is located in another network than the home network of mobile subscriber B, an SRIL message for interrogating the location is sent from the gateway mobile switching centre GMSCA to the home location register HLRB in the home network HPLMN. This location interrogation (send location info) contains a note that - 8 - this is an enquiry for location information in the context of optimal routing. In this process, the SRIL messages is transmitted in accordance with a mobile radio-specific application part (MAP) (3). After receiving the SRIL message, the home location register HLRB checks whether setting-up of the direct connection between the gateway mobile switching centre GMSCA in the IPLMN network and the visited mobile switching centre VMSCP in the other network VPLMN is feasible for reasons of charging for the call. This check consists, for example, of a comparison of country codes which are allocated to the gateway mobile switching centre GMSCA and the visited mobile switching centre VMSCB or, respectively, the home location register HLRB. The charging requirements are specified in this case in such a manner that the charges for a call which is processed in accordance with optimal routing must not be higher than for a call which is conducted via the home network of the called mobile subscriber as in the case of conventional routing. The home location register HLRB therefore checks a country code associated with the visited mobile switching centre VMSCB, on the one hand, with a country code CCH of the home location register HLRB and, on the other hand, with a country code CCI of the gateway mobile switching centre GMSCA. If at least one comparison supplies identity of the countries which corresponds to a positive result of the comparison, the home,location register HLRB determines that setting-up of a direct connection according to optimal routing is possible without violating the requirements with respect to charging for the call. The country codes provide the home location register HLRB with a very simple way of determining whether at least two of the three network facilities affected by the location interrogation and the setting up of the connection are arranged in one and the same country (4). The country code comparison only represents a simple measure for checking whether there are no objections for setting up a direct connection for reasons of - 9 - charging for the call. More elaborate measures for supporting or rejecting the optimal routing for the direct connection of mobile switching centres of different networks can be easily implemented in the home location register HLRB but can also be shifted, as an alternative, to the gateway mobile switching centre which starts the location interrogation, without adversely affecting thereby the principle of determining the location in accordance with the invention. When more elaborate checking measures are shifted to the gateway mobile switching centre, the simple checking capability by country code comparison can remain in the respective home location register. Due to the fact that, according to the invention, the home location register HLRB itself carries out the country code comparison, a modified message PSI can be sent immediately, i.e. without waiting for any further location interrogation from the gateway mobile switching centre GMSCA, to the visitor location register VLRB in the VPLMN network if the result of the comparison is positive. The modified message PSI' (provide subscriber info) is normally used for interrogating subscriber information of the mobile subscriber B and, according to the invention, additionally contains a code PRN for requesting a temporary mobile subscriber roaming number MSRN which is issued by the visitor location register VLRB. The previous check of the feasibility of setting-up a direct connection with respect to charging for the call by the home location register HLRB guarantees that, immediately after the positive result of the check is available, the temporary mobile subscriber roaming number is only reque.sjted if it is sure that it is also needed. This prevents unnecessary issuing of unused temporary mobile subscriber roaming numbers by the visitor location register in each case responsible for the called mobile subscriber B. Before the home location register HLRB sends out the modified message PSI' with the new code PRN according to the mobile-radio specific application part (MAP) to the visitor location register VLRB, it is first - 10 - determined, to be on the safe side, whether or not the visitor location register VLRB supports optimal routing. If the result of the comparison in the home location register HLRB does not provide a correspondence of country codes so that a direct connection between the mobile switching centres GMSCA and VMSCB is not wanted for reasons of charging, the home location register HLRB sends the usual PSI (provide subscriber info) message to the visitor location register VLRB, by means of which the subscriber information is requested (5). In the last-mentioned case, the visitor location register VLRB checks whether the mobile subscriber B is available, i.e. whether his mobile subscriber station is in a switched-off state, in a busy state or the like. The visitor location register VLRB checks every message coming from the home location register HLRB, by means of which subscriber information is requested, for the presence of the PRN code, which means that this is a modified message PSI' for requesting a temporary mobile subscriber roaming number MSRN. If this is so, the visitor location register VLRB issues a temporary mobile subscriber roaming number MSRN which is used for setting up the connection between the gateway mobile switching centre GMSCA and the visited mobile switching centre VMSCB and is released again for further connection setting-up processes after the setting-up of the connection has ended. The visitor location register VLRB checks the incoming message PSI or PSI', respectively, for the presence of the code PRN only if mobile subscriber B can be reached via his mobile subscriber station, i.e. the mobile subscriber station is not in a switched-off state or a state cut-off from mobile coverage (detach status) (6) . If the visitor location register VLRB has not been requested for issuing and transmitting a temporary mobile subscriber roaming number MSRN, it sends a message PSIA to the home location register HLRB, which informs about the status of mobile subscriber B. If, however, the mobile subscriber roaming number MSRN has been issued by -li- the visitor location register VLRB, it is transferred to the home location register HLRB in a message PSIA' , in addition to the information on the status of mobile subscriber B. The visitor location register VLRB acknowledges the interrogation of subscriber information (PSI or PSI', respectively) by the home location register HLRB with the message PSIA or PSIA', respectively (7). If the home location register HLRB receives information that mobile subscriber B is available in the message PSIA as acknowledgement, a message SRILA is generated since no temporary mobile subscriber roaming (number MSRN has been received, and is sent back as acknowledgement for the location interrogation SRIL to the gateway mobile switching centre GMSCA. At the same time, information for identifying the visited mobile switching centre VMSCB responsible for mobile subscriber B is also sent along in the SRILA message. This information preferably consists of the address AVM of the visited mobile switching centre VMSCB. If the home location register HLRB receives a 'temporary mobile subscriber roaming number MSRN from the visitor location register VLRB, a message SRILA' is generated by means of which the location interrogation SRIL is acknowledged and additionally the mobile subscriber roaming number MSRN provided is transmitted in addition to the address AVM to the gateway mobile switching centre GMSCA (8). The gateway mobile switching centre GMSCA receives in the acknowledgement message sent by the home location register HLRB the address of the visited mobile switching centre VMSCB to which the connection is to be set up, cind additionally checks whether the acknowledgement message also contains a temporary mobile subscriber roaming number MSRN. If this is so, the received mobile subscriber roaming number MSRN is used to set up the direct connection according to the optimal routing between gateway mobile switching centre GMSCA and visited mobile switching centre VMSCB and the message IAM trans-mitted to the visited mobile switching centre in accordance with the ISDN user part ISUP (9). - 12 - In this manner, a direct connection- for supporting optimal routing between mobile switching centres of different networks can be set up in the case of a B mobile terminated call, in which, for determining the location of mobile subscriber B, a lower signalling load between the network facilities and a shorter connecting delay is achieved compared with the known method. Reduction of the signalling load and shortening of the connecting delay is possible due to the fact that the home location register HLRB itself can check the feasibility of the direct connection with respect to the charging requirements and, in the case of a positive result of the check, immediately, i.e. without waiting for any further location request by the gateway mobile switching centre, request a temporary mobile subscriber roaming number from the visitor location register in each case currently responsible for mobile subscriber B and can send it back to the gateway mobile switching centre for setting up the connection. In the case where the gateway mobile switching centre GMSCA does not receive a mobile subscriber roaming number MSRN in the acknowledgement message SRILA, a second location interrogation SRIR (send routing info) can be sent to the home location register HLRB in order to obtain a mobile subscriber roaming number MSRN, possibly in a second stage. The last-mentioned procedure is preferably used when home location registers are used in home networks which are not operated in accordance with the method of the present invention. Figure 2 shows a flow chart for processing the location request for determining the location of mobile subscriber B by the home location register HLRB in which the called mobile subscriber B is permanently stored with his subscriber data.. Firstly, the home location register HLRB checks whether the message SRIL is received with which the internetwork location interrogation from the gateway mobile switching centre of another network arrives in the home network. When receiving the message SRIL, the home location register HLRB first determines - 13 - whether the visitor location register VLRB currently-responsible for the called mobile subscriber B basically supports the setting-up of a direct connection between mobile switching centres of different networks in accordance with optimal routing OR. If this is not so, the home location register HLRB generates an error message which signals that optimal routing OR is not allowed. If the addressed visitor location register VLRB supports optimal routing OR, the home location register HLRB checks whether the setting-up of the direct connection between the gateway mobile switching centre and the visited mobile switching centre is feasible for reasons of charging for the call. The checking is done simply by comparing the country codes of the two mobile switching centres or the country codes of the home location register and the visited mobile switching centre. If at least one comparison does not supply identical country codes, the home location register HLRB sends the message PSI to the visitor location register VLRB in order to call up subscriber information. During the check of the subscriber status by the visitor location register VLRB, the home location register HLRB is in a wait state which is maintained until the visitor location register VLRB receives the message PSIA with which the visitor location register VLRB signals the status of mobile subscriber B or of his mobile subscriber station, respectively. If the called mobile subscriber B is in a state in which he cannot be reached (detach status), for example due to a disconnected mobile subscriber station or a lack of radio coverage, the location interrogation is aborted. If mobile subscriber B can be reached, the home location register HLRB provides the address AVM of the visited mobile switching centre VMSCB as routing information or routing address, respectively, and sends it back to the gateway mobile switching centre GMSCA in the message SILA. The home location register HLRB uses the message SRILA to acknowledge the location interrogation initiated by the gateway mobile switching centre, which can be - 14 - recognized from the incoming message SRIL. If the comparison of the respective country codes by the home location register HLRB shows that there are no requirements opposing the setting up of a direct connection between the two mobile switching centres according to optimal routing for reasons of charging for the call, the home location register HLRB sends out the modified message PSI' with an additional code PRN to the responsible visitor location register VLRB immediately after the check. The code PRN here signals the request for a temporary mobile subscriber roaming number MSRN which is temporarily issued by the visitor location register VLRB due to it being responsible for mobile subscriber B for setting up the connection between mobile subscriber A and mobile subscriber B. During the allocation of the temporary mobile subscriber roaming number MSRN from a predetermined set of numbers, the home location register HLRB is in a wait state which is ended when the message PSIA' is received. The message PSIA' is used as acknowledgement for the message PSI' which has previously arrived. The temporary mobile subscriber roaming number MSRN allocated by the visitor location register VLRB is sent back to the home location register HLRB as additional parameter in the message PSIA'. The home location register HLRB then sends the message SRILA' with the mobile subscriber roaming number MSRN back to the gateway mobile switching centre GMSCA in order to acknowledge the location interrogation, which can be recognized from the incoming message SRIL and to signal the support of optimal routing to the gateway mobile switching centre. The gateway mobile switching centre GMSCA can use the incoming mobile subscriber roaming number MSRN for setting up a direct connection to the visited mobile switching centre VMSCB. Further setting-up of the connection via the base station system in the network currently responsible for mobile subscriber B is carried out by using known methods which are not affected by the present invention. Due to the check of feasibility of setting up a direct connection between mobile switch- - 15 - ing centres across the boundaries of networks and by immediately requesting a temporary mobile subscriber roaming number by the home location register in each case responsible for the called mobile subscriber B in his home network if the result of the check is positive, the signalling load can be reduced and the connecting delay shortened. - 16 - 1/ Method for determining the location of a mobile subscriber registered in a cellular radio network for optimal routing in the case of a mobile terminated call, in which - on the basis of the subscriber call number of the called mobile subscriber, an internetwork message (SRIL) for interrogating location is sent from a gateway mobile switching centre (GMSCA) of a first network (IPLMN) to a home location register (HLRB) of another network (HPLMN) in which the mobile subscriber is permanently registered with his subscriber data, - the home location register (HLRB) directs a message {PSI or PSI') for interrogating the location to a visitor location register ,(VLRB) of a further network (VPLMN) in which the mobile subscriber is currently registered due to his current location and allocates a visited mobile switching centre (VMSCB) to the visitor location register (VLRB), and in which - for supporting optimal routing, a check is made whether a direct connection can be established between the gateway mobile switching centre (GMSCA) and the visited mobile switching centre' (VMSCB) for reasons of charging for the call, characterized in that when the message.(SRIL) for location interrogation is received, the home location register (HLRB) checks the feasibility of setting up the direct connection and, if the result of the check is positive, sends a modified message (PSI') additionally containing a code (PRN) for requesting a temporary mobile subscriber roaming number (MSRN) to the visitor location register (VLRB). 2. Method according to Claim 1, characterized in that the visitor location register (VLRB) checks the message (PSI') for interrogating the location for the presence of the code (PRN) and, if the result of the check is positive, issues the mobile subscriber roaming number (MSRN) which is transmitted additionally to the GR 96 P 1998 - 17 - home location register (HLRB) in a message (PSIA' ) by-means of which the request is acknowledged. 3. Method according to Claim 2, characterized in that thejvisitor location register (VLRB) carries out the checking of the message (PSI or PSI') for interrogating the location only in the case where the mobile subscriber is obtainable. 4. Method according to one of Claims 1 to 3, charac terized in that the home location register (HLRB) sends back to the gateway mobile switching centre (GMSCA) a message (SRILA) by means of which the location interroga- tion is acknowledged and at least one information item (AVM)for identifying the visited mobile switching centre (VMSCB) is transmitted. 5. Method according to one of Claims l to 3, charac- terized in that the home location reqister (HLRB) sends back to the gateway mobile switching centre (GMSCA) a message (SRILA') by means.of which the location interro- gation is acknowledged and at least the mobile subscriber roaming number (MSRN) issued by the visitor location register (VLRB) on request is transmitted. 6. Method according to Claim 4 or 5, characterized in that the gateway mobile switching centre (GMSCA) checks the incoming message (SRILA or SRILA') for the presence of the mobile subscriber roaming number (MSRN) and that, if the result of the check is positive, the mobile subscriber roaming number (MSRN) is used for setting up the direct connection to the visited mobile switching centre (VMSCB) or, if the result of the check is negative, a second message (SRIR) for location inter rogation is sent to the home location register (HLRB). 7. Method according to one of the preceding claims, characterized in that the home location register (HLRB) checks the feasibility of setting-up the direct connec- tion by comparing country codes which can be allocated to the gateway mobile switching centre (GMSCA), the visited mobile switching centre (VMSCB) and the home location register (HLRB). 8. Method according to Claim 7, characterized in 5. - 18 - that the country code of the gateway mobile switching centre (GMSCA) is compared with the country code of the visited mobile switching centre (VMSCB) and that, if the two country codes are identical, the home location register (HLRB) requests the temporary mobile subscriber roaming number (MSRN) in the modified message (PSI'). 9. Method according to claim 7, characterized in that the country code of the home location register (HLRB) is compared with the country code of the visited mobile switching centre CVMSCB) and that, if the two country codes are identical, the home location register (HLRB) requests the temporary mobile subscriber roaming number (MSRN) in the modified message (PSI'). 10- A system for carrying out the method as claimed in claim 1 comprising: a gateway mobile switching centre (BNSCA) of a first network (IPLMN), for sending on the basis of the subscriber call number of the called mobile subscriber, an internetwork message CSRIL) far location interrogation to a home location register (HLRB) of another network (HPLMW) in which the mobile subscriber is registered permanently with his subscriber data, said home -19- location register(HLRB) being adapted for sending out a message (PSI or PSI') for interrogating the location to a visitor location register (VLRB) of another network (VPLMN) in which the mobile subscriber is currently registered due to his current location and a visited mobile switching centre (VMSCB) is al located to the visitor location register (VLRB), said horne alocation register (HLRB) additionally configured for supporting" optimal routing for determining whether a direct connection between the gateway mobile switching centre (GMBCA) and the visited mobile switching centre (VHSCB) can be set up for reasons of charging for the call, characterized in that said hone locatior adapted register (HLRB) is adapted for checking the feasibility of setting up the direct connection upon receipt of the message (SRIL) for location interrogation and, if the result of the check is positive, for sending a modified message (PSI*), which additionally contains a code (PRN) for requesting a temporary mobile subscriber roaming number (MSRN), to the visitor location register (VLRB). Method and system for determining the location of a mobile subscriber registered in a cellular mobile radio network A lower signalling load and shorter connecting delay compared with the known two-stage location interro-gation is achieved in the case of optimal routing due to the fact that the home location register (HLRB) itself, when receiving the message (SRIL) for location interroga-tion, checks the feasibility of setting up the direct connection between gateway mobile switching centre (GMSCA) of a first network (IPLMN) and visited mobile switching centre (VMSCB) of another network (VPLMN) for reasons of charging for the call and, if the result of the check is positive, sends a modified message which additionally contains a code (PRN) for requesting a temporary mobile subscriber roaming number (MSRN) to the visitor location egister (VLRB). As a result, the home location register can carry out the feasibility check of setting up the connection for reasons of charging for the call already after the first reception of a location interrogation and call up immediately i.e. without waiting for another location interrogation by the gateway mobile switching centre the mobile subscriber roaming number from the responsible visitor location register and send it to the requesting gateway mobile switching centre.

Full Text

2A
Description
The invention relates to a method and a system for determining the location of a mobile subscriber registered in a cellular mobile radio network, for optimized
routing in the case of an incoming call directed to the mobile subscriber.
A cellular mobile radio network such as, for example the "digital'ladio
communication system defined in accordance with the GSM standard-(Global
System for Mobile Communication) is built up of a large number of"radio cells
and provides a mobile subscriber with a maximum degree of mobility in the
context of radio communication. The cross-border international mobileradio
network according to the GSM standard has a base station for setting up and
clearing down and maintaining radio links between mobile subscriber stations
and base stations, a switching system for setting up, administering and releasing
connections taking into consideration mobility-specific functions and an operating
and maintenance system for monitoring operating conditions and for controlling
the network components arranged distributed in the mobile radio network. The
tasks of the switching system include the administration of the subscriber data of
the mobile subscribers, finding the location of a called mobile subscriber or,
respectively, of his mobile subscriber station anywhere in the GSM coverage
area, setting up the connection and registering the call-charge data for outgoing
calls from the mobile subscriber for incoming calls at the mobile subscriber. To
carry out its tasks, the switching system has mobile switching centres which
handle especially the mobility-related methods and

functions during the setting up and clearing down of connections and during the processing of a connection within the mobile radio network and at the interfaces to other communication networks, and has visitor location registers and home location registers, the visitor location register of which temporarily contains the subscriber data of the mobile subscribers currently located within the coverage area of an associated mobile switching centre whilst in the home location register the subscriber data of the mobile subscribers are permanently administered.
The subscriber data specify the subscriber profile, i.e. the services and authorizations booked by the mobile subscriber. In addition, the home location register stores information on the identification of the visitor location register in which the mobile subscriber is currently being administered because he is located there. As a rule, this is the address of the visitor location register or of the mobile switching centre so that the location of the mobile subscriber can be determined by a location request directed from the mobile switching centre to the home location register. The home location register can use the address of the currently responsible visitor location register for interrogating a mobile subscriber roaming number which is needed for being able to set up a connection from a gateway mobile switching centre to a visited mobile switching centre.
To support optimal routing in the GSM mobile radio network, the gateway mobile switching centre of a first network can send an internetwork message for location interrogation to the home location register of another network in which the called mobile subscriber is permanently registered with his subscriber data according to GSM Recommendation 03.79, version 0.9.0 of 31.07.1996. The purpose of the location interrogation lies in a provision of information by means of which the gateway mobile switching centre can set up a direct connection to a visited mobile switching centre of another network in which the called mobile subscriber is currently regis-

tered due to him being located there.
According to the above-mentioned GSM Recommenda-t ion 03.79, support of optimal routing requires a two-Ht-^p. initially the gateway mobile switching centre only calls up information on the location of the called mobile subscriber, e.g. in the form of the address of the responsible visited mobile switching centre, by means of a first interrogation {send location info) directed to the home location register of the other network. For this purpose, the home location register sends a message for interrogating subscriber information (provide subscriber info) to the visitor location register currently responsible for the mobile subscriber and receives a message (provide subscriber info acknowledge) as acknowledgement. Following this, the home location register sends information for identifying the visited mobile switching centre in a message (send location info acknowledge), by means of which the first interrogation is acknowledged, back to the gateway mobile switching centre.
After that, the gateway mobile switching centre checks whether there are any impediments, for charging reasons, to a direct connection to the visited mobile switching centre. The requirements for the charging of the call when supporting optimal routing are described in Chapter 9.1 on page 24 in GSM Recommendation 03.7 9._ If the result of the check is positive, the gateway mobile switching centre directs a second location request (send routing info) to the home location register in order to request the mobile subscriber roaming number from the visitor location register. The advantage of the two-stage location interrogation which must be initiated in each case by the gateway mobile switching centre lies in the fact that the mobile subscriber roaming number is only requested by the visitor location register if, after the charging requirements have been checked, the utilization of a mobile subscriber roaming number for setting up the connection is ensured and thus the issuing of mobile subscriber roaming numbers which remain unused because

-4-
the charging requirements have not been met is avoided.
It is; tiie object of the invention to specify a method and a system of the type initially mentioned by means of which the location interrogation can be improved with respect to signalling toad and connecting delay for optimal routing.
According to the invention, this object of improving the location interrogation
with respect to a lower signalling bad and shorter connecting delay compared
with the known two-stage location interrogation is achieved by the fact that the
home location register itself, when it receives the message for location
interrogation, checks the feasibility of setting up the direct connection between
the gateway mobile switching centre and the visited mobile switching centre and,
with a positive result of the check, sends a modified message, which additionally
contains a code for requesting a temporary mobile subscriber roaming number,
to the visitor location register. As a result, the home location register can carry
out the feasibility check of setting up the connection for reasons of charging for
the call already after the first reception of a location interrogation and call up
immediately i.e. without waiting for another location interrogation according to
the known method described - the mobile subscriber roaming number from the
responsible visitor location register and send it to the requesting gateway mobile
switching centre. The advantage of the known solution of ensuring that only
those temporary mobile subscriber roaming numbers which are actually needed
are assigned and occupied is retained in the method according to the invention.
The additional advantages of the invention consist in a lower signalling load due
to the omission of a number of signalling messages which are required between
the components for supporting the optimal routing in the two-stage location
interrogation, and in a faster

-5-
setting up of the connection in the case of a direct connection between mobile switching centres of a first and second network.
""~~~""3£cc0r"ding to a further development of the invention, the visitor location register checks the message provided for interrogating subscriber information for the presence of the code and, if the result of the check is positive, issues a mobile subscriber roaming number which is sent back additionally to the home location register in a message by means of which the interrogation is
acknowledged. The visitor location_ register
advantageously carries out the check of the message for_ interrogating subscriber information only in the case where the mobile subscriber can be reached.
According to a further development of the invention, the home location register sends a message back to the gateway mobile switching centre, by means of which the location interrogation is acknowledged and additionally the mobile subscriber roaming number issued by the visitor location register on request is transmitted.
It is of advantage if the gateway mobile switching centre checks the incoming message for the existence of a mobile subscriber roaming number so that, in the case of a positive result of the check, the mobile subscriber roaming number is used for setting up the direct connection to the visited mobile switching centre or, if the result of the check i s nagative a second message for location interrogation is sent to the home location register . Thus both the known method and the novel and inventive method can exist independently of one another and side by side. In the case where a temporary mobile subscriber roaming number has already been transmitted after the first location interrogation from the home location register, the second location interrogation according to the two-stage known method is skipped and the direct connection for the optimal routing can already be set up early directly by means of the temporary mobile subscriber roaming number already available.

- 6 -
The invention will be explained with reference to an illustrative embodiment shown in, in which, in detail,
Figure 1 shows in a block diagram the flow of messages
between the network facilities affected by the
location interrogation for internetwork optimal
routing, and
Figure 2 shows in a flow chart the processing of the
location interrogation by the home location
register in the home network of the called mobile subscriber.
Using as an example the international cellular mobile radio network according to the GSM standard, the block diagram in Figure 1 shows the sequence for deter-
mining the location of a mobile subscriber registered in the cellular mobile radio network. _ In this process, optimal routing for the mobile terminated call is supported. In the clinical present example, it shall be assumed that this is a call which is initiated by a mobile subscriber A and is directed to the mobile subscriber B (mobile-to-mobile call). Mobile subscriber A is located within the coverage area of a first network IPLMN whilst mobile subscriber B is permanently registered with his subscriber data in another network HPLMN and is temporarily registered in another network VPLMN due to his current location. For the called mobile subscriber B, the HPLMN network represents his home PLMN and the VPLMN network represents his visited PLMN. For the sake of simplicity, it will also be assumed that the networks IPLMN, HPLMN, and VPLMN have an identical network structure corresponding to the international GSM mobile radio network,. but are operated by corresponding network operators in different countries. Thus, it will be assumed, for example, that mobile subscriber A is calling from a mobile radio network in Germany and mobile subscriber B has his home in the mobile radio network of Switzerland but is registered as visitor in the mobile radio network of Austria due to his current location.
The block diagram shows a visited mobile switch-

- 7 -
ing centre VMSCA and a gateway mobile switching centre GMSCA in the IPLMN network, a home location register HLRB in a HPLMN network and a visitor location register VLRB and a visited mobile switching centre VMSCB in the VPLMN network. In the present example, the incoming call directed to mobile subscriber B is initiated by a mobile subscriber A which is located in the coverage area of the visited mobile switching centre VMSCA when the call is initiated. Naturally, it is also possible that the call is started by a line-connected party A - for example from the public switched telephone network (PSTN). Both alternatives have in common that the call is forwarded to the gateway mobile switching centre GMSCA which is arranged at the interface to other networks in the IPLMN network. In addition, visited mobile switching centre VMSCA and gatway mobile swiching centre GMSCA can also be collocated.
On the basis of the subscriber call number of mobile subscriber B, dialled by mobile subscriber A by entering it in a mobile subscriber station, the visited mobile switching centre VMSCA receives a (call setup) message via the corresponding base station system in the IPLMN network for setting up a signalling connection (1). The visited mobile switching centre VMSCA sends a request for processing an outgoing call to a visitor location register (not shown), which signals to the visited mobile switching centre VMSCA the permission for setting up the signalling connection. The visited mobile switching centre VMSCA thereupon sends a message IAM (initial address message according to the ISDN user part (ISUP) which is used on the connecting lines between the mobile (switching centres, to the gateway mobile switching centre GMSCA (2). For the present case where the gateway mobile switching centre GMSCA is located in another network than the home network of mobile subscriber B, an SRIL message for interrogating the location is sent from the gateway
mobile switching centre GMSCA to the home location
register HLRB in the home network HPLMN. This location interrogation (send location info) contains a note that

- 8 -
this is an enquiry for location information in the context of optimal routing. In this process, the SRIL messages is transmitted in accordance with a mobile radio-specific application part (MAP) (3).
After receiving the SRIL message, the home location register HLRB checks whether setting-up of the direct connection between the gateway mobile switching centre GMSCA in the IPLMN network and the visited mobile switching centre VMSCP in the other network VPLMN is feasible for reasons of charging for the call. This check consists, for example, of a comparison of country codes which are allocated to the gateway mobile switching centre GMSCA and the visited mobile switching centre VMSCB or, respectively, the home location register HLRB. The charging requirements are specified in this case in such a manner that the charges for a call which is processed in accordance with optimal routing must not be higher than for a call which is conducted via the home network of the called mobile subscriber as in the case of conventional routing. The home location register HLRB therefore checks a country code associated with the visited mobile switching centre VMSCB, on the one hand, with a country code CCH of the home location register HLRB and, on the other hand, with a country code CCI of the gateway mobile switching centre GMSCA. If at least one comparison supplies identity of the countries which corresponds to a positive result of the comparison, the home,location register HLRB determines that setting-up of a direct connection according to optimal routing is possible without violating the requirements with respect to charging for the call. The country codes provide the home location register HLRB with a very simple way of determining whether at least two of the three network facilities affected by the location interrogation and the setting up of the connection are arranged in one and the same country (4).
The country code comparison only represents a
simple measure for checking whether there are no objections for setting up a direct connection for reasons of

- 9 -
charging for the call. More elaborate measures for
supporting or rejecting the optimal routing for the
direct connection of mobile switching centres of different networks can be easily implemented in the home location register HLRB but can also be shifted, as an alternative, to the gateway mobile switching centre which starts the location interrogation, without adversely affecting thereby the principle of determining the location in accordance with the invention. When more elaborate checking measures are shifted to the gateway mobile switching centre, the simple checking capability by country code comparison can remain in the respective home location register.
Due to the fact that, according to the invention, the home location register HLRB itself carries out the country code comparison, a modified message PSI can be sent immediately, i.e. without waiting for any further location interrogation from the gateway mobile switching centre GMSCA, to the visitor location register VLRB in the VPLMN network if the result of the comparison is positive. The modified message PSI' (provide subscriber info) is normally used for interrogating subscriber information of the mobile subscriber B and, according to the invention, additionally contains a code PRN for requesting a temporary mobile subscriber roaming number MSRN which is issued by the visitor location register VLRB. The previous check of the feasibility of setting-up a direct connection with respect to charging for the call by the home location register HLRB guarantees that, immediately after the positive result of the check is available, the temporary mobile subscriber roaming number is only reque.sjted if it is sure that it is also needed. This prevents unnecessary issuing of unused temporary mobile subscriber roaming numbers by the visitor location register in each case responsible for the called mobile subscriber B. Before the home location register HLRB sends out the modified message PSI' with the new code PRN according to the mobile-radio specific application part (MAP) to the visitor location register VLRB, it is first

- 10 -
determined, to be on the safe side, whether or not the visitor location register VLRB supports optimal routing. If the result of the comparison in the home location register HLRB does not provide a correspondence of country codes so that a direct connection between the mobile switching centres GMSCA and VMSCB is not wanted for reasons of charging, the home location register HLRB sends the usual PSI (provide subscriber info) message to the visitor location register VLRB, by means of which the subscriber information is requested (5).
In the last-mentioned case, the visitor location register VLRB checks whether the mobile subscriber B is available, i.e. whether his mobile subscriber station is in a switched-off state, in a busy state or the like. The visitor location register VLRB checks every message coming from the home location register HLRB, by means of which subscriber information is requested, for the presence of the PRN code, which means that this is a modified message PSI' for requesting a temporary mobile subscriber roaming number MSRN. If this is so, the visitor location register VLRB issues a temporary mobile subscriber roaming number MSRN which is used for setting up the connection between the gateway mobile switching centre GMSCA and the visited mobile switching centre VMSCB and is released again for further connection setting-up processes after the setting-up of the connection has ended. The visitor location register VLRB checks the incoming message PSI or PSI', respectively, for the presence of the code PRN only if mobile subscriber B can be reached via his mobile subscriber station, i.e. the mobile subscriber station is not in a switched-off state or a state cut-off from mobile coverage (detach status) (6) .
If the visitor location register VLRB has not been requested for issuing and transmitting a temporary mobile subscriber roaming number MSRN, it sends a message PSIA to the home location register HLRB, which informs about the status of mobile subscriber B. If, however, the mobile subscriber roaming number MSRN has been issued by

-li-
the visitor location register VLRB, it is transferred to the home location register HLRB in a message PSIA' , in addition to the information on the status of mobile subscriber B. The visitor location register VLRB acknowledges the interrogation of subscriber information (PSI or PSI', respectively) by the home location register HLRB with the message PSIA or PSIA', respectively (7).
If the home location register HLRB receives
information that mobile subscriber B is available in the
message PSIA as acknowledgement, a message SRILA is
generated since no temporary mobile subscriber roaming
(number MSRN has been received, and is sent back as acknowledgement for the location interrogation SRIL to the gateway mobile switching centre GMSCA. At the same time, information for identifying the visited mobile switching centre VMSCB responsible for mobile subscriber B is also sent along in the SRILA message. This information preferably consists of the address AVM of the visited mobile switching centre VMSCB. If the home location register HLRB receives a 'temporary mobile subscriber roaming number MSRN from the visitor location register VLRB, a message SRILA' is generated by means of which the location interrogation SRIL is acknowledged and additionally the mobile subscriber roaming number MSRN provided is transmitted in addition to the address AVM to the gateway mobile switching centre GMSCA (8).
The gateway mobile switching centre GMSCA receives in the acknowledgement message sent by the home location register HLRB the address of the visited mobile switching centre VMSCB to which the connection is to be set up, cind additionally checks whether the acknowledgement message also contains a temporary mobile subscriber roaming number MSRN. If this is so, the received mobile subscriber roaming number MSRN is used to set up the direct connection according to the optimal routing between gateway mobile switching centre GMSCA and visited mobile switching centre VMSCB and the message IAM trans-mitted to the visited mobile switching centre in accordance with the ISDN user part ISUP (9).

- 12 -
In this manner, a direct connection- for supporting optimal routing between mobile switching centres of different networks can be set up in the case of a B mobile terminated call, in which, for determining the location of mobile subscriber B, a lower signalling load between the network facilities and a shorter connecting delay is achieved compared with the known method. Reduction of the signalling load and shortening of the connecting delay is possible due to the fact that the home location register HLRB itself can check the feasibility of the direct connection with respect to the charging requirements and, in the case of a positive result of the check, immediately, i.e. without waiting for any further location request by the gateway mobile switching centre, request a temporary mobile subscriber roaming number from the visitor location register in each case currently responsible for mobile subscriber B and can send it back to the gateway mobile switching centre for setting up the connection.
In the case where the gateway mobile switching centre GMSCA does not receive a mobile subscriber roaming number MSRN in the acknowledgement message SRILA, a second location interrogation SRIR (send routing info) can be sent to the home location register HLRB in order to obtain a mobile subscriber roaming number MSRN, possibly in a second stage. The last-mentioned procedure is preferably used when home location registers are used in home networks which are not operated in accordance with the method of the present invention.
Figure 2 shows a flow chart for processing the location request for determining the location of mobile subscriber B by the home location register HLRB in which the called mobile subscriber B is permanently stored with his subscriber data.. Firstly, the home location register HLRB checks whether the message SRIL is received with which the internetwork location interrogation from the gateway mobile switching centre of another network arrives in the home network. When receiving the message SRIL, the home location register HLRB first determines

- 13 -
whether the visitor location register VLRB currently-responsible for the called mobile subscriber B basically supports the setting-up of a direct connection between mobile switching centres of different networks in accordance with optimal routing OR. If this is not so, the home location register HLRB generates an error message which signals that optimal routing OR is not allowed.
If the addressed visitor location register VLRB supports optimal routing OR, the home location register HLRB checks whether the setting-up of the direct connection between the gateway mobile switching centre and the visited mobile switching centre is feasible for reasons of charging for the call. The checking is done simply by comparing the country codes of the two mobile switching centres or the country codes of the home location register and the visited mobile switching centre. If at least one comparison does not supply identical country codes, the home location register HLRB sends the message PSI to the visitor location register VLRB in order to call up subscriber information. During the check of the subscriber status by the visitor location register VLRB, the home location register HLRB is in a wait state which is maintained until the visitor location register VLRB receives the message PSIA with which the visitor location register VLRB signals the status of mobile subscriber B or of his mobile subscriber station, respectively. If the called mobile subscriber B is in a state in which he cannot be reached (detach status), for example due to a disconnected mobile subscriber station or a lack of radio coverage, the location interrogation is aborted. If mobile subscriber B can be reached, the home location register HLRB provides the address AVM of the visited mobile switching centre VMSCB as routing information or routing address, respectively, and sends it back to the gateway mobile switching centre GMSCA in the message SILA. The home location register HLRB uses the message SRILA to acknowledge the location interrogation initiated by the gateway mobile switching centre, which can be

- 14 -
recognized from the incoming message SRIL.
If the comparison of the respective country codes by the home location register HLRB shows that there are no requirements opposing the setting up of a direct connection between the two mobile switching centres according to optimal routing for reasons of charging for the call, the home location register HLRB sends out the modified message PSI' with an additional code PRN to the responsible visitor location register VLRB immediately after the check. The code PRN here signals the request for a temporary mobile subscriber roaming number MSRN which is temporarily issued by the visitor location register VLRB due to it being responsible for mobile subscriber B for setting up the connection between mobile subscriber A and mobile subscriber B. During the allocation of the temporary mobile subscriber roaming number MSRN from a predetermined set of numbers, the home location register HLRB is in a wait state which is ended when the message PSIA' is received. The message PSIA' is used as acknowledgement for the message PSI' which has previously arrived. The temporary mobile subscriber roaming number MSRN allocated by the visitor location register VLRB is sent back to the home location register HLRB as additional parameter in the message PSIA'. The home location register HLRB then sends the message SRILA' with the mobile subscriber roaming number MSRN back to the gateway mobile switching centre GMSCA in order to acknowledge the location interrogation, which can be recognized from the incoming message SRIL and to signal the support of optimal routing to the gateway mobile switching centre. The gateway mobile switching centre GMSCA can use the incoming mobile subscriber roaming number MSRN for setting up a direct connection to the visited mobile switching centre VMSCB. Further setting-up of the connection via the base station system in the network currently responsible for mobile subscriber B is carried out by using known methods which are not affected by the present invention. Due to the check of feasibility of setting up a direct connection between mobile switch-

- 15 -
ing centres across the boundaries of networks and by immediately requesting a temporary mobile subscriber roaming number by the home location register in each case responsible for the called mobile subscriber B in his home network if the result of the check is positive, the signalling load can be reduced and the connecting delay shortened.

- 16 -

1/ Method for determining the location of a mobile subscriber registered in a cellular radio network for optimal routing in the case of a mobile terminated call, in which
- on the basis of the subscriber call number of the
called mobile subscriber, an internetwork message (SRIL)
for interrogating location is sent from a gateway mobile
switching centre (GMSCA) of a first network (IPLMN) to a
home location register (HLRB) of another network (HPLMN)
in which the mobile subscriber is permanently registered
with his subscriber data,
- the home location register (HLRB) directs a message
{PSI or PSI') for interrogating the location to a visitor
location register ,(VLRB) of a further network (VPLMN) in
which the mobile subscriber is currently registered due
to his current location and allocates a visited mobile
switching centre (VMSCB) to the visitor location register
(VLRB), and in which
- for supporting optimal routing, a check is made whether
a direct connection can be established between the
gateway mobile switching centre (GMSCA) and the visited
mobile switching centre' (VMSCB) for reasons of charging
for the call,
characterized in that when the message.(SRIL) for location interrogation is received, the home location register (HLRB) checks the feasibility of setting up the direct connection and, if the result of the check is positive, sends a modified message (PSI') additionally containing a code (PRN) for requesting a temporary mobile subscriber roaming number (MSRN) to the visitor location register (VLRB).
2. Method according to Claim 1, characterized in that the visitor location register (VLRB) checks the message (PSI') for interrogating the location for the presence of the code (PRN) and, if the result of the check is positive, issues the mobile subscriber roaming number (MSRN) which is transmitted additionally to the

GR 96 P 1998 - 17 -
home location register (HLRB) in a message (PSIA' ) by-means of which the request is acknowledged.
3. Method according to Claim 2, characterized in
that thejvisitor location register (VLRB) carries out the
checking of the message (PSI or PSI') for interrogating
the location only in the case where the mobile subscriber
is obtainable.
4. Method according to one of Claims 1 to 3, charac
terized in that the home location register (HLRB) sends
back to the gateway mobile switching centre (GMSCA) a
message (SRILA) by means of which the location interroga-
tion is acknowledged and at least one information item
(AVM)for identifying the visited mobile switching centre
(VMSCB) is transmitted.
5. Method according to one of Claims l to 3, charac-
terized in that the home location reqister (HLRB) sends
back to the gateway mobile switching centre (GMSCA) a
message (SRILA') by means.of which the location interro-
gation is acknowledged and at least the mobile subscriber
roaming number (MSRN) issued by the visitor location
register (VLRB) on request is transmitted.
6. Method according to Claim 4 or 5, characterized
in that the gateway mobile switching centre (GMSCA)
checks the incoming message (SRILA or SRILA') for the
presence of the mobile subscriber roaming number (MSRN)
and that, if the result of the check is positive, the
mobile subscriber roaming number (MSRN) is used for
setting up the direct connection to the visited mobile
switching centre (VMSCB) or, if the result of the check
is negative, a second message (SRIR) for location inter
rogation is sent to the home location register (HLRB).
7. Method according to one of the preceding claims,
characterized in that the home location register (HLRB)
checks the feasibility of setting-up the direct connec-
tion by comparing country codes which can be allocated to
the gateway mobile switching centre (GMSCA), the visited
mobile switching centre (VMSCB) and the home location
register (HLRB).
8. Method according to Claim 7, characterized in
5.
- 18 -
that the country code of the gateway mobile switching centre (GMSCA) is compared with the country code of the visited mobile switching centre (VMSCB) and that, if the two country codes are identical, the home location register (HLRB) requests the temporary mobile subscriber roaming number (MSRN) in the modified
message (PSI').
9. Method according to claim 7, characterized in that the
country code of the home location register (HLRB) is compared
with the country code of the visited mobile switching centre CVMSCB) and that, if the two country codes are identical, the home location register (HLRB) requests the temporary mobile subscriber roaming number (MSRN) in the modified message (PSI'). 10- A system for carrying out the method as claimed in claim 1 comprising:
a gateway mobile switching centre (BNSCA) of a first network (IPLMN), for sending on the basis of the subscriber call number of the called mobile subscriber, an internetwork message CSRIL) far location interrogation to a home location register (HLRB) of another network (HPLMW) in which the mobile subscriber is registered permanently with his subscriber data, said home

-19-
location register(HLRB) being adapted for sending out a message (PSI or PSI') for interrogating the location to a visitor location register (VLRB) of another network (VPLMN) in which the mobile subscriber is currently registered due to his current location and a visited mobile switching centre (VMSCB) is
al located to the visitor location register (VLRB), said horne
alocation register (HLRB) additionally configured for supporting"
optimal routing for determining whether a direct connection between the gateway mobile switching centre (GMBCA) and the visited mobile switching centre (VHSCB) can be set up for reasons
of charging for the call, characterized in that said hone locatior
adapted register (HLRB) is adapted for checking the feasibility
of setting up the direct connection upon receipt of the message (SRIL) for location interrogation and, if the result of the check is positive, for sending a modified message (PSI*), which additionally contains a code (PRN) for requesting a temporary mobile subscriber roaming number (MSRN), to the visitor location register (VLRB).

Method and system for determining the location of a mobile subscriber registered in a cellular mobile radio network
A lower signalling load and shorter connecting delay compared with the known two-stage location interro-gation is achieved in the case of optimal routing due to the fact that the home location register (HLRB) itself, when receiving the message (SRIL) for location interroga-tion, checks the feasibility of setting up the direct connection between gateway mobile switching centre (GMSCA) of a first network (IPLMN) and visited mobile switching centre (VMSCB) of another network (VPLMN) for reasons of charging for the call and, if the result of the check is positive, sends a modified message which additionally contains a code (PRN) for requesting a temporary mobile subscriber roaming number (MSRN) to the visitor location egister (VLRB). As a result, the home location register can carry out the feasibility check of setting up the connection for reasons of charging for the call already after the first reception of a location interrogation and call up immediately i.e. without waiting for another location interrogation by the gateway mobile switching centre the mobile subscriber roaming number from the responsible visitor location register and send it to the requesting gateway mobile switching centre.

Documents:

01533-cal-1997 abstract.pdf

01533-cal-1997 claims.pdf

01533-cal-1997 correspondence.pdf

01533-cal-1997 description(complete).pdf

01533-cal-1997 drawings.pdf

01533-cal-1997 form-1.pdf

01533-cal-1997 form-2.pdf

01533-cal-1997 form-3.pdf

01533-cal-1997 form-5.pdf

01533-cal-1997 gpa.pdf

01533-cal-1997 priority document.pdf

1533-CAL-1997-(28-09-2012)-FORM-27.pdf

1533-CAL-1997-FORM-27.pdf

1533-CAL-1997-OTHER PATENT DOCUMENT.pdf

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Patent Number

194083

Indian Patent Application Number

1533/CAL/1997

PG Journal Number

30/2009

Publication Date

24-Jul-2009

Grant Date

06-May-2005

Date of Filing

20-Aug-1997

Name of Patentee

SIEMENS AKTIENGESELLSCHAFT

Applicant Address

WITTELSBACHERPLATZ 2, 80333 MUNCHEN

Inventors:

#	Inventor's Name	Inventor's Address
1	ULRICH WIEHE	GEORG-AUGUST-MOELLELR-STR. 21A, 36251 BAD HERSFELD

PCT International Classification Number

H04R 7/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	19635581.8	1996-09-02	Germany