LOCATION MANAGEMENT OF A WIRELESS TERMINAL

Abstract: Location data of a subscriber terminal (TE) are maintained by means of intelligent network technique. Signalling between a telephone exchange (EXC) and a PBX is supplemented with extra information including the information on the location of the subscriber TE. A roaming number ROAM# is allocated to a TE moving into the area of a Visited PBX (VPBX). Call setup protocol between the PBX and the EXC is supplemented with an extra packet (EI) supporting the subscriber mobility in such a way that the information on the subscriber's location can be transmitted to a Service Control Point (SCP) of the intelligent network. In connection with location updating, the VPBX informs the intelligent network (SCP) that the TE tries to register to the area of the VPBX. The intelligent network (SCP) checks whether said subscriber has the right to use the services of the VPBX. In case of a call to the TE, the EXC asks the intelligent network (SCP) for the location information of the TE on the basis of the subscriber number of the TE. Subsequently, the EXC establishes a connection with the PBX indicated by the location information, which PBX sets up a call to said TE.

Description: LOCATION MANAGEMENT OF A WIRELESS TERMINAL FIELD OF THE INVENTION The invention relates to supporting the mobility of wireless termi- nals, such as DECT telephones, in a telephone network. BACKGROUND OF THE INVENTION With reference to Figure 1 , wireless terminals, such as DECT telephones, as described in ETSI Standard 300 175 Radio Equipment and System: Digital Cordless European Telephone, Common Interface, Sections 1 to 9, can be connected to a Public Integrated Services Network PISN. The DECT System comprises a base station FP (Fixed Part), usually connected to the PISN via a Private Branch Exchange PBX. There are three main types of base stations FP: a home base station or a base station to be connected to an office PBX and so-called telepoint base stations. In a conventional wired tele- phone network, e.g. signalling protocols DPNSS and DSS.1 are used, which are described in the CCITT (now ITU) Specification: "DSS.1 , Q.930 to Q.940, 1989, Digital Subscriber Signalling System No. 1 , Network Layer, User- Network Management". These signalling protocols support the mobility of the subscriber very poorly or not at all. To support the subscriber mobility, services of a PBX network can be supplemented with Intelligent Network (IN) technique determined e.g. in the specifications of ITU Q.1200 series. By IN technique, it is possible to combine telecommunications networks of different types, such as the PISN and cellular mobile systems, e.g. GSM and NMT, not shown separately in Figure 1. The principle of IN technique is that the signalling needed for establishing a speech connection takes place controlled by the IN, but the actual speech connection is switched by known functions of the communications network in question. One of the services provided by the IN is Follow Me Destination (FMD) call transfer. By means of this service, the subscriber may control his incoming calls to a desired number, which can be e.g. an extension number of the PBX network or a mobile network number. In Figure 1 , for example, a Terminal Equipment TE1 user moving from a first DECT system DECT1 to a second system DECT2 may order a call transfer to an extension number of this second system. The main problem with the solution described is that a call transfer requires activity and carefulness of the subscriber. In solutions of the prior art, the subscriber has to know the extension number to which calls shall be transferred and to remember to give this information to the operator. SUMMARY OF THE INVENTION The object of the invention is to develop a method and an equipment implementing the method in such a way that the above problems with the subscriber mobility and location management can be solved. The objects of the invention are achieved by a method and a system, which are characterized in what is set forth in the independent claims. Preferred embodiments of the invention appear from the dependent claims. The invention is based on the fact that subscriber location data are maintained by means of IN technique. Signalling between a telephone ex- change and a PBX is supplemented with extra information on the location of the subscriber terminal. An advantage of the method and system of the invention is an improved support to the mobility of the subscriber. The subscriber does not need to determine separately the extension number to which he wishes to transfer his calls. It is enough that the subscriber starts his phone in the area of a new PBX. The invention does not require changes in existing terminals. The invention can also be applied to double-mode terminals, such as GSM/DECT telephones, which means that the invention saves radio resources, since the greatest possible part of the signalling takes place via a wired telephone net- work. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in greater detail by means of preferred embodiments with reference to the attached drawings, in which Figure 1 shows such parts of a known telecommunications system which are substantial for the understanding of the invention; Figures 2A and 2B show a location updating according to the invention in a DECT system; and Figure 3A shows signalling in case of a mobile terminated call; and Figure 3B shows signalling in case of an internal call in a PBX. DETAILED DESCRIPTION OF THE INVENTION With reference to Figure 1 , the invention suggests that the functionality of a PBX is supplemented in a way which is to some extent analogous with the home and/or visitors location register of mobile systems. A home PBX (HPBX) is allocated to each subscriber of a wireless system. In this application, a PBX other than HPBX is called a Visited PBX (VPBX). Each PBX comprises both HPBX and VPBX functionality. Within the scope of this application, a transmitting exchange EXC is any exchange via which the PBXs are con- nected to the PISN and/or mobile networks. The EXC is supposed 1) to have an interface to the PBXs for a speech connection, 2) to support an interface to a Service Switching Point SSP of the IN for a signalling connection and 3) to support the INAP signalling protocol extended for this purpose (INAP extensions). According to the invention, a roaming number ROAM# is allocated to a subscriber moving to the area of a VPBX. In the numbering plan, a fixed area can be reserved from the number space of said PBX for the roaming numbers. In this way, it is possible to avoid consuming the numbers of the PISN. A functionality supporting subscriber mobility can be implemented for instance by a suitable addition to the conventional call setup protocol between the PBX and the EXC. Messages used for call setup may include an extra packet El (Extra Information). The El packet can be coded in different ways in different signalling protocols. In case of the DSS.1 protocol of the ex- ample, suitable information elements are e.g. FACILITY and USER_TO_USER. A separate specific field can also be defined for this purpose. The extra packet El is transparent to the EXC (the exchange does not react to it). The purpose of the El packet is to support the subscriber's mobility in such a way that an information on the subscriber's location can be trans- mitted via the SSP of the IN to a Service Control Point SCP of the IN. On the other hand, the SCP maintains data in a Service Data Point SDP. By means of the extra packet, information on subscriber identification or authentication, for instance, can be transferred. A logic interface between the PBX and the IN - especially its SCP - comprises two functionalities according to the invention: location updating and location cancellation. At Location Updating LU, the VPBX informs the SCP of the IN that the terminal TE tries to register to the area of a new PBX. Upon receiving this information, the SCP checks from the SDP the subscriber data and especially whether said subscriber has the right to use the services of the new VPBX. At Location Cancellation LC, the SCP removes from the SDP the information on that the terminal TE is in the area of the VPBX. Figure 2A shows a possible signalling when a terminal registers to the area of a VPBX. To keep the figure illustrative, only steps essential for the invention are shown. In this application, reference numerals 2A-1 , 2B-1 , etc. signify corresponding steps in Figures 2A, 2B, etc. In step 2A-1 , the terminal TE sends to the VPBX a Location Update Request including the identity of the TE or its subscriber. It is assumed initially that the identity is e.g. an International Portable User Identity IPUI. The VPBX notices that said terminal is not registered to this PBX and that the HPBX of the terminal is other than the VPBX. Therefore, a calling subscriber's roaming number (CLG#ROAM#, Calling Number Roaming Number) is allocated to the terminal. The roaming numbers are preferably reserved from the number space of the PBX. In this way, it is possible to avoid consuming the numbers of the PISN. In step 2A-2, the PBX sends the EXC a call setup request SETUP including, in addition to the number of the called subscriber, i.e. subscriber B, also the roaming number allocated in step 2A-1 and the above-mentioned extra packet El. The El packet includes the information on that the type of the task is location updating LU of a terminal/subscriber whose identity is IPUI. The EXC performs a number analysis of the called subscriber number and notices that an IN service request has to be made for location updating of the terminal TE in the SDP of the intelligent network. In step 2A-3, the EXC sends a service request INVOKE to the SCP of the IN. This joins together the identity of the terminal or its subscriber, such as the IPUI number, and the subscriber number of the terminal, such as the TE_MSISDN number, which is returned to the EXC in a Connect message in step 2A-4. In step 2A-5, the EXC sends the HPBX a location cancellation message LC, which can be for instance a call setup request SETUP supplemented with an extra packet El according to the invention. The El packet in- eludes in this step an information on that the subscriber location of the terminal in the area of the HPBX is cancelled. In step 2A-6, the HPBX sends an ALERT message to the EXC. In step 2A-7, the EXC sends a corresponding ALERT message to the VPBX, which in step 2A-8 acknowledges the location updating of the terminal TE. In steps 2A-9 and 2A-10, the signalling connections are cancelled. If an International Portable Equipment Identity IPEI is used instead of the subscriber's IPUI, the signalling functions as described above, except that the location data of the physical terminal TE are maintained, instead of those of the subscriber. By implementing the location management of the invention by means of the signalling relating to a call setup, the existing signal- ling and the SCP interface can be used without any great changes. If the TE moves from the area of a first VPBX into the area of a second VPBX, the signalling takes place as above, except that the location cancellation LC is sent to that VPBX where the subscriber's IPUI (or the IPEI of the terminal) last was updated. Figure 2B shows the signalling in case if the TE returns to the area of its HPBX. The signalling corresponds to the steps described in connection with Figure 2A, but the tasks of the HPBX and VPBX are inverse during the steps 2B-1 to 2B-9. The steps 2A-n and 2B-n can be indicated by a common marking 2x-n. The location of the TE is updated from the VPBX to the HPBX. With reference to Figure 3A, it is assumed that the terminal TE receives a call, when it is within the area of a VPBX. In case of an incoming call, the signalling takes place as follows. In step 3A-1 , a call comes to an EXC from another exchange EXC2 not shown, which can be an exchange of the PISN or equally well a mobile network exchange. In step 3A-2, the EXC sends the SCP of the IN a service request INVOKE including the TE_MSISDN number of the terminal. In step 3A-3 the SCP returns to the EXC a roaming number CLD#ROAM# allocated to the terminal. In step 3A-4, the EXC concludes from the roaming number that the TE exists in the area of the VPBX and sends said PBX a call setup request. The steps 3A-5 to 3A-10 correspond to conventional call setup. In step 3A-5, the terminal TE is paged and, in step 3A- 6, it responds to the paging, etc. In step 3A-10, the EXC sends an Ac- cess_Complete Message to the other exchange EXC2. Figure 3B shows signalling in case of an internal call in an HPBX of a DECT system. It is assumed that subscriber A is TE1 and subscriber B is TE2, respectively. The signalling takes place in the same way as in a conventional DECT call. No service request to the SCP of the IN is needed, because the HPBX notices in step 3B-2 that the subscriber B is in the area of the same PBX and can start paging according to the prior art. If the subscriber B were in the area of a VPBX, the signalling would take place in the same way as in Figure 3A, but the call would be started from the terminal TE1 of the subscriber A, instead of starting from the EXC2. A physical implementation of the invention presupposes that location updating and call setup messages according to the prior art are supplemented with extra information elements of the invention. This is implemented in the easiest way by changes in software. To be precise, the arrangement of the invention comprises the following changes- - a PBX comprises means for indicating location information for a terminal TE of a wireless network; - the PBX comprises means for adding the location information and the identity (IPUI/IPEI) of the TE to a call setup message SETUP; - an EXC comprises means for sending the location information and the identity of the TE to a node SCP of an IN in connection with a service request INVOKE; - the node SCP of the IN comprises means for adding the location information and the identity of the TE to the ISDN number of the TE. The invention has been described by way of example in connection with the DECT system and assuming that DSS.1 signalling is used between the PBXs and the exchanges On the basis of the above description, it is easy for one skilled in the art to apply the invention to other wireless telephone systems as well. It is also clear that the invention is equally suitable for loca- tion management of all kinds of mobile terminals, not only of a telephone. The invention and its embodiments are thus not restricted to the above examples, but they can vary within the scope of the claims.

Claims: CLAIMS 1 Method for location updating of a wireless terminal (TE) in a communications system comprising a number of Private Branch Exchanges (HPBX, VPBX) and at least one telephone exchange (EXC) and being con- nected to a Public Integrated Services Network (PISN) and an intelligent network, in which method the terminal (TE) sends (2A-1, 2B-1) in connection with a call setup a location updating message to a PBX and the PBX sends (2A-2, 2B-2) a call setup message to the exchange (EXC), characterized in that, additionally in the method, - the PBX adds (2A-2, 2B-2) the location information and the identity of the terminal (TE) to the call setup message, - the EXC sends a node (SCP) of the intelligent network a service request (2A-3, 2B-3), including the location information and the identity of the terminal (TE), and - the node (SCP) of the intelligent network adds the location information of the terminal (TE) to the subscriber number, preferably to the MSISDN number, of said terminal (TE) 2 Method according to claim 1 , cha racte rized in that in case of an incoming call (3A-1) to the terminal (TE) - the exchange (EXC) sends (3A-2) the node (SCP) of the intelligent network a service request comprising the subscriber number, preferably the MSISDN number, of the terminal (TE), - the node (SCP) of the intelligent network returns (3A-3) the loca- tion information of the terminal (TE) to the exchange (EXC), - the exchange (EXC) establishes (3A-4) a connection with the PBX indicated by the location information of the terminal (TE), which PBX sets up (3A-5) a call with said terminal (TE) 3 Method according to claim 1 or2, characterized in that at least one Home Private Branch Exchange (HPBX) is allocated to each terminal (TE), which HPBX notices in case of an internal call that both the calling and the called subscriber are in the area of the same PBX, and in this case the HPBX sets up a call without any service request to the intelligent network 4 Method according to any one of the claimsl to 3, c h a rac - t e r i z e d in that the PBX (HPBX, VPBX) reserves for the terminal (TE) a roaming number (CLG#ROAM#) used as location information of the terminal (TE). 5. Method according to claim 4, ch a ra cteri zed in that a fixed area from a number space of the PBX (HPBX, VPBX) in question is re- served for roaming numbers (CLG#ROAM#) in the numbering plan. 6. Method according to any one of the claims 1 to 5, c ha ra c terized in that the terminal (TE) is a terminal of the DECT system and the identity of the terminal (TE) is IPUI or IPEI. 7. Method according to claim 6, characterized in that the method uses DSS.1 signalling protocol and the location information is positioned in a FACILITY or USER TO USER information element. 8. Private Branch Exchange (PBX), comprising means for connection to a Service Switching Point (SSP) of an intelligent network and to base stations (DECT-FP) of a telephone system supporting wireless terminals (TE); characterized in that the PBX additionally comprises - means for indicating location information for a subscriber (TE) of a wireless network; and - means for sending the location information and the identity of the terminal (TE) to an exchange (EXC) in connection with a location updating performed by the terminal (TE). 9. Private Branch Exchange (PBX) according to claim 8, c ha racterized in that the location information of a terminal (TE) is a roaming number (CLG#ROAM#), which is preferably reserved from the number space of said PBX. 10. Arrangement for location updating of a wireless terminal (TE) in a communications system, the arrangement comprising a number of PBXs (HPBX, VPBX) and being in connection with a Public Integrated Services Network (PISN) and an intelligent network; in which arrangement the terminal (TE) comprises means for send- ing a location updating message (LOC_UPD_REQ) in connection with a call setup to a PBX and the PBX comprises means for sending a call setup message (SETUP) to an exchange (EXC); characterized in that additionally - the PBX comprises means for allocating location information to the terminal (TE) of the wireless network; - the PBX comprises means for adding the location information and the identity of the terminal (TE) to the call setup message (SETUP); - the exchange (EXC) comprises means for sending the location information and the identity of the terminal (TE) to a node (SCP) of the intelli- gent network in connection with a service request (INVOKE); - the node (SCP) of the intelligent network comprises means for adding the location information and the identity of the terminal (TE) to the subscriber number, such as a MSISDN number, of the terminal (TE). 11. Arrangement according to claim 10, c h a r a c t e r i z e d in that the location information of the terminal (TE) is a roaming number (CLG#ROAM#) allocated by the PBX.

Inventors: LAHTINEN LAURI, LAHTINEN, LAURI
Applicants: LAHTINEN LAURI, NOKIA TELECOMMUNICATIONS OY, LAHTINEN, LAURI
Application year: 1997
Main classification: H04Q7
IPC codes: H04W84