METHOD FOR PROCESSING CALL ESTABLISHMENT REQUESTS

Abstract: The invention relates to a method for processing a call establishment request in a telecommunication system, comprising the steps of receiving a call establishment request, deducing the destination of the call, and forwarding the call establishment request to the destination of the call for establishing a call. In order that a system operator could offer more flexible solutions to the subscribers the method comprises the steps of: defining several parallel number spaces for use, and defining numbers in said several parallel number spaces for at least some of the system terminals, receiving the call establishment request for establishing a new call, deducing the number space, to which the number included in the call establishment request belongs, and the destination of the call to be established on the basis of the line data included in the call establishment request and the source of the call establishment request, converting the number included in the call establishment request from the format according to the deduced number space to a number according to the format number space required by the destination of the call, and replacing the number included in the call establishment request by said number according to the number space required by the destination of the call before forwarding the call establishment request.

Description: METHOD FOR PROCESSING CALL ESTABLISHMENT REQUESTS The invention relates to processing call establishment requests in telecommunication systems and particularly to a number conversion of a new call to be established. In the following the invention is described by way of example mainly with reference to mobile systems, even though the invention can also be applied to other telecommunication systems. In known GSM mobile systems (Global System for Mobile communication) the dialling in a call establishment request transmitted to the system associated with a new call to be established is in the format required by a public switched telephone network irrespective of whether the call concerned is a call between mobile stations, a call to be made from a mobile system to a public switched telephone network or to a PABX network or a call to be made from a public switched telephone network or from a PABX network to a mobile sta- tion. Here, the PABX network refers to a network that includes one or more private automatic branch exchanges (PABX). A call establishment request including a number in the public switched telephone network format is thus transmitted to the mobile system for analysis. Here, the call establishment request refers to an entity formed of one or more signalling messages or frames transmitted to a call control process of the system, when a subscriber dials a number through his/her terminal in order to make a new call. The term call refers to any telephone connection that can be formed through the telecommunication system such as a speech call or a data call. The public switched telephone network format refers to an MSISDN format that includes three parts and is thus formed of a country code, a national area code and a subscriber number. The length of the country code cannot exceed three digits, and the total length of the MSISDN number is 15 digits at the most (a country code is, however, not needed when calling within the same country). The public switched telephone network format described above and what is known as an analysing tree, through which for example in the GSM system a number included in a call establishment request is analysed via a Home Location Register (HLR), is a fairly static and inflexible solution. There are a fair amount of restrictions associated with known mobile systems concerning, for example, the chances the operator has to flexibly offer subscriber group specific numbers to be used by the subscribers. Such restrictions may for instance be placed on such subscriber groups that include both mobile network terminals and fixed PABX network terminals. The idea of the invention is to remove the restrictions that may occur in the above described known solutions and to provide a solution that allows the system operator to offer more flexible solutions than before for the subscriber groups to make internal calls. This goal is achieved with the method of the invention for processing a call establishment request in a telecommunication system comprising the steps of: receiving a call establishment request, deducing the destination of the call, and forwarding the call establishment request to the destination for establishing a call. The method of the invention is characterized by comprising the steps of: defining several parallel number spaces for use, and defining numbers in said several parallel number spaces for at least some of the system terminals, receiving the call establishment request for establishing a new call, deducing the number space, to which the number included in the call establishment request belongs, and the destination of the call to be established on the basis of the line data included in the call establishment request and the source of the call establishment request, converting the number included in the call establishment request from the format according to the deduced number space to a number according to the number space required by the destination of the call, and replacing the number in- eluded in the call establishment request by said number according to the number space required by the destination of the call before forwarding the call establishment. The invention also relates to a system for processing call establishment requests comprising at least a master process and an analysing process, whereby the analysing process deduces the destination of the call establishment request received by the master process, and the master process forwards the call establishment request for establishing a call. The system of the invention is characterized in that said system uses several parallel number spaces, in which case the number included in the call establishment re- quest can be a number in any of the number spaces in use, the analysing process deduces the destination of the call and the number space, to which the number included in the call establishment request belongs, on the basis of the line data in the call establishment request and the source of the call establishment request, the system further comprises a conversion process that on the basis of the number included in the call establishment request and the number space deduced by the analysing process retrieves from a memory a number corresponding to the number included in the call establishment request, said retrieved number being a number of the number space required by the destination of the call, and the system replaces the number included in the call establishment request by the number retrieved from the memory using the conversion process before the master process forwards the call establishment request. The invention is based on the idea that making calls and feeding diallings associated therewith will become more flexible when several parallel number spaces are determined for use in the system of the invention. Then the subscriber of the system can make a call using a number according to any number space in use, in which case the analysing process of the system attends to the deduction of the number space used, and the conversion process thereafter converts the number in the number space used into such a format that the number should take in order for the call to be routed to the correct destination, i.e. to the correct network. The number of number spaces in use can be two or more depending on the implementation. A significant advantage with the solution of the invention is that it allows to flexibly process numbers belonging to different number spaces and thus to transmit call establishment requests between systems using different number spaces. The deduction of a number space used does not have to be based on merely analysing the number fed, instead the source of the call establishment request can be utilized when deducing the number space. The source of the call establishment request describes, for example, from which system the call establishment request originates. The line data included in the call establishment request, i.e. information indicating the network to which the call should be directed can also be utilized when deducing the number space. When the processing system of call establishment requests is made modular so that the system is divided into several independent sub-processes a system is achieved that is able to process various types of calls in a tailor- made manner. The sub-processes can also, if desired, be distributed between the different network elements of the network so that the different partial processes of the system can be carried out in the appropriate network elements. The modular system also provides the advantage that the system can be very flexibly changed as new later arising needs require. The preferred embodiments of the method and system of the invention are disclosed in the attached dependent claims 2 - 3 and 5 - 8. In the following the invention will be described in greater detail by way of example with reference to the attached drawings, in which Figure 1 is a flow chart showing a first preferred embodiment of the method of the invention, and Figures 2 is a block diagram showing a first preferred embodiment of the system of the invention Figure 3 illustrates a call TETRA - PSTN, Figure 4 illustrates a call TETRA - PABX, Figure 5 illustrates a call PSTN - TETRA, and Figure 6 illustrates a call PABX - TETRA. Figure 1 is a flow chart showing a first preferred embodiment of the method of the invention. The flow chart in Figure 1 can be utilized, for example, in a TETRA mobile network (Terrestrial Trunked Radio) when processing call establishment requests associated with new calls to be established. In block A a number is defined for a mobile station of the system from the parallel number spaces in use. In a TETRA network, from the mobile station of which calls can be made within the TETRA network, to a public switched telephone network and to a PABX network of the specific organization thereof, a subscriber number, or an ITSI number (Individual TETRA Sub- scriber Identity), has to be determined for an individual mobile station from the TETRA network. A call can be made from a TETRA network mobile station to another TETRA network mobile station by directly selecting said ITSI number. If two mobile stations of the same TETRA network are concerned, calls can be made directly from one mobile station to another using an SSI number (Short Subscriber Identity). A public switched telephone network number, in other words an MSISDN number, should also be determined for the TETRA network mobile station. Calls can be made from the public switched telephone network to the TETRA network mobile station by using the MSISDN number. In addition, a user group specific number, FSSN number (Fleet Specific Short Num- ber) has to be determined for the mobile station in order that the terminals belonging to the specific organization of the mobile station could make calls to the mobile station from the PABX network of the organization using an internal telephone number of the organization. Hence, the system uses three parallel number spaces, and each number space include a number that allows to make for example a speech call to the same mobile station. In block B a new call establishment request is received. The call establishment request then comprises at least a number that indicates the terminal, to which the new call should be established, in other words the number of subscriber B. The number included in the call establishment request can be a number in any of the number spaces defined to be used in the system, i.e. an ITSI, an MSISDN or an FSSN number. The call establishment request, here referring to an entity transmitted to the call control of the system through one or more signalling messages, comprises in practice also other data than the identifier of subscriber B, such as an identifier of subscriber A indicating the terminal from which the new call to be established originates. Block C deduces to which number space the identifier of subscriber B included in the call establishment request belongs. The destination of the call is also deduced, in other words to which network the call should be routed. If the call establishment request concerned originates from the TETRA system mobiie station, then line data is transmitted from said mobile station indicating the network to which the call should be routed. The deduction of the number space to which the number included in the call establishment request belongs is also based on said line data, i.e. the number is assumed to be in accordance with the number space required by the destination indicated by the line data. In practice, the mobile station user indicates the network (for example the PSTN or PABX) to the mobile station to which he/she is making the call, for example by feeding a predetermined number before the dialling associated with the call or for example by pressing a predetermined key in the mobile station. After this the mobile station transmits the line data to the TETRA network over the radio path in such a manner that it can be utilized, for example, in number conversions. If, in turn, the call establishment request originates from somewhere else than the TETRA network mobile station, the call destination is deduced on the basis of the source of the call establishment request. If the source of the call establishment request is an inter-exchange circuit of a public switched telephone network or of a PABX network of an organization, the TETRA network is noted as the destination of the call. The number space of the number included in the call establishment request is also deduced on the basis of the source of the call. If the source is an inter-change circuit of the public switched telephone network it is assumed that the number included in the call estab- lishment request is in MSISDN format, and correspondingly if the source is an inter-exchange circuit of a PABX network of an organization it is assumed that the number included in the call establishment request is in FSSN format. In block D the number included in the call establishment request is converted into the number space required by the destination. The conversion can case-specifically be carried out for example by retrieving from the memory a conversion table listing the numbers corresponding to one another in different number spaces. Alternatively the number of an individual mobile station in different number spaces can be stored in the subscriber data thereof. If the mobile station, whose number is being converted, is then identified, the conversion can be carried out by retrieving the number in the correct number space from the subscriber data of said mobile station. In block E the number included in the call establishment request is replaced by the number produced in the conversion of block D, the number being in the format of the number space required by the destination of the call. In block F the call establishment request is forwarded to the call control so that the new call can be established. Figure 2 is a block diagram showing a first preferred embodiment of the system of the invention. A system 2 shown in Figure 2 for processing call establishment requests can be utilized for example in the TETRA network. The system 2 shown in Figure 2 for processing call establishment requests is formed of modules or sub-processes controlled by a master process 3 of the system for processing a call establishment request as required by the call concerned. The sub-processes can be carried out among each other in different network elements depending on the implementation of the system, i.e. software to be carried out in different telephone exchanges may for in- stance be in question. The call establishment requests are transmitted to the master process 3 from a call control unit 1 , to which the call establishment request is also returned after the number conversion for establishing a call. All modules shown in Figure 2 are not used in each call, and the order in which the modules participate in the number conversion depends on which type of call is concerned. The master process 3 attends to transferring the data needed between different modules. The modules operate in such a manner that certain parameters are fed thereto as starting data, and based on the parameters the modules produce results that the master process can feed, if needed, to another module as starting data. The modules operate irrespec- tive of one another. An identification process 4 included in the system 2 attends to pro- viding the necessary data in order to carry out the number analysis and the conversion. The identification module comprises an organization module 4.1 , which identifies the organization/user group, to which the subscriber belongs, based on the terminal ITSI number or the inter-exchange circuit (line data) used. A user module 4.2 identifies the subscriber on the basis of the ITSI number. A cell module 4.3 identifies the cell, in which the mobile station is located, based on the data transmitted from the base station and produces a cell code describing the location. This code can be utilized for example in emergency calls. An inter-exchange circuit module 4.4 identifies the inter-exchange circuit, from which the call establishment request is received and produces the parameters of the organization corresponding to said inter-exchange circuit based thereupon. A number identification module 5.1 of an analysing process 5 receives, for example, the dialling, the service type, the subscriber parameters, the organization parameters, the line data, the cell code, the inter-exchange circuit identifier, the number of the caller and the time and the date. Based on said data the number identification module 5.1 deduces the destination of the call and the number space, to which the number of the call establishment request belongs. Said data becomes apparent from the call destination pa- rameter and the call type parameter produced by the number identification module 5.1. A conversion process 6 receives the number and the data concerning the number space, to which said number belongs, and the number space, whose number is searched for. Based on said data the conversion process directs the received number to a correct module 6.1 - 6.4 where the conversion takes place. Each module 6.1 - 6.4 is able to attend to one conversion in the case shown in Figure 2. The conversion process thus produces a number in the number space required by the destination. A checking process 7 carries out the necessary checks for deducing whether the call, with which the call establishment request is associated, is allowed. A check module 7.1 of the call rights deduces on the basis of the type of the call, the subscriber parameters and the organization parameters whether the subscriber concerned can make a call of said type. A CLIP/CLIR/COLP module 7.2 deduces on the basis of the subscriber data whether the number of the caller (identifier of subscriber A) is known and whether the transmission of the caller number to the recipient of the call is al- lowed (CLIP, Calling Line Identification Presentation; CLIR, Calling Line Identification Restriction; and COLP, Connected Line Identification Presentation). A transmission module 7.3 checks on the basis of the ITSI number whether said subscriber has activated call forwarding. The transmission module produces data that indicate whether the call forwarding is activated, the number into which the call forwarding is activated, and the destination (TETRA/PSTN/PABX) into which the call forwarding is activated. A modification process 8 adds and deletes individual numbers from the number included in the call establishment request. If, for example, the number is provided in the form 0605551234, but should be in the form 5551234 in order to be correctly routed, then the modification process 8 attends to the deletion of the additional numbers. A cutting module 8.1 of the numbers and an adding module 8.2 of the numbers are provided with a number and the type of call as starting data, and based thereupon they will modify the number into a predetermined format. Figure 3 illustrates a call TETRA - PSTN referring to a call that is made from the TETRA network mobile station MS to a public switched telephone network subscriber. Figures 3 - 6 illustrate different calls so as to show the order in which the processes are performed. However, the data does not necessarily move as shown by the arrows. In practice the data can be transmitted from one process to another through the master process shown in Figure 2. In Figure 3 the identification process 4 identifies the mobile station (the user) based on the ITSI number thereof, the cell code based on data transmitted by the base station and the organization of the user based on the mobile station subscriber data. An analysing process 5 detects on the basis of the line data that the call concerned is one made to the public switched telephone network. Then the analysing process assumes that the number of subscriber B is in the MSISDN format, and does not require any changes. In con- trast, as the call is one originating from a mobile station (the cell is known) the number identification module detects that the number of the caller, or the identifier of subscriber A is in ITSI format, whereby it requires conversion. The checking process 7 deduces on the basis of the subscriber data that calls can be made from said mobile station to a public switched tele- phone network, and that call forwarding is not activated. If the call is not allowed the processing of the call establishment request in block 9 is inter- rupted, and the call fails. The conversion process 6 receives the identifier of subscriber A in ITSI format that it converts to MSISDN format. The conversion is carried out in order to transmit a number to subscriber B that allows subscriber B to call sub- scriber A. Calls cannot be made from the public switched telephone network to the TETRA network mobile station using the ITSI number thereof, and the ITSI number is therefore converted to an MSISDN number, whereby a number is transmitted to subscriber B allowing him/her to call subscriber A. The number of subscriber B does not require conversion (since the analysing process noted that it was a number in the correct number space). Then again the modification process 8 may have to delete or add some numbers (for example a country code) so that the number will be in the correct format. Correspondingly the modification process 8 may have to add or delete numbers also from the identifier of subscriber A. Finally the checking process 7 checks whether the identifier of subscriber A is to be transmitted to subscriber B. Thereafter the call establishment request is returned through the master process to the call control for establishing the call to subscriber B. Figure 4 illustrates a call TETRA - PABX referring to a call made from the TETRA network mobile station MS to the PABX network of the specific organization of the mobile station. The identification process 4, the analysing process 5 and the check process 7 operate exactly as described in Figure 3 with the exception that this time the analysing process 5 detects based on the line data that the call concerned is one to be made to the PABX net- work. The analysing process then assumes that the number of subscriber B is in the format according to the PABX network and does not require any changes. Number B is thus modified only in the modification process 8 by adding/deleting individual numbers. In contrast, the number of subscriber A in ITSI format is converted to FSSN format, i.e. to the number of the number space, allowing the subscriber of the PABX network to call the mobile station MS. After this the processing of the call establishment request proceeds as shown in Figure 3. Figure 5 illustrates a call PSTN - TETRA referring to a call that is made from a public switched telephone network terminal 10 to the TETRA network mobile station MS. The analysing process 5 then detects that the source of the call establishment request is a public switched telephone net- work; the call establishment request is thus received from the inter-exchange circuit XX (the inter-exchange circuit between the TETRA network and the PSTN network). The analysing process then assumes that the number included in the call establishment request, or the identifier of subscriber B, as well as the identifier of subscriber A are in PSTN format and that the destination of the call is a TETRA network. The conversion process 6 converts the identifier of subscriber B to the number space required by the TETRA network, i.e. to an ITSI number. The number of subscriber A does not require conversion since a call can directly be made from the TETRA network mobile station using a number of the public switched telephone network. After this the identification process 4 identifies the mobile station and the organization and retrieves the subscriber data of the mobile station. The checking process 7 deduces whether the mobile station MS has the right to receive a call from the public switched telephone network, whether the identifier of subscriber A is to be transmitted to the mobile station, and whether the mobile station has activated call forwarding. If the mobile station has activated call forwarding that requires conversion between different number spaces (a transfer to a public switched telephone network number, for example) then the conversion process 6 performs the conversion needed. Finally the modification process 8 modifies the numbers of subscriber A and subscriber B by adding/deleting numbers as required so as to obtain the number in a predetermined format. Then the call establishment request is returned to the call control through the master process. Figure 6 illustrates a call PABX - TETRA referring to a call made from the PABX network terminal 10 using a user group specific number to such a terminal, which is a TETRA network mobile station MS. The identification process 4 then detects that the source of the call establishment request is an inter-exchange circuit 14, i.e. a particular PABX network. Based thereupon the identification process 4 identifies said organization, whereby it retrieves the user group data of said organization. The analysing process 5 detects that the source of the call establishment request is a PABX network, i.e. the call establishment request is received from the inter-exchange circuit 14 (the inter-exchange circuit between the PABX network and the TETRA network). The analysing process then as- sumes that the number included in the call establishment request, or the identifier of subscriber B, as well as the identifier of subscriber A are in the format according to the PABX network and that the destination of the call is a TETRA network. The conversion process 6 converts the number of subscriber B to the format according to the number space required by the TETRA network, or as an ITSI number. The number of subscriber A does not require conversion since a call can be made directly from the TETRA network mobile station using a PABX network number. The identification process 4 retrieves the mobile station subscriber data based on the ITSI number allowing the check process 7 to deduce, for example, call rights and possible transfers. The modification process 8 modifies the number of subscriber A and the number of subscriber B into a predetermined format, whereafter the call establishment request is conveyed back to the call control from the master process. It is to be understood that the above description and the appended drawings are merely intended to illustrate the present invention. The invention can thus also be applied to other systems than to the TETRA system only described above by way of example. It is obvious for those skilled in the art that the invention can be varied and modified in various ways without deviating from the scope and the spirit of the invention disclosed in the attached claims.

Claims: CLAIMS 1. A method for processing a call establishment request in a telecommunication system, comprising the steps of: receiving a call establishment request, deducing the destination of the call, and forwarding the call establishment request for establishing a call to the destination of the call, characterized by comprising the steps of: defining several parallel number spaces for use, and defining numbers in said several parallel number spaces for at least some of the system terminals, receiving the call establishment request for establishing a new call, deducing the number space, to which the number included in the call establishment request belongs, and the destination of the call to be established on the basis of the line data included in the call establishment request and the source of the call establishment request, converting the number included in the call establishment request from the format according to the deduced number space to a number according to the number space required by the destination of the call, and replacing the number included in the call establishment request by said number according to the number space required by the destination of the call before forwarding the call establishment request. 2. A method as claimed in claim 1, characterized in that at least two parallel number spaces are determined for use. 3. A method as claimed in claim 1, characterized in that said telecommunication system is a mobile system including terminals, for which a number is determined from at least three different number spaces so that the number included in the call establishment request may be a number in a public switched telephone network, in a PABX network or in a mobile system. 4. A system for processing call establishment requests comprising at least a master process (3) and an analysing process (5), whereby the analysing process (5) deduces the destination of the call establishment request received by the master process, and the master process (3) forwards the call establishment request for establishing a call, characterized in that said system uses several parallel number spaces, in which case the number included in the call establishment request can be a number in any of the number spaces in use, the analysing process (5) deduces the destination of the call and the number space, to which the number included in the call establishment request belongs, on the basis of the line data in the call establishment request and the source of the call establishment request, the system further comprises a conversion process (6) that on the basis of the number included in the call establishment request and the number space deduced by the analysing process (5) retrieves from a memory a number corresponding to the number included in the call establishment request, said retrieved number being a number of the number space required by the destination of the call, and the system (3) replaces the number included in the call establishment request by the number retrieved from the memory using the conversion process before the master process (3) forwards the call establishment request. 5. A system as claimed in claim 4, c h a r a c t e r i z e d in that the analysing process (5) deduces that the number included in the call establishment request is in the format according to the public switched telephone network number space, if the line data indicates that the destination of the call is a public switched tele- phone network (PSTN), the number included in the call establishment request is in the format according to the PABX network number space, if the line data indicates that the destination of the call is a PABX network, the destination of the call is a mobile network (TETRA) and that the number included in the call establishment request is in the format according to the PABX network number space, if the source of the call establishment request is an inter-exchange circuit of the PABX network, and the destination of the call is a mobile network (TETRA), and that the number included in the call establishment request is in the format according to the public switched telephone network number space, if the source of the call establishment request is formed of the inter-exchange circuit of the public switched telephone network. 6. A system as claimed in claim 4 or 5, c h a r a c t e r i z e d in that the analysing process (5) and the conversion process (6) are two independent processes separate from the master process (6). 7. A system as claimed in claims 4-6, characterized in that the master process (3), the analysing process (5) and the conversion process (6) are decentralized into different network elements. 8. A system as claimed in claims 4-7, characterized in that said system (2) for processing call establishment requests is a part of the TETRA mobile system.

Inventors: PESONEN TERO, PESONEN, TERO
Applicants: NOKIA NETWORKS OY, PESONEN TERO, PESONEN, TERO
Application year: 1999
Main classification: H04M3
IPC codes: H04M3, H04W84