Method of transferring between switching exchanges for mobile services, the handling of an active connection

Abstract: Known methods of transferring between centres the handling of an active connection between a user and a mobile terminal in a telecommunication system designed for mobile communication generally have the disadvantage that the routing obtained is inefficient. By investigating both a first route between a first switching centre and the user and a second route between a second switching centre and the user for common centres which are able to handle call control and connection control separately, of which the common centre situated nearest the first switching centre is designated as central intelligence point or, if the latter is not found, by designating the centre situated nearest the user as central intelligence point and then setting up a connection between a central intelligence point found in this way and the second switching centre, the most efficient routing is obtained.

Description: A. BACKGROUND OF THE INVENTION The invention relates to a method of transferring between centres the handling of an active connection between a user, on the one hand, and a mobile terminal, on the other hand, in a telecommunication system designed for mobile communication, comprising at least one mobile terminal, a first and a second switching centre designed for mobile services and each having a working region with a limited range, and a section of a network designed for nonmobile telecommunication, which section is able to interact with the switching centres, there being a first route between the first switching centre and the user, via which first route the active connection has been set up, and there being a second route between the second switching centre and the user, which routes each have at least one intelligence point where connection control and call control can be handled separately. Such a method is disclosed by EP 0 421 535 A1. The latter describes how an existing method for transferring between two switching centres designed for mobile services the active connection to a mobile terminal, better known under the designation "handover procedure" and as defined, for example, in GSM recommendations for the future pan-European digital mobile telecommunication system, can be improved. In addition to a number of attractive aspects, this existing method has the great drawback that the switching centre via which the active connection is initiated remains incorporated in the communication path to the mobile terminal for the entire duration of the connection, even if said connection moves to the working region of another switching centre. Another drawback of this existing method is that the first switching centre involved in an active connection provides the billing for the entire time that the connection is active, as a result of which it is not possible to adjust the billing if the mobile station moves to a region having a different charge rate. The method described in EP 0 421 535 A1 does not have the above drawbacks because, in this method, in addition to a connection set up between the centre designed for nonmobile telecommunication and the first switching centre, a connection is set up between the first and the second switching centre and between the centre designed for nonmobile telecommunication and the second switching centre, and the entire handling of the connection is taken over by the second switching centre, after which the connection between the two switching centres and between the centre designed for nonmobile telecommunication and the first switching centre is disconnected. As a result, the switching centre via which the active connection is initiated is not incorporated in the communication path to the mobile terminal for the entire duration of the connection and it is possible to adjust the billing. This known method described in EP 0 421 535 A1 has the disadvantage that the setting up of the connection between the second switching centre and the centre designed for nonmobile telecommunication to which the first switching centre is already connected may result in inefficient routing depending on the way in which the user may be coupled to one or both switching centres via various centres designed for nonmobile telecommunication or via a third switching centre and depending on the facilities of said centres designed for nonmobile telecommunication and on the switching centres. Some switching centres, for example, have the possibility of being able to handle connection control and call control separately, as a result of which it becomes possible to reroute an existing connection without having to interrupt or disconnect it for a long time. As defined, for example, in GSM recommendations, at least one such switching centre is always present in every route between the mobile terminal and the user. B. SUMMARY OF THE INVENTION The object of the invention is, inter alia, to provide a method of the type stated in the introduction, in which routing is carried out as efficiently as possible and in which the possibilities of centres designed for nonmobile telecommunication and of the switching centres are optimally utilised. For the sake of completeness, it is pointed out in this connection that the application of the method provided does not have to be limited to GSM but is also possible in other mobile telecommunication systems. For this purpose, the method according to the invention has the characteristic that, for a predetermined time interval, both routes are investigated for common intelligence points belonging to the first route and the second route, and if one common intelligence point is found it is designated as a central intelligence point, if several common intelligence points are found, an intelligence point situated nearest the first switching centre is designated as a central intelligence point, and if no common intelligence point is found an intelligence point of the first route, which intelligence point is situated nearest the user, is designated as a central intelligence point, a connection also being set up between the central intelligence point and the second switching centre, information needed for the transfer of the handling of the active connection being transferred from at least one centre situated on the first route to at least one centre situated in the connection set up, and the connection via the first switching centre between the central intelligence point and the mobile terminal being disconnected after the active connection to the mobile terminal has been taken over by the second switching centre. The invention is based on the insight that, with future signalling and control signals in telecommunication networks such as the recently developed ISCP ( I ntegrated Services Digital Network S ignalling C ontrol P art) which forms a component of the signalling system No. 7 (C7), it becomes possible to arrange for centres designed for nonmobile telecommunication to handle the connection control and the call control separately and that it is, of course, possible to provide different switching centres with this possibility. In this way, the most efficient routing is obtained with the given possibilities of centres designed for nonmobile telecommunication and the switching centres by investigating the first and the second route for common intelligence points belonging to both routes (read: by investigating for the presence of one or more common switching centres and/or centres designed for nonmobile telecommunication having the possibility of separately handling the connection control and the call control), by choosing, if one common intelligence point is found, said intelligence point as central intelligence point, by choosing, if several common intelligence points are found, an intelligence point situated nearest the first switching centre as central intelligence point, and by choosing, if no common intelligence point is found, an intelligence point of the first route, which intelligence point is not common and is situated nearest the user, as central intelligence point, and by then setting up a connection between the central intelligence point and the second switching centre, information needed for the transfer of the handling of the active connection being transferred from at least one centre situated on the first route to at least one centre situated in the connection set up and the connection via the first switching centre between the central intelligence point and the mobile terminal being disconnected after the active connection to the mobile terminal has been taken over by the second switching centre. Whereas it was still necessary in the known method as described in EP 0 421 535 A1 to transfer both signalling information and data such as speech from the first switching centre to the second switching centre for a short time (the so-called GSM step), in the method according to the invention it is only the signalling information which has to be transferred from a centre (switching centre or centre designed for nonmobile telecommunication) situated on the first route between the central intelligence point and the first switching centre (both included) to a centre (switching centre or centre designed for nonmobile telecommunication) situated in the connection set up, and this results in a further increase in the efficiency. A first embodiment of the method according to the invention has the characteristic that, if the predetermined time interval is exceeded, an intelligence point situated nearest the user and belonging both to the first route and to a route situated between the first and second switching centre is designated as a central intelligence point. The "handover procedure" is a process which is critical with respect to time, and consequently the chosen predetermined time interval must not be too long. If the predetermined time interval is exceeded, this first embodiment establishes a (temporary) routing via which the handover can take place. A second embodiment of the method according to the invention has the characteristic that, if no common intelligence point is found as a consequence of the predetermined time interval being exceeded, a route found between the second switching centre and the user via the central intelligence point, and the second route are then investigated for common intelligence points. If no common intelligence points are found during the predetermined time interval, although they are nevertheless present, the choosing of another intelligence point may result in less efficient routing. As a result of then investigating the route found between the second switching centre and the user via the central intelligence point, and the second route for common intelligence points, the most efficient routing is nevertheless ultimately obtained without the connection between the user and the mobile terminal having to be disconnected or interrupted for a long time as a result of the temporarily less efficient routing. A third embodiment of the method according to the invention has the characteristic that the common intelligence point functions as a switching centre or as a centre designed for nonmobile communication having a bridge setting facility. A centre may have switching facilities in which a primary connection is coupled to a first secondary connection or to a second secondary connection. In this connection, the disadvantage arises that a switching click cannot always be avoided during the switching. If a centre has a bridge setting facility, in which case a primary connection is first coupled to the first secondary connection, then both to the first and the second secondary connection and then to the secondary connection alone, this disadvantage does not arise. As a result of the abovementioned ISCP techniques, centres designed for nonmobile telecommunication are also able to have bridge setting facilities. From "Enlarging technologies based on no. 7 signalling system for mobile communication network" by A. Nekajima, H. Sawada and N. Shinagawa, it is known that there are two kinds of handover functions: an inter-radiozone handover (the changing of channels between radiozones belonging to the same mobile switch) and an inter-office handover (handover capability between mobile switches). By establishing a new wire speech path before a radio channel changes a so-called high-speed handover is created. It is not known from this document to investigate two routes for common intelligence points belonging to the first route and the second route, and it is not known to, in dependence of a result, designate a certain intelligence point as a central intelligence point for setting up a connection between the central intelligence point and a second switching centre and for disconnecting a connection via a first switching centre between the central intelligence point and the mobile terminal after the active connection to the mobile terminal has been taken over by the second switching centre. C. REFERENCE EP 0 421 535 A1 "Enlarging technologies based on no. 7 signalling system for mobile communication network" by A. Nakajima, H. Sawada and N. Shinagawa, NTT Mobile Communications Division, NTT Laboratories, Tokyo, Japan, Globecom 1987, IEEE D. EXEMPLARY EMBODIMENTS The invention will be explained in greater detail by reference to an exemplary embodiment shown in the figures. In the figures: Figure 1 shows a diagrammatic representation of a telecommunication system, designed for mobile communication, in which routing is carried out efficiently by applying the method according to the invention, and Figure 2 shows a flow chart of an embodiment of the method according to the invention. Figure 1 shows diagrammatically a telecommunication system designed for mobile communication. Said system comprises a mobile terminal 1 (mobile station or MS) which can be coupled via a radio path to switching centres 2, 3, 4, 5, 6 and 7 (mobile switching centre or MSC). MSC 2 and 3 can be coupled to a centre 8 (EXchange or EX) for nonmobile telecommunication, MSC 4 can be coupled to an EX 10 and MSC 5 and 6 can be coupled to an EX 9. MSC 7 can be coupled to MSC 6. EX 8 can furthermore be coupled to an EX 11, EX 10 can furthermore be coupled to EX 11 and EX 9, and EX 9 and EX 11 can each furthermore be coupled to an EX 12, which is connected to a user 13. The application of the method in this system proceeds as follows. If MS 1 is situated in the working region of MSC 2, MS 1 is coupled via a radio path to MSC 2 which is connected to the user 13, for example, via EX 8, EX 11 and EX 12, and communication takes place between MS 1 and user 13. If MS 1 moves from the working region of MSC 2 to the working region of MSC 3, the first, or old, route expressed in numbers is in this case 2-8-11-12-13 and the second, or new, route expressed in numbers is, for example 3-8-11-12-13 and both routes are investigated in the course of a predetermined time interval for common intelligence points belonging to both routes, in which process one of the three following cases A, B and C arises: A) One of the EXs 8, 11 and 12 is found to be the common intelligence point: A1) If EX 8 is found to be the common intelligence point (that is to say EX 8 has the possibility of handling the connection control and the call control separately), EX 8 is designated as central intelligence point, in which case a connection is set up between EX 8 and MSC 3, the information needed for the transfer of the handling of the active connection is transferred from MSC 2 to MSC 3 via EX 8 and the connection via MSC 2 between EX 8 and MS 1 is disconnected after the active connection to MS 1 has been taken over by MSC 3. A2) If EX 11 is found to be the common intelligence point (that is to say EX 11 has the possibility of handling the connection control and the call control separately) EX 11 is designated as central intelligence point, in which case a connection is set up between EX 11 and MSC 3 via EX 8, information needed for the transfer of the handling of the active connection is transferred from MSC 2 to MSC 3 via EX 8 and the connection between EX 11 and MS 1 via MSC 2 is disconnected after the active connection to MS 1 has been taken over by MSC 3. A3) If EX 12 is found to be the common intelligence point (that is to say EX 12 has the possibility of handling the connection control and the call control separately), EX 12 is designated as central intelligence point, in which case a connection is set up between EX 12 and MSC 3 via EX 11 and EX 8, information needed for the transfer of the handling of the active connection is transferred from MSC 2 to MSC 3 via EX 8 and the connection via MSC 2 between EX 12 and MS 1 is disconnected after the active connection to MS 1 has been taken over by MSC 3. B) Two or three of the EXs 8, 11 and 12 are found to be the common intelligence point: B1) If both EX 8 and EX 11 and/or EX 12 are found, EX 8 is designated as central intelligence point because, of all the common intelligence points found, EX 8 is situated nearest MSC 2, and the further procedure is as in A1). B2) If both EX 11 and EX 12 are found and EX 8 is not found, EX 11 is designated as central intelligence point because, of all the common intelligence points found, EX 11 is situated nearest MSC 2, and the further procedure is as in A2). C) None of the EXs 8, 11 and 12 is found to be a common intelligence point: MSC 2 is designated as central intelligence point because MSC 2 is in this case the intelligence point located on the first route and situated nearest the user 13, in which case a connection is set up between MSC 2 and MSC 3 via EX 8 and the information needed for the transfer of the handling of the active connection is transferred from MSC 2 to MSC 3 via EX 8 and the connection between MSC 2 and MS 1 is disconnected after the active connection to MS 1 has been taken over by MSC 3. If the predetermined time interval is exceeded, EX 8 is designated as central intelligence point if EX 8 is the intelligence point situated nearest the user 13 and belonging both to the first route and to the route between MSC 2 and MSC 3, and the further procedure is as in A1). If EX 8 is not an intelligence point, MSC 2 is designated as central intelligence point in this case of transgression, and the further procedure is as in C). Then, if no common intelligence points are found as a consequence of the predetermined time interval being exceeded, a (suboptimal) route found between the second switching centre (MSC 3) and the user 13 via the central intelligence point, and the second route can then [sic] be investigated for common intelligence points, in which case, the cases A), B) or C) may again arise, etc. In this connection it should be pointed out that both the second route and the suboptimal route each proceed from MSC 3 and that, in this case, the first and the second switching centres therefore coincide. Of course it is also possible to make do immediately with the connection found in the case C) without investigating the routes yet again. If MS 1 is located in the working region of MSC 3, MS 1 is coupled via a radio path to MSC 3, which is connected, for example, via EX 8, EX 11 and EX 12 to the user 13 and communication takes place between MS 1 and user 13. If MS 1 moves from the working region of MSC 3 to the working region of MSC 4 during said communication, the first, or old, route expressed in numbers is in this case 3-8-11-12-13 and the second, or new, route expressed in numbers is, for example, 4-10-11-12-13, and both routes are investigated during the predetermined time interval for common intelligence points belonging to both routes, in which case one of the three following cases D, E and F arises: D) One of the EXs 11 and 12 is found to be the common intelligence point: D1) If EX 11 is found to be the common intelligence point (that is to say EX 11 has the possibility of handling the connection control and the call control separately), EX 11 is designated as central intelligence point, in which case a connection is set up between EX 11 and MSC 4 via EX 10, information needed for the transfer of the handling of the active connection is transferred from MSC 3 to MSC 4 via EX 8, EX 11 and EX 10 and/or information is transferred from EX 8 to EX 10 via EX 11, and the connection via MSC 3 between EX 11 and MS 1 is disconnected after the active connection to MS 1 has been taken over by MSC 4. D2) If EX 12 is found to be the common intelligence point (that is to say EX 12 has the possibility of handling the connection control and the call control separately), EX 12 is designated as central intelligence point, in which case a connection is set up between EX 12 and MSC 4 via EX 11 and EX 10, information needed for the transfer of the handling of the active connection is transferred from MSC 3 to MSC 4 via EX 8, EX 11 and EX 10 and/or information is transferred from EX 8 to EX 10 via EX 11, and the connection via MSC 3 between EX 12 and MS 1 is disconnected after the active connection to MS 1 has been taken over by MSC 4. E) Both EXs 11 and 12 are found to be common intelligence points: EX 11 is designated as central intelligence point because, of the two common intelligence points, EX 11 is located nearest MSC 3, and the further procedure is as in D1). F) None of the EXs 11 and 12 is found to be a common intelligence point: F1) If EX 8 is adequate as an intelligence point, EX 8 is designated as central intelligence point because EX 8 is in this case the intelligence point located on the first route and is the intelligence point which is not common and which is located nearest the user 13 (with respect to MSC 3), in which case a connection is set up between EX 8 and MSC 4 via EX 11 and EX 10, information needed for the transfer of the handling of the active connection is transferred from MSC 3 to MSC 4 via EX 8, EX 11 and EX 10 and the connection via MSC 3 between EX 8 and MS 1 is disconnected after the active connection to MS 1 has been taken over by MSC 4. F2) If EX 8 is not adequate as an intelligence point, MSC 3 is designated as central intelligence point because MSC 3 is in this case the intelligence point located on the first route and the intelligence point which is not common and is situated nearest the user 13, in which case a connection is set up between MSC 3 and MSC 4 via EX 8, EX 11 and EX 10, information needed for the transfer of the handling of the active connection is transferred from MSC 3 to MSC 4 via EX 8, EX 11 and EX 10, and the connection between MSC 3 and MS 1 is disconnected after the active connection to MS 1 has been taken over by MSC 4. If the predetermined time interval is exceeded, EX 11 is designated as central intelligence point if EX 11 is the intelligence point situated nearest user 13 and belonging both to the first route and to the route situated between MSC 3 and MSC 4, and the further procedure is as in D1). If EX 11 is not an intelligence point, EX 8 is, in this case of transgression, designated as central intelligence point, and the further procedure is as in F1), and if EX 8 is not an intelligence point, MSC 3 is designated as central intelligence point, and the further procedure is as in F2). Then, if no common intelligence point is found as a consequence of the predetermined time interval being exceeded, a (suboptimal) route found between the second switching centre (MSC 4) and the user 13 via the central intelligence point, and the second route can then [sic] be investigated for common intelligence points, in which case the cases D), E) or F) may again arise, etc. In this connection, it should be pointed out that both the second route and the suboptimal route each originate from MSC 4 and that, in this case, the first and second switching centres therefore coincide. Of course, it is also possible to make do with the connection found in the case F) without investigating both routes yet again. If MS 1 is located in the working region of MSC 4, MS 1 is coupled via a radio path MSC 4 which is connected to the user 13, for example via EX 10, EX 11 and EX 12, and communication takes place between MS 1 and user 13. If MS 1 moves from the working region of MSC 4 to the working region of MSC 5 during this communication, the first, or old, route expressed in numbers is in this case 4-10-11-12-13 and the second, or new, route expressed in numbers is, for example, 5-9-12-13, and both routes are investigated during the predetermined time interval for common intelligence points belonging to both routes, in which case one of the two following cases G and H arises: G) EX 12 is found to be the common intelligence point (that is to say EX 12 has the possibility of handling the connection control and the call control separately): EX 12 is designated as central intelligence point, in which case a connection is set up between EX 12 and MSC 5 via EX 9, information needed for the transfer of the handling of the active connection is transferred from MSC 4 to MSC 5 via EX 10 and EX 9 and/or information is transferred from EX 10 and/or EX 11 to EX 9, and the connection via MSC 4 between EX 12 and MS 1 is disconnected after the active connection to MS 1 has been taken over by MSC 5. H) EX 12 is not found to be a common intelligence point: H1) If EX 11 is adequate as an intelligence point, EX 11 is designated as central intelligence point because EX 11 is, in this case, the intelligence point which is located on the first route and the intelligence point which is not common and which is situated nearest the user 13 (with respect to EX 10 and MSC 4), in which case a connection is set up between EX 11 and MSC 5 via, for example, EX 12 and EX 9, information needed for the transfer of the handling of the active connection is transferred from MSC 4 to MSC 5 via EX 10 and EX 9, and the connection via MSC 4 between EX 11 and MS 1 is disconnected after the active connection to MS 1 has been taken over by MSC 5. H2) If EX 11 is not adequate as an intelligence point and EX 10 is in fact adequate as an intelligence point, EX 10 is designated as central intelligence point because EX 10 is, in this case, the intelligence point located on the first route and the intelligence point which is not common and which is nearest the user 13 (with respect to MSC 4) in which case a connection is set up between EX 10 and MSC 5 via EX 9, information needed for the transfer of the handling of the active connection is transferred from MSC 4 to MSC 5 via EX 10 and EX 9, and the connection via MSC 4 between EX 10 and MS 1 is disconnected after the active connection to MS 1 has been taken over by MSC 5. H3) If EX 11 and EX 10 are not adequate as intelligence point, MSC 4 is designated as central intelligence point because MSC 4 is, in this case, the intelligence point located on the first route and the intelligence point which is not common and is situated nearest the user 13, in which case a connection is set up between MSC 4 and MSC 5 via EX 10 and EX 9, information needed for the transfer of the handling of the active connection is transferred from MSC 4 to MSC 5 via EX 10 and EX 9, and the connection between MSC 4 and MS 1 is disconnected after the active connection to MS 1 has been taken over by MSC 5. If the predetermined time interval is exceeded, EX 10 is designated as central intelligence point if EX 10 is the intelligence point situated nearest user 13 and belonging both to the first route and to the route situated between MSC 4 and MSC 5, and the further procedure is as in H2). If EX 10 is not an intelligence point, MSC 4 is designated as central intelligence point, and the further procedure is as in H3). Then, if no common intelligence point is found as a consequence of the predetermined time interval being exceeded, a (suboptimal) route found between the second switching centre (MSC 5) and the user 13 via the central intelligence point, and the second route can then [sic] be investigated for common intelligence points, in which case the cases G) or H) may again arise, etc. In this connection, it should be pointed out that both the second route and the suboptimal route each originate from MSC 5 and that, in this case, the first and second switching centres therefore coincide. Of course, it is also possible to make do with the connection found in the case H) without investigating both routes yet again. If MS 1 is located in the working region of MSC 5, MS 1 is coupled via a radio path to MSC 5 which is connected, for example, via EX 9 and EX 12 to the user 13, and communication takes place between MS 1 and user 13. If MS 1 moves from the working region of MSC 5 to the working region of MS 6 during said communication, the first, or old, route expressed in numbers is in this case 5-9-12-13 and the second, or new, route expressed in numbers is, for example, 6-9-12-13, and both routes are investigated during the predetermined time interval for common intelligence points belonging to both routes, in which case one of the three following cases I, J and K arises: I) One of the EXs 9 and 12 is found to be the common intelligence point: I1) If EX 9 is found to be the common intelligence point (that is to say EX 9 has the possibility of handling the connection control and the call control separately), EX 9 is designated as central intelligence point, in which case a connection is set up between EX 9 and MSC 6, information needed for the transfer of the handling of the active connection is transferred from MSC 5 to MSC 6 via EX 9, and the connection via MSC 5 between EX 9 and MS 1 is disconnected after the active connection to MS 1 has been taken over by MS 6. I2) If EX 12 is found to be the common intelligence point (that is to say EX 12 has the possibility of handling the connection control and the call control separately), EX 12 is designated as central intelligence point, in which case a connection is set up between EX 12 and MSC 6 via EX 9, information needed for the transfer of the handling of the active connection is transferred from MSC 5 to MSC 6 via EX 9, and the connection via MSC 5 between EX 12 and MS 1 is interrupted after the active connection to MS 1 is taken over by MSC 6. J) Both EXs 9 and 12 are found to be common intelligence points: EX 9 is designated as central intelligence point because, of the two common intelligence points, EX 9 is located nearest MSC 5, and the further procedure is as in I1). K) Neither of the EXs 9 and 12 is found to be a common intelligence point: MSC 5 is designated as central intelligence point because MSC 5 is in this case the intelligence point located on the first route and the intelligence point which is not common and is situated nearest the user 13, in which case a connection is set up between MSC 5 and MSC 6 via EX 9, information needed for the transfer of the handling of the active connection is transferred from MSC 5 to MSC 6 via EX 9, and the connection between MSC 5 and MS 1 is disconnected after the active connection to MS 1 has been taken over by MSC 6. If the predetermined time interval is exceeded, EX 9 is designated as central intelligence point if EX 9 is the intelligence point situated nearest the user 13 and belonging both to the first route and to the route situated between MSC 5 and MSC 6, and the further procedure is as in I1). If EX 9 is not an intelligence point, MSC 5 is designated as central intelligence point, and the further procedure is as in K). Then, if no common intelligence points are found as a consequence of the predetermined time interval being exceeded, a (suboptimal) route found between the second switching centre (MSC 6) and the user 13 via the central intelligence point, and the second route can then be investigated for common intelligence points, in which case the cases I), J) or K) may again arise, etc. In this connection it should be pointed out that both the second route and the suboptimal route each originate from MSC 6 and that, in this case, the first and second switching centres therefore coincide. Of course, it is also possible to make do directly with the connection found in the case K without investigating both routes yet again. If MS 1 is located in the working region of MSC 6, MS 1 is coupled via a radio path to MSC 6 which is connected, for example, via EX 9 and EX 12 to the user 13, and communication takes place between MS 1 and user 13. If MS 1 moves from the working region of MSC 6 to the working region of MSC 7 during said communication, which MSC 7 forms part, for example, of a private or individual network, the first, or old, route expressed in numbers is in this case 6-9-12-13 and the second, or new route expressed in numbers is, for example, 7-6-9-12-13, and both routes are investigated during the predetermined time interval for common intelligence points belonging to both routes, in which case MSC 6 is normally found to be the common intelligence point and is consequently designated as central intelligence point because, regardless of whether EX 9 and EX 12 are or are not found to be common intelligence points, MSC 6 is, of all the possible common intelligence points found, the nearest to the first switching centre (=MSC6). A connection is then set up between MSC 6 and MSC 7, information needed for the transfer of the handling of the active connection is transferred from MSC 6 to MSC 7 and the connection between MSC 6 and MS 1 is interrupted after the active connection to MS 1 has been taken over by MSC 7. The above description of Figure 1 must under no circumstances be regarded as limiting since many other situations are also conceivable, both as regards the configuration of the telecommunication system and as regards the chosen routings. Thus, it is possible, for example, that the MS 1 located in the working region of MS 5 communicates with user 13 via MSC 5, EX 9, EX 10, EX 11 and EX 12 because the link between EX 9 and EX 12 is temporarily overloaded. In this case, the first, or old, route expressed in numbers is 5-9-10-11-12-13 (and therefore not 5-9-12-13). If, during said communication, MS 1 moves from the working region of MSC 5 to the working region of MSC 6 at an instant when said link is again free of overloading, the second, or new, route expressed in numbers is, for example, 6-9-12-13, and both routes are investigated during the predetermined time interval for common intelligence points belonging to both routes, in which case one of the three following cases L, M and N arises: L) One of the EXs 9 and 12 is found to be the common intelligence point: L1) If EX 9 is found to be the common intelligence point (that is to say EX 9 has the possibility of handling the connection control and the call control separately), EX 9 is designated as central intelligence point, in which case a connection is set up between EX 9 and MSC 6, information needed for the transfer of the handling of the active connection is transferred from MSC 5 to MSC 6 via EX 9, and the connection via MSC 5 between EX 9 and MS 1 is disconnected after the active connection to MS 1 has been taken over by MS 6. L2) If EX 12 is found to be the common intelligence point (that is to say EX 12 has the possibility of handling the connection control and the call control separately), EX 12 is designated as central intelligence point, in which case a connection is set up between EX 12 and MSC 6 via EX 9, information needed for the transfer of the handling of the active connection is transferred from MSC 5 to MSC 6 via EX 9, and the connection via MSC 5 between EX 12 and MS 1 is disconnected after the active connection to MS 1 has been taken over by MSC 6. M) Both EXs 9 and 12 are found to be a common intelligence point: EX 9 is designated as central intelligence point because, of the two common intelligence points, EX 9 is located nearest MSC 5, and the further procedure is as in L1). N) Neither EXs 9 and 12 is found to be a common intelligence point: N1) If EX 11 is adequate as an intelligence point, EX 11 is designated as central intelligence point because EX 11 is in this case the intelligence point located on the first route and the intelligence point which is not common and which is situated nearest the user 13 (with respect to EX 10 and MSC 5), in which case a connection is set up between EX 11 and MSC 6 via, for example, EX 12 and EX 9, information needed for the transfer of the handling of the active connection is transferred from MSC 5 to MSC 6 via EX 9, and the connection via MSC 5 between EX 11 and MS 1 is disconnected after the active connection to MS 1 has been taken over by MSC 6. N2) If EX 11 is not adequate as an intelligence point and EX 10 is in fact adequate as an intelligence point, EX 10 is designated as central intelligence point because EX 10 is in this case the intelligence point located on the first route and the intelligence point which is not common and is nearest the user 13 (with respect to MSC 5), in which case a connection is set up between EX 10 and MSC 6 via EX 9, information needed for the transfer of the handling of the active connection is transferred from MSC 5 to MSC 6 via EX 9, and the connection via MSC 5 between EX 10 and MS 1 is disconnected after the active connection to MS 1 has been taken over by MSC 6. N3) If EX 11 and EX 10 are not adequate as an intelligence point, MSC 5 is designated as central intelligence point because MSC 5 is in this case the intelligence point located on the first route and the intelligence point which is not common and is situated nearest the user 13, in which case a connection is set up between MSC 5 and MSC 6 via EX 9, information needed for the transfer of the handling of the active connection is transferred from MSC 5 to MSC 6 via EX 9, and the connection between MSC 5 and MS 1 is disconnected after the active connection to MS 1 has been taken over by MSC 6. If the predetermined time interval is exceeded, EX 9 is designated as central intelligence point if EX 9 is the intelligence point situated nearest the user 13 and belonging both to the first route and to the route situated between MSC 5 and MSC 6, and the further procedure is as in L1). If EX 9 is not an intelligence point, MSC 5 is designated as central intelligence point, and the further procedure is as in N3). Then, if no common intelligence points are found as a consequence of the predetermined time interval being exceeded, a (suboptimal) route found between the second switching centre (MSC 6) and the user 13 via the central intelligence point, and the second route can then be investigated for common intelligence points, in which case the cases L), M) or N) can again arise, etc. In this connection it should be pointed out that both the second route and the suboptimal route each originate from MSC 6 and that, in this case, the first and second switching centre thus coincide. Of course, it is also possible to make do with the connection found in case K) without investigating both routes yet again. It is pointed out that the cases L) and M) completely correspond to the cases I) and J) respectively, whereas the case N) clearly differs from the case K) because of the temporary overloading of the link between EX 9 and EX 12. The position of user 13 in Figure 1 must also not be regarded as limiting. Thus, it is possible, for example, that the user is a mobile terminal, hereinafter referred to as MS 14, who is not shown in Figure 1 and who is located, for example, in the working region of MSC 6. If, while MS 1 is located in the working region of MSC 5 and is coupled via a radio path to MSC 5 which is coupled, for example, via EX 9 to MSC 6 which is coupled via a radio path to MS 14, and communication takes place between MS 1 and MS 14, MS 1 moves during said communication from the working region of MSC 5 to the working region of MSC 6, the first, or old, route expressed in numbers is in this case 5-9-6-14 and the second, or new, route expressed in numbers is, for example, 6-14, and both routes are investigated during the predetermined time interval for common intelligence points belonging to both routes. In this situation MS 14 acts as the user, MSC 5 forms the first switching centre and MSC 6 the second switching centre, and one of the two following cases P and Q arises: P) MSC 6 is found to be the common intelligence point: MSC 6 is designated as central intelligence point, in which case information needed for the transfer of the handling of the active connection is transferred from MSC 5 to MSC 6, and the connection via MSC 5 between MSC 6 and MS 1 is disconnected after the active connection to MS 1 has been taken over by MSC 6. Q) MSC 6 is not found to be the common intelligence point: Q1) If EX 9 is adequate as intelligence point, EX 9 is designated as central intelligence point because EX 9 is in this case the intelligence point located on the first route and the intelligence point which is not common and which is nearest the user MS 14 (with respect to MSC 5), in which case a connection is set up between EX 9 and MSC 6, information needed for the transfer of the handling of the active connection is transferred from MSC 5 to MSC 6 via EX 9, and the connection via MSC 5 between EX 9 and MS 1 is disconnected after the active connection to MS 1 has been taken over by MSC 6. Q2) If EX 9 is not adequate as intelligence point, MSC 5 is designated as central intelligence point because in this case MSC 5 is the intelligence point located on the first route and the intelligence point which is not common and nearest the user MS 14, in which case a connection is set up between MSC 5 and MSC 6 via EX 9, information needed for the transfer of the handling of the active connection is transferred from MSC 5 to MSC 6 via EX 9, and the connection between MSC 5 and MS 1 is disconnected after the active connection to MS 1 has been taken over by MSC 6. If, while MS 1 is located in the working region of MSC 5 and is coupled via a radio path to MSC 5, which is coupled, for example, via EX 9 and MSC 6 to MSC 7, which is coupled via a radio path to MS 14, and communication takes place between MS 1 and MS 14, MS 1 moves during said communication from the working region of MSC 5 to the working region of MSC 6, the first, or old, route expressed in numbers is in this case 5-9-6-7-14 and the second, or new, route expressed in numbers is, for example, 6-7-14, and both routes are investigated during the predetermined time interval for common intelligence points belonging to both routes. In this situation MS 14 acts as the user, MSC 5 forms the first switching centre and MSC 6 forms the second switching centre, and one of the three following cases R, S and T arises: R) One of the MSCs 6 and 7 is found to be the common intelligence point: R1) If MSC 6 is found to be the common intelligence point (that is to say MSC 6 has the possibility of handling the connection control and the call control separately), MSC 6 is designated as central intelligence point, in which case information needed for the transfer of the handling of the active connection is transferred from MSC 5 to MSC 6 via EX 9 and the connection via MSC 5 between MSC 6 and MS 1 is disconnected after the active connection to MS 1 has been taken over by MSC 6. R2) If MSC 7 is found to be the common intelligence point (that is to say MSC 7 has the possibility of handling the connection control and the call control separately), MSC 7 is designated as central intelligence point, in which case a connection is set up between MSC 7 and MSC 6, information needed for the transfer of the handling of the active connection is transferred from MSC 5 to MSC 6 via EX 9, and the connection via MSC 5 between MSC 7 and MS 1 is disconnected after the active connection to MS 1 has been taken over by MSC 6. S) Both MSCs 6 and 7 are found to be a common intelligence point: MSC 6 is designated as central intelligence point because, of the two common intelligence points, MSC 6 is located nearest the first switching centre (=MSC 5), and the further procedure is as in R1). T) Neither of the MSCs 6 and 7 is found to be a common intelligence point: T1) If EX 9 is adequate as intelligence point, EX 9 is designated as central intelligence point because EX 9 is in this case the intelligence point located on the first route and the intelligence point which is not common and is situated nearest the user MS 14 (with respect to MSC 5), in which case a connection is set up between EX 9 and MSC 6, information needed for the transfer of the handling of the active connection is transferred from MSC 5 to MSC 6 via EX 9, and the connection via MSC 5 between EX 9 and MS 1 is disconnected after the active connection to MS 1 has been taken over by MSC 6. T2) If EX 9 is not adequate as intelligence point, MSC 5 is designated as central intelligence point because MSC 5 is in this case the intelligence point located on the first route and the intelligence point which is not common and is situated nearest the user MS 14, in which case a connection is set up between MSC 5 and MSC 6 via EX 9, information needed for the transfer of the handling of the active connection is transferred from MSC 5 to MSC 6 via EX 9, and the connection between MSC 5 and MS 1 is interrupted after the active connection to MS 1 has been taken over by MSC 6. If, while MS 1 is located in the working region of MSC 6 and is coupled via a radio path to MSC 6 which is coupled to MSC 7 which is coupled via a radio path to MS 14, and communication takes place between MS 1 and MS 14, MS 1 moves during said communication from the working region of MSC 6 to the working region of MSC 7, the first, or old, route expressed in numbers is in this case 6-7-14 and the second, or new, route expressed in numbers is, for example, 7-14, and both routes are investigated during the predetermined time interval for common intelligence points belonging to both routes. In this situation MS 14 acts as the user, MSC 6 forms the first switching centre and MSC 7 forms the second switching centre and one of the two following cases U and V arises: U) MSC 7 is found to be the common intelligence point: MSC 7 is designated as central intelligence point, in which case information needed for the transfer of the handling of the active connection is transferred from MSC 6 to MSC 7, and the connection via MSC 6 between MSC 7 and MS 1 is interrupted after the active connection to MS 1 has been taken over by MSC 7. V) MSC 7 is not found to be a common intelligence point: MSC 6 is designated as central intelligence point, in which case information needed for the transfer of the handling of the active connection is transferred from MSC 6 to MSC 7, and the connection between MSC 6 and MS 1 is disconnected after the active connection to MS 1 has been taken over by MSC 7. In the flow chart, shown in Figure 2, of an embodiment of the method according to the invention the blocks have the following meaning: block: meaning: 20 during an active call, a first, or old, MSCo via which a mobile terminal is communicating with a user receives an inter-MSC handover request, and MSCo asks a second, or new, MSCn whether it has sufficient radio capacity; simultaneously a timer is started to detect the elapse of a predetermined time interval. 21 has MSCn sufficient radio capacity? no : to block 22. yes : to block 23. 22 an inter-MSC handover does not take place as a result of insufficient radio capacity. 23 MSCo passes data relating to a first, or old, route between MSCo and the user to MSCn and inquires whether centres situated on the old route are intelligence points (that is to say whether the latter have the possibility of handling the connection control and the call control separately). 24 MSCn compares the data relating to the old route with connection lists for the purpose of establishing a second or new route between itself and the user. 25 is at least one centre in the data relating to the old route known from the connection list of MSCn? no : to block 26. yes : to block 27. 26 MSCn requests a connection list from a centre situated adjacently on the new route; block 24 then follows. 27 MSCn passes data relating to the known centres to MSCo; these known centres are designated as common centres. 28 is the common centre located nearest MSCo an intelligence point according to the data of MSCo? no : to block 29. yes : to block 31, the common centre is designated as central intelligence point. 29 are other common centres intelligence points according to the data of MSCo? no : to block 30. yes : to block 31, the common centre which is situated nearest MSCo and is adequate as an intelligent point is designated as central intelligence point. 30 the old route intelligence point which is not common and which is situated nearest the user is designated as central intelligence point. 31 a connection is set up between the central intelligence point and MSCn, information needed for the transfer of the handling of the active connection is transferred from at least one centre situated on the old route to at least one centre situated in the connection set up and the connection via MSCo between the central intelligence point and the mobile terminal is disconnected after the active connection to the mobile terminal has been taken over by MSCn. 32 as a consequence of the elapse of the predetermined time interval detected by the timer, the intelligence point situated nearest the user which is located both on the old route and on the route between MSCo and MSCn is designated as central intelligence point, then block 31 follows. The embodiment of the method as specified in the flow chart in Figure 2 proceeds as follows. As soon as a mobile terminal located in the working region of an MSCo and communicating with a user via a radio path and MSCo moves to the working region of an MSCn, MSCo files an inter-MSC handover request (possibly on the initiative of the mobile terminal) and it asks MSCn whether the latter has sufficient radio capacity. Because the handover procedure is a process which is critical with respect to time, a timer is immediately started in order to detect the elapse of a predetermined time interval (block 20). If MSCn has insufficient radio capacity, no inter-MSC handover takes place (block 21, 22). If MSCn has sufficient radio capacity, MSCo passes data relating to a first, or old, route between MSCo and the user to MSCn, and it inquires whether centres situated on the old route are intelligence points (that is to say whether they have the possibility of handling the connection control and the call control separately (block 21, 23)). MSCn has connection lists which make it possible to establish a second or new route between MSCn and the user, and it compares the data obtained from MSCo relating to the old route with said connection lists (block 24). If at least one centre situated on the old route is known from the connection lists, at least one common centre is consequently found by MSCn, which is then transmitted to MSCo (block 25, 27). If no centres situated on the old route are known from the connection lists of MSCn, the latter are supplemented with connection lists of an adjacent centre (block 25, 26) situated on the new route. This takes place as long as no common centre has been found and as long as there are still centres remaining on the new route (block 26, 24, 25). MSCo has data relating to whether centres situated on the old route are intelligent or not and investigates whether the common centres are intelligence points, the common centre which is situated nearest MSCo and which is also an intelligence point being designated as central intelligence point (block 28, 29). If no common centre which is also an intelligence point is found, an intelligence point of the old route, which intelligence point is not common and is situated nearest the user, is designated as central intelligence point (block 30). If the elapse of the predetermined time interval is detected by the timer, the intelligence point which is situated nearest the user and which is located both on the old route and on the route between MSCo and MSCn is designated as central intelligence point (block 32). A connection is then set up between the central intelligence point and MSCn, information needed for the transfer of the handling of the active connection is transferred from at least one centre situated on the old route to at least one centre situated in the connection set up, and the connection via MSCo between the central intelligence point and the mobile terminal is disconnected after the active connection to the mobile terminal has been taken over by MSCn (block 31). If no common intelligence point is found as a consequence of the predetermined time interval being exceeded or if the most optimally situated intelligence points have not been found as a consequence of, for example, a malfunction or an overload, the suboptimal route found and the second route can then be investigated for common points (block 24 et seq.). In this connection it is pointed out that the old and the new switching centre then coincide because the suboptimal route and the second route both run via said switching centre. A number of variations are possible on the embodiment of the method according to the invention shown in Figure 2. Thus, for example, tasks of MSCo (the transmission of data relating to the old route between MSCo and the user to MSCn, inquiring whether centres situated on the old route are intelligence points, and investigating whether common centres are intelligence points) and tasks of MSCn (having connection lists, comparing the data obtained from MSCo with said connection lists, and possibly supplementing the connection lists) can be distributed in another way between the two switching centres or they may be allotted to a greater or lesser degree to one particular centre to be chosen arbitrarily.

Claims: Method of transferring between centres the handling of an active connection between a user (13), on the one hand, and a mobile terminal (1) on the other hand, in a telecommunication system designed for mobile communication, comprising at least one mobile terminal, a first (2) and a second (3) switching centre designed for mobile services and each having a working region with a limited range, and a section of a network designed for nonmobile telecommunication, which section is able to interact with the switching centres, there being a first route between the first switching centre (2) and the user (13), via which first route the active connection has been set up, and there being a second route between the second switching centre (3) and the user, which routes each have at least one intelligence point (8) where connection control and call control can be handled separately, characterised in that, for a predetermined time interval, both routes are investigated for common intelligence points belonging to the first route and the second route, and if one common intelligence point is found it is designated as a central intelligence point, if several common intelligence points are found, an intelligence point situated nearest the first switching centre is designated as a central intelligence point, and if no common intelligence point is found an intelligence point of the first route, which intelligence point is situated nearest the user, is designated as a central intelligence point, a connection also being set up between the central intelligence point and the second switching centre, information needed for the transfer of the handling of the active connection being transferred from at least one centre situated on the first route to at least one centre situated in the connection set up, and the connection via the first switching centre between the central intelligence point and the mobile terminal being disconnected after the active connection to the mobile terminal has been taken over by the second switching centre. Method according to Claim 1, characterised in that, if the predetermined time interval is exceeded, an intelligence point situated nearest the user and belonging both to the first route and to a route situated between the first and second switching centre is designated as a central intelligence point. Method according to Claim 1 or 2, characterised in that, if no common intelligence point is found as a consequence of the predetermined time interval being exceeded, a route found between the second switching centre and the user via the central intelligence point, and the second route are then investigated for common intelligence points. Method accord:ng to Claim 1, 2 or 3, characterised in that the common intelligence point functions as a switching centre or as a centre designed for nonmobile communication having a bridge setting facility.

Inventors: VAN NIELEN MARCUS JOSEPHUS JOH, VAN NIELEN, MARCUS JOSEPHUS JOHANNES
Applicants: NEDERLAND PTT, KONINKLIJKE PTT NEDERLAND N.V.
Application year: 1992
Main classification: H04Q3
IPC codes: H04Q3, H04W36