Abstract:
A telecommunications system including a plurality of mobile telephones has a switch network including: data storage units (HLR) for storing connection data relating to respective mobile telephones; a register ( 15 ) for storing associations between data storage units and respective identification codes; inputs for inputting an identification code; and a switch unit ( 30, 31 ) for interrogating the register ( 15 ) to permit determination of the data storage unit (HLR) associated with that identification code. The switch network then uses the connection data stored by the data storage unit (HLR) to form a telecommunication link with the corresponding mobile telephone. The register unit ( 15 ) has two states. In a first state the register unit ( 15 ) and switch unit ( 30, 31 ) determine the data storage unit (HLR) associated with the input identification code. In a second state, the register unit ( 15 ) is linked to a routing unit ( 40 ). The routing unit ( 40 ) may then handle the call in one of various different ways such as re-routing the call back to the network or terminating the call. The state of the register unit ( 15 ) is determined by a condition such as time of day or origin of call.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a telecommunication system. It is particularly, but not exclusively, concerned with a telecommunications system for mobile telephones. 
     2. Summary of the Prior Art 
     The present invention arises as a development of the ideas disclosed in WO 96/11557. A call to a mobile telephone is not to a fixed point, and therefore the system must determine the location of the destination. In arrangements prior to that disclosed in WO96/11557, a call to a mobile telephone results in a signal being transmitted to a data storage unit in the form of a Home Location Register unit (HLR) which determines the location of the mobile telephone, and so permits routing of the call to occur. Inevitably, HLRs have a limited capacity, and some arrangement is therefore necessary to enable telecommunication systems to access multiple HLRs. Therefore, WO96/11557 proposed that the switch network which connects users to other users, HLRs, and system services, had a register unit associated therewith, which register unit contained information relating each telephone number to a corresponding one of a plurality of HLRs. The relationship between telephone numbers and HLRs was then freely selectable within the register unit, so that the register unit acted as a converter between the number and the information identifying the HLR. By providing such a register unit, the fixed relationship between numbers and HLRs was broken, and any telephone number was then assignable to any HLR, assuming space permitted. Note that, although not explicitly mentioned in WO96/11557, it is not necessary that the different HLRs belong to a single service provider thus, it was possible for a user to have the same telephone number even when changing from one service provider to another. 
     WO96/11557 also mentioned that the register unit may also store further information associated with the mobile telephones which permitted the switch network to enable calls from mobile telephones to be routed to different services, depending on the calling mobile telephone itself, in addition to the number dialled. 
     SUMMARY OF THE INVENTION 
     In the disclosure of WO96/11557, such additional routings were triggered by the user inputting appropriate codes. However, it has been realised that by providing additional processing at the register unit, the functioning of the system disclosed in WO96/11557 may be further developed. 
     The present invention proposes that predetermined conditions are stored within the register unit for individual telephone numbers, or for groups of telephone numbers, which conditions control the register unit to cause the register unit to switch between a first state in which it operates as in WO96/11557 to cause appropriate access to an HLR, and at least a second state in which the call is directed to one or more further processing units (hereinafter referred to as routing units). The or each routing unit may handle the call in various different ways, such as re-routing the call back to the telephone network, or terminating the call at the routing unit, possibly in combination with a message being returned to the telephone that originated the call. 
     In addition to the second state, it is possible for the register unit to be controlled to have a third state in which it neither operates as in WO96/11557 nor directs the call to one or more routing units. In this third state, the register unit may perform other actions, such as a general override of the predetermined conditions to allow correct interaction with other telecommunication services in the switch network. A different signal to the register unit at a later point in the call setup may result in the register unit reverting to the second state. 
     It is preferable for the register unit and the or each routing unit to be separate physical components. In such circumstances in the second state, the call is directed from the register unit to one of the routing units, before being handled by that routing unit. However, it is not excluded from the present invention that the register unit and the or all routing units are integrated into a single structure, and have components in common. The register unit and routing unit(s) of the invention may then be considered as separate functions within that structure. In such a case, since the call will be handled within the structure, it is not appropriate to think of the call being passed from the register unit to the routing unit. 
     Suppose, for example, the predetermined conditions relate co times of the day. At first time of the day, eg normal working hours, a call to a mobile telephone received by the telephone network results in a signal to the register unit which converts the number in the received signal to information identifying the appropriate HLR, and the signal is then routed to the mobile telephone in the normal way. This is thus as described in WO96/11557. However, at other times of the day, the register unit directs the call to the routing unit, which may then re-direct the call to some other number, such as the home telephone number of the owner of the mobile telephone. From the point of view of the person initiating the call, the same number is used at all times, but the destination number changes. That change is controlled by predetermined conditions in the register unit, and also in the routing unit. 
     It should be noted that the present invention is not limited to the case where the predetermined conditions relate to times of day, week, etc. They may, for example, relate to the origin of the call, the availability of the destination mobile telephone, or may simply be set on and off on a manual basis. 
     It is also not necessary in the present invention that there is only a single routing unit; in practice there may be a plurality of them. Where a plurality of routing units are associated with a single register unit, the selection of the appropriate routing unit may depend on both the source of the call and its destination. Different services may be provided via different routing units, and thus the selection of the routing unit may depend on the service that is needed by the incoming call. 
     Furthermore, the same service may be provided by all or many routing units and selection of the routing unit may depend on the location of the call, with the most conveniently located routing unit being used. 
     It can be noted that the choice of routing unit is, at least partially, affected by the requirements for information storage in the system. The predetermined is conditions, which may vary from one mobile telephone to another, need to be stored at, or associated with, the register unit. However, any further information about subsequent routing, such as alternative destinations for the call, etc, may then be stored at the routing unit. 
     In the arrangements described above, one type of call may cause problems in this arrangement, namely calls to the originally dialled mobile telephone which originate at the routing unit itself. Those calls, after they have been returned to the network by the routing unit, must not be returned to the routing unit by the action of the register unit. It is therefore necessary that the register unit recognises calls of this type it receives which have already passed back to the network by the routing unit, so that the register will not route them to that further routing unit again. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An embodiment of the present invention will now be described in detail, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 is a schematic block diagram of a telecommunication system incorporated in the present invention; and 
     FIG. 2 shows part of the telecommunication system of FIG. 1 in more detail. 
    
    
     DETAILED DESCRIPTION 
     Referring first to FIG. 1, and as described in WO 96/11557, a switched network  10  interconnects land-based and mobile telephones. If a call to a mobile telephone is made from a land-based telephone, the call is routed via the public switch telephone network (PSTN)  11  to the switch network, and from that switch network  10  to the mobile telephone (BSS)  12 . To do this, the switched network  10  must determine routing information, and to determine that routing information it must determine the location of the mobile telephone  12 , which it does via a HLR to which the mobile telephone  12  is associated. When there are multiple HLRs  13 , 14 , it is necessary for the switched network  10  to determine which HLR  13 , 14  must be accessed, on the basis of the telephone number (MSISDN number) of the mobile telephone input by the originator of the call. 
     The switch network  10  accesses a register unit  15 , which identifies the called number and addresses it to a particular HLR  13 , 14  with which the mobile telephone  12  is associated. The register unit  15  permits the relationship between any given mobile telephone number and the HLRs  13 , 14  to be determined freely, so that the number is unaffected by the particular HLR  13 , 14  with which it is associated. The register unit  15  removes the need for a particular mobile telephone number to be associated with a fixed HLR  13 , 14 . 
     Once the particular HLR  13 , 14  with which the mobile telephone  12  is associated has been identified, signalling can occur to that HLR, and information derivable therefrom, in the usual way. This information is used to “set-up” the call to the mobile telephone  12 , which may then be routed to the destination telephone or to some other destination as is normal. 
     Similarly, if a call originates at the mobile telephone  12 , the switched network  10  must again determine the routing of that call. If the call is to a land-based telephone, connected to the switched network  10  via the PSTN  11 , then this routing can be on the basis of the telephone number of the destination telephone, in the normal way. 
     If a call is made from a mobile telephone  12  to one of a plurality of voice processing systems  16 , 17  or to services  18  associated with the switch network using a particular code (e.g.  123 ) the relationship between the mobile telephone  12  and the corresponding service must be determined by the register unit  15  before the switch network can determine the appropriate voice processing system  16 , 17  or services  18  to be accessed. 
     The above description corresponds to the operations carried out in the arrangement described in WO96/11557. In the present invention, however, the addressing of a call to a particular HLR by the register unit  15  occurs only when one set of predetermined conditions, such as the time of day being within predetermined time limits, holds. Under other predetermined conditions, the call is directed from the register unit  15  to a routing unit  40  or even to a final destination. The routing unit  40  then contains information which re-routes the call back to the switched network  10 , but now to another destination telephone, which may either be the same mobile telephone, another mobile telephone, a land-based telephone, or other telecommunications termination service (eg, VPS or other service platform). 
     In FIG. 1, the register unit  15  and the routing unit  40  are shown as separate components which is currently preferred to an integral arrangement. A call which reaches the register unit under the other predetermined conditions causes the call to be directed to the routing unit  40 . 
     Moreover, there may be circumstances in which the routing unit does not re-route the call back into the switch network  10 , but instead acts as a destination for the call. For example, if the mobile telephone which is the desired destination of the call is not available for any reason, the routing unit  40  may terminate the call, possibly transmitting a message to the originating telephone that the desired mobile telephone is not available. 
     FIG. 2 shows the switched network  10  in more detail. It has a plurality of mobile switching centres (MSC)  20 , 21  and  22 , and a call destined for any given mobile telephone results in signalling between that MSC  20  to  22  and one of a plurality of signalling transfer points (STP)  30 , 31 , which signal to the register unit  15 . 
     Under one set of predetermined conditions, scored in the register unit  15 , the register unit  15  determines the HLR  13 , 14  which is appropriate to the mobile telephone  12 . The register unit  15  determines that information from the telephone number (MSISDN number) of the mobile telephone  12 . It would then be possible for the register unit  15  to forward the signal directly to the appropriate HLR  13 , 14  but, as shown in FIG. 2, it is preferable that the information is passed back to the corresponding STP  30 , 31  which then passes the signalling to the correct HLR  13 , 14 . 
     A similar signalling flow is seen when the user of the mobile telephone  12  tries to access one of the voice processing systems (VPS)  16 , 17 . This is described in more detail in WO96/11557 and therefore will not be described now. 
     As was mentioned above, this operation only holds for one set of predetermined conditions for a call to the corresponding mobile telephone. Under other predetermined conditions, the call which has passed to the register unit  15  from the corresponding STP  30 ,  31  is passed to the routing unit  40 , which determines a (possibly) new destination for the call and potentially passes the call back to one of the MSCs  20 ,  21 ,  22 . The switched network  10  then routes that call to an appropriate destination, in the usual way. For example, the call originally destined for a mobile telephone may be re-routed to a land-based telephone, and therefore passed via the switched network  10  to the land-based telephone via the PSTN  11  shown in FIG.  1 . 
     The predetermined conditions under which the register unit  15  operates to signal to the HLRs  13 ,  14 , and those in which it directs the signal to the routing unit  40  will normally vary between one mobile telephone and another. Thus, the register unit must store appropriate conditions for each mobile telephone number. Therefore, it may be necessary to provide an additional register unit  41 , connected co the register unit  15 , which additional register unit stores various predetermined conditions and which is accessed by the register unit  15  when a signal is received. It may be possible for the user of an individual mobile telephone to signal (possibly via a routing unit  40 ) to the additional register unit  41  to change the predetermined conditions. 
     It is not necessary for the additional register unit  41  to be a separate component, and it may be integrated with the register unit  15 . 
     Once the call has been directed by register unit  15  to the routing unit  40 , the routing unit  40  must determine its new routing, which new routing may be to terminate the call. Thus, there may be one or more possible routings (for example, depending on time of day) stored by the routing unit for any particular mobile telephone. It may also be noted that although a single routing unit  40  is shown in FIG. 2, there may be multiple routing units, with different mobile telephone numbers associated with different routing units. Furthermore, it is possible to have multiple routing units associated with any particular mobile telephone. This is advantageous when the same service is provided by multiple routing units, and selection of the routing unit which responds to a particular call may depend on the location of the call, with the most convenient located routing unit being used. Suppose now that, under one set of predetermined conditions, all calls are passed to the mobile telephone, and under another set of predetermined conditions only certain types of calls (eg, calls from particular origins such as specified telephone numbers, local calls, etc). In such circumstances, there are some calls that the routing unit  40  has to route to the mobile telephone itself. When such a signal has passed from the routing unit  40  to the connected MSC  20 , and from there to the appropriate STP  30 ,  31 , a signal will pass to the register unit  15  since the call is a call to a mobile telephone. However, at that point, the register unit  15  must not pass the call to the routing unit  40  again, even though the conditions for passing a call to the routing unit  40  are met. Otherwise, the call enters a loop. 
     Thus, in those circumstances, the register unit  15  must detect that the call has already passed via the routing unit  40 , and over-ride the call routing to the routing unit  40 , despite the predetermined conditions being met. Thus, calls to the originally dialled mobile telephone which have passed through the routing unit  40  must be modified to indicate that routing has already occurred. Preferably, this is carried out by the routing unit  40  and the MSC  20 , which can regularly distinguish such calls from the routing unit  40 . Therefore, calls from the routing unit  40  can indicate an override operation, for example by being given a revised sub-system number (the allocation of sub-system numbers being a normal function of the MSCs  20 ,  21 ,  22 ). When such signals pass via the STPs  30 ,  31  to the register unit  15 , the register unit detects the override and re-directs the calls to the appropriate HLR  13 ,  14  as discussed in WO96/11557. A loop is thus avoided. 
     Thus, the present invention permits different call routings to be applied under different conditions, which routings are transparent to the user originating the call. There is no need for that user to be told to dial a different number, or for the destination number to have some separate re-routing function, as exists in some PABXs. The destination number may be a normal mobile telephone (or indeed a land-based telephone or some other service), and all routing is controlled within the switch network  10 , the register unit  15  and the routing unit  40 . 
     Only limited modification to the register unit  15  used in WO96/11557 is needed in order to carry out the present invention; that register unit must be able to direct calls to the or one of the routing unit(s) rather than direct them to the appropriate HLR  13 ,  14 , and must contain a database which stores the predetermined conditions under which the register unit  15  passes the calls to the HLRs  13 ,  14  or directs the calls to the routing unit  40 . In general, the register unit  15 , or the additional register unit  41 , will store routing service information (for example, in the form of a table) for each mobile telephone number. 
     As in WO96/11557, the signal which a mobile telephone passes to the switch network, and by which the mobile telephone is recognised, need not be fixed, but may be alterable, for example by insertion into the telephone of a card carrying data. Thus, a user can identify himself or herself to the switch network by insertion inch a mobile telephone of a personal card which identifies him or her, and subsequent routing to an appropriate VPS or other service can be performed on the basis of the user&#39;s identity.