Abstract:
In a first node of a home network, such as a GMSC, on receiving a request message ( 50 ), requesting call set-up to a called terminal, a message ( 52 ) is sent to a second node of the home network, such as an HLR, to obtain an address of a mobile switching centre where the called terminal is located. On receiving a reply ( 58 ) from the second node, the first node initiates ( 60 ) a missed call notification service if it is determined that the called terminal is in a visited network. The first node then initiates a call set-up ( 64 ) to the called terminal and, if it is notified that the call has been released ( 66 ), with no call forwarding having taken place, it notifies ( 68 ) the missed call notification service that the call has been released. The missed call notification service causes ( 72 ) a message to be sent ( 74 ) to the called terminal, notifying it of the missed call.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to a mobile telecommunications network, and in particular to a method for notifying a roaming subscriber of a missed call. 
       BACKGROUND 
       [0002]    Voicemail systems are widely used in telecommunications systems, such as cellular communication systems. When a calling subscriber (the A-party) places a call to a called subscriber (the B-party) and the B-party does not answer, is busy or is not reachable, the call is forwarded to the voicemail system of the relevant communications network. Many voicemail systems used by mobile network operators will then send a Short Message System (SMS) to the B-party, informing the subscriber about the missed call, and thus allowing him to place a return call. 
         [0003]    Mobile networks typically have a limited geographical extent, and therefore, in order to allow maximum accessibility, mobile network operators typically have roaming agreements with other mobile network operators, whose networks cover other geographical areas. This allows a call to be placed to a called subscriber, even when he is outside the geographical coverage area of his home network. However, when the B-party is roaming, and misses a call, the process of forwarding the call to the voicemail system in the user&#39;s home network, as described above, may be somewhat expensive. 
         [0004]    One known alternative solution is the Local Voicemail Deposit (LVD) solution, described briefly in the document “IN and NGIN applications portfolio” from Ericsson. With this solution, when the B-party is roaming and misses a call, the call will be forwarded locally to the voicemail. The advantage of this solution is that the local call forwarding is free of charge. However, this solution only works in a straightforward manner for postpaid subscribers. The solution for prepaid subscribers is very complex, and the result is that many operators do not use LVD for prepaid subscribers. 
         [0005]    Instead, operators may simply disable call forwarding in the case when the B-party is roaming. That is, calls are not forwarded to voicemail, and no SMS messages notifying the B-party of the missed call are sent. This makes the system less convenient for users, and also results in a loss of revenue for the network operator because the roaming subscriber will not make the return call in response to the SMS message notifying him of the missed call. 
       SUMMARY 
       [0006]    The present invention therefore seeks to provide a system that allows a roaming subscriber to be notified of a missed call, while mitigating at least some of the disadvantages of the systems described above. 
         [0007]    According to a first aspect of the present invention, there is provided a method of handling calls in a mobile communication network, the method comprising: in a first node of a home network, receiving a request message, requesting call set-up to a called terminal; and sending a message to a second node of the home network to obtain an address of a mobile switching centre where the called terminal is located. On receiving a reply from the second node, the first node initiates a missed call notification service if it is determined that the called terminal is in a visited network. The first node then initiates a call set-up to the called terminal; and, if it is notified that the call has been released, with no call forwarding having taken place, it notifies the missed call notification service that the call has been released. The missed call notification service causes a message to be sent to the called terminal, notifying it of the missed call. 
         [0008]    This has the advantage that the roaming subscriber can be notified of the missed call, without requiring call forwarding involving the visited network. 
         [0009]    The step of determining that the called terminal is in a visited network can be accomplished by determining if a Mobile Station Roaming Number contains a code, such as a country code or an operator code, that does not belong to the home network. 
         [0010]    The step of causing a message to be sent to the called terminal may comprise sending a request to a Short Message Service Centre, causing a Short Message Service message to be sent to the called terminal. 
         [0011]    According to further aspects of the present invention, there are provided a method including steps of the method according to the first aspect, performed in the first node, and a Mobile Switching Centre configured to perform the method. 
         [0012]    According to a further aspect of the invention, there is provided a method of handling calls in a service control node of a mobile communication network, comprising receiving a command to initiate a missed call notification service from a mobile switching centre if it is determined that a called terminal is in a visited network. On subsequently receiving a notification that the call has been released, with no call forwarding having taken place a message is caused to be sent to the called terminal, notifying it of the missed call. 
         [0013]    The step of causing a message to be sent to the called terminal may comprise sending a request to a Short Message Service Centre, causing a Short Message Service message to be sent to the called terminal. 
         [0014]    According to a further aspect of the invention, there is provided a Service Control Point, configured to perform the method. 
         [0015]    According to a still further aspect of the present invention, there is provided a method whereby, during a location update, when a first terminal is found to be in a visited network, and when a call forwarding number is found not to be equal to a predetermined number, subscriber data including said call forwarding number is copied to a Visitor Location Register of the visited network. When the first terminal is found to be in a visited network, and when a call forwarding number is found to be equal to the predetermined number, the subscriber data excluding the call forwarding number is copied to a Visitor Location Register of the visited network. 
         [0016]    The predetermined number may be a voicemail system number. 
         [0017]    According to a further aspect of the present invention, there is provided a Home Location Register for a mobile communication network, configured to perform the method. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  shows a telecommunication network in accordance with an aspect of the present invention. 
           [0019]      FIG. 2  is a flow chart, illustrating a process performed in a Home Location Register of the network shown in  FIG. 1 , in accordance with an aspect of the present invention. 
           [0020]      FIG. 3  illustrates a message flow in the network of  FIG. 1 , in accordance with another aspect of the present invention. 
           [0021]      FIG. 4  is a flow chart, illustrating a process performed in a Gateway Mobile Switching Centre of the network shown in  FIG. 1 , in accordance with another aspect of the present invention. 
           [0022]      FIG. 5  is a flow chart, illustrating a process performed in a Service Control Point of the network shown in  FIG. 1 , in accordance with another aspect of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]      FIG. 1  shows a part of a cellular telecommunication network  10 , which at this level of generality is essentially conventional, and will therefore be described only in so far as is necessary for an understanding of the present invention. 
         [0024]    As is known, the network  10  includes a Gateway Mobile Switching Centre (GMSC)  12  having a processor  12   a  for controlling its operation and interface circuitry for interfacing as required with other network nodes. The GMSC  12  is connected to the radio access network (not shown) of the cellular network, so that calls are passed therethrough. The GMSC  12  is connected to a Service Control Point (SCP)  14  in the Intelligent Network architecture, that is able to take part in various additional functions of the network, for example as described in more detail below. The SCP  14  has a processor  14   a  for controlling its operation, and appropriate interface circuitry  14   b,  and is connected in turn to a Short Message Service Centre (SMS-C)  16 , which is able to handle Short Message Service (SMS) messages between subscribers. 
         [0025]    Provided in the network  10  is one or more Home Location Register (HLR)  18 , which has a processor  18   a  for controlling its operation, a database  18   b  for storing data including location information for (i.e. the network address of) the Visited Mobile Switching services Centre (VMSC) where the called terminal is currently registered, and interface circuitry  18   c  for connecting to other network nodes. Thus, for example, a cellular network will typically include many cells, served by respective base stations of the radio access network, and each active user equipment (i.e. each cellular phone or other mobile device) has a connection with one of these base stations. When the GMSC  12  receives a call to a called terminal, it can retrieve the necessary information from the HLR  18 , allowing the call to be routed through the correct VMSC of the cellular network. 
         [0026]    A typical cellular network has a limited geographical coverage area, for example one country or a part of a country, and contains multiple GMSCs, such as the GMSC  12 , and multiple HLRs, such as the HLR  18 . 
         [0027]    It is also possible for a user to roam into the geographical coverage areas of other networks, and  FIG. 1  shows a part of the network infrastructure in one other network, used for handling calls with user equipments that have roamed into its coverage area. Specifically,  FIG. 1  shows the Visited Mobile Switching Centre (VMSC) and Visitor Location Register (VLR) of that other network.  FIG. 1  shows the VMSC/VLR as a single block  20 , although it will be appreciated that the relevant functionality can be provided in separate equipment if required. 
         [0028]      FIG. 2  is a flow chart, illustrating a procedure performed in a HLR in accordance with an aspect of the invention, either when a mobile terminal is first attaching to the network, or when the mobile terminal is performing a location update procedure. 
         [0029]    Specifically, in step  30 , the HLR determines that an attach procedure or a location update procedure is being performed. In step  32 , the HLR, as is conventional, identifies the location of the Mobile Switching Centre (MSC) where the mobile terminal is now located, and specifically in step  32  identifies the VLR associated with that MSC. In step  34 , it is determined whether the VLR is located in the Home Private Land Mobile Network (HPLMN) of the mobile terminal, or whether the VLR address is an address outside the network of the operator providing the service according to the invention. If it is determined in step  34  that the VLR is in the HPLMN, the process passes to step  36 , in which the subscriber data is copied from the HLR to the VLR as is conventional. 
         [0030]    If it is determined in step  34  that the VLR is not in the HPLMN, that is, the subscriber is roaming, the process passes to step  38 . In step  38 , it is determined whether the subscriber has set up a call forwarding number that is not the voicemail system number. If the subscriber has set up a call forwarding number that is not the voicemail system number, the process passes to step  36  as before, and the subscriber data is copied from the HLR to the VLR as is conventional. 
         [0031]    However, if it is determined in step  38  that the available call forwarding number is the voicemail system number, the process passes to step  40 . In step  40 , the subscriber data excluding this call forwarding number is copied from the HLR to the VLR. 
         [0032]    Thus, in accordance with this embodiment of the invention, the HLR  18  does not copy the call forwarding number to the VLR if the call forwarding number equals the voicemail system number and if the subscriber is roaming outside his HPLMN. 
         [0033]      FIG. 3  then illustrates the message flow, when attempting to set up a call, in a process in accordance with an aspect of the present invention. The invention is described with reference to a specific embodiment, in which the cellular network is a Global System for Mobile communication (GSM) network, or a Universal Mobile Telecommunications System (UMTS) network, or another cellular network using an Intelligent Network (IN) architecture, with the messages between nodes of the network being in accordance with the known system of Customised Applications for Mobile networks using Enhanced Logic (CAMEL). Thus,  FIG. 3  shows the flow of messages between the Service Switching Function (SSF) located in the Gateway Mobile Switching Centre (GMSC)  12 ; the Home Location Register (HLR)  18 ; a Missed Call SMS Roaming subscriber Service (MCSRS) deployed on the Service Control Point (SCP)  14 ; and the Short Message Service Centre (SMS-C)  16 ; as well as the Visited Mobile Switching Centre (VMSC)/Visitor Location Register (VLR)  20  of another network. 
         [0034]    The procedure for setting up a call from a calling subscriber (the A-party) to a called subscriber (the B-party) starts with an Initial Address Message (IAM)  50 , sent to the GMSC  12  from the radio access network. As is conventional, the GMSC  12  sends a Provide Subscriber Information (PSI) message  52  to the HLR  18 . Then, the HLR  18 , having being notified by the other network that the called subscriber is roaming in that other network, sends a Provide Subscriber Information (PSI) message  54  to the VMSC/VLR  20  of the other network to obtain a Mobile Station Roaming Number (MSRN). 
         [0035]    The VMSC/VLR  20  of the other network returns a Provide Subscriber Information result (PSI-res) message  56  to the HLR  18 , containing the MSRN, which contains the current visitor country code, the visitor national destination code (VNDC), the identification of the current MSC, and the subscriber number. The HLR  18  returns a further PSI-res message  58  to the GMSC  12 . 
         [0036]    When the GMSC  12  receives the returned MSRN, it performs the procedure shown in  FIG. 4 . Specifically, having received the MSRN in step  80 , it determines in step  82  whether the MSRN contains a country code and/or operator code that does not belong to its own network operator, indicating that the B-party is roaming. If it is determined in step  82  that the B-party is not roaming, the procedure passes to step  84 , in which the call set-up proceeds in a conventional manner. However, if it is determined in step  82  that the B-party is roaming, the procedure passes to step  86 , in which the GMSC  12  triggers an Intelligent Networks solution, namely the Missed Call SMS Roaming subscriber service (MCSRS). It is noted that, in this embodiment of the invention, the solution is triggered on the roaming call forwarding leg in the GMSC. 
         [0037]    Specifically, the GMSC  12  triggers the MCSRS by sending an Initial Detection Point (IDP) message  60  to the SCP  14 . The SCP  14  responds by sending a message to the GMSC  12  asking it to continue the call set-up, and to report its state in the Basic Call State Model (BCSM), that is, a continue and Request Report BCSM (CUE+RRB) message  62 . Thus, the MCSRS service monitors the result of the call set-up. 
         [0038]    As is conventional, the GMSC  12  attempts to set up the call, by sending an Initial Address Message (IAM)  64  to the VMSC  20  of the B-party. When the B-party is busy, or does not answer, or is Not Reachable, the VMSC will check the VLR to see if the call forwarding numbers are set. 
         [0039]    Because the call forwarding numbers were not set by the HLR, as described with reference to  FIG. 2 , the VMSC will release the call, by sending a conventional release (REL) message  66  to the GMSC  12 , containing a conventional cause value (specifying whether the B-party is Busy, or is Not Reachable, or whether the call was not answered). 
         [0040]    When the GMSC  12  receives the REL message  66 , it reports the release to the MCSRS service via a standard Event Report BCSM (ERB) message  68 . In addition, the release is sent to the A-party as the REL message  70 , and the call is cleared. 
         [0041]      FIG. 5  shows the response of the IN Missed Call SMS Roaming subscriber service (MCSRS) deployed on the Service Control Point (SCP)  14  at this point. In step  90 , the MCSRS receives the ERB message  68 . In response, in step  92 , the MCSRS sends a Mobile Originating Forward SMS (MOFSMS) message  72  to the Short Message Service Centre (SMS-C)  16 , causing the SMS-C to send an SMS  74  to the B-party. The SMS  74  notifies the B-party of the missed call, and in particular contains the A-number in international format, thereby allowing the B-party to place a return call to the A-party if desired. 
         [0042]    Thus, call forwarding is disabled when the B-party is roaming, and as a result the network will release the call if the B-party does not answer. The call release is intercepted, and a missed call SMS is nevertheless sent to the B-party. 
         [0043]    The process described so far assumes that the B-party is a postpaid subscriber. However, if the B-party is a prepaid subscriber, the only change is that, on receiving the IAM  50 , the GMSC  12  will first trigger the prepaid service, based on the Terminating IN Category Key (TICK) or Terminating CAMEL Subscription Information (T-CSI). Then, when the prepaid service sets up the call, the GMSC will trigger the MCSRS service as discussed previously. As before, when the B-party is busy, does not answer or is not reachable, the call is released. As a result, the prepaid service will not charge for the call. 
         [0044]    There is thus described a solution that works equally for both postpaid and prepaid subscribers, providing an enhanced service for subscribers, while being simple for operators to use and potentially generating additional calls for which the operator is able to charge.