Abstract:
Disclosed is a method for providing a roaming service among private mobile switching centers (MSCs) interconnected to one another via a public switched telephone network (PSTN). The method comprises connecting the private mobile switching centers to a virtual private network (VPN) via the PSTN; if a mobile station sends a private mobile communication service registration request to a selected one of the private mobile switching centers, storing, by the selected private mobile switching center, information about the mobile station registered for the private mobile communication service and associated mobile station location information; transmitting the mobile station information and the mobile station location information to other private mobile switching centers via the virtual private network; and if the mobile station sends a private mobile communication service request to a selected one of the private mobile switching centers, providing, by the selected private mobile switching center, the private mobile communication service using the stored mobile station information and mobile station location information, and the virtual private network.

Description:
CLAIM OF PRIORITY  
       [0001]    This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C §119 from an application entitled Method for providing Roaming Service among Private Mobile Switching Centers earlier filed in the Korean Industrial Property Office on Aug. 18, 2000, and there duly assigned Serial No. 2000-47872 by that Office. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates generally to a mobile communication system, and in particular, to a method for providing a roaming service among private mobile switching centers.  
           [0004]    2. Description of the Related Art  
           [0005]    In general, private (or local) mobile switching centers (MSCs) provide the mobile communication service only to the mobile subscribers registered therein. Therefore, the mobile subscribers cannot be provided with the mobile communication service, when they move into a service area (or coverage area) of a private mobile switching center in which they are not registered. That is, a mobile subscriber registered in a certain private mobile switching center can be provided with a call originating service, a call terminating service and other additional services only in a service area of the private mobile switching center.  
           [0006]    Utilization of a virtual private network in a mobile communication system is described in the following references, incorporated by reference herein: U.S. Pat. No. 6,029,067 to Matthias Pfundstein entitled  Virtual Private Network for Mobile Subscribers;  U.S. Pat. No. 6,101,382 to Christer Granberg entitled  Transfer of Calling Party Identification in a Mobile Communication System;  and U.S. Pat. No. 6,175,622 to Sima Chiniwala et al. entitled  Virtual Private Network for a Telephone Network.    
         SUMMARY OF THE INVENTION  
         [0007]    It is, therefore, an object of the present invention to provide a method for providing a roaming service among private mobile switching centers.  
           [0008]    It is another object of the present invention to provide a method for enabling a mobile subscriber to be provided with a call terminating service and a call originating service in any service area of a plurality of private mobile switching centers.  
           [0009]    To achieve the above and other objects, there is provided a method for providing a roaming service among private mobile switching centers (MSCs) interconnected to one another via a public switched telephone network (PSTN). The method comprises connecting the private MSCs to a virtual private network (VPN) via the PSTN; if a mobile station sends a private mobile communication service registration request to a selected one of the private MSCs, storing, by the selected private MSC, information about the mobile station registered for the private mobile communication service and associated mobile station location information; transmitting the mobile station information and the mobile station location information to other private MSCs via the VPN; and if the mobile station sends a private mobile communication service request to a selected one of the private MSCs, providing, by the selected private MSC, the private mobile communication service using the stored mobile station information and mobile station location information, and the VPN. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    A more complete appreciation of the present invention, and many of the attendant advantages thereof, will become readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein:  
         [0011]    [0011]FIG. 1 is a diagram illustrating the connection between private mobile switching centers;  
         [0012]    [0012]FIG. 2 is a diagram illustrating a network structure for providing a roaming service among private mobile switching centers according to an embodiment of the present invention;  
         [0013]    [0013]FIG. 3 is a detailed block diagram illustrating the call managers shown in FIG. 2; and  
         [0014]    [0014]FIG. 4 is a flow chart illustrating a procedure for providing a roaming service among private mobile switching centers according to an embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]    Referring to FIG. 1, private mobile switching centers  2  and  12  are connected in common to a public switched telephone network (PSTN)  10 . Further, the private mobile switching centers (MSCs)  2  and  12  include radio interfaces (I/F)  4  and  14 , respectively. The private mobile switching center  2  provides the mobile communication service only to mobile stations (MSs)  6  and  8  registered therein, while the private mobile switching center  12  provides the mobile communication service only to mobile stations  16  and  18  registered therein. Therefore, when the mobile stations  16  and  18  registered in the private mobile switching center  12  move into a service area  20  of the mobile switching center  2 , they cannot be provided with the mobile communication service. Likewise, when the mobile stations  6  and  8  registered in the private mobile switching center  2  move into a service area  22  of the mobile switching center  12 , they cannot be provided with the mobile communication service. The private mobile switching centers and shown in FIG. 1 are chiefly designed to manage in-building mobile switching, so that they cannot be connected to a public mobile communication network.  
         [0016]    [0016]FIG. 2 shows a network structure for providing a roaming service among private mobile switching centers according to an embodiment of the present invention.  
         [0017]    Referring to FIG. 2, a public mobile communication network  33  includes a mobile switching center (MSC)  38 , a plurality of base station controllers (BSCs)  40 - 1  to  40 -N, and a plurality of base station transceiver subsystems (BTSs)  42 - 1  to  42 -N.  
         [0018]    A public mobile communication network  53  includes a mobile switching center (MSC)  58 , a plurality of base station controllers (BSCs)  60 - 1  to  60 -N, and a plurality of base station transceiver subsystems (BTSs)  62 - 1  to  62 -N.  
         [0019]    A public mobile communication network  73  includes a mobile switching center (MSC)  78 , a plurality of base station controllers (BSCs)  80 - 1  to  80 -N, and a plurality of base station transceiver subsystems (BTSs)  72 - 1  to  72 -N. A plurality of private mobile switching centers  30 ,  50  and  70  are connected to the public mobile communication networks  33 ,  53  and  73 , respectively.  
         [0020]    As illustrated, the private mobile switching centers  30 ,  50  and  70  share public/private common cells  36 , 56  and  76  with their associated public mobile communication networks  33 ,  53  and  73 , respectively. That is, the base station transceiver subsystems (BTSs)  42 -N,  62 -N and  72 -N in the public/private common cells  36 ,  56  and  76  are commonly used for both the public mobile communication service and the private mobile communication service. The other cells serviced by the BTSs of the public mobile communication networks  33 ,  53  and  73 , except the public/private common cells  36 ,  56  and  76 , are used as public-only cells  37 ,  57  and  77 , as shown in FIG. 2.  
         [0021]    In FIG. 2, the private mobile switching centers  30 ,  50  and  70  include radio interfaces (I/F)  31 ,  51  and  71 , respectively, and are connected to their associated public mobile communication networks  33 ,  53  and  73  via the radio interfaces  31 ,  51  and  71 . To connect the private mobile switching centers  30 ,  50  and  70  to their associated public mobile communication networks  33 ,  53  and  73 , there are provided call managers  32 ,  52  and  72 , which include message (MSG) routers  34 ,  54  and  74 , respectively.  
         [0022]    In FIG. 2, the message routers  34 ,  54  and  74  are separated from the call managers  32 ,  52  and  72 , for convenience of explanation. However, it is preferable that the message routers  34 , 54  and  74  are included in the call managers  32 ,  52  and  72 , respectively. The message routers  34 ,  54  and  74  are connected to the BTSs  42 -N,  62 -N and  72 -N in the public/private common cells  36 ,  56  and  76 , respectively, and also connected to the base station controllers (BSCs)  40 -N,  60 -N and  80 -N, respectively, which are upper BSCs of the BTSs  42 -N,  62 -N and  72 -N.  
         [0023]    In addition, the message routers  34 ,  54  and  74  are also connected to the private mobile switching centers  30 , 50  and  70 , respectively. The message routers  34 ,  54  and  74  analyze such event messages as a call origination message, a call termination message, a location registration message and an SMS (Short Message Service) message, and then, designate a path according to the analyzed results. The message routers  34 ,  54  and  74  each have a router table, in which the designated path information is mapped with the associated events, and transmit a received message to a related device by consulting the router table.  
         [0024]    The call managers  32 ,  52  and  72  are connected to the private mobile switching centers  30 ,  50  and  70  via a local area network (LAN). The call managers  32 ,  52  and  72  analyze the messages - received from the message routers  34 ,  54  and  74  to determine whether the received messages are for the public mobile communication service or the private mobile communication service, and then, perform the service control according to the determined results.  
         [0025]    [0025]FIG. 3 shows a detailed structure of the call managers  32 ,  52  and  72  of FIG. 2. Referring to FIG. 3, the call manager includes a private BSC  92  and a private MSC  94  corresponding to the BSC and the MSC of the public mobile communication network, and has a VLR (Visitor Location Register)  96 , connected to the private MSC  94 , for registering mobile stations intended to be provided with the private mobile communication service. Further, the call manager has a database (DB)  98  connected to the private BSC  92 . In addition, the call manager includes a radio interface connected to the private MSC  94 , for communication with its associated private mobile switching center.  
         [0026]    Turning back to FIG. 2, the private mobile switching centers  30 ,  50  and  70  are connected in common to the PSTN  44 . In order to provide the roaming service among the private mobile switching centers  30 ,  50  and  70  according to an embodiment of the present invention, the private mobile switching centers  30 ,  50  and  70  are connected in common to a virtual private network (VPN) via the PSTN  44 .  
         [0027]    [0027]FIG. 4 shows a procedure for controlling a roaming service among the private mobile switching centers  30 ,  50  and  70  connected to the virtual private network.  
         [0028]    Now, a method for providing the roaming service among the private mobile switching centers  30 ,  50  and  70  according to an embodiment of the present invention will be described in detail with reference to FIGS.  2  to  4 .  
         [0029]    For the roaming service among the private mobile switching centers  20 ,  50  and  70 , information about the mobile stations registered for the private mobile communication service and location information of the registered mobile stations are stored in each VLR  96  of the call managers  32 ,  52  and  72  associated with the private mobile switching centers  30 ,  50  and  70  connected to the virtual private network.  
         [0030]    The mobile station location information includes information about a virtual private network prefix for the private mobile switching center where the mobile station is located. After storage of the mobile station location information, the information about the mobile stations registered for the private mobile communication service and the location information of the registered mobile stations are also sent to the call managers associated with the other mobile switching centers connected to the virtual private network. The detailed description will be given below.  
         [0031]    The call managers  32 ,  52  and 72  manage the mobile stations registered for the private mobile communication service using their VLR  96  shown in FIG. 3. If a new mobile station is registered for the private mobile communication service, the call manager for the associated public/private common cell provides the information about the mobile stations registered for the mobile communication service to the call managers associated with the private mobile switching centers connected to the virtual private network.  
         [0032]    If, for example, a new mobile station located in the public/private common cell  36  is registered in the call manager  32  for the private mobile communication service, the call manager  32  provides the information about the mobile stations registered for the private mobile communication service to the call managers  52  and  72  associated with the private mobile switching centers  50  and  70  connected to the virtual private network, through the private mobile switching center  30  and the PSTN  44 . The other call managers  52  and  72  then store the information about the mobile stations registered for the private mobile communication service in their VLR  96 , together with the mobile station location information.  
         [0033]    In this state, if a certain mobile station moves into a public/private common cell of another private mobile communication network, the call manager for this public/private common cell updates the mobile station location information stored in its VLR  96  through the location registration process or the call origination process, and provides the updated mobile station location information to the call managers associated with the other private mobile switching centers connected to the virtual private network. The call managers then update the mobile station location information stored in their VLR  96 .  
         [0034]    In the state where the mobile station information and the associated mobile station location information are stored and updated in the call managers  32 ,  52  and  72  so as to enable the roaming service among the private mobile switching centers, an originating call from the mobile station belonging to any one of the public/private common cells  36 ,  56  and  76  is managed in the common process for the mobile originating call.  
         [0035]    Distinguishing the private mobile communication service from the public mobile communication service is performed by the call managers  32 ,  52  and  72 . After a mobile communication network to provide the mobile communication service is determined by the call managers  32 ,  52  and  72 , a message is provided to the determined mobile communication network to perform the call service.  
         [0036]    Meanwhile, a terminating call in the public mobile communication networks  33 ,  53  and  73  is managed in the common call terminating process of the public mobile communication network, and the call managers  32 ,  52  and  72  provide the received message intact to the BTSs  42 -N,  62 -N and  72 -N.  
         [0037]    On the other hand, a terminating call in the private mobile communication network is provided to the call managers  32 ,  52  and  72 . The call managers  32 ,  52  and  72  then receive a call termination request message in step  200  of FIG. 4, and consult their VLR  96  in step  202 . More specifically, when the terminating call is provided to the MSC  94  of the call managers  32 ,  52  and  72 , the MSC  94  acquires the location information of the corresponding mobile station by consulting the VLR  96 , to thereby detect a location of the mobile station.  
         [0038]    After step  202 , the call managers  32 , 52  and  72  determine in step  204  whether the location of the mobile station belongs to their public/private common cells or another public/private common cell. If the location of the mobile station belongs to their public/private common cells, the call managers  32 ,  52  and  72  perform the call termination process in step  206 .  
         [0039]    Otherwise, if the location of the mobile station belongs to another public/private common cell, a call termination message is provided to the corresponding mobile station through the roaming service among the private mobile switching centers according to an embodiment of the present invention. More specifically, if it is determined in step  204  that the location of the mobile station belongs to another public/private common cell, the call managers  32 ,  52  and  72  search in step  208  the VLR  96  for a virtual private network prefix corresponding to the private mobile communication network where the mobile station is located.  
         [0040]    Thereafter, in step  210 , the call managers  32 ,  52  and  72  transmit the call termination message to the private mobile communication network where the mobile station is located, by consulting the searched virtual private network prefix.  
         [0041]    More specifically describing the operation performed in step  210 , the call managers  32 ,  52  and  72  transmit the call termination request message to a target private mobile switching center in the private mobile communication network where the mobile station is located, through their associated message routers  34 ,  54  and/or  74 , private mobile switching centers and the PSTN. The call manager for the target mobile switching center then performs the call terminating service through steps  200  to  206 .  
         [0042]    As described above, the mobile subscriber registered in both the public mobile communication network and the private mobile communication network can be provided with the call originating service, call terminating service and other additional services, even though the mobile subscriber moves to any cell where the private mobile switching center sharing the public/private common cell with the public communication network is connected to the virtual private network. In addition, it is also possible to service not only a call terminated in a specific area but also a call terminated in another area through the PSTN.  
         [0043]    While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. That is, although the invention has been described with reference to the roaming service among the private mobile switching centers in a system providing both the public mobile communication service and the private mobile communication service, the invention can also be applied to a roaming service among the private mobile switching centers connected to the virtual private network.