Abstract:
A communication system that manages heterogeneous networks including a Circuit Switched (CS) network and an Internet Protocol (IP) Multimedia Subsystem (IMS) network, and a method for processing a voice call in the communication system are provided. When a User Equipment (UE) requests the call setup by sending a Subscribe message including a subscriber identification number to a voice call management server of the IMS network, the voice call management server registers the UE in the IMS network and performs location registration in a Home Location Register (HLR) of the CS network using the subscriber identification number.

Description:
PRIORITY 
       [0001]    This application claims priority under 35 U.S.C. § 119(a) to a Korean Patent Application filed in the Korean Intellectual Property Office on Dec. 4, 2006 and assigned Serial No. 2006-121839, the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to a method and system for processing a voice call in a communication system, and, in particular, to a method and system for processing a voice call in a communication system that manages heterogeneous networks. 
         [0004]    2. Description of the Related Art 
         [0005]    With the rapid progress of the mobile communication and Internet technologies targeted to meet various needs of the subscribers, the recent mobile communication services have reached the phase of providing not only the existing voice call services but also the high-speed packet data services capable of transmitting high-capacity digital data as well as E-mail and still images via a mobile terminal. Accordingly, the mobile communication systems are evolving from the voice-based Circuit Switched (CS) domain into the packet-based Packet Switched (PS) domain. 
         [0006]    The Core Network (CN) that provides multimedia services over the Internet has changed from the existing circuit-based CN into the packet-based CN, and is now evolving into an Internet Protocol (IP)-based CN. A communication system that provides IP Multimedia services (IM services) to the subscribers over the IP-based CN is called an IMS, and third Generation Partnership Project (3GPP)/3GPP2 is conducting various researches to smoothly provide ALL IP services over the IMS. 
         [0007]    The IMS is composed of a set of signaling and bearers related to the network elements, and should be able to approach the web-based technology for audio, video and message data, and wireless subscribers. Because the IMS provides various types of packet data services based on an IP transport protocol, the IMS users can exchange multimedia-type contents, such as picture, video clip and sound clip, with each other over Session Based Messages. 
         [0008]    The mobile communication systems are now developing into the heterogeneous communication systems that manage heterogeneous networks such as the CS domain and PS domain networks in an integrated way. Herein, the ‘PS domain’ is also called an ‘IMS domain’ and the two terms are used interchangeably. 
         [0009]    Describing voice call processing in the heterogeneous communication system, Voice Call Continuity (VCC) supports both terminating domain selection between the CS domain and the IMS domain, and IMS-to-CS and CS-to-IMS domain transfer. To this end, all calls of the VCC subscriber are anchored in a VCC Application Server (AS). Therefore, a terminating CS call is anchored in the VCC AS after being rerouted to the IMS domain. All terminating calls incoming from the external network are input to the IMS network via a Media Gateway Control Function (MGCF), and then transmitted to the selected terminating domain via the VCC AS. 
         [0010]    Generally, in the heterogeneous communication system, the CS domain and the IMS domain are different in their service providers. Therefore, when the user uses the subscriber identification number, or Mobile Station ISDN Number (MSISDN), that is used in the CS domain, even in the IMS domain, all voice calls are rerouted to the IMS domain after terminating at the CS domain. That is, the IMS domain anchors the corresponding call in the VCC AS, and the VCC AS selects a terminating domain and reroutes the call to the corresponding terminating domain, which unnecessarily performing many procedures. 
       SUMMARY OF THE INVENTION 
       [0011]    An aspect of the present invention addresses at least the problems and/or disadvantages and provides at least the advantages described below. Accordingly, an aspect of the present invention is to provide a method and system for fast processing of a voice call in a heterogeneous communication system that manages a CS domain and an IMS domain. 
         [0012]    Another aspect of the present invention is to provide a call processing method and system for sharing subscriber information between mutual domains in a heterogeneous communication system that manages a CS domain and an IMS domain. 
         [0013]    According to one aspect of the present invention, there is provided a method for processing a call in a heterogeneous communication system that manages heterogeneous networks including a circuit network and an Internet Protocol (IP) Multimedia Subsystem (IMS) network. The call processing method includes registering a User Equipment (UE) in the IMS network by a voice call management server of the IMS network at the request of the UE; receiving by the voice call management server a subscribe message including a subscriber identification number from the UE; allocating by the voice call management server a transfer number needed by the UE to transfer from the IMS network to the circuit network, in response to the subscribe message, and delivering the transfer number to the UE; and performing, by the voice call management server, location registration for the UE in the circuit network using the subscriber identification number. 
         [0014]    According to another aspect of the present invention, there is provided a heterogeneous communication system that manages heterogeneous networks including a circuit network and an Internet Protocol (IP) Multimedia Subsystem (IMS) network. The heterogeneous communication system includes a voice call management server for registering a User Equipment (UE) in the IMS network at the request of the UE, and upon receipt of a subscribe message including a subscriber identification number from the UE, allocating a transfer number needed by the UE to transfer from the IMS network to the circuit network, in response to the subscribe message, delivering the transfer number to the UE, and performing location registration for the UE in the circuit network using the subscriber identification number; and a home location register for performing location registration to the circuit network for the UE at the request of the voice call management server. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The above and other aspects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: 
           [0016]      FIG. 1  illustrates a configuration of a heterogeneous communication system according to an embodiment of the present invention; 
           [0017]      FIG. 2  illustrates an IMS registration method of a VCC subscriber in a heterogeneous communication system according to an embodiment of the present invention; and 
           [0018]      FIG. 3  illustrates a terminating call setup method according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    Preferred embodiments of the present invention will now be described in detail with reference to the annexed drawings. In the drawings, the same or similar elements are denoted by the same reference numerals even though they are depicted in different drawings. In the following description, a detailed description of known functions and configurations incorporated herein has been omitted for clarity and conciseness. 
         [0020]    The present invention provides a system for processing a call by sharing information on a User Equipment (UE) between a Home Location Register (HLR) of a CS domain and a VCC AS of an IMS domain, to efficiently process a terminating call (or incoming call) in a heterogeneous communication system that manages the CS domain and the IMS domain. A description will now be made of a heterogeneous communication system, a location registration method in a UE, and a terminating call processing method according to the present invention. 
         [0021]      FIG. 1  illustrates a configuration of a heterogeneous communication system according to an embodiment of the present invention. The terms used in the drawing are defined in 3GPP/3GPP2, as known to those of skill in the art, for conciseness, a separate description thereof is not provided herein. 
         [0022]    Referring to  FIG. 1 , a heterogeneous communication system  100  according to an embodiment of the present invention includes a CS network  110 , an IMS network  120 , and a UE  101 . The IMS network  120  includes a Call Session Control Function (CSCF)  130  for voice call processing, a Home Subscriber Server (HSS)  123  for providing subscriber information, and a VCC AS  121  for taking charge of IMS-to-CS domain transfer. 
         [0023]    The UE  101 , preferably a dual-mode phone supporting both the CS network  110  and the IMS network  120 , supports domain transfer between CS and IMS networks. In addition, the UE  101  supports a Mobility Event Package (MEP) method, which is an information exchange method with the VCC AS  121 , and also supports a function in which the user can select an IMS-Only mode according to the user preference. Further, the UE  101  should be able to recognize an IMS deregistration state when leaving the IMS domain, and in this case, the user preference state should change from the IMS Only Mode to the IMS preferred mode. 
         [0024]    The VCC AS  121  supports the MEP that exchanges information with the UE  101  immediately after the registration or exchanges information with the UE  101  when the session information changes due to the selection of the operator and the user. 
         [0025]    A Serving-CSCF (S-CSCF)  133  takes charge of call setup/release between terminating and originating UEs, and updates service subscriber information (or Service Profile) at the request of the HSS  123  when IMS mode information of the UE  101  is delivered to the VCC AS  121 . When an unregistered VCC user (i.e., VCC user unregistered in the IMS) has moved from the IMS domain  120  to the CS domain  110  for the terminating call setup, if another IMS subscriber sends an originating call (or outgoing call) to the VCC user that has moved from the IMS domain to the CS domain, the S-CSCF  133  receives a profile (or unregistered user profile) of the VCC user from the HSS  123 , determining that the corresponding VCC user is a VCC user unregistered in the IMS domain depending on an INVITE message of the corresponding call. Thereafter, the S-CSCF  133  forwards the corresponding call to the VCC AS  121  through the profile of the VCC user. Thereafter, the VCC AS  121  reroutes the corresponding call to the CS domain through HLR inquiry. 
         [0026]    The HSS  123  stores the service subscriber information. When the IMS-Only mode information is delivered from the user to the VCC AS  121 , the HSS  123  updates the service subscriber information at the request of the VCC AS  121 . Further, the HSS  123  updates service subscriber information of the S-CSCF  133  by interworking with the S-CSCF  133  via a Cx interface. In addition, the HSS  123  stores the profile of the unregistered VCC user for the originating call setup of the unregistered user. 
         [0027]    An HLR  115  manages service subscriber information in the CS domain. Herein, when the subscriber performs IMS registration, recognizing the VCC AS  121  as a logical Mobile Switching Center (MSC), the VCC AS  121  performs subscriber location registration on the HLR  115 , like the MSC  111 . When a call request is received at the service subscriber, the HLR  115  allows, for the call request, the MSC  111  to which the corresponding subscriber belongs to be allocated a Temporary Local Directory Number (TLDN) which is identification information of a Media Gateway Control Function (MGCF)  125  and a Media Gateway (MGW)  127 , to deliver the TLDN to the call-requested MSC  111 , achieving the requested call. When the location-registered MSC  111  is the VCC AS  121 , the VCC AS  121  allocates and sends an IMS Routing Number (IMRN) other than TLDN, and the call-requesting MSC  111  terminates the corresponding call to the IMS network  120 . 
         [0028]    A description will now be made of a method for registering VCC subscriber information in the HLR for interworking of subscriber information with the CS domain in the heterogeneous communication system according to an embodiment of the present invention. 
         [0029]      FIG. 2  illustrates an IMS registration method of a VCC subscriber in a heterogeneous communication system according to an embodiment of the present invention. Herein, the transfer method between the IMS domain and the CS domain will be described based on the 3GPP and 3GPP2 standards. 
         [0030]    Referring to  FIG. 2 , a UE  101  performs a standard IMS registration process with an IMS domain  120  in step  201  for its registration in the IMS domain, and then performs service registration (VCC 3rd Party Registration) of the UE  101  in step  203 . Thereafter, the UE  101  sends a request for MEP registration to a VCC AS  121  using an MEP subscribe message, in steps  205  through  209 . The subscribe message, providing a unique identification number of a UE used in the CS domain, is sent to the VCC AS  121  along with a Mobile Identification Number/Electronic Serial Number (MIN/ESN) when the UE operates in the Code Division Multiple Access (CDMA) system, and with an International Mobile Subscriber Identity/International Mobile Equipment Identity (IMSI/IMEI) when the UE operates in the Global System for Mobile telecommunication (GSM) system. 
         [0031]    Upon receipt of the subscribe message with MIN/ESN or IMSI/IMEI, the VCC AS  121  sends a response message (e.g. a 200 OK message) to the UE  101 , in steps  211  to  215 . Further, in steps  217  to  219 , the VCC AS  121  allocates a VCC Domain Transfer Number (VDTN) to be used when the UE  101  will make domain transfer from the IMS domain  120  to the CS domain  110 , and delivers it to the UE  101  using a MEP Notify message, in step  221 . 
         [0032]    Upon receipt of the Notify message, the UE  101  sends a response message i.e. 200 OK message) to the VCC AS  121  in response thereto, in steps  223  to  226 , completing IMS registration. 
         [0033]    After completion of the IMS registration, the VCC AS  121  performs location registration in the HLR  115 . To this end, the VCC AS  121  sends a Registration Notification (RegNot) message for location registration to the HLR  115  in step  227 . Upon receipt of the Request message or the Registration Notification (RegNot) message, the HLR  115  sends a Response message (RepNot) to the VCC AS  121  in response thereto in step  229 , completing the location registration process. The location registration by the HLR  115  in steps  227  and  229  uses the MIN/ESN or IMSI/IMEI of the UE  101 . 
         [0034]    Next, with reference to  FIG. 3 , a description will be made of a terminating call setup method according to an embodiment of the present invention. 
         [0035]      FIG. 3  illustrates a terminating call setup method according to an embodiment of the present invention, and the process shown in  FIG. 3  is a process of terminating a terminating call from a CS network to an IMS network. 
         [0036]    Referring to  FIG. 3 , when a terminating call has arrived at an MSC  111  of a CS domain  110  from other network such as Public Switched Telephone Network/Public Land Mobile Network (PSTN/PLMN), the MSC  111  sends a request for call termination information to an HLR  115  using a VCC subscriber number, or Mobile Station ISDN Number (MSISDN), of the terminating UE  101  in step  301 . In response, the HLR  115  checks, in step  303 , HLR location registration information according to the standard procedure, and then sends a request for location information to the VCC AS  121  in which the terminating UE  101  is now registered. At this point, the VCC AS  121 , because it is operating as a logical MSC, allocates an IMRN for the subscriber and returns the allocated IMRN to the HLR  115  in step  305 . Upon receipt of the IMRN, the HLR  115  delivers the IMRN to the MSC  111 , in step  307 . The MSC  111  reroutes the terminating call to the IMS domain  120  using the IMRN received from the HLR  115 . 
         [0037]    For rerouting, the MSC  111  routes, in step  309 , the terminating call to an MGCF  125  of the IMS domain  120  using an Initial Address Message (IAM) including the IMRN. The MGCF  125  sends in step  311  an INVITE message with the IMRN to an Interrogating-CSCF (I-CSCF)  131 . Thereafter, the I-CSCF  131  analogizes a VCC AS Public Service Identity (PSI) using the IMRN, and checks an address of the VCC AS from the HSS  123  in step  312 . The I-CSCF  131  sends an INVITE message to the corresponding VCC AS  121  in step  313 , and the VCC AS  121  performs call termination in step  315 . 
         [0038]    In step  317 , the VCC AS  121  finds a MSISDN number, which is the original VCC subscriber number of the call-requested UE  101 , using the IMRN included in the received INVITE message, and sends an INVITE message back to the S-CSCF  133  of the IMS, requesting the call origination. 
         [0039]    In step  319 , the S-CSCF  133  processes a terminating initial Filter Criteria (iFC) of the subscriber profile for the requested INVITE message, and routes the INVITE message to the VCC AS  121  for anchoring, after determining that the terminating UE  101  is a VCC subscriber. 
         [0040]    The VCC AS  121  anchors the call of the terminating UE in step  321 , and then performs call termination to the terminating UE  101 , in steps  323  and  325 . 
         [0041]    In the embodiment of the present invention, the termination process from the CS call to the IMS call has been described. However, the call termination to the CS domain does not pass through the VCC AS by using the subscriber information shared between the HLR of the CS network and the VCC AS of the IMS network, as done in the embodiment of the present invention. Therefore, the terminating CS call can be processed according to the normal terminating call processing process. The normal terminating call processing process is-known to those skilled in the art, and a detailed description thereof is omitted for conciseness. 
         [0042]    As is apparent from the foregoing description, the voice call processing method according to the present invention shares subscriber information between the CS domain and the IMS domain, thereby enabling fast call processing and allowing the UE to perform handoff from the IMS domain to the CS domain. In addition, the terminating call processing between the CS calls does not pass through the IMS domain, facilitating the efficient processing. 
         [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.