Abstract:
Provided is a method and system for supporting IMS VCC based on an MIH. In a method of supporting a multimedia service for an MIH-based VCC, neighbor network information is obtained from an MIH server periodically or according to an event trigger and scanning the neighbor network. The capacity of at least one more candidate networks is detected from the scanning results to prepare a handover. A target network is determined among the candidate networks to reserve resources and a handover command event is generated to perform a domain transfer. The handover is completed after the performing of the domain transfer.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY 
       [0001]    This application claims priority under 35 U.S.C. §119 to an application filed in the Korean Intellectual Property Office on Sep. 28, 2007 and assigned Serial No. 2007-97831, the contents of which are incorporated herein by reference. 
       TECHNICAL FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to IP Multimedia Subsystem (IMS) Voice Call Continuity (VCC) and, in particular, to a method and system for supporting IMS VCC based on a Media-Independent Handover (MIH). 
       BACKGROUND OF THE INVENTION 
       [0003]    Integration of a wired/wireless data network with a mobile communication network (i.e., fixed mobile convergence (FMC)) aims at providing users with a consistent and seamless service regardless of the communication network types. The distinction between voice and data is eliminated because of the widespread use of third-generation (3G) mobile communications and multimedia communications. In this context, the FMC integrates services for Unlicensed Mobile Access (UMA) networks, such as mobile communication networks, wired telephone networks, Bluetooth, Wireless Local Area Networks (WLANs), and Ultra Wide Band (UWB) based on Internet Protocol (IP). The initial attention to FMC started with the IP Multimedia Subsystem (IMS) standard (i.e., the next-generation multimedia service based standard of the 3rd Generation Partnership Project (3GPP) standardization organization). 
         [0004]    The ultimate goal of FMC pursued by the 3GPP is to link all heterogeneous networks to an IP core network, to provide an integrated service through the IMS, and to comply with the IMS VCC as the standard for providing a seamless service between UMA networks such as mobile communication networks and wired telephone networks. Meanwhile, a UMA-based seamless service providing method is being standardized as an intermediate stage evolving into the integrated IMS. 
         [0005]      FIG. 1  is a diagram illustrating a conventional VCC reference model. 
         [0006]    Referring to  FIG. 1 , a VCC application server (AS)  103  is introduced and an IMS controlled in a call procedure is defined, thereby maintaining VCC. To this end, a voice call is controlled by a Call Continuity Control Function (CCCF) element present in an IMS domain. This means that calls originated from a circuit switching (CS)-based cellular domain, which were controlled by a Mobile Switching Center (MSC)  116 , is controlled in the IMS domain. The MSC  116  needs to route all the calls, originated from the CS-based cellular domain, to the CCCF element. This is performed by the VCC AS  103  present in the IMS domain. 
         [0007]    In the scenario of a handover from a Voice-over-IP (VoIP) network to a CS network, it is assumed that a VoIP call is initially established between a Multi-Mode Terminal (MMT)  120  and an Other End Point (OEP) through a serving base station (BS)  115  and packet data switch  114 . When the MMT  120  is located near a coverage boundary of a serving network, it transmits a call origination message through a target base station (BS)  118  to the network in order to initiate a handover. The MSC  116  performs an authentication process and generates a call origination trigger in the VCC AS  103 . The VCC AS  103  determines a domain switch together with network entities, such as a Home Location Register (HLR)  101 , a Media Gateway Control Function (MGCF)  112 , Call/Session Control Functions  105 ,  106  and  111 , and Wireless Intelligent Network Service Control Point (WIN SCP)  102 , and performs a domain transfer. In this process, a Media Gateway (MGW)  113  interprets routing information and a bearer path updated by opinion exchange between the VCC AS  103  and the OEP. After establishment of a new opinion exchange, the VCC AS  103  transmits a SIP release message to the MMT  120 . The new bearer path passes through the MSC  116  and the MGW  113 . 
         [0008]    In the scenario of a handover from a CS network to a VoIP network, a basic signaling process is similar to that described above. After a domain transfer process, the MGW  113  is disregarded in a bearer path, and new routing information is updated by opinion exchange between the OEP and the VCC AS  103 . 
         [0009]    The Institute of Electrical and Electronics Engineers (IEEE) 802.21 standard provides a framework that enables seamless service continuity while a User Equipment (UE) is switching between heterogeneous link layer. This framework depends on a Media-Independent Handover Function (MIHF) performed by both the network entities such as a UE, a BS, and an Access Service Network-GateWay (ASN-GW). Also, an MIH server is introduced in a home network in order to support an MIH information service. 
         [0010]    The MIHF provides upper layers and lower layers with an asymmetric service, such as a Media-Independent Event Service (MIES), and a symmetric service, such as a Media-Independent Command Service (MICS), through a well-defined Service Access Point (SAP). Also, the MIHF provides a Media-Independent Information Service (MIIS) that provides information about homogeneous or heterogeneous networks present in a certain geographical area. 
         [0011]    As described above, in order to support a domain transfer between IMS and CS cellular networks during a voice call service, a multi-mode terminal needs to transmit a call origination message to a target network in order to perform a handover by triggering a mobile event. However, research is not yet being conducted on how the terminal generates and transmits the trigger message. 
       SUMMARY OF THE INVENTION 
       [0012]    To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to substantially solve at least the above problems and/or disadvantages and to provide at least the advantages below. Accordingly, an object of the present invention is to provide a call origination method and system for allowing a UE to trigger a VCC process. 
         [0013]    Another object of the present invention is to provide a method and system for guaranteeing a seamless VCC service. 
         [0014]    Still another object of the present invention is to provide a method and system for supporting an IMS VCC service based on an MIH. 
         [0015]    According to an aspect of the present invention, a method of supporting a multimedia service for an MIH-based VCC comprises: obtaining neighbor network information from an MIH server periodically or according to an event trigger and scanning the neighbor network; detecting the capacity of at least one more candidate networks from the scanning results to prepare a handover; determining a target network among the candidate networks to reserve resources, and generating a handover command event to perform a domain transfer; and completing the handover after the performing of the domain transfer. 
         [0016]    Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts: 
           [0018]      FIG. 1  is a diagram illustrating a conventional VCC reference model; 
           [0019]      FIGS. 2A and 2B  illustrate a process for a domain transfer from a WLAN VoIP network to a CDMA2000 1x CS network according to an embodiment of the present invention; 
           [0020]      FIG. 3  is a flow chart illustrating a process for supporting an MIH-based IMS VCC according to an embodiment of the present invention; 
           [0021]      FIGS. 4A to 4D  illustrate a process for a signal strength-based voice call handover from an IMS network to a CS network according to an embodiment of the present invention; and 
           [0022]      FIGS. 5A to 5D  illustrate a process for a policy-based voice call handover from a CS network to an IMS network according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]      FIGS. 1 through 5D , discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged communication network. 
         [0024]    The present invention is intended to provide a method and system for supporting IP Multimedia Subsystem (IMS) Voice Call Continuity (VCC) based on a Media-Independent Handover (MIH). The VCC controls a domain selection process and a domain switch process in a core network, and the MIH manages handover initiation and neighbor network information search in a User Equipment (UE) and a radio access network (e.g., a base station (BS) or an Access Service Network-Gateway (ASN-GW)). 
         [0025]      FIGS. 2A and 2B  illustrate a process for a domain transfer from a WLAN VoIP network to a CDMA2000 1x Circuit Switching (CS) network according to an embodiment of the present invention. Herein, it is assumed that a User Equipment (UE)  1  is a multi-mode terminal supporting a WLAN and a CDMA2000 1x CS system and is successfully assigned a VoIP session  200  through an Other End Point (OEP) (e.g., an IMS user and a PSTN MGCF/MGW). That is, the UE performs a VoIP service through a WLAN. 
         [0026]    Referring to  FIGS. 2A and 2B , when a handover from the WLAN to the 1x CS network is needed, the UE transmits a 1x call origination message to an MSC/VLR in step  201 . 
         [0027]    In step  202 , before approving registration and assigning a 1x traffic channel, the MSC/VLR transmits an AUTHREQ message to a Home Location Register (HLR) in order to authenticate the UE. 
         [0028]    In step  203 , the HLR transmits an authreq message to the MSC/VLR in response to the AUTHREQ message. 
         [0029]    In step  204 , the MSC/VLR transmits a REGistration NOTification (REGNOT) message for location registration to the HLR. 
         [0030]    In step  205 , the HLR transmits a regnot message to the MSC/VLR in response to the REGNOT message. 
         [0031]    In step  206 , the MSC/VLR transmits an ORigination REQuest (ORREQ) message containing an origination number and a termination number to a VCC AS through a Wireless Intelligent Network Service Control Point (WIN SCP). That is, the MSC/VLR obtains a service profile for an origination subscriber (e.g., through step  203 ) and requests a call origination trigger in order to obtain routing information. 
         [0032]    In step  208 , by referring to the called number (and the calling number) contained in the ORREQ message, the VCC AS determine whether to perform a domain transfer, and assigns an IP Multimedia Subsystem (IMS) routing number. Thereafter, the VCC AS transmits an orreq message to the MSC/VLR through the WIN SCP. 
         [0033]    In step  209 , based on an operation policy according to interpretation of the called number, the MSC/VLR transmits an ISDN User Part (ISUP) Initial Address Message (IAM) message to a Public Switched Telephone Network (PSTN) or a Media Gateway Control Function (MGCF) present in a serving network. 
         [0034]    In step  210 , based on a local policy, the MGCF transmits an Address Complete Message (ACM) message to the MSC/VLR in response to the IAM message. The MGCF requests a Media GateWay (MGW) to generate two terminations. The first termination is a connection between the visited MGW and the visited MSC. The second termination is a Real-time Transport Protocol (RTP)/User Datagram Protocol (UDP)/IP ephemeral termination. 
         [0035]    In step  212 , the MSC/VLR transmits a 1x channel assignment message to the UE through a base station (BS). Step  212  may occur at any time after step  201 . 
         [0036]    In step  213 , the MGCF transmits a SIP INVITE message containing a Request-URI (Uniform Resource Identifier), a P-Asserted-ID and a Session Description Protocol (SDP) offer to the VCC AS through an interrogating CSCF (I-CSCF). The Request-URI is based on an IAM called number, the P-Asserted-ID is based on an IAM calling number, and the SDP offer is based on the visited MGW SDP information. Step  213  may occur at any time after step  209 . Herein, the I-CSCF is the first access point of the UE to a home network, and several I-CSCFs may be present in one network domain. Also, a SIP INVITE message received from a Serving CSCF (S-CSCF) is routed to the S-CSCF. 
         [0037]    In step  213 ′, in order to determine which subscriber terminal performs a WLAN VoIP-to-1x CS voice domain transfer (DT), the VCC AS detects a P-Asserted-Identify header of the INVITE and transmits an SIP Session Progress message to the MGCF. 
         [0038]    In step  214 , the VCC AS transmits an SIP re-INVITE message, which contains an SDP offer based on the visited MGW SDP information and a Request-URI originated from the OEP, to the S-CSCF. In step  215 , the S-CSCF forwards a re-INVITE message to the OEP. The S-CSCF is a subsystem that controls a session of the UE. The S-CSCF registers a subscriber in a Home Subscriber Service (HSS), downloads subscriber information, and stores/manages a service profile. Also, the S-CSCF manages a register user session state and performs a control service. For example, the S-CSCF transmits a call request message to a home domain of a termination user through a dialed called number or a termination URL. Thereafter, the S-CSCF transmits a response message received from the I-CSCF/MGCF to a Proxy CSCF (P-CSCF) or the I-CSCF. 
         [0039]    In step  216 , the OEP corrects its own RTP bearer termination according to the visited MGW SDP and transmits an SIP 200 OK message containing an SDP answer having OEP SDP information to the S-CSCF. In step  217 , the S-CSCF forwards a SIP 200 OK message to the VCC AS. 
         [0040]    In step  218 , the VCC AS transmits an SIP 200 OK message an SDP answer having OEP SDP information to the MGCF through the I-CSCF. 
         [0041]    In step  219 , the MGCF requests a change of an ephemeral termination using the OEP SDP information. To this end, the MGCF transmits an ISUP ANM (Address Completion Message) message to the MSC/VLR. 
         [0042]    In step  220 , the MGCF transmits a SIP ACK message to the VCC AC through the I-CSCF. This completes the establishment of a SIP call session between the MGCF and the VCC AS. The VCC AS records the location of the UE in a 1x CS domain. 
         [0043]    In step  221 , the VCC AS transmits a SIP ACK message to the S-CSCF. In step  222 , the S-CSCF forwards a SIP ACK message to the OEP. 
         [0044]    In step  223 , the VCC AS transmits a SIP BYE message, which is used to terminate a generated SIP session, to the UE through the S-CSCF. 
         [0045]    In step  224 , the UE transmits a SIP 200 OK message through the S-CSCF to the VCC AS in response to the SIP BYE message. Accordingly, the UE performs a 1x voice call ( 230 ) with the OEP. 
         [0046]    Herein, steps  213  to  224  correspond to a domain switch procedure in a core network. 
         [0047]    Thereafter, the domain transfer process is ended. 
         [0048]      FIG. 3  illustrate a process for supporting an MIH-based IMS VCC according to an embodiment of the present invention. 
         [0049]    Referring to  FIG. 3 , in step  300 , a UE obtains neighbor network information from an MIH server periodically or according to an event trigger. 
         [0050]    In step  302 , based on the obtained neighbor network information, the UE determines whether a candidate network is a CS or an IMS. That is, the UE determines whether it performs a voice call through a CS or receives an IMS-based VoIP service. 
         [0051]    In step  304 , the UE scans each candidate network to obtain information about a physical layer and a link layer (e.g., a signal strength). 
         [0052]    In step  306 , the UE transmits a query message through a serving network to each candidate network to detect the network capacity. 
         [0053]    In step  308 , based on a handover algorithm, the UE determines a target network and a handover type. 
         [0054]    In step  310 , the UE notifies the handover determination to the network (the target network or the serving network) and reserves resources of the target network. 
         [0055]    In step  312 , the UE determines whether there are available resources in the target network. If there are available resources in the target network (in step  312 ), the process proceeds to step  314 . In step  314 , by being triggered by an MIH handover command message, the UE transmits a call origination message to the network in order to initiate a handover. Herein, a domain transfer process is initiated and performed in the core network according to the call origination message transmitted to the target network. 
         [0056]    In step  316 , the UE terminates the previous link after establishing a new link. 
         [0057]    Thereafter, the process is ended. 
         [0058]      FIGS. 4A to 4D  illustrate a process for a signal strength-based voice call handover from an IMS network to a CS network according to an embodiment of the present invention. 
         [0059]    Referring to  FIGS. 4A to 4D , it is assumed that a VoIP session for a UE is established in a serving network (an IP-based IMS network) through a VCC AS in step  400 . 
         [0060]    In step  401 , a MAC layer of the serving network triggers a link parameter change event due to a change in a radio channel. That is, a Link_Parameters_Change_Indication link event is transmitted to an MIHF. 
         [0061]    Instep  402 , the MIHF transmits an MIH link parameter report indication MIH event (MIH_Link_Paramters_Report_Indication) to an MIH user. 
         [0062]    In order to obtain network information in step  403 , the MIH user transmits an information request MIH command (MIH_Get_Info. request) to the MIHF in step  404 . 
         [0063]    In step  405 , the MIHF transmits an information request message (MIH_Get-Information REQUEST FRAME) to an MIH server. 
         [0064]    In step  406 , the MIH server transmits an information response message (MIH_Get_Information RESPONSE FRAME) to the MIHF. 
         [0065]    In step  407 , the MIHF transmits an MIH event (MIH_Get_Info. confirmation) to the MIH user. The MIH user can be connected to the MIH server according to the event and/or the command, and the MIH user can obtain general network information, access network information, Point of Attachment (POA) information, and upper layer information according to a Query/Response. 
         [0066]    Thereafter, the MAC layer of the serving network triggers a link down event (MIH_Going_Down. Indication) due to the degradation of signal quality when the UE continues to move out of the coverage area of the serving network. That is, in step  408 , the MAC layer of the serving network transmits an MIH_Going_Down. Indication link event to the MIHF. 
         [0067]    In step  409 , the MIHF transmits a link down MIH command (MIH_Link_Going_Down. Indication) to the MIH user. 
         [0068]    In order to activate a candidate network in step  410 , the MIH user transmits a scan request MIH command (MIH_scan.request) to the MIHF in step  411 . Herein, the MIH user can detect a neighbor network by performing a scanning process. 
         [0069]    In step  412 , the MIHF transmits a scan request (Scan_request) link command to a MAC layer of a target network. 
         [0070]    In step  413 , the MAC layer of the target network receives a broadcast message from a Radio Access Network (RAN) of the target network to receive the target network physical layer/link layer information. The target network may be selected after a scanning process. 
         [0071]    In step  414 , the MAC layer of the target network transmits a scan response (Scan_response) link event to the MIHF. 
         [0072]    In step  415 , the MIHF transmits a scan response MIH event (MIH_Scan_response) to the MIH user. 
         [0073]    In step  416 , the MIH user transmits an MIH command (MIH_MN_HO_Candidate_Query.request), which is used to detect the capacity of a candidate network obtained from the scanning process, to the MIHF to prepare a handover. 
         [0074]    In step  418 , the MIHF transmits an MIH_MN_HO_Candidate_Query.REQUEST FRAME message, which is used to detect the capacity of a candidate network, to an MIHF (POA) of a serving network (IMS). 
         [0075]    In step  419 , the MIHF (POA) of the serving network (IMS) transmits a response message (MIH_N2N_HO_Query_Resources.request), which is used to detect the capacity of a candidate network, to an MIHF (POA) of a target network (CS). 
         [0076]    In step  420 , the MIHF (POA) of the target network (CS) transmits a link event (MIH_N2N_HO_Query_Resources. response) as a response for detecting the capacity of a candidate network to the MIHF (POA) of the serving network (IMS). 
         [0077]    In step  421 , the MIHF (POA) of the serving network (IMS) transmits a response message (MIH_MN_HO_Candidate_Query.RESPONSE FRAME) for the capacity of a candidate network to the MIHF. 
         [0078]    In step  422 , the MIHF transmits an MIH_MN_HO_Candidate_query.response MIH event to the MIH user. 
         [0079]    In step  423 , the MIH user determines a handover to a target BS on the basis of a signal strength. That is, based on available information, the MIH user determines a handover according to an information processing function including the resource reservation results and the upper layer information from the MIH server as well as the physical layer information from a scanning processor. 
         [0080]    In step  424 , the MIH user transmits an MIH command (MIH_MN_HO_Commit request) notifying a handover to a target network to the MIHF. 
         [0081]    In step  425 , the MIHF transmits an MIH_MN_HO_Commit REQUEST Frame message notifying a handover to a target network to an MIHF (POA) of a serving network. 
         [0082]    In step  426 , the MIHF (POA) of the serving network transmits a resource reservation message (MIH_N2N_HO_Commit REQUEST Frame) to the MIHF (POA) of the target network. 
         [0083]    In step  427 , the MIHF (POA) of the target network transmits a resource reservation notification message (MIH_N2N_HO_Commit RESPONSE Frame) to the MIHF (POA) of the serving network. 
         [0084]    Instep  428 , the MIHF (POA) of the serving network transmits a resource reservation notification message (MIH_MN_HO_Commit RESPONSE Frame) to the MIHF. 
         [0085]    In step  429 , the MIHF transmits an MIH command (MIH_MN_HO_Commit confirmation) notifying a handover to a target network to the MIH user. 
         [0086]    In step  430 , the MIHF transmits a Handover Command event of the MIH user to a MAC layer of a target network. 
         [0087]    In step  431 , while receiving a response message from the network, the MAC layer of the target network transmits a call origination request message to an MSC through a RAN of the target network. 
         [0088]    In steps  432  and  433 , the MSC and the HLR perform an authentication request/response. That is, when an MSC in a target network receives a call origination request message, the MSC transmits an AUTHENREQ message and receives an authenreq message in order to perform user authentication. In steps  434  and  435 , the MSC and the VCC AS transmits/receives an REGNOT/regnot message in order to perform a location registration request/response. 
         [0089]    In step  439 , the MSC transmits an IAM message to an MGCF in order to perform trunk establishment in a target network. In step  440 , the MGCF transmits an ACM message to the MSC in response to the IAM message. 
         [0090]    In steps  441  and  442 , the MGCF and the VCC AS exchange a SIP INVITE message and a SIP 200 OK message to perform a domain switch process, thereby connecting a session call with a target network. Accordingly, a SIP message exchange/process is performed. 
         [0091]    In step  443 , the VCC AS transmits a SIP BYE message to the MIH user to terminate an SIP session. 
         [0092]    In step  436 , a RAN of the target network transmits a resource assignment message to a MAC layer of a target network of the UE. Step  436  may be performed at any time after the call origination request in step  431 . 
         [0093]    In step  437 , the MAC layer of the target network transmits a link connection event (Link Up) for the target network to the MIHF. 
         [0094]    In step  438 , the MIHF transmits a link connection indication MIH event (MIH_Link Up.indication) to the MIH user. 
         [0095]    In step  444 , an application layer of the UE transmits a Handover Complete message to the MIH user. 
         [0096]    In step  445 , the MIH user transmits an MIH command (MIH_MN_HO_Complete.request) notifying handover completion to the MIHF. 
         [0097]    In step  446 , the MIHF transmits a handover completion notification message (MIH_MN_HO_Complete.REQUEST Frame) to an MIHF (POA) of a target network. 
         [0098]    In step  447 , the MIHF (POA) of the target network transmits an MIH_N2N_HO_Complete REQUEST Frame message notifying handover completion of the UE to an MIHF (POA) of a serving network. 
         [0099]    In step  448 , the MIHF (POA) of the serving network transmits a response message (MIH_N2N_HO_Complete RESP Frame) for the handover completion notification of the UE to an MIHF (POA) of a target network. 
         [0100]    In step  449 , the MIHF (POA) of the target network transmits a response message (MIH_MN_HO_Complete.RESP Frame) for the handover completion notification to the MIHF. 
         [0101]    In step  450 , the MIHF transmits an MIH command (MIH_MN_HO_Complete.response) for the handover completion notification to the MIH user. 
         [0102]    In step  451 , the MIH user transmits a Handover Complete Confirm message to the application layer. 
         [0103]    In step  452 , the application layer of the UE transmits a SIP 200 OK message to the VCC server in response to a SIP BYE message. 
         [0104]    Thereafter, a call dialogue between the VCC server and the MGCF of the target network is opened in step  453 , and a call dialogue between the VCC server and the OEP is opened in step  454 . 
         [0105]    In step  455 , a domain transfer from the IMS and the CS is performed to perform a voice service from the CS of the target network. 
         [0106]    Thereafter, the process is ended. 
         [0107]      FIGS. 5A to 5D  illustrate a process for a policy-based voice call handover from a CS network to an IMS network according to an embodiment of the present invention. 
         [0108]    Referring to  FIGS. 5A to 5D , it is assumed that voice call traffic for a UE is established in a serving network (a CS network) through a VCC AS in step  500 . 
         [0109]    In step  501 , an MIH user of the UE periodically searches an MIH server for neighbor network information. A trigger operation may be performed by a timer set in the UE. To this end, in step  502 , the MIH user transmits an information request MIH command (MIH_Get_Info.request) to the MIHF in order to obtain the network information. 
         [0110]    In step  503 , the MIHF transmits an information request message (MIH_Get-Information REQUEST FRAME) to an MIH server. 
         [0111]    In step  504 , the MIH server transmits an information response message (MIH_Get_Information RESPONSE FRAME) to the MIHF. 
         [0112]    In step  505 , the MIHF transmits an MIH event (MIH_Get_Info. response) to the MIH user. The MIH user can be connected to the MIH server according to the event and/or the command, and the MIH user can obtain general network information, access network information, Point of Attachment (POA) information, and upper layer information according to a Query/Response. 
         [0113]    In order to activate a candidate network in step  506 , the MIH user transmits a scan request MIH command (MIH_scan.request) to the MIHF in step  507 . Herein, the MIH user can detect a neighbor network by performing a scanning process. 
         [0114]    In step  508 , the MIHF transmits a scan request message (Scan_request) to a MAC layer of a target network. 
         [0115]    In step  509 , the MAC layer of the target network receives a broadcast message from a Radio Access Network (RAN) of the target network to receive information necessary for scanning. The target network may be selected after a scanning process. 
         [0116]    In step  510 , the MAC layer of the target network transmits a scan response message (Scan_response) to the MIHF. 
         [0117]    In step  511 , the MIHF transmits a scan response MIH event (MIH_Scan_response) to the MIH user. 
         [0118]    Thereafter, during preparation of a handover, a policy-based handover is triggered, and the UE determines a handover based on the priority order configured for each network. A network with a higher priority order is selected as a target network. To this end, in step  512 , the MIH user transmits an MIH command (MIH_MN_HO_Candidate_Query.request), which is used to detect the capacity of a candidate network obtained from the scanning process, to the MIHF to prepare a handover. 
         [0119]    In step  513 , the MIHF transmits an MIH_MN_HO_Candidate_Query.REQUEST FRAME message, which is used to detect the capacity of a candidate network, to an MIHF (POA) of a serving network (CS). 
         [0120]    In step  514 , the MIHF (POA) of the serving network (CS) transmits an MIH_N2N_HO_Query_Resources.request message, which is used to detect the capacity of a candidate network, to an MIHF (POA) of a target network (IMS). 
         [0121]    In step  515 , the MIHF (POA) of the target network (IMS) transmits a response message (MIH_N2N_HO_Query_Resources.response) for detecting the capacity of a candidate network to the MIHF (POA) of the serving network (CS). 
         [0122]    In step  516 , the MIHF (POA) of the serving network (CS) transmits a response message (MIH_MN_HO_Candidate_Query.RESPONSE FRAME) for the capacity of a candidate network to the MIHF. 
         [0123]    In step  517 , the MIHF transmits an MIH event (MIH_MN_HO_Candidate_query.response) as a response for the capacity of the neighbor network to the MIH user. 
         [0124]    Thereafter, if there is an available target network in step  518 , the MIH user transmits an MIH command (MIH_MN_HO_Commit request) notifying a handover to a target network to the MIHF in step  519 . 
         [0125]    In step  520 , the MIHF transmits an MIH_MN_HO_Commit REQUEST Frame message notifying a handover to a target network to an MIHF (POA) of a serving network. 
         [0126]    In step  521 , the MIHF (PbA) of the serving network transmits an MIH_MN_HO_Commit REQUEST Frame message notifying a handover to a target network to the MIHF (POA) of the target network. 
         [0127]    In step  522 , the MIHF (POA) of the target network transmits a response message (MIH_MN_HO_Commit RESPONSE Frame) notifying a handover to a target network to the MIHF (POA) of the serving network. 
         [0128]    In step  523 , the MIHF (POA) of the serving network transmits a response message (MIH_MN_HO_Commit RESPONSE Frame) notifying a handover to a target network to the MIHF. 
         [0129]    In step  524 , the MIHF transmits an MIH command (MIH_MN_HO_Commit confirmation) confirming a handover to a target network to the MIH user. 
         [0130]    In step  525 , the MIHF transmits a Handover Command event of the MIH user to a MAC layer of a target network. 
         [0131]    In step  526 , the MAC layer of the target network exchanges a Link Connection Request/Response message with a RAN of the target network (IMS). 
         [0132]    In step  527 , the MAC layer of the target network transmits Switch Response message to the MIHF. 
         [0133]    In step  528 , the MIHF transmits an MIH_Link_Up.Indication command to the MIH user. 
         [0134]    Thereafter, in order to allocate an IP address from a DHCP server, an application layer of the UE transmits a DHCP Discover message to a packet service node in step  529 , and the packet service node transmits a DHCP Offer message to the application layer of the UE in step  530 ; the application layer of the UE transmits a DHCP Request message to a packet service node in step  531 , and the packet service node transmits a DHCP ACK message to the application layer of the UE in step  532 . 
         [0135]    In step  533 , an application layer transmits a SIP INVITE message to a VCC AS through a P-CSCF, and the VCC AS forwards an SIP re-INVITE message to an S-CSCF. 
         [0136]    In step  534 , the S-CSCF transmits a SIP re-INVITE message to an OEP. 
         [0137]    In step  535 , the VCC AS transmits a SIP BYE message for removal of a CS call to an MGCF. 
         [0138]    In step  536 , the MGCF transmits a control message for termination of a CS call connection to the application layer. 
         [0139]    Herein, steps  533  to  536  are a domain switching process that switches from the CS network to the IMS network to establish a VoIP session in step  537 . 
         [0140]    In step  538 , the application layer of the UE transmits a Handover Complete message to the MIH user. 
         [0141]    In step  539 , the MIH user transmits an MIH_MN_HO_Complete request command to the MIHF. 
         [0142]    In step  540 , the MIHF transmits an MIH_MN_HO_Complete.REQUEST Frame message to an MIHF (POA) of a target network. 
         [0143]    In step  541 , the MIHF (POA) of the target network transmits an MIH_N2N_HO_Complete REQUEST Frame for request of a handover to the UE to an MIHF (POA) of a serving network. 
         [0144]    In step  542 , the MIHF (POA) of the serving network transmits a response message (MIH_N2N_HO_Complete response) for the handover completion request of the UE to the MIHF (POA) of the target network. 
         [0145]    In step  543 , the MIHF (POA) of the target network transmits a response message (MIH_MN_HO_Complete.RESPONSE) for the handover completion request to the MIHF. 
         [0146]    In step  544 , the MIHF transmits an MIH command (MIH_MN_HO_Complete.response) for the handover completion request to the MIH user. 
         [0147]    In step  545 , the MIH user transmits a Handover Complete message to an application layer. 
         [0148]    Thereafter, the process is ended. 
         [0149]    As described above, the multi-mode UE of the present invention supports an MIH-based IMS VCC service, thereby making it possible to provide an IMS VCC service support solution to the UE. 
         [0150]    Although the present disclosure has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.