Abstract:
Disclosed herein is a method and system for Mobile Internet Protocol version 4 (MIPv4)-based fast handoff between heterogeneous networks. The method includes the first step of an Mobile Station (MS) acquiring information about a second Foreign Agent (FA) pertaining to a second wireless network to be newly accessed from a first FA pertaining to a first wireless network that is different from the first wireless network and is previously accessed; the second step of the MS requesting registration from an integrated Home Agent (HA) through the first FA and the second FA; the third step of generating a temporary tunnel between the first FA and the second FA; and the fourth step of the HA transmitting a reply to the registration request to the MS through the second FA.

Description:
RELATED APPLICATIONS  
       [0001]     The present application is based on, and claims priority from, Korean Application Number 2004-0104957, filed Dec. 13, 2004, the disclosure of which is incorporated by reference herein in its entirety.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to a method and system for Mobile Internet Protocol version 4-based fast handoff between heterogeneous networks and, more particularly, to a method and system for Mobile Internet Protocol version 4-based fast handoff in regions where heterogeneous networks, such as a portable Internet service network, a Code Division Multiple Access2000 wireless Internet access service network, and an IEEE 802.11-based public wireless local area network service network, overlap each other.  
         [0004]     2. Description of the Related Art  
         [0005]     Generally, handoff is a scheme for maintaining the connectivity of communication path and service as a mobile terminal moves around. Conventional handoff schemes include a low latency handoff scheme that is applied to the Mobile Internet Protocol version 4 (MIPv4) of a network layer and a fast handoff scheme that is applied to Mobile Internet Protocol version 6 (MIPv6).  
         [0006]     The low latency handoff scheme that is one of the conventional handoff schemes and is applied to MIPv4 includes a pre-registration scheme that performs mobile Internet Protocol (IP) registration first and a post-registration scheme that uses a Bi-directional Edge Tunnel (BET) between Foreign Agents (FAs). All of the two schemes perform handoff using an L2 trigger. The post-registration scheme chiefly uses a method of using a network trigger. In contrast, in the case of the pre-registration scheme, there exists a method of using a mobile trigger. The L2 trigger refers to information relating to an indication transferred from a layer  2  to a layer  3 , and functions to inform the layer  3  of a specific event that happens in the layer  2 . L2 triggers are classified according to the event that drives the L2 triggers, and are divided into a source trigger, a target trigger, a link down trigger, a link up trigger and a mobile trigger.  
         [0007]     However, in the case of the post-registration scheme, a handoff procedure is carried out only by operations between FAs without the involvement of a terminal, so that a mobile trigger is not applied. In the case of the pre-registration scheme, a serious problem may occur such that a service is discontinued due to the loss of a packet if the L2 handoff is completed before mobile IP registration.  
       SUMMARY OF THE INVENTION  
       [0008]     Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a method and system for supporting stable and fast handoff between heterogeneous networks on an MIPv4 basis without the loss of packets or interruption.  
         [0009]     In order to accomplish the above object, the present invention provides a method for MIPv4-based fast handoff between heterogeneous networks, including the first step of an Mobile Station (MS) acquiring information about a second Foreign Agent (FA) pertaining to a second wireless network to be newly accessed from a first FA pertaining to a first wireless network that is different from the first wireless network and is previously accessed; the second step of the MS requesting registration from an integrated Home Agent (HA) through the first FA and the second FA; the third step of generating a temporary tunnel between the first FA and the second FA; and the fourth step of the HA transmitting a reply to the registration request to the MS through the second FA.  
         [0010]     In order to accomplish the above object, the present invention provides a system for MIPv4-based fast handoff between heterogeneous networks, including an MS capable of accessing a plurality of heterogeneous networks; a first FA pertaining a first wireless network that is previously accessed by the MS, the first FA being configured to process routing and mobile IP and to provide information about a second wireless network that is different from the first wireless network and will be accessed by the MS; a second FA pertaining to the second wireless network, the second FA being configured to process routing and mobile IP and to generate a tunnel through which packets will be transferred to the MS; and an integrated HA connected to the plurality of heterogeneous networks through an IP network, the integrated HA being configured to register information about a location of the MS so as to continuously provide a service as the MS moves through the heterogeneous networks. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0012]      FIG. 1  is a configuration diagram showing a system for MIPv4-based fast handoff between heterogeneous networks in accordance with an embodiment of the present invention;  
         [0013]      FIG. 2  is a diagram showing a message call processing flow in a method for MIPv4-based fast handoff between heterogeneous wireless networks in accordance with an embodiment of the present invention;  
         [0014]      FIG. 3  is a diagram showing the format of a proxy router solicitation message according to an embodiment of the present invention;  
         [0015]      FIG. 4  is a diagram showing the format of a proxy router advertisement message according to an embodiment of the present invention;  
         [0016]      FIG. 5  is a diagram showing the format of a registration request message that is added with a fast handoff extension and is used in MIPv4, in accordance with an embodiment of the present invention; and  
         [0017]      FIG. 6  is a diagram showing the format of a registration reply message that is added with a fast handoff acknowledge extension and is used in MIPv4, in accordance with an embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]     Reference now should be made to the drawings, in which the same reference numerals are used throughout the different drawings to designate the same or similar components.  
         [0019]      FIG. 1  is a configuration diagram showing a system for MIPv4-based fast handoff between heterogeneous networks in accordance with an embodiment of the present invention.  
         [0020]     Referring to  FIG. 1 , the system for MIPv4-based fast handoff between heterogeneous wireless networks in accordance with the embodiment of the present invention includes a plurality of heterogeneous wireless networks  110 ,  120  and  130  that overlap each other, an MS  140  that is capable of accessing the heterogeneous networks  110 ,  120  and  130 , an integrated HA  160  that connects via an IP network  150  using IP, and an integrated AAA server  170 . The IP network  150  is connected to the public Internet  180 .  
         [0021]     The plurality of heterogeneous wireless networks  110 ,  120  and  130  may include a Code Division Multiple Access (CDMA) mobile communication wireless Internet access service network  110 , a portable Internet service network  120  (for example, a WiBro network) and an IEEE 802.11-based Public Wireless Local Area Network (PWLAN) service network  130 . The CDMA mobile communication wireless Internet access service network  110  includes a Base Transceiver Station (BTS)  111  that the MS accesses, a Base Station Controller/Packet Control Function (BSC/PCF)  112  that is in charge of the control and management of the BTS and the control of packets, and a Packet Data Serving Node (PDSN)  113  that is in charge of the routing of packets and functions as an FA. The portable Internet service network  120  includes a Radio Access (RAS)  121  through which the MS  140  accesses the portable Internet service network  120 , and an Access Control Router (ACR)  122  that is in charge of the routing of packets and functions as an FA. The PWLAN service network  130  includes an Access Point (AP)  131  through which the MS  140  accesses the PWLAN service network  130 , and a WLAN Access Router (WAR)  132  that is in charge of the routing of packets and functions as an FA.  
         [0022]     The PDSN  113 , the WAR  132  and the ACR  122  perform an FA function of carrying out work related to routing and mobile IP as the MS  140  moves through the heterogeneous networks  110 ,  120  and  130 . To continue service in the overlapping regions between the heterogeneous networks  110 ,  120  and  130 , a heterogeneous network access function and handoff between different frequencies must be provided. Such type of handoff is called “vertical handoff.” It is assumed that the CDMA mobile communication Internet access service network  110  can be accessed from anywhere. The CDMA mobile communication Internet access service network  110  may be constructed in a form that complements the portable Internet service network  120  and compensates for the shadow area of the PWLAN service network  130 .  
         [0023]     The MS  140  is a multi-mode terminal that supports multiple wireless access to the heterogeneous networks  110 ,  120  and  130 , that is, the CDMA mobile communication wireless Internet access service network  110 , the portable Internet service network  120  and the IEEE 802.11-based PWLAN service network  130 . The MS  140  contains a wireless access unit (not shown) that is capable of accessing the heterogeneous networks  110 ,  120  and  130 , and message exchange and other operations can be smoothly performed because the wireless access unit is operated on an IP basis. The integrated HA  160  functions to register the location of the MS  140 . That is, whenever the MS  140  moves into a new network, the MS  140  acquires a new care-of address and performs a registration procedure to inform the integrated HA  160  of the acquisition of the new care-of address. The integrated AAA server  170  accesses the heterogeneous networks  110 ,  120  and  130  using the MS  140 , and functions to provide AAA services to subscribers who want to use service.  
         [0024]      FIG. 2  is a diagram showing a message call processing flow in the method for MIPv4-based fast handoff between heterogeneous wireless networks in accordance with the embodiment of the present invention.  
         [0025]     The handoff method of the present invention modifies the pre-registration scheme of low latency handoff and adopts the BET of the post-registration scheme. Furthermore, the pre-registration scheme of the low latency handoff substantially constitutes the main part of network-initiated handoff and employs a method using an L2-source trigger (which is generated in a currently connected FA) or an L2-target trigger (which is generated in a newly connected FA), whereas the present invention is related to mobile-initiated handoff and uses an L2-mobile trigger.  
         [0026]     In  FIG. 2 , the MS  140  is a multi-mode terminal that supports multiple wireless access. An FA 1  is an entity that functions as an FA, like the ACR  122  of the portable Internet service network  120 , or the AR  132  of the PWLAN service network  120  into which APs  131  are concentrated, and an FA 2  is assumed to be the PDSN  113  of the CDMA mobile communication service network  110 . However, it can be understood that the FA 1  or FA 2  may correspond to any one of the FAs  113 ,  122  and  132 . The FA 1  and the FA 2  are previously aware of mutual information by sharing the mutual information through router discovery. When the MS  140  performs L2 handoff in response to an L2 trigger, a handoff procedure is initiated. With reference to  FIG. 2 , the message call processing procedure in the method for MIPv4-based fast handoff between heterogeneous wireless networks in accordance with the embodiment of the present invention is described in detail below.  
         [0027]     A handoff procedure is initiated by the generation of an L2-mobile trigger in the wireless link layer of the MS  140  at step  200 . Then the MS  140  transfers a proxy router solicitation (ProxyRtSol) message, which requests information about the FA 2  to be newly connected, to the FA 1  previously connected, based on information acquired from the trigger. The proxy router solicitation message includes the link Identification (ID) of a wireless access network to which handoff is attempted. In the case of accessing the CDMA mobile communication wireless Internet access service network  110 , a 5-byte Access Network ID (ANID) including a 2-byte System ID (SID), a 2-byte Network ID (NID) and a 1-byte Packet Zone ID (PZID) may be used. In the case of accessing the portable Internet service network  120 , a 6-byte Base station ID may be used. In the case of accessing the PWLAN service network  130 , a 6-byte Media Access Control (MAC) address may be used.  
         [0028]     Thereafter, when the FA 1  receives the proxy router solicitation message, the FA 1  replies to the proxy router solicitation message with a proxy router advertisement message that includes the CoA of the FA 2  corresponding to the link ID that the MS  140  requested, at step  202 . That is, the proxy router advertisement message includes information about the FA 2 . The CoA is an address that is assigned whenever the MS  140  moves to a new network, and is different from a home address.  
         [0029]     The MS  140  finds the CoA of the FA 2  from the proxy router advertisement message received from the FA 1  and transmits a registration request (RRqst) message to the FA 1  at step  203 .  
         [0030]     The FA 1  transfers a registration request with a fast handoff extension (RRqst with FH) message to the integrated HA through the FA 2 . The fast handoff extension corresponds to an IP extension for generating a tunnel between the previously connected FA 1  and the FA 2  to be newly connected. The fast handoff extension includes information about the generation of the tunnel and the IP address of the edge of the tunnel. The FA 1  detects handoff through the fast handoff extension, and transfers a registration request message to the FA 2 , which is indicated in the fast handoff extension, to request the bi-directional edge tunnel, at step  204 .  
         [0031]     Subsequently, the FA 2  transfers the registration request to the integrated HA  160  at step  205 .  
         [0032]     Furthermore, the FA 2  accepts the tunnel generation request and generates the tunnel in such a way as to transfer the registration request message to the integrated HA  160  and to transmit a temporary registration reply message, together with a fast handoff acknowledge extension message, to the FA 1  in reply to the tunnel generation request, at step  206 . Then the FA 1  can transfer packets, which will be received by the MS  140 , to the FA 2  through the tunnel until a mobile IP registration procedure is completed. That is, after a connection to a service has been blocked, the MS  140  can reestablish the connection using the generated tunnel.  
         [0033]     Thereafter, the integrated HA  160  transfers a general mobile IP registration reply message to the FA 2  at step  207 .  
         [0034]     Thereafter, the FA 2  completes the mobile IP registration procedure by transferring a general registration reply message to the MS  140 . When this procedure is completed, the FA 2  can transmit packets to the MS  140 .  
         [0035]      FIG. 3  is a diagram showing the format of a proxy router solicitation message according to an embodiment of the present invention.  
         [0036]     Referring to  FIG. 3 , the proxy router solicitation message according to the embodiment of the present invention includes the following information. A Type is entered with “41” to designate the proxy router solicitation message that is one of the fields reserved by the Internet Assigned Numbers Authority (IANA). A one-byte Code value is set to “0,” and a Checksum is calculated in the same manner as the checksum of an IP header and the checksum of all the packets is entered therein. The Number of IDs field indicates the number of link IDs included. A Reserved field is a field-not in use and may be used for a specific use later. 8-byte ID fields are added in proportion to the number of link IDs later.  
         [0037]     In the case of the link ID of a general wireless access network, a 5-byte ANID, including a 2-byte SID, a 2-byte NID and a 1-byte PZID, may be used for CDMA-based mobile communication access, a 6-byte base station ID may be used for a WiBro network and a 6-byte MAC address may be used for a WLAN, so that a maximum of a 6-byte ID region is defined, and a 1-byte ID Type and a 1-byte IDLEN are used to designate an ID type and an ID length, respectively.  
         [0038]      FIG. 4  is a diagram showing the format of a proxy router advertisement message according to an embodiment of the present invention.  
         [0039]     Referring to  FIG. 4 , the proxy router solicitation message according to the embodiment of the present invention includes the following information. A Type is entered with “42” to designate the proxy router advertisement message that is one of the fields reserved by the IANA. A 1-byte Code value is set to “0” if a care-of address corresponds to a link ID that is requested by the MS. If not, an actual communication service provider assigns a different value to the 1-byte Code value according to the situation during application, thus notifying the MS of current status. A Checksum is calculated in the same way as the checksum of an IP header, and is entered with the checksum of all the packets. In the Number of Addresses, the number of CoAs contained in a message may be designated, and a reference level, other than the CoA, may be designated according to AddrEntSize. Generally, a 4-byte IP address is represented by “1.” In the CoA field, the CoAs of link IDs requested by the proxy router solicitation message of the MS are sequentially indicated, and null values are filled for an unknown link ID.  
         [0040]      FIG. 5  is a diagram showing the format of a registration request message that is added with a fast handoff extension and is used in MIPv4, in accordance with an embodiment of the present invention.  
         [0041]     Referring to  FIG. 5 , the registration request message requests the generation of a tunnel from the newly connected FA 2  by setting an F bit in a form that is newly added with a fast handoff extension  500 .  
         [0042]     The definitions and values of the fast handoff extension  500  are used as follows. A Type uses “43” to designate the fast handoff extension that is one of the fields reserved by the IANA. A Length indicates the entire length of the fast handoff extension, and an F bit is set to “1” to request the generation of a tunnel. Since an A bit is used for a reply to the request for the generation of the tunnel, the A bit is set to “0.” A Reserved field corresponds to a field not in use and may be used for a specific use later. A CoA indicates the IP address of the edge of the tunnel. That is, the CoA is the IP address of the previous FA.  
         [0043]      FIG. 6  is a diagram showing the format of a registration reply message that is added with a fast handoff acknowledge extension and is used in MIPv4, in accordance with an embodiment of the present invention.  
         [0044]     Referring to  FIG. 6 , the registration reply message indicates a reply message by setting an A bit in a form that is newly added with a fast handoff acknowledge extension  600 .  
         [0045]     The definitions and values of the fast handoff acknowledge extension  600  are used as follows. A Type uses “44” to designate the fast handoff acknowledge extension that is one of the fields reserved by the IANA. A Length indicates the entire length of the fast handoff acknowledge extension, and an F bit is set to “0” to be used to request the generation of a tunnel. An A bit is set to “1” to reply to the request for the generation of the tunnel. A Code is used to indicate the result of a reply to the request for the generation of the tunnel. When the Code is set to “0,” the Code indicates success, and when the Code is set to “1,” the Code indicates failure. A Reserved field is a field not in use, and will be utilized later by a communication service provider according to the cause of failure in the generation of a tunnel or network setting information.  
         [0046]     The method for MIPv4-based fast handoff between heterogeneous networks according to the present invention may be implemented using computer-readable code stored in one of computer-readable recording media. The computer-readable media include all types of recording devices in which data readable by a computer system are stored. The computer-readable recording media are exemplified by Read-Only Memory (ROM), Random Access Memory (RAM), Compact Disk (CD)-ROM, a magnetic tape, a floppy disk and an optical data recording device. The computer-readable recording media includes a carrier wave form, such as transmission via the Internet. Furthermore, a computer-readable recording medium may be distributed throughout a computer system connected via a network, so that computer-readable code can be stored and executed in a distributed manner.  
         [0047]     As described above, in accordance with the present invention, when performing handoff between the heterogeneous networks, the MS uses the L2 trigger as a signal indicating the generation of the handoff, and can perform the MIPv4 registration procedure during L2 handoff, so that there is an advantage in that the delay in the mobile IP registration process can be considerably reduced.  
         [0048]     Furthermore, in accordance with the present invention, the tunnel is generated between the previously connected FA and the FA to be newly connected and packets are transmitted to the MS through buffering even though the registration procedure is not completed, so that there is an advantage in that the loss of packets can be prevented, and the packets are transmitted immediately when the MS is link-connected to a new wireless network, so that there is an advantage in that the continuance of the service can be maintained.  
         [0049]     As a result, in accordance with the present invention, fast handoff that is more stable and can guarantee QoS can be performed between the heterogeneous networks that are being diversified to provide broadband wireless Internet service.  
         [0050]     Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.