Abstract:
A system and method in a mobile network in which a first router manages a first subnet including at least one second router and the at least one second router manages a second subnet including at least one mobile node. In a method for recovering a routing path between the first router and the at least one mobile node, the first router receives, from the at least one second router, information of neighboring routers included in the first subnet, and stores the received neighboring router information. An occurrence of routing path failure is recognized when a periodic report message is not received from the at least one second router within a preset time. An alternative router is selected from among the neighboring routers when the failure occurrence is recognized, and a routing path recovery request is sent to the alternative router. Data is routed to the at least one mobile node through the alternative router when the alternative router positively responds to the routing path recovery request.

Description:
PRIORITY  
       [0001]     This application claims priority to an application entitled “SYSTEM AND METHOD FOR RECOVERING A DAMAGED ROUTING PATH IN A MOBILE NETWORK”, filed in the Korean Intellectual Property Office on Apr. 19, 2004 and assigned Serial No. 2004-26779, the contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to a mobile network, and more particularly to a system and method for recovering a routing path in Mobile Internet Protocol version 6 (MIPv6).  
         [0004]     2. Description of the Related Art  
         [0005]     An Internet Protocol (IP) network, i.e., an Internet network, is being extended, and simultaneously a wired section within a cellular network is developing into an IP-based Internet network. Devices that were developed for operation only within a wired environment must provide service, while now maintaining seamless continuity in a high-speed wireless environment.  
         [0006]     More specifically, the previous Internet environment took into account only a wired environment. Accordingly, when it is assumed that a terminal does not move in the wired environment, the terminal maintains connections with other nodes through an IP address assigned only once.  
         [0007]     However, with the development of wireless technology, terminals located in the current IP network must be able to stably transmit and receive voice and data while being mobile.  
         [0008]     Accordingly, a home network (HN) continuously tracks the location of a terminal changing location and stores information of the tracked location in a home agent (HA), such that the terminal to which a fixed IP address is assigned can normally transmit and receive voice and data while on the move. The term “HN” refers to a network in which the terminal to which an IP address is assigned is initially registered.  
         [0009]     With ever increasing demand for Internet service, Internet Protocol version 4 (IPv4), which is currently being used, has problems of a growing shortage of available resources such as IPv4 addresses, IPv4 mobility and security weakness, etc. Therefore to address theses problems, Internet Protocol version 6 (IPv6) has been developed. Further, Mobile IPv6 (MIPv6) supports mobility of the IPv6.  
         [0010]      FIG. 1  illustrates a network architecture based on a basic configuration of a conventional MIPv6. Referring to  FIG. 1 , MIPv6 network components include mobile nodes (MNs), a home agent (HA), a router, etc. Further, MIPv6 networks can be an HN, an Internet network, a foreign network (FN), etc.  
         [0011]     More specifically, MN 1   110  and MN 2   170 , which are mobile terminals for performing a packet communication function, are assigned mobile IP addresses. An HN  100  is a network in which the MNs  110  and  170  are initially registered, and an HA  120  manages registration information of the MNs  110  and  170 . Further, the MN 2   170 , which is initially registered in the HN  100 , can move from the HN  100  to a different network, i.e., an FN  140 .  
         [0012]     As described above, when moving from the HN  100  to the FN  140 , the MN 2   170  cannot use the IP address initially assigned thereto by the HN  100 . Accordingly, the FN  140  newly assigns, to MN 2   170 , a care of address (CoA) available therein, such that MN 2   170  can communicate within the FN  140 .  
         [0013]     A size of an IP address assigned to the MN in the MIPv6 environment is 128 bits. More significant bits of the 128 bits are designated as a prefix value for identifying a network, and less significant bits of the 128 bits are designated as an address value of Layer 3 (L3) for identifying a terminal. When MN 2   170  moves from the HN  100  to the FN  140 , a router  150  of the FN  140  identifies L3 information of the IP address of MN 2   170 , and determines that the FN  140  has been visited by MN 2   170 . In this case, the router  150  identifies a prefix value of the IP address of MN 2   170 , and generates a new L3 address according to predetermined guidelines. More specifically, the router  150  determines if a duplicate address corresponding to the generated L3 address is present. If no duplicate address is present, the generated L3 address is assigned to MN 2   170 .  
         [0014]     When MN 2   170  moves from the current network to another network, the FN  140  assigns, to the MN 2   170 , a CoA, which is as a temporary IP address, separately from an IP address assigned by the HN  100 , such that MN 2   170  can communicate using the CoA.  
         [0015]     Even though MN 2   170  has moved to the FN  140 , all data transmitted to MN 2   170  is sent to a network in which MN 2   170  was initially registered, i.e., the HN  100 . Therefore, the HN  100  must have location information of MN 2   170  in order to transmit the data to MN 2   170 .  
         [0016]     When MN 2   170  moves to the FN  140  and is assigned a new CoA, the router  150  of the FN  140  binds the temporary IP address, i.e., the CoA information and the IP address of MN 2   170  used in the HN  100 , includes a result of the binding in a binding update (BU) message, and transmits the BU message to the HA  120  through an Internet network  130  (as indicated by reference numeral  180 ).  
         [0017]     Upon receiving the BU message, the HA  120  identifies the BU message and stores the IP address of MN 2   170  used in the HN  100  and the CoA assigned by the FN  140  in a predetermined table. Thereafter, the HA  120  intercepts packets transmitted to a home IP address of MN 2   170 , i.e., a network address of the HN  100 , as a destination address, and transmits the intercepted packets to the FN  140 .  
         [0018]     More specifically, the HA  120  determines that a received packet is to be transmitted to MN 2   170 , and identifies the CoA of MN 2   170  by referring to the table. Then, the HA  120  encapsulates the packet to attach a header to the packet, sets a destination address to the CoA of MN 2   170 , and transfers the encapsulated packet to MN 2   170  (as indicated by reference numeral  185 ). In this case, the HN  100  and the FN  140  are tunneled for the MN 2   170 .  
         [0019]     Conventionally, only a single network was taken into account. However, with the development of various wireless Internet environments, a mobile network environment has an increasingly complex structure in which a network includes a subnet and the subnet includes a smaller subnet, etc.  
         [0020]     The conventional IPv6 technology does not support multiple and nested subnets, and thus has a problem in which a packet transfer may be interrupted. To address this problem, the Internet Engineering Task Force (IETF), the standards-setting body of the Internet, has organized a Network Mobility (NEMO) working group (WG) to develop the mobile technology standardized by the conventional mobile IP WG.  
         [0021]      FIG. 2  illustrates a network architecture using a conventional NEMO basic support protocol. Referring to  FIG. 2 , the NEMO basic support protocol supports transparent NEMO for all MNs located within a mobile network (MONET) using bi-directional tunnels  260  and  270  between MRs and HAs.  
         [0022]     An MR is responsible for managing NEMO. When moving from an HN  200  or  215  to an FN  230 , the MR registers its own location information and a mobile network prefix (MNP) used for the MONET in an HA  205  or  220  located in the HN  200  or  215 . In the location registration, prefix scope binding update (PSBU) is performed in extended MIPv6.  
         [0023]     For convenience of explanation, an HA in which a predetermined MR is initially registered is denoted by “MR_HA”. Accordingly, an HA of MR 1   210  of  FIG. 2  is MR 1 _HA  205 , and an HA of MR 2   225  is MR 2 _HA  220 . When a new network, i.e., an FN, is visited by a predetermined MR, the MR is assigned a CoA. The assigned CoA is denoted by “MR_CoA”. As described above, the MR 1 _HA  205  and the MR 2 _HA  220  store location information of the MR 1   210  and the MR 2   225 . Whenever the MR is on the move, binding update (BU) is performed and then location information of the MR is stored.  
         [0024]     After the MNP is registered, the bi-directional tunnel  260  is established between the MR 1   240  and the MR 1 _HA  205 . A correspondent node (CN)  280  serving as an arbitrary Internet node and MNs (i.e., MN 1  and MN 2 ) can transmit and receive data under transparent mobility support.  
         [0025]     In  FIG. 2 , when the MR 1   210  moves to the FN  230  (as indicated by reference numeral  250 ), the FN  230  assigns a CoA to MR 1   240  moved thereto.  
         [0026]     The CN  280  stores a home IP address of MR 1   210 , and transmits a packet to an address of the MN 2  serving as a destination address. Because the destination address of the transmitted packet is a home IP address of the MN 2 , the packet is transferred to the MR 1 _HA  205  through an Internet network.  
         [0027]     The MR 1 _HA  205  intercepts a packet associated with an MNP of MN 2 , and acquires a CoA of a point connected to the current MONET from information registered in a binding cache (BC). Thereafter, MR 1 _HA  205  refers to an acquired CoA of MR 1 , and tunnels the intercepted packet through the bi-directional tunnel  260 . The tunneled packet is encapsulated such that it has a source address of MR 1 _HA, and a destination address corresponding to a CoA of MR 1  (i.e., MR 1 _CoA). The packet is transferred to the MR 1   240  through a router  235  of the FN  230  according to a tunneled path. The MR 1   240 , receiving the tunneled packet, serves as an endpoint of the tunnel, and transfers the packet to the MN 2 , which is as a destination within the network, after decapsulating the packet.  
         [0028]     Now, a packet transfer process from the MN 1  to the CN  280  will be described with reference to  FIG. 2 .  
         [0029]     The MR 1   240  encapsulates the packet transferred from an ingress interface, and transfers the encapsulated packet to the tunnel  260  established between MR 1   240  and the HA  205  (i.e., MR 1 _HA). A source address of the encapsulated packet is a CoA of MR 1   240  (i.e., MR 1 _CoA), and a destination address of the encapsulated packet is an address of an HA registered in a binding update list (BUL). Here, the BUL is used to manage the BU performed by MR 1   240 . When a tunneled packet  265  arrives at the MR 1 _HA  205 , the MR 1 _HA  205  decapsulates the packet and routes the decapsulated packet to the CN  280  serving as the final destination.  
         [0030]     When the MONET is present in the original HN, a packet is transferred by a conventional IPv6 routing technique. The HA maintains and manages the BC to determine if the MONET is present in the HN. When a BU with a lifetime value of 0 is received from an MR, an entry registered in the BC is invalid. That is, when the MR determines that it is located in the HN, the MR transmits, to the HA, a BU message in which a lifetime value is set to zero, and notifies the HA of its own presence in the HN.  
         [0031]     In  FIG. 2 , the MR 2   225  is similar to the MR 1   210 . That is, the MR 2   225  can move from the HN  215  of MR 2   225  to a new network (i.e., the FN  230 ). In this case, MNs (i.e., MN 3  and MN 4 ) associated with MR 2   225  move together. When the FN  230  assigns a new CoA to the MR 2   245  according to the move and transmits, to MR 2 _HA, a BU message corresponding to CoA assignment information, the tunnel  270  is established between the MR 2   245  and the MR 2 _HA  220 .  
         [0032]     As described above, a packet from the CN  280  to the MN 3  or the MN 4  is intercepted by the MR 2 _HA  220 , and the intercepted packet is transmitted to the MR 2   245  through a path formed by the tunnel  270 . When the packet received by the MR 2   245  is destined for an MN (i.e., MN 3  or MN 4 ) managed by MR 2   245 , it is transmitted to a corresponding MN.  
         [0033]     In the NEMO service, multi-homing in which one MONET has a plurality of interfaces is enabled. That is, the one MONET can have at least one MR, and an MR can have at least one interface. Accordingly, when an obstacle occurs in an arbitrary MR or a service for access to the MR, an access connection must be able to be dynamically changed. Accordingly, the MR needs to determine if a neighboring MR with an alternative path in the current network is present. To discover an alternative MR, the MR collects information of neighboring MRs by transmitting and receiving a router advertisement (RA) message of the existing IPv6.  
         [0034]     The format of the conventional RA message is shown in Table 1 below.  
               TABLE 1                                                                                
 
         [0035]     As seen from Table 1, the IPv6 header includes a 40-byte common header field and a destination address field. For security, a rear part of the packet is encrypted using a security parameter index of the IPsec Encapsulating Security Payload (ESP) header shared between the MR and the HA. A “MOBILITY HEADER” field is provided in relation to the MIPv6. A BU message or binding acknowledgement message associated with a type of the “MOBILITY HEADER” field is included in a “MOBILITY HEADER CONTENT” field. A necessary option is additionally included in a “MOBILITY OPTION” field.  
         [0036]     A conventional process for identifying neighboring routers through an RA message exchange and recovering a tunnel when radio link failure occurs will be described with reference to  FIGS. 3 and 4  below.  
         [0037]      FIG. 3  illustrates a network architecture for identifying neighboring routers by exchanging an RA message between conventional MRs. Referring to  FIG. 3 , MR 1   306  and MR 2   314  include their router information in RA messages, and transmit the RA messages to neighboring routers. The RA message can be transmitted in response to a router solicitation (RS) message. Alternatively, the MRs  306  and  314  may periodically transmit the RA messages.  
         [0038]     Upon receiving the RA messages, the MRs  306  and  314  acquire home addresses (HoAs), CoAs, and MNPs associated with the neighboring MRs. That is, MR 1   306  and MR 2   314  transfer CoAs assigned from access routers (ARs)  304  and  312  newly accessing HA 1   302  and HA 2   310  and the MNPs assigned to internal networks managed by the MRs  306  and  314  to HA 1   302  and HA 2   310  through BU messages, such that data can be transferred to the ARs  304  and  312  currently performing access. The BU messages are periodically transferred from the MRs  306  and  314  to the HAs  302  and  310 , such that information of current connection states of the MRs  306  and  314  is reported. In this case, the MRs  306  and  314  transmit the RA messages to report the presence of the MRs  306  and  314  to the neighboring routers and MNs  308 ,  316 , and  318  of subnets managed thereby. When receiving an RA message from a neighboring MR, an arbitrary MR acquires information of the neighboring MR.  
         [0039]      FIG. 4  illustrates a network architecture for recovering a tunnel by an MR when radio link failure occurs. Referring to  FIG. 4 , when a link currently being used between HA 1   402  and MR 1   404  is damaged due to signal reduction of a radio channel or failure of the link itself, the MR 1   404  refers to the known information and generates a new tunnel directed to a neighboring MR (e.g., MR 2   412 ). The MR 1   404  is assigned a new CoA, and transmits a BU message to HA 1   402  through the MR 2   412 . In this case, a tunnel must be present or generated between HA 1   402  and HA 2   416  serving as a home agent of MR 2   412 . MR 1   404  maintains communication with the HA 1   402  by using the newly generated tunnel and the existing tunnel.  
         [0040]     An MR-based tunnel recovery process after a radio link failure has been described with reference to  FIG. 4 . However, there is also a possibility that a tunnel cannot be recovered due to failure of the MR itself. In a process for selecting a neighboring MR as an alternative router in an MR having suffered radio link failure, reliable tunnel recovery may be difficult due to the presence of a fake MR.  
         [0041]     Accordingly, the prior art has the following problems. 
        (1) Link loss due to the occurrence of radio link failure.     (2) Tunnel recovery disabled due to failure of an MR itself.        
 
         [0044]     The first problem, i.e., the link loss due to the occurrence of radio link failure, may be caused by an increased error rate of a radio channel, an increased interference signal, etc. To address this problem, the MR whose communication function is disabled because of the radio link failure selects one of the neighboring MRs, and generates a new tunnel to maintain the current connection through the selected MR.  
         [0045]     In the second problem, a router node may be disabled because of computational resource loss, buffer resource loss, or network resource loss caused by a denial of service (DoS) attack launched by a malicious user. When the router node is shut down because of a physical bug or software bug, service can be disabled. When the router node malfunctions, tunnel recovery based on the router node cannot be performed.  
         [0046]     More specifically, when the router node is disabled by an attack launched by a malicious user, data to be transferred to the router node may be wrongly transferred to the malicious user. Accordingly, a need exists for a method capable of reliably recovering a tunnel for an MR while avoiding such an attack.  
       SUMMARY OF THE INVENTION  
       [0047]     It is, therefore, an aspect of the present invention to provide a method and system that can quickly recover a tunnel when radio link failure occurs by registering in advance neighboring mobile routers (MRs) in a home agent (HA) provided in a mobile network.  
         [0048]     It is another aspect of the present invention to provide a method and system that can reliably recover a home agent (HA)-based tunnel according to neighboring mobile router (MR) information registered in advance when operation of an MR is disabled in a mobile network.  
         [0049]     The above and other aspects of the present invention can be achieved by a method for recovering a routing path between a first router and at least one mobile node in a mobile network including the first router for managing a first subnet having at least one second router and the at least one second router managing a second subnet including the at least one mobile node. The method comprises receiving, from the at least one second router, information of neighboring routers included in the first subnet; storing the received neighboring router information in the first router; recognizing a routing path failure when a periodic report message is not received from the at least one second router within a preset time; selecting an alternative router among the neighboring routers, when the routing path failure is recognized; requesting a routing path recovery to the alternative router; and routing data to the at least one mobile node through the alternative router, when the alternative router positively responds to the routing path recovery request.  
         [0050]     The above and other aspects of the present invention can be achieved by a method for registering, in a home agent, a location of at least one neighboring mobile router included in a different network in a mobile network including a first network and a second network, which is different from the first network, each of the first and second networks including a home agent, each of the home agents storing location information of a plurality of mobile routers of the network to which the home agent belongs. The method comprises receiving, from the at least one neighboring mobile router located in the different network, a router advertisement message in a mobile router located in the network in which the home agent is present; acquiring address information of the at least one neighboring mobile router included in the router advertisement message in the mobile router; transmitting the acquired address information from the mobile router to the home agent thereof; and registering the location of the at least one neighboring mobile router by storing the address information in the home agent.  
         [0051]     The above and other aspects of the present invention can be achieved by a system for recovering a routing path between a first router and at least one mobile node in a mobile network having a nested structure in which the first router manages a first subnet including at least one second router and the at least one second router manages a second subnet including the at least one mobile node. The system comprises a plurality of neighboring routers included in the first subnet; and a home agent for receiving, from the at least one second router, information of the plurality of neighboring routers included in the first subnet, storing the received neighboring router information, recognizing a routing path failure when a periodic report message is not received from the at least one second router within a preset time, selecting an alternative router from among the plurality of neighboring routers when the routing path failure is recognized, sending a routing path recovery request to the alternative router, and routing data to the at least one mobile node through the alternative router, when the alternative router positively responds to the routing path recovery request, wherein the neighboring routers each transmit a tunnel recovery response to the home agent in consideration of a load of processing data traffic, when a tunnel recovery request is received from the home agent.  
         [0052]     The above and other aspects of the present invention can be achieved by a system for registering, in a home agent, a location of at least one neighboring mobile router included in a different network, in a mobile network including a first network and a second network, which is different from the first network, each of the first and second networks including a home agent, each of the home agents storing location information of a plurality of mobile routers of the network to which the home agent belongs. The system comprises a home agent; and a mobile router for receiving a router advertisement message from the at least one neighboring mobile router located in the different network, acquiring address information of the at least one neighboring mobile router included in the router advertisement message, and transmitting the acquired address information to the home agent, wherein the home agent registers the location of the at least one neighboring mobile router by receiving and storing the acquired address information.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0053]     The above and other aspects 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:  
         [0054]      FIG. 1  illustrates a network architecture based on a basic configuration of a conventional Mobile Internet Protocol version 6 (MIPv6);  
         [0055]      FIG. 2  illustrates a network architecture using a conventional Network Mobility (NEMO) basic support protocol;  
         [0056]      FIG. 3  illustrates a network architecture for discovering neighboring routers by exchanging an RA message between conventional mobile routers (MRs);  
         [0057]      FIG. 4  illustrates the network architecture for recovering a tunnel by an MR when radio link failure occurs;  
         [0058]      FIG. 5  illustrates a network architecture for identifying, authenticating, and registering a router node on the basis of a home agent (HA) of a mobile network in accordance with an embodiment of the present invention;  
         [0059]      FIG. 6  is a ladder diagram illustrating a procedure for identifying, authenticating, and registering a router node using an HA of a mobile network in accordance with an embodiment of the present invention;  
         [0060]      FIG. 7  illustrates the network architecture for performing a tunnel recovery procedure using an HA of the mobile network in accordance with an embodiment of the present invention; and  
         [0061]      FIG. 8  is a ladder diagram illustrating the tunnel recovery procedure of an HA of the mobile network in accordance with an embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0062]     Preferred embodiments of the present invention will be described in detail herein below with reference to the accompanying drawings. In the following description, a detailed description of known functions and configurations incorporated herein will be omitted for conciseness.  
         [0063]     The present invention relates to a method for recovering a damaged tunnel in the proposed Mobile Internet Protocol version 6 (MIPv6) for supporting host mobility in Internet Protocol version 6 (IPv6) serving as the next generation Internet protocol. Moreover, the present invention proposes a method for quickly and reliably recovering a router path or tunnel damaged due to the occurrence of radio link failure or a disabled router node.  
         [0064]     A large amount of research is being done to develop an all-IP based network for assigning an IP address to all nodes of the mobile network. Accordingly, the IPv6 for extending the length of an IP address of IPv4 from 32 bits to 128 bits is being studied. The MIPv6 enables support for mobility in the IPv6. Basic service requirements necessary for Network Mobility (NEMO) based on the MIPv6 are defined in the NEMO basic support protocol proposed by the NEMO Working Group (WG).  
         [0065]     The NEMO basic support protocol defines a function for integrating and managing mobility of mobile nodes (MNs) belonging to a subnet managed by a mobile router (MR) and a new binding update (BU) protocol function for location registration, etc. Further, the NEMO basic support protocol proposes a multihoming scheme having a plurality of MRs or interfaces, or a plurality of MRs and home agents (HAs) for connecting one mobile network (MONET) to another network. The multihoming scheme has been proposed to generate multiple connections when a terminal does not receive service after a radio link of the MONET is released or a router malfunctions. The multihoming scheme can be used to dynamically distribute a load by replacing a specific router path with an alternative router path. For example, when the overload of data traffic processing occurs, an MR of the present invention may not arbitrarily transmit a periodic BU message or may release a link without sending a router advertisement message to neighboring MRs. In this case, a neighboring MR can serve as an alternative MR in place of the MR whose link is released.  
         [0066]     Because a router node or router can perform the same function as the MR, the MR is referred to as the router node or router. When a tunnel is recovered, an arbitrary router node can be selected among a plurality of neighboring router nodes located on a router path. Herein, the selected router node is referred to as the alternative router.  
         [0067]     When one of the MRs is disabled as indicated by the problems occurring in the prior art, communication functions of low-level mobile nodes (MNs) associated with the disabled MR are also disabled. Further, a delay time occurs due to tunnel recovery when a radio link or router node fails in the MONET, such that a continuous communication service cannot be provided between nodes.  
         [0068]     Accordingly, the present invention performs an HA-based tunnel recovery, which is different from the conventional MR-based tunnel recovery. The HA authenticates and registers in advance neighboring router nodes, i.e., neighboring MRs, and selects the optimum alternative MR among the registered MRs when a radio link or router node has failed, such that a tunnel can be quickly recovered. The HA defines a new message format and hence can perform tunnel recovery based on enhanced security. In the present invention, the HA performs the following functions to overcome the problems occurring in the conventional tunnel recovery. 
        A. Neighboring router detection, authentication, and registration.     B. Neighboring router list deletion and tunnel connection release.     C. Tunnel recovery through an alternative router.        
 
         [0072]      FIG. 5  illustrates a network architecture for identifying, authenticating, and registering a router node using an HA of the MONET in accordance with an embodiment of the present invention. Referring to  FIG. 5 , HA 1   502  and HA 2   504  manage MR 1   510  and MR 2   512 , respectively. MR 1   510  and MR 2   512  manage a plurality of MNs in respective subnets.  
         [0073]     In the present invention, the HA 1   502  and the HA 2   504  perform the following procedures until a neighboring router is registered. 
        A1. Neighboring router detection     A2. Neighboring router authentication     A3. Neighboring router registration        
 
         [0077]     The neighboring router detection will be described herein below. The HA 1   502  and the HA 2   504  assign care of addresses (CoAs) to MR 1   510  and MR 2   512  through access routers (ARs). The MR 1   510  and the MR 2   512  to which the CoAs are assigned transmit mobile network prefixes (MNPs), assigned to subnets, to their HAs through BU messages. A BU message is periodically transmitted to an HA, such that the HA can identify nodes registered therein or a tunnel state from the BU message. Here, the MRs  510  and  512  transmit and receive router advertisement (RA) or router solicitation (RS) messages to report the presence of the MRs  510  and  512  to the neighboring MRs and MNs  514 ,  515 ,  518 , and  520  of subnets.  
         [0078]     Upon receiving the RA or RS message, the MR records its own address information, transmits the address information to other neighboring MRs, and records, in the neighboring MR list, a neighboring MR transmitting the RA or RS message. The MR discovers the neighboring MRs by transmitting the RA or RS message, and information of the discovered neighboring MRs is transmitted to the HA through the BU message, such that the neighboring MR detection procedure is completed.  
         [0079]     Subsequently, the HA performs an authentication procedure according to the information of the detected neighboring MRs. The authentication procedure uses a return routability procedure as one of the basic procedures defined in the conventional MIPv6. That is, the return routability procedure is an authentication procedure for identifying a home address (HoA) and a CoA. Messages, used to identify the HoA and CoA, include a home test initiation message, a home test message, a CoA test initiation message, and a CoA test message. The messages are transmitted between MRs and their neighboring MRs and between the MRs and HAs. That is, the MR transmits the CoA test message and the CoA test initiation message to, and receives the CoA test message and the CoA test initiation message from, a neighboring MR, thereby identifying the neighboring MR. The MR transmits the home test message and the home test initiation message to, and receives the home test message and the home test initiation message from, a corresponding HA of the neighboring MR, thereby determining if the neighboring MR is a fake MR through a double authentication procedure.  
         [0080]     Upon completing the return routability procedure, the MR stores neighboring MR information, i.e., an HoA, a CoA, and an MNP, in a neighboring MR list, and transmits a BU message to an HA associated therewith.  
         [0081]     In accordance with the present invention, the BU message includes a neighboring MR registration option in a mobility option field. Accordingly, the HA identifies an HoA, a CoA, and an MNP of a neighboring MR from the received BU message.  
         [0082]     Table 2 shows a format of the neighboring MR registration option message included in the mobility option field of the BU message.  
                                         TABLE 2                                   Type   Length   Reserved   Prefix Length                                    Home Address (HoA)       Care of Address (CoA)       Mobile Network Prefix (MNP)                  
 
         [0083]     As shown in Table 2, the format of the neighboring MR registration option message includes a “Type” field for indicating the neighboring MR registration option message, a “Length” field for indicating the total length of the option message, a “Prefix Length” field for indicating the length of an MNP, an “HoA” field for indicating an HoA of the MR, a “CoA” field for indicating a CoA of the MR, and an “MNP” field for indicating the MNP. The neighboring MR registration option message may include a plurality of option messages corresponding to the number of neighboring MRs.  
         [0084]     Upon receiving the neighboring MR registration option message from the MR, the HA registers the HoA, the CoA, and the MNP as neighboring MR information.  
         [0085]      FIG. 6  is a ladder diagram illustrating a procedure for detection, authenticating, and registering a router node using an HA of a mobile network in accordance with an embodiment of the present invention. Referring to  FIG. 6 , the MR 2   604  transmits an RS message to MR 1   602  serving as a neighboring router node to determine the presence of MR 1   602  in Step  610 . In response to the RS message, the MR 1   602  transmits an RA message to MR 2   604  in Step  612 . The RA message can be transmitted as a response to the RS message, and may be an unsolicited message capable of being transmitted without receiving the RS message.  
         [0086]     After steps  610  and  612  are performed, the MR 2   604  determines the presence of the MR 1   602  serving as the neighboring router node. As described above, the MR 2   604  transmits the RS message to the MR 1   602  serving as the neighboring router node. Alternatively, MR 2   604  may be the neighboring router node of MR 1   602 .  
         [0087]     After performing a neighboring MR detection procedure, the MR 2   604  transmits a home test initiation message to the HA 1   606 , such that an authentication procedure of MR 1   602  can be performed in Step  614 . The MR 2   604  transmits a CoA test initiation message to MR 1  in Step  616 . The MR 2   604  receives, from the MR 1   602 , a CoA test message as a response to the CoA test initiation message in Step  618 , and receives, from the HA 1   606 , a home test message as a response to the home test initiation message in Step  620 . After the authentication procedure of MR 1   602  is completed in step  620 , the MR 2   604  transmits a BU message to the HA 2   608  in accordance with the present invention in Step  622 .  
         [0088]     The HA 2   608  identifies information of an HoA, a CoA, and an MNP recorded in a neighboring MR registration option field included in a mobility option field of the BU message transmitted from the MR 2   604 , registers the information of the MR 1   602 , and transmits a response to MR 2   604  in Step  624 .  
         [0089]     A neighboring MR registered in the HA can be deleted from the neighboring MR list in the following case. That is, the neighboring MR may be out of the range of a network managed by the HA or its radio link may fail. In this case, the neighboring MR transmits, to its neighboring MRs, an RA message whose router lifetime field has been set to 0, such that the fact that it does not periodically transmit an RA message to the MRs, or no longer serves as a neighboring MR can be reported.  
         [0090]     When a corresponding MR does not periodically transmit an RA message or transmits an RA message whose router lifetime field has been set to 0, it is deleted from the neighboring MR list.  
         [0091]     Subsequently, when transmitting a BU message newly defined in accordance with the present invention, an arbitrary MR does not include information of a failed neighboring MR in the BU message. Immediately before the lifetime of a BU message expires, the HA sends a request message to request that an MR transmit a new BU message. When the MR does not transmit a new BU message in response to the BU message request, the HA determines that the MR or its link has failed.  
         [0092]     When an MR or its radio link has failed, the HA selects the optimum alternative MR from among the registered neighboring MRs and recovers a tunnel, such that data can be smoothly transmitted and received. A process in which the HA recovers a tunnel by using the alternative MR will be described herein below.  
         [0093]     First, the HA recognizes the occurrence of tunnel failure when it does not receive a periodic BU message or a heartbeat message for checking a tunnel connection state, or does not detect data transferred through a bi-directional tunnel for a predetermined time.  
         [0094]     Upon recognizing the occurrence of tunnel failure, the HA selects an alternative MR from the neighboring MR list in place of an MR associated with the failure. In this case, a message to be sent from the HA to the alternative MR uses a tunnel recovery request message inserted into a destination option header of a BU message newly defined in accordance with the present invention. The format of the tunnel recovery request message is shown in Table 3 below.  
                                         TABLE 3                                   Next Hdr   Length   Reserved   Prefix Length                                    Home Address (HoA)       Care of Address (CoA)       Mobile Network Prefix (MNP)                  
 
         [0095]     As shown in Table 3, the format of the tunnel recovery request message includes a “Next Hdr” field for indicating a type of the next header, a “Length” field for indicating the total length of the message, a “Prefix Length” field for indicating the length of an MNP, an “HoA” field for indicating an HoA, a “CoA” field for indicating a CoA, and an “MNP” field for indicating the MNP.  
         [0096]     The HA transmits a BU message including the tunnel recovery request message to the alternative MR. Upon receiving the BU message, the alternative MR transmits a tunnel recovery response message to the HA. The format of the tunnel recovery response message is shown in Table 4 below.  
                                 TABLE 4                       Next Hdr   Payload Length   G   Reserved                                MR Care-of-Address (CoA)                  
 
         [0097]     As shown in Table 4, the tunnel recovery response message is included in a destination option header as in the tunnel recovery request message. A “G” field is indicated by a binary value. The HA identifies the binary value indicated in the “G” field to determine if the alternative MR has granted or denied the tunnel recovery request. For example, when the binary value of the “G” field is 1, the alternative MR has granted the tunnel recovery. However, when the binary value of the “G” field is 0, the alternative MR has denied the tunnel recovery.  
         [0098]     When the HA has received the tunnel recovery response message indicating that the alternative MR has granted the tunnel recovery, it tunnels data through the alternative MR. However, when the alternative MR has not granted the tunnel recovery, the HA identifies another alternative MR to send the tunnel recovery request to the another alternative MR.  
         [0099]      FIG. 7  illustrates a network architecture for performing a tunnel recovery procedure using an HA of the mobile network in accordance with an embodiment of the present invention. Referring to  FIG. 7 , when the HA 1   702  does not receive a periodic BU message, it recognizes the occurrence of failure of a tunnel or the MR 1   706 . Upon recognizing the failure occurrence, the HA 1   702  sends a tunnel recovery request message to MR 2   708  serving as an alternative MR, and then attempts to recover the tunnel.  
         [0100]     Upon receiving the tunnel recovery request message, the MR 2   708  sends, to the HA 1   702 , a response message indicating that the tunnel recovery request has been granted. Then, the HA 1   702  can recover the tunnel according to nested tunneling of HA 1 -&gt;HA 2 -&gt;MR 2  using the NEMO basic support protocol.  
         [0101]     When a tunnel from the HA 1   702  to the MR 2   708  is recovered, the MR 2   708  receives data to be transferred to the MR 1   706 , and decapsulates the received data, such that a packet is relayed to MN  712  through a MR  710 . Consequently, the HA 1   702  can quickly and securely recover a tunnel when tunnel or MR failure occurs.  
         [0102]      FIG. 8  is a ladder diagram illustrating a tunnel recovery procedure using an HA of the mobile network in accordance with an embodiment of the present invention. Referring to  FIG. 8 , HA 1   802  recognizes a failure of a bi-directional tunnel connected to a corresponding MR when it does not receive a periodic BU message or a heartbeat message for checking a tunnel connection state in Step  812 . Accordingly, the HA 1   802  sends a tunnel recovery request message to a destination of the MR 2   806  selected as an alternative MR for tunnel recovery. The tunnel recovery request message is first sent to the HA 2   804  in Step  814 . The HA 2   804  relays the tunnel recovery request message to the MR 2   806  in Step  816 .  
         [0103]     When receiving the tunnel recovery request message, the MR 2   806  determines a response to the tunnel recovery request by taking into account the presence of idle resources.  
         [0104]     When the MR 2  grants a tunnel recovery request, the MR 2   806  sends, to the HA 1   802 , a tunnel recovery response message indicating that tunnel recovery has been granted. The tunnel recovery response message is sent to HA 2   804  in Step  818 . The HA 2   804  relays the message to the HA 1   802  in Step  820 . According to the granted tunnel recovery, the HA 1   802  tunnels data to the MR 2   806 , such that a previous session between the HA 1   802  and the MR 1   808  can be maintained. When a tunnel from the HA 1   802  to the MR 2   806  is recovered in Step  822 , the MR 2   806  decapsulates encapsulated data and generates a tunnel between the MR 2   806  and the MR 1   808  in Step  824 , such that data is routed to an MN  810 .  
         [0105]     As is apparent from the above description, the present invention can register, in advance, neighboring router nodes through authentication and registration procedures, and can delete a corresponding router node from a registration list when the router node has moved to a different network or has failed. Because a neighboring MR list capable of being registered or deleted is managed, the present invention can quickly and securely recover a tunnel when a radio link or equipment has failed.  
         [0106]     Although 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 spirit and the scope of the present invention. Therefore, the present invention is not limited to the above-described embodiments, but is defined by the following claims, along with their full scope of equivalents.