Abstract:
A method and apparatus for managing a mobile Internet protocol (IP) using network address translation (NAT) in a mobile network are provided. The method includes periodically receiving an agent information message from an agent on a network, and checking a connection to a home network or a foreign network. If a connection to the home network is determined based on the agent information message, a global IP address received from the agent of the home network and local IP addresses set a plurality of hosts included in the mobile network are registered, and communication with the home network is performed through conversion between the registered global IP address and each of the registered local IP addresses. If a connection to the foreign network is determined based on the agent information message, a temporary IP address is received from the agent of the foreign network. The temporary IP address is registered with the local IP addresses set at the hosts, and communication with the foreign network is performed through conversions between the registered temporary IP address and each of the registered local IP addresses.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the priority of Korean Patent Application No. 02-20240, filed Apr. 13, 2002, which is incorporated herein in its entirety by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a mobile Internet protocol (IP) service, and more particularly, to a method and apparatus for managing a mobile IP using network address translation (NAT) in a mobile network. 
   2. Description of the Related Art 
   Generally, a mobile IP service allows a terminal, after being moved, to have the same IP address that it had before moving. 
   As shown in  FIG. 1A , a mobile host is allocated a unique IP address by a home agent in a home network. As shown in  FIG. 1B , when the mobile host moves to a foreign network, it can access the Internet without changing its unique IP address. Here, the mobile host cannot access the Internet using an IP address that is allocated in one network in another network (or foreign network). In this case, a foreign agent in the foreign network allocates the mobile host a temporary address referred to as a care-of address (COA), so that the mobile host can communicate with the foreign network. Accordingly, a conventional mobile IP service provides an Internet service for only when a single host (for example, a cellular phone or a notebook) moves. 
   In the meantime, passengers in an airplane, ship, or train may want to use the Internet while seated. Here, the seats form a network, which is referred to as a mobile network. In order to accomplish a mobile IP for each host connected to the mobile network, a home agent, a foreign agent, and a host are required. However, conventionally, since all hosts at the individual seats connected to the mobile network are allocated an IP address, the network is inefficient in using and managing IP addresses, and also some IP addresses are wasted. 
   SUMMARY OF THE INVENTION 
   To solve the above-described problems, it is a first object of the present invention to provide a method for managing a mobile Internet protocol (IP) to accomplish a mobile IP for a mobile network having a plurality of hosts and save IP addresses using network address translation (NAT). 
   It is a second object of the present invention to provide an apparatus for managing a mobile IP to accomplish a mobile IP for a mobile network having a plurality of hosts. 
   To achieve the first object and other objects of the present invention, a method for managing a mobile IP in a mobile network having a plurality of hosts includes the steps of: (a) periodically receiving an agent information message from an agent on a network, and checking a connection to a home network or a foreign network; (b) if a connection to the home network is determined based on the agent information message received in step (a), registering a global IP address received from the agent of the home network and local IP addresses set at the hosts, and communicating with the home network through conversion between the registered global IP address and each of the registered local IP addresses; and (c) if a connection to the foreign network is determined based on the agent information message received in step (a), receiving a temporary IP address from the agent of the foreign network, registering it with the local IP addresses set at the hosts, and communicating with the foreign network through conversion between the registered temporary IP address and each of the registered local IP addresses. 
   To achieve the second object and other objects of the present invention, an apparatus for managing a mobile IP in a mobile network having a plurality of hosts includes a table unit for storing IP addresses; a NAT unit for performing conversion between a global IP address and each of local IP addresses set at the hosts with reference to the IP addresses stored in the table unit; and a controller for periodically receiving an agent information message from one of agents in a network, registering the global IP address received from the agent and each of the local IP addresses in the table unit, and connecting each of the hosts to a remote host based on the result of the conversion performed by the NAT unit. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objects and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which: 
       FIGS. 1A and 1B  are diagrams showing a conventional network in which a mobile IP is managed; 
       FIGS. 2A and 2B  are diagrams showing a network in which a mobile IP is managed according to the present invention; 
       FIG. 3  is a detailed diagram of the mobile network address translation (NAT) host (MNH) shown in  FIGS. 2A and 2B , according to an embodiment of the present invention; 
       FIG. 4  is a flowchart of a method for managing a mobile IP, which is performed by an MNH, according to an embodiment of the present invention; 
       FIG. 5  is a detailed flowchart of the step of registering addresses for home network connection, which is shown in  FIG. 4 ; 
       FIG. 6  is a detailed flowchart of the step of performing NAT and communication in the home network shown in  FIG. 4 ; 
       FIG. 7  is a detailed flowchart of the step of registering addresses for foreign network connection, which is shown in  FIG. 4 ; and 
       FIG. 8  is a detailed flowchart of the step of performing NAT and communication in the foreign network shown in  FIG. 4 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. 
     FIGS. 2A and 2B  are diagrams showing a network in which a mobile IP is managed according to the present invention.  FIG. 2A  shows a network in which a mobile network is connected to a home network, while  FIG. 2B  shows the network in which the mobile network is connected to a foreign network. 
   Referring to  FIGS. 2A and 2B , a plurality of hosts are connected to a representative host, i.e., a mobile network address translator (NAT) host (MNH), thereby forming a mobile network. The MNH may be a router or personal computer (PC) having an NAT function or an NAT device. The MNH manages a plurality of hosts. Whenever the mobile network moves, the MNH is allocated a temporary address, i.e., a care-of address (COA), by a foreign agent (FA) in a foreign network and registers the COA in a home agent (HA) in a home network through the FA, as shown in  FIG. 2B . If the FA is rebooted or if the life time of a registration expires almost immediately, the MNH needs to request the FA to re-register the COA. Here, the MNH needs to keep the link-layer address information of the FA and its COA in order to request to re-register the COA. 
   The MNA also performs an NAT function, i.e., conversion between a local IP address and a global IP address. The NAT is an address conversion technique that is used to convert a local IP address into a global IP address on the layer  3 , referring to the network layer of the Open Systems Interconnection (OSI). The MNH uses the NAT function for the following two purposes. First, the MNH uses the NAT function to convert a local IP address into a global IP address or a global IP address into a local IP address so that a plurality of users can use a single global IP address. Second, the MNH uses the NAT function to install a firewall between the open Internet and a local network so that a user&#39;s communication network can be protected from external attacks. 
   A network with which the mobile network can communicate includes an FA, an HA, and a remote host. When a mobile node disconnects from the home network, the HA transmits packets to the mobile node through an IP channel and maintains and manages the position information of the mobile node. The FA receives the packets from the HA and transmits them to the mobile node. 
     FIG. 3  is a detailed diagram of the MNH shown in  FIGS. 2A and 2B , according to an embodiment of the present invention. Referring to  FIG. 3 , a NAT table unit  320  stores a global IP address for NAT, local IP addresses of a plurality of hosts connected to the MNH, and the address of a remote host related to the plurality of hosts. A NAT unit  310  performs conversion between a global IP address and a local IP address, both received through a controller  330 . 
   The controller  330  periodically receives agent advertisement messages from the HA and the FA, checks the connections of the MNH with the home network and the foreign network based on the received agent advertisement messages, registers a global IP address received from the HA and the FA and local IP addresses set at the hosts in the NAT table unit  320 , and controls the connection between the plurality of hosts and the remote host using an IP address obtained from the conversion performed by the NAT unit  310 . 
     FIG. 4  is a flowchart of a method for managing a mobile IP, which is performed by an MNH, according to an embodiment of the present invention. The MNH periodically receives agent advertisement messages from an HA and an FA in step  410 , and analyzes prefixes and life times contained in the messages in order to check its connections with a home network and a foreign network in step  420 . For example, when the MNH is in the home network, the MNH receives an agent advertisement message which is periodically broadcasted from the HA. The MNH compares a prefix or life time, which is contained in an agent advertisement message that has been received before, with a prefix or life time, which is contained in a new agent advertisement message that is received at a present time. Here, if the MNH receives an agent advertisement message transmitted from the FA, it can recognize that a prefix or life time contained in the message is changed. In other words, the MNH recognizes that its position has moved from the home network to the foreign network. 
   If the MNH determines that it is connected to the home network based on the agent advertisement messages, as shown in  FIG. 2A , the MNH registers a global IP address received from the HA of the home network and a local IP address of each host in step  430 , and enables the hosts to communicate with the remote host in the home network through conversion between the local IP addresses and the global IP address in step  440 . Here, the global IP address is referred to as a home address. 
   If the MNH determines that it is connected to the foreign network based on the agent advertisement messages, as shown in  FIG. 2B , the MNH registers a COA received from the FA and the local IP addresses of the respective hosts in a NAT table in step  450 , and enables the hosts to communicate with the remote host in the foreign network through conversion between the local IP addresses and the COA address in step  460 . 
   Thereafter, the MNH repeats the above steps until it recognizes the end of connection based on an agent advertisement message in step  470 . 
     FIGS. 5 through 8  will be described in detail with reference to the network shown in  FIGS. 2A and 2B . 
     FIG. 5  is a detailed flowchart of the step  430  of registering the addresses for home network connection, which is shown in  FIG. 4 . If the MNH is connected to the home network, the HA having the prefix 147.46.115.1 allocates the global IP address 147.46.115.100 to the MNH in step  510 . The global IP address 147.46.115.100 is referred to as a home address and does not change even when the mobile network moves. 
   Subsequently, the MNH initializes the NAT table using the global IP address 147.46.115.100 in step  520 . For example, the home address, i.e., the global IP address 147.46.115.100, the local IP addresses 10.0.0.1 through 10.0.0.10 of the respective hosts managed by the MNH, and the destination addresses of the respective hosts are registered in the NAT table. 
   The MNH operates such that only the global IP address 147.46.115.100 allocated thereto is open to the outside, but the local IP addresses 10.0.0.1 through 10.0.0.10 are used only within the mobile network. 
     FIG. 6  is a detailed flowchart of the step  440 , shown in  FIG. 4 , of performing NAT and communication in the home network. A host having the local IP address 10.0.0.1 within the mobile network transmits a data packet to the MNH to communicate with a remote host having the address 147.46.117.1 outside the mobile network in step  610 . Then, the MNH converts a source address into its home address before transmitting the data packet to a network including the remote host in step  620 . That is, the source address, i.e., the local IP address 10.0.0.1, is converted into the MNH&#39;s home address, i.e., the global IP address 147.46.115.100. 
   Next, the MNH registers the content of the address conversion in the NAT table and transmits the data packet to the HA in step  630 . Next, the HA having the address 147.46.115.1 analyzes the data packet received from the MNH and transmits it to the remote host having the address 147.46.117.1 in step  640 . Next, the remote host (147.46.117.1) sets a destination address to the home address of the MNH and transmits a packet to the HA (147.46.115.1) in step  650 . Next, the HA (147.46.115.1) analyzes the packet received from the remote host (147.46.117.1) and transmits it to the MNH in step  660 . Next, the MNH confirms that the source address of the packet is the address of the remote host (147.46.117.1) and transmits it to the destination host (10.0.0.1), which has been registered in the NAT table, within the mobile network in step  670 . 
     FIG. 7  is a detailed flowchart of the step  450  of registering the addresses for foreign network connection, which is shown in  FIG. 4 . If the MNH is connected to the foreign network, the FA having the prefix 147.46.116.1 temporarily allocates the global IP address 147.46.116.100 to the MNH for a predetermined period of time in step  710 . The temporary address is referred to as a COA and unlike the home address, changes whenever the mobile network moves. 
   Subsequently, the MNH initializes the NAT table using the COA 147.46.116.100 in step  720 . Here, the hosts managed by the MNH have the same local IP addresses 10.0.0.1 through 10.0.0.10 as those when the mobile network is connected to the home network. In other words, the home address, i.e., the global IP address 147.46.115.100, the COA 147.46.116.100, the local IP addresses 10.0.0.1 through 10.0.0.10 of the respective hosts managed by the MNH, and the destination addresses of the respective hosts are registered in the NAT table. 
   Next, the MNH requests the HA to register the allocated COA (147.46.116.100) in step  730 . Here, registration information contains only the home address and COA, but does not contain the IP addresses of the hosts within the mobile network. 
   The MNH manages such that only the COA (147.46.116.100) allocated thereto is open to the outside, but the local IP addresses 10.0.0.1 through 10.0.0.10 are used only within the mobile network. 
     FIG. 8  is a detailed flowchart of the step  460 , shown in  FIG. 4 , of performing NAT and communication in the foreign network. A host having the local IP address 10.0.0.1 within the mobile network transmits a data packet to the MNH to communicate with a remote host having an address 147.46.117.1 outside the mobile network in step  810 . Then, the MNH converts a source address, i.e., the local IP address 10.0.0.1, into its COA 147.46.116.100 corresponding to the global IP address before transmitting the data packet to a network including the remote host in step  820 . 
   Next, the MNH registers the content of the address conversion in the NAT table and transmits the data packet and its home address 147.46.115.100 to the FA having the address 147.46.116.1 in step  830 . Next, the FA transmits the packet to the HA in step  840 . Next, the HA having the address 147.46.115.1 analyzes the data packet received from the FA (147.46.116.1) and transmits it to the remote host (147.46.117.1) in step  850 . Next, the remote host (147.46.117.1) sets a destination address to the COA of the MNH and transmits a packet to the HA (147.46.115.1) in step  860 . Next, the HA (147.46.115.1) analyzes the packet received from the remote host (147.46.117.1) and transmits it to the FA (147.46.116.1) in step  870 . Next the FA analyzes the packet received from the HA (147.46.115.1) and transmits it to the MNH in step  880 . Next, the MNH confirms that the source address of the packet is the address of the remote host (147.46.117.1) and transmits it to the destination host (10.0.0.1), which has been registered in the NAT table, within the mobile network in step  890 . 
   The present invention is not restricted to the above-described embodiments, and it will be apparent that various changes can be made by those skilled in the art without departing from the spirit of the invention. For example, when a router or PC instead of a NAT device is used as the MNH, the NAT function can be embodied as either software or hardware. 
   The present invention can be realized as a code which is recorded on a computer readable recording medium and can be read by a computer. The computer readable recording medium may be any type on which data which can be read by a computer system can be recorded, for example, a ROM, a RAM, a CD-ROM, a magnetic tape, a hard disc, a floppy disc, a flash memory, or an optical data storage device. The present invention can also be realized as carrier waves (for example, transmitted through Internet). Alternatively, computer readable recording media are distributed among computer systems connected through a network so that the present invention can be realized as a code which is stored in the recording media and can be read and executed in the computers. 
   As described above, the present invention manages a mobile IP using NAT in a mobile network, thereby increasing efficiency in using and managing IP addresses, and preventing waste of IP addresses.