Abstract:
A method of transmitting data from a Virtual Private Network (“VPN”) server to a Mobile Node (“MN”) is provided. Upon sensing generation of data destined for the MN in the VPN server, a Customer Premise Equipment (“CPE”) router requests an Internet Service Provider (“ISP”) router connected to a VPN to search for an address of a Foreign Agent (“FA”) to which the MN belongs. The ISP router searches for the FA address through a Home Agent (“HA”) and routes the data to the FA identified by the searched FA address. The FA then locates the MN and forwards the data to the MN.

Description:
PRIORITY  
         [0001]    This application claims priority to an application entitled “Method of Transmitting Data from Server of Virtual Private Network to Mobile Node” filed in the Korean Industrial Property Office on Jul. 3, 2001 and assigned Serial No. 2001-39567, the contents of which are hereby incorporated by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates generally to a data transmission method in a VPN (Virtual Private Network), and in particular, to a data transmitting method to a mobile node over a VPRN (Virtual Private Routed Network).  
           [0004]    2. Description of the Related Art  
           [0005]    As is implied by its name, a mobile node (“MN”) is characterized by its mobility. With mobility guaranteed, a mobile user uses the MN for a voice call or data communication. In light of no limitations in a location, MNs allow multiple users to receive data services such as Internet access, while roaming. Methods and systems for providing mobile services more reliably are currently being developed. Assignment of permanent Internet Protocol (“IP”) addresses to MNs is essential in stably providing a data service with ensured mobility. Therefore, studies are made on assignment of mobile IP addresses to MNs.  
           [0006]    [0006]FIG. 1 illustrates the configuration of a mobile IP network for assigning mobile IP addresses to MNs. The configuration of the network and location registration will be described. Referring to FIG. 1, an MN  10  performs a location registration with a base station at system initialization, or when location registration is needed. Since the MN  10  is mobile station as stated above, it may send a location registration signal when it is away from its home network, for example, from the U.S. even though it has been registered with a service provider in Korea. This is possible if a particular service protocol is set between mobile service providers. The location registration will be described with reference to FIG. 1.  
           [0007]    The MN  10  wirelessly sends a Registration Request to a Foreign Agent (“FA”)  20  acting as a base station. The FA  20  then forwards the Registration Request with the address of the FA  20  included to a Home Agent (“HA”)  30  of the MN  10  over a predetermined network  25 . The HA  30  stores the address of the FA  20  from the data received from the FA  20 . That is, the HA  30  stores a temporary address of the MN (which is referred to as a care-of-address (“COA”)) This temporary address is typically the address of the FA  20 . Then the HA  30  sends a Registration Reply for the Registration Request to the FA  20 . By this procedure, the location of the MN  10  is registered. In one aspect, the MN  10  can receive data from a Correspondent Node (“CN”)  40  only after the location registration with the HA  30 . The CN  40  is a host in a general network, which sends/receives data to/from the MN  10 . A procedure for data transmission between the MN  10  and the CN  40  will be described with reference to FIG. 2.  
           [0008]    [0008]FIG. 2 is a schematic diagram illustrating data transmission over a network for assigning a mobile IP address to an MN. First, a description will be made below of data transmission between the CN  40  and the MN  10  after the MN&#39;s registration with the HA in the procedure explained above. Networks  25  between the FA  20  and the HA  30 , between the HA  30  and the CN  40 , and between the FA  20  and the CN  40  may be the same or different. In one aspect, the networks  25  are IP networks.  
           [0009]    The CN  40  is a computer that is to send data to the MN  10 . For data transmission, the CN  40  sends the data to the HA  30  over the IP network  25 . The HA  30 , which has the addresses of FAs  20  under its management, forwards the data to the IP address of an FA  20  that the MN  10  belongs to. Then the FA  20  forwards the data to the MN  10 . The data includes the address of the CN  40 . On the other hand, when the MN  10  is to send data to the CN  40 , it sends the data to the FA  20  and the FA  20  forwards the data to the CN  40  without passing through the HA  30  because the MN  10  has requested data transmission with the destination address included, for example, the address of the CN  40 . Accordingly, data is transmitted and received using different routes.  
           [0010]    As the Internet can be accessed at lower costs all over the world, communication networks including private networks are being developed to accommodate the Internet service. In this context, studies are vigorously made on VPNs with no limitations in location and assignment of permanent IP addresses to MNs that roam.  
           [0011]    There are two kinds of VPNs: one is a dedicated Wide Area Network (“WAN”) connecting sites by permanent links and the other is a dial network using dial-up connections over the PSTN (Public Switched Telephone Network). Connections between IP-based VPNs through routers and data transmission over the VPNs will be described below in connection with FIG. 3.  
           [0012]    In FIG. 3, an IP backbone is connected to routers. Internet Service Provider (“ISP”) routers  120 ,  130  and  140  are edge routers connected to Customer Premise Equipment (“CPE”) routers  110 ,  150 ,  160  and  170 . A CPE router connects a mobile subscriber at a certain point to a VPN, and an ISP router is an equipment operated by an ISP to route data received from a CPE router to a desired VPN. The ISP routers  120 ,  130  and  140  in an IP network  100  carry out data transmission/reception by IP tunneling. A stub link is established between an ISP router and a CPE router. When necessary, a backup link is established between a CPE router and an ISP router, and a backdoor link is established between CPE routers at different locations. Accordingly, the configured network shown in FIG. 3 generally provides an Internet service and various communications.  
           [0013]    The existing VPNs support data communication for users over the Internet by forming IP tunnels wherever the users are located. However, since MNs roam, it is impossible to store all information about the MNs to an ISP in a certain area for data transmission/reception. This means that a server in a VPN cannot initiate data transmission to an MN.  
         SUMMARY OF THE INVENTION  
         [0014]    It is, therefore, an object of the present invention to provide a method of enabling a server in a VPN to carry out an initial data transmission to an MN.  
           [0015]    It is another object of the present invention to provide a method of enabling a server in a VPN to initially send data to an MN with no communication link established between the server and the MN.  
           [0016]    To achieve the above and other objects, there is provided a method of transmitting data from a VPN server to an MN. Upon sensing generation of data destined for the MN in the VPN server, a CPE router requests an ISP router connected to a VPN to search for an address of an FA to which the MN belongs. The ISP router searches for the FA address through an HA and routes the data to the FA identified by the searched FA address. The FA then locates the MN and forwards the data to the MN.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:  
         [0018]    [0018]FIG. 1 schematically illustrates the configuration of a mobile IP network for assigning mobile IP addresses to MNs;  
         [0019]    [0019]FIG. 2 schematically illustrates data transmission over a network for assigning mobile IP addresses to MNs;  
         [0020]    [0020]FIG. 3 schematically illustrates the configuration of a network where IP-based VPNs are connected through routers;  
         [0021]    [0021]FIG. 4 schematically illustrates the configuration of a VPN over which a server sends data to an MN in one embodiment;  
         [0022]    [0022]FIG. 5 illustrates the devices of FIG. 4 with their IP addresses assigned;  
         [0023]    [0023]FIG. 6 illustrates the format of an Inquire COA message by which the IP address of an FA to which an MN belongs is inquired according to an embodiment of the present invention;  
         [0024]    [0024]FIG. 7 illustrates the format of an Inform COA message according to one embodiment of the present invention; and  
         [0025]    [0025]FIG. 8 is a diagram illustrating a signal flow for sending data from a server to an MN over the VPN according to one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0026]    A preferred embodiment of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.  
         [0027]    For clarity of description, a type of VPN, a Virtual Private Routed Network (“VPRN”) will be described. A VPRN is defined to be an emulation of a dedicated IP-based routed network between customer sites.  
         [0028]    Referring to FIG. 4, an IP backbone is connected to routers. ISP edge routers  411 ,  413 ,  415  and  417  are connected to a CPE router  419 . The CPE router  419 , for example, is an equipment used for an MN  421  at a certain location to connect to a VPN. The ISP edge routers  411 ,  413 ,  415  and  417  are ISP-operated devices for connecting data received from the CPE router  419  to a desired VPN. The ISP edge routers  411 ,  413 ,  415  and  417  typically are an IP network and data transmission between them is carried out by IP tunneling. A stub link is established between the CPE router  419  and the ISP edge routers  411 ,  413 ,  415  and  417 .  
         [0029]    The MN  421  sends a Registration Request to an FA  423  and the FA  423  forwards the Registration Request with the address of the FA  423  to an HA  425  of the MN  421  over an IP network. The HA  425  stores the address of the FA  423  where the MN  421  is located, that is, the COA of the MN  421 . Then the HA  425  sends a Registration Reply for the Registration Request to the FA  423 . Thus, the MN  421  completes its location registration with the HA  425 . In one aspect, the registration allows the MN  421  to receive data from a CN  427 .  
         [0030]    In one aspect, when a VPN server  429  connected to the CPE router  419  is to send data to the MN  421 , the VPN server  429  obtains the address of the FA  423  to which the MN  421  belongs from the HA  425 . Thus, it is possible for the VPN server  429  to initiate data transmission to the MN  421  at the address of the FA  423 .  
         [0031]    Now a description will be made of initial data transmission from the VPN server to the MN over a VPN with IP addresses assigned to them with reference to FIG. 5. FIG. 5 illustrates the devices of FIG. 4 with their IP addresses assigned.  
         [0032]    Referring to FIG. 5, if the VPN server  429  at an IP address of 5.5.5.5, for example, has data destined for the MN  421 , it must search for an FA to which the MN  421  belongs. The IP address of the MN  421  shown in FIG. 5, for example, is 1.1.1.1. To do so, the VPN server  429  requests its CPE router  419  to search for the FA  423  of the MN  421 . Here, the CPE router  419  has an IP address of 5.5.5.X. The CPE router  419  sends a request to an ISP router A  411  at 5.5.X.X, to which the CPE router  419  is connected, to search for the FA  423  of the MN  421 .  
         [0033]    The ISP router A  411  sends a request to the HA  425  to search for the FA  423  by an Inquire COA message, telling it the IP address of the MN  421 . The Inquire COA message will be described later referring to FIG. 6. For the VPN server  429  to detect the IP address of the FA  423 , the ISP router A  411  requests the HA  425  at 1.1.X.X to search for the FA  423  of the MN  421 . Here, the ISP router A  411  tells the HA  425  the IP address, 1.1.1.1 of the MN  421  to enable the HA  425  to detect the IP address of the FA  423 . The HA  425  then notifies the ISP router A  411  of the IP address of the FA  423  by an Inform COA message. The Inform COA message will be described later referring to FIG. 7.  
         [0034]    Upon receipt of the IP address of the FA  423 , for example, 2.2.2.2 of the MN  421 , the ISP router A  411  detects an ISP router corresponding to the IP address of the FA  423 , that is, the ISP router B  415  among its connected ISP routers  413 ,  415  and  417 . For example, the ISP router  415  has an IP address of 2.2.X.X. Then, a connecting path between the ISP routers is determined to allow communication from the FA  423  to the VPN Server  429 . For example, it is determined that the ISP router A  411  is connected to the ISP router B  415 , which is in turn connected to the CPE router  419 , to thereby allow the VPN server  429  to send data to the ISP router B  415 . Upon receipt of the data, the ISP router B  415  chooses the FA  423  according to the IP address of the MN  421  and sends the data to the FA  423 . The FA  423  then forwards the data to the MN  421 .  
         [0035]    [0035]FIG. 6 illustrates the format of an Inquire COA message according to the embodiment of the present invention. Referring to FIG. 6, for the VPN server  429  to detect the IP address of the FA  423 , the ISP router A  411  sends an Inquire COA message in the format illustrated in FIG. 6 to the HA  425 . The Inquire COA message may be configured in any format for communicating a request, and thus need not be limited to the format shown in FIG. 6. The Inquire COA message comprises a message type area  611 , a destination IP address  613  indicating the IP address of the MN  421 , and a reserved area  615 . With the IP address of the MN  421 , the HA  425  can detect the FA to which the MN  421  belongs. That is, the HA  425  searches for the FA of the MN  421  among its stored FA IP addresses. Then, the HA  425  sends an Inform COA message responding to the Inquire COA message. The Inform COA message may also be configured in any format for communicating the information, and accordingly the format need not be limited to the one shown in FIG. 7.  
         [0036]    [0036]FIG. 7 illustrates the format of the Inform COA message corresponding to the Inquire COA message directed from the ISP router A  411  to the HA  425  in one aspect. The HA  425  detects the FA of the MN  421  referring to the IP address of the MN  421  included in the Inquire COA message. Then, the HA  425  sends the Inform COA message including the IP address of the FA  423 . Referring to FIG. 7, the Inform COA message is comprised of a message type area  711 , a COA area  713  indicating the IP address of the FA  423 , and a reserved area  715 .  
         [0037]    Now a description will be made of data transmission from the VPN server to a particular MN with reference to FIG. 8. FIG. 8 is a diagram illustrating a signal flow for data transmission from the VPN server to the MN according to the embodiment of the present invention. Referring to FIG. 8, upon generation of data destined for the MN  421  in the VPN server  429  in step  811 , the CPE router  419  requests its connected ISP router A  411 , that is, the ISP router A  411  to search for the FA to which the MN  421  belongs in step  813 . Then, the ISP router A  411  sends an Inquire COA message to the HA  425  in step  815 . The HA  425  then detects the IP address of the FA  423  of the MN  421  using the IP address of the MN  421  included in the Inquire COA message in step  817 . In step  819 , the HA  425  sends an Inform COA message including the IP address of the FA  423  to the ISP router A  411 . The ISP router A  411  routes to an ISP router corresponding to the IP address of the FA  423 , that is, the ISP router B  415  in step  821 . Thus, connections are made between the ISP router A  411  and the ISP router B  415  and between the CPE router  419  and the ISP router B  415 . Then, the VPN server  429  sends the data to the ISP router B  415  in step  823  and the ISP router B  415  detects the FA  423  having the IP address set in the Inform COA message and forwards the data to the FA  423  in step  825 . Finally, the FA  423  forwards the data to the MN  421  referring to the IP address of the MN  421  in step  827 .  
         [0038]    In accordance with the present invention as described above, it is possible that a server in a VPN may search for an FA to which an MN belongs in real time. Therefore, the server may initiate data transmission to the MN.  
         [0039]    While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.