Abstract:
A routing system operably links a mobile platform to the Internet. The system includes a ground based communications link manager linkable to the mobile platform. At least one ground based prefix server can communicate with the communications link manager. An initial Internet address is assigned to the mobile platform. A prefix server program communicates the initial destination address of the mobile platform to the communications link manager and to the Internet. During a travel segment of the mobile platform a new destination address can be communicated to the Internet using the prefix server to maintain communication between the mobile platform and the Internet.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to the routing of Internet protocol (IP) packets and more specifically to a system and method for routing IP packets to/from a mobile platform where a contiguous network infrastructure may not be available.  
       BACKGROUND OF THE INVENTION  
       [0002]     Common network routing protocols for the Internet assume that sub-networks each having one or more routers remain fixed or are maintaining a continuous connection to a network architecture. IP packets and necessary routing information are able to be transferred between autonomous systems by first establishing a communications link between at least the sending terminal and the receiving terminal having a plurality of data routers and sub-networks. An Internet routing protocol such as Border Gateway Protocol 4 (BGP-4) can be used to establish communications paths. A preferred routing path can be determined, for example using BGP-4 by assigning various preference attribute values to each available route and selecting the best route in a multi-step process.  
         [0003]     Mobile platforms including for example aircraft, ships, trains, busses, automobiles, etc. (hereinafter referred to for simplicity as aircraft) can encounter difficulties with IP packet transfer because one or more of the sub-networks must either change as the aircraft changes location, or the preferred route must continuously change, which can result in “flapping” as line update messages continuously change as the preferred route changes. One common way to avoid flapping is to “backhaul” all data to the originating sub-network for transfer over the fixed path originally linked. This is often not the most efficient or cost effective way to transfer data.  
         [0004]     U.S. Pat. No. 6,604,146 to Rempe et al., issued Aug. 5, 2003, discloses a centralized route-server architecture permitting Internet Protocol (IP) services to be offered over satellite mesh networks. The centralized route-server is implemented on a standard workstation. Routing information is only exchanged between a master terminal and each other terminal in the network. If a connection does not exist to the destination terminal or increased bandwidth is required for the destination terminal, the entry terminal must make a request to the master terminal for a satellite connection or (temporarily) increased bandwidth. If the destination terminal is a moving platform, all routing information must backflow through the master terminal and IP packets are held up pending confirmation of a new route. No allowance is made for an Internet address which changes during a travel segment of a mobile platform.  
       SUMMARY OF THE INVENTION  
       [0005]     According to a preferred embodiment of the present invention, a global Internet protocol prefix number mobility system operable to link a mobile platform to the Internet includes a ground based communications link manager communicatively linkable to the mobile platform. At least one ground based prefix server is in operable communication with the communications link manager. An initial address is assignable to the mobile platform. A prefix server program is operable to communicate the initial Internet address of the mobile platform to the communications link manager and to the Internet.  
         [0006]     According to yet another preferred embodiment of the present invention a method for maintaining communications contact between a mobile platform and the Internet during a travel segment of the mobile platform using at least one ground based communications link manager includes: creating at least one ground based prefix server operable to communicatively link the mobile platform and the communications link manager; programming the prefix server to operatively select a prefix number for the mobile platform from a plurality of prefix numbers; assigning the prefix number to the mobile platform for the travel segment; and signaling via the prefix server a destination address of the mobile platform using the prefix number communicated via the communications link manager.  
         [0007]     A global Internet protocol prefix number mobility system of the present invention provides several advantages. By locating the prefix server of the present invention adjacent to or within the ground based communications link manager, system hardware or software to perform the functions of the prefix server can be removed from the mobile platform and positioned in the ground based portion of the flow path to the Internet. This can reduce mobile platform complexity and cost and permit limited numbers of prefix servers to serve a fleet of mobile platforms. By assigning prefix numbers to a mobile platform using a prefix server of the present invention, a local pool of prefix numbers can be retained. The use of a prefix server can reduce the total number of prefixes required to serve the fleet of aircraft by performing prefix management functions. A travel segment for the mobile platform can be provided with Internet access while permitting switching of the prefix number between communications links during travel if necessary.  
         [0008]     The features, functions, and advantages can be achieved independently in various embodiments of the present invention or may be combined in yet other embodiments. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0010]      FIG. 1  is a diagrammatic view of a global Internet protocol prefix number mobility system according to a preferred embodiment of the present invention;  
         [0011]      FIG. 2  is a diagrammatic view showing exemplary Internet system connections for prefix servers of the present invention; and  
         [0012]      FIG. 3  is a diagrammatic view showing communication and data flow paths of a mobile routing system according to a preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]     The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0014]     According to a preferred embodiment of the present invention, and referring generally to  FIG. 1 , a mobile routing system  10  of the present invention can include a user electronic device  12  positioned on a mobile platform such as an aircraft  14 . Internet  16  can be provided with a communication path to user electronic device  12  using a prefix server  18  of the present invention.  
         [0015]     To communicate with the Internet  16 , user electronic device  12  can be connected via one or more Internet service providers (ISP)  20  connectable to prefix server  18 . Prefix server  18  can be in turn connectable to a ground based communication link manager (GCLM)  22 . GCLM  22  can communicate via a two-way communication path  23  to a ground based transmitter/receiver (GBT/R)  24 . GBT/R  24  can transmit electronic signals to and from a communications satellite  26  via a signal path  28 . These electronic signals can be communicable to an antenna  30  of aircraft  14  via a satellite/aircraft communication path  32 . Within aircraft  14  communications signals can be transferred to and from an aircraft data transfer system  34  which can transfer or receive signals to/from user electronic device  12  via a signal path  36 . Signal path  36  can be a hard wired signal path or a radio frequency signal path.  
         [0016]     During a travel segment of aircraft  14 , herein defined as a flight originating at a point “A” and ending at a point “B”, communication between user electronic device  12  and the Internet  16  can be substantially provided by communications satellite  26 . During at least a portion of the travel segment, communication path  32  may be interrupted or broken due to inability of antenna  30  to receive or transmit signals to or from communications satellite  26 . During this condition, a new communications path can be opened between antenna  30  of aircraft  14  and Internet  16 . This can be accomplished by transferring signals to or from antenna  30  and a communication satellite  38  via a satellite/aircraft communication path  40 . From communication satellite  38  signals can be transferred to and from a GBT/R  42  via a communication path  44 . GBT/R  42  can be in turn connected to a GCLM  46  via a two-way communication path  47 . GCLM  46  can be connected to a prefix server  48  which can directly communicate with Internet  16  or alternately can communicate with Internet  16  via one or more Internet service provider(s)  50  (shown in phantom). Either GBT/R  24  or GBT/R  42  can also communicate directly with aircraft  14 , for example via a direct communication path  51 . Direct communication path  51  can be used for example when aircraft  14  is preparing for take-off or when aircraft  14  has landed.  
         [0017]     Referring generally to  FIG. 2 , an exemplary functional connection to prefix servers of the present invention is illustrated. Prefix server  18  can be connected between GCLM  22  and a route reflector  52  via an internal BGP connection  54 . Route reflector  52  can be in turn connected to a router  56  via an internal BGP connection  58 . Router  56  can be connected to ISP  20  via an external BGP connection  60 . Additional external connection for signals transferred to and from route reflector  52  can be via a router  62  connected to route reflector  52  via an internal BGP connection  64 . Communication signals from GCLM  22  can be transferred to or from communications satellite  26  via a first router  66   a  connected to a modem  84   a  associated with a GBT/R  86 . A second router  66   b  connected to modem  84   b  associated with GBT/R  86  can also provide a signal transfer path from GCLM  22  to and from communication satellite  26 .  
         [0018]     A second prefix server  68  can transfer communication signals between GCLM  22  and a route reflector  70  via an internal BGP connection  72 . A router  74  can be connected to route reflector  70  via an internal BGP connection  76 . Router  74  is in turn connectable to ISP  50  via an external BGP connection  78 .  
         [0019]     ISP  20  forms a first autonomous system “C”. ISP  50  forms a second autonomous system “D”. A router  80  can be connected to route reflector  70  via an internal BGP connection  82 . Each of the routers and route reflectors identified in  FIG. 2  are commonly known in the art. Devices  18 ,  52 ,  56 ,  62 ,  66   a ,  66   b ,  68 ,  70 ,  74 , and  80  can form an autonomous system “E”. Each route reflector  52 , 70  can be cross connected to opposing auxiliary system routers. Connections  60 ,  78  permit communications between the Internet and the ground based network system. The external BGP connections  60 ,  78  permit various routes to be formed between the ground based network system, such as autonomous system “E”, Internet service providers ( 20  or  50 ), and the Internet  16 .  
         [0020]     Each of router  62  and router  80  can communicate with modem  84   a  and modem  84   b , respectively. Modem  84   a  and modem  84   b  both in turn can communicate with a GBT/R  86 . GBT/R  86  can provide an alternate communication path to Internet  16  as commonly known. Modem  84   a  and modem  84   b  are exemplary of a plurality of modems which can be linked to GBT/R  86  from additional autonomous systems (not shown).  
         [0021]     Prefix server  68  can also be connected to a GCLM  88  via an IP traffic tunnel path  90  which may exist within an autonomous system “F”. IP tunnel connections are commonly known and can provide global connectivity between individual IP networks.  
         [0022]     Referring generally to  FIG. 3 , basic functions of a prefix server of the present invention are shown. In this example, prefix server  18  can communicate between ISP  20  and aircraft  14 . Initially, each aircraft  14  can be provided with an aircraft unique identification number  92 . GCLM  22 , prefix server  18 , route reflector  52 , and router  56  can be provided with an autonomous system number  94 . When aircraft  14  initiates the travel segment, a prefix number  96  can be selected from one of at least two sources using prefix server  18 . Each autonomous system such as autonomous system “E” can be assigned a local pool of prefix numbers. In this example autonomous system “E” is assigned a local pool of prefix numbers  98 . Local pool  98  is initially empty and is provided with each of its plurality of prefix numbers generally at the completion of individual travel segments of aircraft  14  or additional aircraft (not shown). Local pool  98  includes a volume allowing a predetermined number or limit of prefix numbers associated with it. If local pool  98  is empty of prefix numbers, prefix server  18  can next search a global pool  100  of prefix numbers. Global pool  100  can provide a plurality of prefix numbers available from a plurality of autonomous systems. After selecting prefix number  96  from either local pool  98  or global pool  100 , prefix server  18  can map the prefix number  96  against the unique identification number  92  of aircraft  14  to a local destination address  102  for aircraft  14 . Destination address  102  can be subsequently identified by prefix server  18  as an available site to each of the plurality of autonomous systems which form a possible path of communications of data to or from aircraft  14  and Internet  16  via internal BGP connection  54 . If two-way communication path  23  is open, a plurality of route data in the form of network layer reachability information (NLRI)  104  can be transmitted to the plurality of autonomous systems via a plurality of route paths. As known in the art, network layer reachability information can include for example information such as “NEXT_HOP”, “UPDATE”, “KEEP ALIVE”, “LOCAL_PREF”, “AS_PATH” and “NOTIFICATION” messages. The plurality of route paths can include a first route path  106 , a second route path  108 , a third route path  110  connected to Internet  16 , and a fourth route path  112  connected to Internet  16 . These route paths are exemplary and are indicative of possible route paths for NLRI  104 .  
         [0023]     A mobile autonomous system number (MASN)  115  may also be linked to prefix number  96 . Prefix server  18  uses the MASN  115  to modify NLRI  104 . Some forms of border gateway protocol may require the originating autonomous system number for a prefix to be generally static in nature. MASN  115  provides the prefix server information to modify the AS_PATH to allow for Internet Service Provider  20  to authenticate and authorize the propagation of NLRI information throughout the Internet  16 . The use of MASN  115  also allows prefix server  18  to aggregate a plurality of routes within Local Pool  98  to reduce the need to propagate an exact NLRI to the Internet  16  for each prefix number  96 . The use of an aggregate NLRI using MASN  115  also provides for the ability to insert a single NLRI covering all routes within Local Pool  98 . A single large prefix number may be preferable by some Internet service providers.  
         [0024]     In some cases it may be desirable to modify the assigned prefix number to an aircraft  14 . Prefix server  18  can request a new prefix number  114  by first querying local pool  98  and subsequently querying global pool  100  if new prefix number  114  is not available from local pool  98 . Similar to prefix number  96 , new prefix number  114  can be mapped with unique identification number  92  to form a new destination address  116 . Prior to transmission of new destination address  116 , each of the open route paths including route paths  106 ,  108 ,  110 , and  112  are closed by prefix server  18 . New destination address  116  is then identified to the various autonomous systems by prefix server  18  and a plurality of new routes (not shown) are subsequently identified by prefix server  18  to transfer NLRI  104  via the newly open routes. Prefix server  18  returns prefix number  96  to either local pool  98  or global pool  100  when new prefix number  114  is withdrawn.  
         [0025]     Upon completion of the travel segment (in this example from point “A” to point “B”), prefix number  96  (if still current) or new prefix number  114  are returned to local pool  98  if local pool  98  has not reached its maximum volume. If local pool  98  has reached its maximum volume, the prefix number ( 96  or  114 ) is returned to global pool  100 . Returning prefix numbers as a first priority to local pool  98  reduces the possibility of external “route flapping” by maintaining the prefix numbers for immediate reuse by the associated autonomous system. It is therefore possible for aircraft  14  to reuse the prefix number just returned to local pool  98  upon initiation of a new travel segment, or another aircraft (not shown) can reuse the prefix number from local pool  98 , thus reducing the need to pull prefix numbers from global pool  100 .  
         [0026]     When GCLM  22  can no longer communicate via two-way communication path  23  to aircraft  14 , the handoff process from GCLM  22  to a subsequent GCLM (for example GCLM  46  shown in  FIG. 1 ), includes steps in the following order. The GCLM at the new ground station (in this example GCLM  46 ) can notify GCLM  22  that unique identification number  92  is now available via a new destination address (for example  116 ). Prefix server  48  can then inject NLRI  104  as new NLRI via an internal BGP connection. GCLM  22  can then notify prefix server  18  that unique identification number  92  is no longer reachable. Prefix server  18  can then withdraw the original routes for NLRI  104 . Border routers (for example routers  74  and  80  shown in  FIG. 2 ) can receive the new NLRI from prefix server  48  (or prefix server  68 ) via IP tunneled connections such as  90 . These border routers can announce the new NLRI to other routers (such as routers  56  to autonomous system “C”) which reopens the connection for Internet service provider  20  between aircraft  14  and Internet  16 .  
         [0027]     On landing the following steps are taken. The active GCLM (GCLM  22 , GCLM  46 , or GCLM  88 ) can notify prefix server  18  of the landed status of aircraft  14 . Prefix server  18  can return the prefix number (prefix number  96 ) to either local pool  98  or global pool  100 . Prefix server  18  can then notify other prefix servers, such as prefix server  68  shown in  FIG. 2 , that unique identification number  92  mapping is now invalid.  
         [0028]     Prefix servers of the present invention are computer programs performing the functions identified herein. Prefix server programming can be written using existing open source code such as GNU Zebra or other source code. Prefix servers of the present invention are also identified in terms using border gateway protocol 4 (BGP-4). The present invention is not limited to BGP-4 protocol. Other protocols can be used with modifications inherent to the protocol used which are known to a person of skill in the art.  
         [0029]     A global Internet protocol prefix number mobility routing system of the present invention provides several advantages. By locating prefix servers of the present invention adjacent to or within the ground based communications link manager, system hardware or software performing the functions of the prefix server can be removed from the mobile platform and positioned in the ground based portion of the flow path to the Internet. This can reduce mobile platform complexity and cost and permit limited numbers of prefix servers to serve a fleet of mobile platforms. By assigning prefix numbers to a mobile platform using a prefix server of the present invention, a local pool of prefix numbers can be retained. Retaining these prefix numbers can reduce the potential for external route flapping. A system of the present invention makes use of existing protocols and does not require modifications to existing Internet infrastructure to support prefix number mobility of the system. A prefix server of the present invention acts as an internal BGP route server and a dynamic prefix assignment server. Prefix servers of the present invention are therefore capable of adding routes and setting NLRI data such as NEXT_HOP attributes as well as withdrawing routes when an active GCLM signals that the two-way communication path is no longer available.  
         [0030]     While various preferred embodiments have been described, those skilled in the art will recognize modifications or variations which might be made without departing from the inventive concept. The examples illustrate the invention and are not intended to limit it. Therefore, the description and claims should be interpreted liberally with only such limitation as is necessary in view of the pertinent prior art.