Abstract:
This is a method and system to efficiently do handovers for mobile IP. The mobile node registers itself with several foreign agents using a new registration type. Only one of the foreign agents is selected to forward the data packets of a data message to the mobile node. The selection algorithm may be one based on randomness, dynamic learning, message traffic congestion, or statistical information collected at the mobile node.

Description:
FIELD OF THE INVENTION 
     Mobile communications networks are being used to support the Internet. Mobile Internet terminals (mobile nodes) require support as they move within the wireless network. The present invention efficiently solves the problem of mobile Internet connectivity while preserving bandwidth. 
     
       
         
               
             
               
               
             
           
               
                   
               
               
                 DEFINITIONS 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Care-of-Address 
                 Termination point of a tunnel 
               
               
                   
                 toward a mobile node, for data packets 
               
               
                   
                 forwarded to the mobile node while it 
               
               
                   
                 is away from home. There are two 
               
               
                   
                 different types of care-of-address: a 
               
               
                   
                 foreign agent care-of-address is an 
               
               
                   
                 address of a foreign agent with which 
               
               
                   
                 the mobile node is registered; a 
               
               
                   
                 co-located care-of-address is an 
               
               
                   
                 externally obtained local address which 
               
               
                   
                 the mobile node has associated with 
               
               
                   
                 one of its own network interfaces. 
               
               
                 Foreign Agent 
                 A router on a mobile node&#39;s visited network 
               
               
                   
                 that cooperates with the home agent to complete 
               
               
                   
                 the delivery of data packets to the mobile node 
               
               
                   
                 while it is away from home. 
               
               
                 Home Address 
                 An IP address assigned to a mobile node 
               
               
                 Home Agent 
                 A router on a mobile node&#39;s home 
               
               
                   
                 each. 
               
               
                 Host 
                 Any node that is not a router 
               
               
                 IP 
                 Internet Protocol 
               
               
                 Interface 
                 A node&#39;s attachment to a link. 
               
               
                 Link 
                 A communication facility or medium over which 
               
               
                   
                 nodes can communicate at the link layer, such 
               
               
                   
                 as Ethernet (simple bridged). A link is the 
               
               
                   
                 layer immediately below IP. 
               
               
                 Mobile Node 
                 A node that can change its point of contact to a 
               
               
                   
                 network. 
               
               
                 Mobility Binding 
                 The association of a home address with care-of- 
               
               
                   
                 address, for the remaining lifetime of that 
               
               
                   
                 association 
               
               
                 Node 
                 A device that implements IP. 
               
               
                 Packet 
                 An IP header plus payload. 
               
               
                 Tunnel 
                 The path followed by a data packets while it is 
               
               
                   
                 encapsulated. While encapsulated a data packet 
               
               
                   
                 is routed to a knowledgeable agent, that 
               
               
                   
                 decapsulates the data packet and then forwards 
               
               
                   
                 it to its ultimate destination. 
               
               
                   
               
             
          
         
       
     
     BACKGROUND OF THE INVENTION 
     Mobile communications networks, commonly designated as cellular networks, are rapidly expanding to support more services beyond voice service. One of the new services is the running of Internet Protocols (IP) to support mobile access to the Internet. When mobile users access the Internet and are moving geographically the connection must be handed over between connection nodes to maintain the connection to the Internet. Handovers result from a range limitation due to the geographic limitation of communication distances between nodes within a mobile communication network. 
     Handovers are likely to occur while the terminal is moving within a wireless network with several access points. Simultaneous bindings are used to ensure that handovers are as smooth as possible. Using this type of binding, data packets are simultaneously routed through several access points within the geographical area surrounding the user&#39;s last access point called a mobile node. 
     The problem with this solution is that excess bandwidth is used because the same data packet is sent through many access points to the terminal. The excess data packets are simply discarded at the terminal resulting in wasted transmission capacity. It is more efficient to send data packets only once to a mobile terminal. 
     Current Solutions to IP Mobility: 
     One system for providing mobility to the Internet is described in a paper published in IEEE May 1997 issue at pages 84-99, by Charles E. Perkins, of Sun Microsystems. In addition, an Internet document specifies protocol enhancements that allow transparent routing of IP datagrams to mobile nodes in the Internet and can be found at http://sunsite.auc.dk/RFC/rfc/ rfc2002.html (incorporated herein by reference in its entirety). In his May 1997 article, Mr. Perkins describes Agent Advertisement, Registration, and Tunneling as methods to support mobile IP. He further describes route optimization techniques. The following is an excerpt from Mr. Perkins paper describing the protocol, found at page 86. 
     “Mobile IP is a way of performing three related functions: 
     Agent Discovery—Mobility Agents advertise their availability on each link for which they provide service. 
     Registration—When the mobile node is away from home, it registers care-of-address with its home agent.” 
     Tunneling—In order for datagrams to be delivered to the mobile node when it is away from home, the home agent has to tunnel the datagrams to the care-of-address. 
     “The following will give a rough outline of operation of the mobile IP protocol, making use of the above-mentioned operations. FIG. 1 (not shown) may be used to help envision the roles played by the entities. 
     Mobility agents make themselves known by sending agent advertising messages. An impatient mobile node may optionally solicit an agent advertisement message. 
     After receiving an agent advertisement, a mobile node determines whether it is on its home or a foreign network. A mobile node basically works like any other node when it is at home. 
     When a mobile node moves away from its home network, it obtains a care-of-address on the foreign network for instance, by soliciting or listening for agent advertisement, or contacting Dynamic Host Configuration Protocol (DHCP) or Point-to-Point (PPP). 
     While away from home, the mobile node registers each new care-of-address with its home agent, possibly by way of a foreign agent. 
     Datagrams sent to the mobile node&#39;s home address are intercepted by its home agent, tunneled by its home agent to the care-of-addresses, received at the tunnel endpoint (at either a foreign agent or the mobile node itself), and finally delivered to the mobile node. 
     In the reverse direction, datagrams sent by the mobile node are generally delivered to their destination using standard IP routing mechanisms, not necessarily passing through the home agent (but see the eighth section).” 
     “When the home agent tunnels a datagram to the care-of-address, the inner IP header destination (i.e., the mobile node&#39;s home address) is effectively shielded from the intervening routers between its home network and its current location. At the care-of-address, the original datagram exits from the tunnel and is delivered to the mobile node.” 
     “It is the job of every home agent to attract and intercept datagrams that are destined to the home address of any of its registered mobile nodes. The home agent basically does this by using a minor variation on Address Resolution Protocol (ARP), and to do so in the natural mode it has to have a network interface on the link indicated by the mobile node&#39;s home address. However, the latter requirement is part of the mobile IP specification. When foreign agents are in use, similarly, the natural mode of operation suggests that the mobile node be able to establish a link to its foreign agent. Other configurations are possible, however, using protocol operations not defined by (and invisible to) mobile IP. Notice that, if the home agent is the only router advertising reachability to the home network, but there is no physical link instantiating the home network, then all datagrams transmitted to mobile nodes addressed on that home network will naturally reach the home agent without any special link operations.” 
     “FIG. 1 (not shown) illustrates the routing of datagrams to and from a mobile node away from home, once the mobile node has registered with its home agent. The mobile node is presumed to be using a care-of-address provided by the foreign agent: 
     A datagram to the mobile node arrives on the home network via standard IP routing. 
     The datagram is intercepted by the home agent and is tunneled to the care-of-address, as depicted by the arrow going through the tube. 
     The datagram is de-tunneled and delivered to the mobile node. 
     For datagrams sent by the mobile node, standard IP routing delivers each to its destination. In the FIG. ( 1 ) sic, the foreign agent is the mobile node&#39;s default router.’ 
     Further background on mobile IP can be found in another paper by Mr. Charles Perkins, Sun Microsystems and David B. Johnson, Carnegie Mellon University prepared for by the Mobile IP Working Group of the Internet Engineering Task Force (IETF), dated Feb. 25, 1999. Online reference: http://search.ietf.org/internet-drafts/. In their paper they describe a system for route optimization in Mobile IP. The system described allows for routing to a mobile node without going to the home agent first to reduce traffic and optimize routing. 
     Messrs. Johnson and Perkins published another IETF paper on Jun. 25, 1999 setting forth a mobility support protocol IPv6. In it each mobile node is always identified by its home address, regardless of its current point of attachment to the Internet. When a terminal is operating away from home it accesses the Internet via a care-of-address to give the current location. It allows IPv6 nodes to cache the binding of a mobiles node&#39;s home address to its care-of-address to send the mobile packets directly to the latter. This protocol envisions searching for neighboring nodes to handover connections but does not solve the problem of duplicate data packets being sent by several nodes to a moving user. The above reference papers describe systems that support mobile IP and the invention disclosed herein. These papers are incorporated herein by reference. 
     Currently, mobile nodes are serviced using a simultaneous binding. In a simultaneous binding a mobile node has many care-of- addresses. When there is more than one care-of address active for a mobile node, the home agent is instructed to send a duplicated encapsulated datagram to each care-of address for forwarding by multiple foreign agents to the same mobile node. 
     OBJECTS OF THE INVENTION 
     An object of the Invention is to provide binding techniques between nodes in a mobile communications network for efficient data transmission to mobile users. 
     Another object of the invention is to save bandwidth when delivering data packets to mobile users of a mobile network. 
     Yet another object is to enable efficient access to the Internet by mobile users. 
     SUMMARY OF THE INVENTION 
     This invention is a novel binding technique for mobile Internet Protocol (IP). The present use of simultaneous bindings waste bandwidth because all foreign agents forward data packets of a data message to a mobile node. The excess packets are discarded wasting bandwidth. In contrast, the new Anycast binding registers itself in several IP sub-networks simultaneously as before but only one of the foreign agents delivers certain data packets to the mobile node. Because only one foreign agent is selected to deliver the data packets of a data message rather then many, bandwidth is saved. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a representation of a data message transmission from an Internet Host to a mobile node. 
     FIG. 2 is a representation of data message routing from the Internet Host through a single foreign agent to a mobile node. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is set forth in the drawings and the following description. 
     Referring to FIG. 1, the present method of delivering data packets uses an Internet Host  2  to deliver data packets to a mobile network where they are forwarded by home agent  4  to a set of foreign agents  6 . The foreign agents  6  simultaneously broadcast the same data packet to a mobile node  8  within their geographic reach. When simultaneous bindings are used to forward data packets to a mobile node  8 , multiple foreign agents  6  are used to forward the data packet to the mobile node  8 . This system works but uses substantial bandwidth, 
     As described in the papers referenced above, mobile nodes can be serviced the same as a stationary node if they are assigned a new address to identify their location. 
     Referring to FIG. 2, in the present invention, the home agent  4  encapsulates the original data packets of a data message and chooses one prevailing care of address  14  using the algorithm of this invention. Only one foreign agent then forwards the data packets of a data message to the mobile node  8 . More specifically, referring to FIG. 2, an Internet host  2  communicates over a mobile network as before to a home agent  4 . The home address  10  of a mobile node  8  is always the same. Data packets caught by the home agent  4  always include a home address  10  of a mobile node  8 . The data packets of a data message are copied and tunneled  12  to each foreign agent  6   a, b, c, d  using a corresponding care-of-addresses  14  in the encapsulating packets. Both the Anycast Bindings  18  described herein and the presently used simultaneous bindings have many care-of-addresses  14 . The difference is in the selection of only one foreign agent  6  to forward the data packets of the data message to the mobile node  8 . 
     With the new Anycast Binding  18 , the home agent  4  encapsulates the original data packets of the data message and chooses one prevailing care-of-address  14  using the algorithm hereafter described. With the selection of one care-of-address  14  associated with one foreign agent  6   b  it alone forwards data packets of the data message to the mobile node  8 . In contrast, when simultaneous binding is used to maintain communication with a mobile node  8 , the data packets of the data message are copied to all foreign agents  6   a, b, c, d  thereby wasting bandwidth. 
     The mobile node  8  binds itself to a set of foreign agents  6   a, b, c, d  within its geographical area. Anycast binding  18  selects one foreign agent  6   b  to deliver the data packet to the mobile node  8  as follows. 
     The home agent  4  makes the choice of the foreign agent to deliver the data packets of the data message from the set bound to the mobile node  8  if a non-hierarchical environment is in place. In a hierarchical environment, an intermediate agent common to all foreign agents  6  bound to a mobile node  8  makes the choice of a foreign agent  6   b  to forward the data packet to the mobile node  8 . 
     The algorithm that may choose one of the foreign agents  6  in the above environment is set forth below. In its simplest form the Anycast Binding algorithm  18  selects the foreign agent  6   b  in a random manner from the set of foreign agents  6  bound to the mobile node  8 . 
     Another variation of the algorithm is to consider congestion information  21  of message traffic in the bound foreign agents  6   a, b, c, d  based on real time or statistical information to select the most efficient foreign agent  6 . To support this decision process congestion information  14  is accessed by Anycast Binding  18  for use in its decision algorithm. 
     Historical information may also be accumulated and stored in a file  20  for access by Anycast Binding algorithm  18 , The historical data may be used to predict which of the foreign agents  6  is the most efficient to service a mobile node  8  bound to it. 
     Also, a statistical file  22  may be created and accessed by the Anycast Binding algorithm  18  to select a foreign agent  6   b  to forward the data packet to the mobile node  8 . The algorithm may include probability predictions of message traffic over a bound set of foreign agents as a basis for assigning a data packets of a data message to a foreign agent for forwarding to a mobile node  8 . 
     A mathematical representation of the algorithm follows: 
     //Random selection of the destination&#39;s care-of-address 
     //in case of Anycast Binding to be used in a mobile node 
     //destined packet. 
     // 
     address select_coa (address destination) 
     { 
     return a randomly selected care-of-address from 
     the set of active Anycast Binding of this destination; 
     { 
     // 
     //Congestion information based selection of the destination&#39;s 
     //care-of-address in case of Anycast Binding to be used in 
     //mobile node destined packet. 
     // 
     //address select_coa(address destination) 
     { 
     return a care-of-address from the set of 
     active Anycast Bindings of this destination that belongs to the least congested route; 
     }. 
     A mobile node  8  capable of sending Anycast Bindings registers with every foreign agent  6  that it can hear. The mobile node also does the book keeping function on the previous hop of the received data packets. With this information the mobile node  8  has information on which foreign agent  6  is giving the most efficient service. This accumulated data is usable in constructing a decision to select foreign agents  6  based on historical usage. This data is also usable by the mobile node  8  to select the next best hop to a foreign agent  8  for the mobile node originated data transmission. 
     There are several alternatives for implementing the signaling messages for Anycast Bindings  18 . A separate Anycast binding  18  could be used, or the existing mobile IP messages can be enhanced to support Anycast Bindings  18 . The best method is to use the existing mobile IP registration message and add an extension or by defining a new flag. 
     The previous description of the invention does not limit it to alternate embodiments that may be used to practice it and is not a disclaimer of these embodiments.