Abstract:
A system and method for route optimization in PMIP having a first mobile node having a local mobility anchor and anchored at an access router and a second mobile node anchored at an access router is presented. The method includes establishing a binding cache at one access router comprising a mapping of mobile node addresses to access router addresses, populating the binding cache, and updating the mapping of the mobile node addresses in response to a handoff of a mobile node from one access router to another access router, so that a packet is transmitted from the first mobile node to the second mobile node using the mapping in the binding cache. The second access router address is obtained by either transmitting the packet from the first mobile node to the local mobility anchor, or querying neighboring access routers, or broadcasting access router addresses from the local mobility anchor.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present invention claims the benefit of U.S. provisional patent application 60/930,407 filed May 16, 2007, the entire contents and disclosure of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to mobility management in next generation wireless networks. In particular, the invention relates to route optimization techniques for proxy mobile IP dedicated to support both local mobility and global mobility and provide seamless communication. 
     BACKGROUND OF THE INVENTION 
     Wireless Service Providers, or WISPs, strive to provide secured and seamless connectivity to the roaming users. Quality of existing communication gets degraded when a mobile is subjected to repeated handoff due to delay and packet loss. There are several transition events during the handoff such as discovery, configuration, authentication, security association, binding update and media redirection that contribute to the handoff delay and the associated packet loss. Several optimization techniques are being developed to address each of these handoff components. Currently, there are several types of mobility protocols, or mobile internet protocols (MIP), at different layers such as MIPv4, MIPv6, Host Identity Protocol (HIP), Session Initiation Protocol (SIP) and their faster variants such as Fast Mobile IPv6 (FMIPv6), and regional MIPv4 that can be used to take care of these handoff events. These mobility protocols are meant to reduce the packet loss and handoff delay during a mobile&#39;s change of connectivity from one point-of-attachment to another. However, these mobility protocols are not very suitable when a mobile&#39;s movement is confined to a domain and the communicating host is far off, or if both the communicating hosts are away from home. In order to reduce the delay due to binding update and associated one-way delay due to media transfer when a mobile&#39;s movement is confined to a specific domain, various local mobility management protocols have been designed. These include Cellular IP, Handoff Aware Wireless Access Internet Interface (HAWAII), Intra-Domain Mobility Management Protocol (IDNP), Hierarchical Mobile IPv6 (HMIPv6), among others. Proxy MIP (PMIP) is one such localized mobility protocol that helps to reduce the delay due to long binding update. It takes much of the burden away from the mobile and puts it on the access routers or proxy mobility agents within the network. Proxy mobility agents send the binding update to the home agents on behalf of the mobiles. Each mobile is anchored with a certain PMA (Proxy Mobility Agent) until it hands off to a new PMA. 
     In order to avoid the drawbacks associated with the global mobility protocols, such as MIP and SIP, that heavily depend upon mobility stack on the mobile node and optimize the mobility for a localized mobility domain, Network-based Localized Mobility Management (NETLMM) working group of the Internet Engineering Task Force (IETF) was created. NETLMM working group has created several Request for Comments documents, e.g., RFC 4830, RFC 4831, and RFC 4832, outlining the guidelines for designing a localized mobility protocol that will avoid the dependence upon the host to do binding update (BU) and limit the signaling updates when the mobile node moves within a domain. A few candidate protocols are currently being discussed, such as network-controlled local mobility and Proxy Mobile Internet Protocol (PMIP), including PMIPv4 and PMIPv6. These protocols are designed to take care of local mobility and, instead of depending upon a mobility stack in the mobile node, are controlled by the network elements in the edge routers. 
     PMIP, for example, does not use any mobility stack on the mobile node but rather uses Proxy Mobile Agents (PMAs) that can co-locate with the edge routers to help perform the mobility functions, such as the BU to the home agent (HA). As long as the mobile node moves within the same domain that has PMAs, the mobile node assumes that it is in a home link. The PMA is responsible for sending the proper mobile prefix as part of the router advertisement for stateless auto-configuration, or the PMA can also act as a Dynamic Host Configuration Protocol (DHCP) relay agent for stateful auto-configuration. In some cases, PMA can be referred to as a MAG (Mobility Access Gateway) and HA can be replaced by LMA (Local Mobility Agent). Thus, PMA and MAG can be used interchangeably and HA and LMA can be used interchangeably. 
       FIG. 1  describes the network elements and processes associated with PMIP operation. After the mobile node  10  connects to the new point-of-attachment as part of the initial bootstrapping process, or after the movement from the home network  12  to a new domain, e.g., Visited 1   16 , access is authenticated with the designated AAA server  14  (1: access initiation; 2: AAA Request/Reply). During this process, PMA 1   18  sends the BU to the HA  20  with the address of the PMA that is specific to the home prefix of the mobile node  10 , i.e., PMA 1   18 , (3: Proxy BU) and receives an acknowledgement (ACK) (4: Proxy ACK). In the absence of a pre-existing tunnel, this process helps to set up a tunnel, i.e., PMIP tunnel- 1   22 , between the HA  20  and the respective PMA (5: PMIP Tunnel- 1 ). The mobile node  10  configures its address using the prefix included in the router advertisement and interface-id, which can be assigned by PMA 1   18  or created by itself (6: home prefix advertisement). 
       FIG. 1  also illustrates the movement of the mobile node from one domain, Visited 1   16 , to another domain, Visited 2   24 . After the move, access is authenticated with the designated AAA server  14  (7: access initiation; 8: AAA Request/Reply). During this process, as before, PMA sends the BU to the HA  20  with the address of the PMA that is specific to the home prefix of the mobile node  10 , i.e., PMA 2   26 , (9: Proxy BU), and receives a reply (10: AAA Query/Reply). If no tunnel exists, a tunnel, i.e., PMIP Tunnel- 2   28 , between the HA  20  and the respective PMA, i.e., PMA 2   26 , (11: PMIP Tunnel  2 ) is set up by the process. 
     The PMIP-based mobility protocol is preferred when mobility is confined within a domain and wireless service providers do not want to overload the mobile node&#39;s stack by setting up a tunnel between the mobile node and the HA. A tunnel is not desirable on the mobile node because it adds extra processing and bandwidth constraints to the wireless hop. 
     Although PMIP provides optimization compared to other global mobility protocols, it still needs improvement in certain areas such as route optimization. Route optimization reduces the delay due to media delivery between the two communicating mobile nodes by reducing the traversal distance between the communicating hosts. The present invention fulfills a need for route optimization techniques for PMIP that will further improve the effectiveness of PMIP for both intra-domain and inter-domain movement. Several scenarios can be realized by using route optimization technique. In all the scenarios, both the correspondent node and mobile belong to a PMIP domain. In one specific scenario, the mobile node and correspondent node belong to two different MAGs that are part of the same HA or LMA. In a second scenario, the mobile and the correspondent node belong to two MAGs (PMAs) that are under different HA (LMA). Thus, in this second case, the communicating nodes belong to two different PMIP domains, where the PMIP domains may belong to the same administrative domain or different one. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention advantageously provides a solution to some of the problems of mobility management, that is, roaming and service continuity, in next generation wireless networks. 
     A system and method for route optimization in a proxy mobile internet protocol-based mobility management protocol is presented. The protocol has a plurality of mobile nodes each having a mobile node address and a plurality of access routers each having an access router address, the plurality of mobile nodes comprising at least a first mobile node having a local mobility anchor and being anchored at a first access router of the plurality of access routers and a second mobile node anchored at a second access router having a second access router address. The method has steps of establishing a first binding cache of the first access router, the first binding cache comprising a mapping of the mobile node addresses to the access router addresses, populating the first binding cache using an approach, and updating the mapping of the second mobile node address to a third access router address in the first binding cache in response to a handoff of the second mobile node from the second access router to a third access router, such that a packet is transmitted from the first mobile node via the first access router to the second mobile node via the mapped access router using the mapping of the second mobile node address. The approach can be either transmitting the packet from the first mobile node via the first access router to the local mobility anchor to obtain the second access router address from the local mobility anchor, or querying neighboring access routers to obtain the second access router address from the queried neighboring address routers, or broadcasting access router addresses from the local mobility anchor to obtain the second access router address from the broadcast access router addresses. 
     In another embodiment, the access routers are connected using a topology, such as ring, bus, or mesh, and the method includes sending a packet from the first mobile node to a first access router and from the first access router to a connected access router connected to the first access router, and if the connected access router is the second access router, sending the packet to the second mobile node via the second access router, or if the connected access router is not the second access router, transmitting the packet to another access router connected to the connected access router, the another access router becoming the connected access router, and repeating the step of transmitting until the another access router is the second access router. 
     The foregoing and other objects, aspects, features, advantages of the invention will become more apparent from the following description and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is further described in the detailed description that follows, by reference to the noted drawings by way of non-limiting illustrative embodiments of the invention, in which like reference numerals represent similar parts throughout the drawings. As should be understood, however, the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings: 
         FIG. 1  illustrates network elements associated with PMIP; 
         FIG. 2  illustrates a block diagram of general PMIP-based architecture; 
         FIG. 3  illustrates the path optimization from mobile  1  to mobile  2  in a first approach; 
         FIG. 4  illustrates the path optimization from mobile  2  to mobile  1  in the first approach; 
         FIG. 5  illustrates the path optimization after handover from mobile  1  to mobile  2  in the first approach; 
         FIG. 6  illustrates the path optimization after handover from mobile  2  to mobile  1  in the first approach; 
         FIG. 7  illustrates the optimized route from mobile  1  to mobile  2  in a second approach; 
         FIG. 8  illustrates network configuration topologies; 
         FIG. 9  illustrates the path optimization of the ring topology; 
         FIG. 10  illustrates path optimization from mobile  1  to mobile  2  in a fourth approach; 
         FIG. 11  shows the path optimization in the first approach, from mobile  1  in one PMIP domain to mobile  2  in another PMIP domain, where each PMIP domain may or may not belong to the same administrative domain; 
         FIG. 12  shows the flows associated with the route optimization procedure associated with mobiles having separate domains and MN 2 &#39;s attachment to a MAG; and 
         FIG. 13  shows the flows associated with the route optimization procedure and handoff associated with mobiles having separate domains and MN 2 &#39;s movement from one MAG to another MAG. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Inventive route optimization techniques that could be applied to PMIP-based mobility are described below.  FIG. 2  shows a generic architecture, that is, the basic network configuration, of proxy PMIP architecture that will be used to illustrate the inventive optimization techniques. Each of the Access GateWays (AGW) is actually the access router and acts like Proxy Mobility Agent (PMA). PMAs are actually Mobile Access Gateways (MAGs) in NETLMM terminology. HA is the home agent and can act like a Local Mobility Anchor (LMA). Similar architecture can span across multiple domains, with each domain being equipped with a combination of LMA and MAGs, as shown in  FIG. 11 . 
     Typically, there are several mobile nodes that communicate with each other. They could be part of the same PMIP domain, as shown in  FIG. 2 , or different, as shown in  FIG. 11 . In the scenario illustrated in  FIG. 2 , there is one mobile node anchored at each of the AGW or MAG  18 ,  26 ,  32 . Specifically, MN 1   10  is anchored at AGW 1   18 , MN 2   30  is anchored at AGW 2   26 . MN 2   30  establishes a communication with MN 1   10  and then hands off to AGW 3   32 . By default, the communication between MN 1   10  and MN 2   30  before the handover goes via AGW 1   18 , HA  20  and AGW 2   26 , and after the handover the communication goes via AGW 3   32 . If the HA  20  is placed too far away from AGW  18 ,  26 ,  32 , then there will be considerable one-way delay for the data traveling between the mobile nodes  10 ,  30 . Thus, it is desirable to reduce the route associated with the data traversal. As discussed above, in this general architecture, AGWs can be compared with PMA or MAG. HA can be compared with LMA in NETLMM terminology. 
     Approach 1: Binding Cache Entry (BCE) at HA and MAG 
       FIGS. 3-6  show the basic optimization procedure associated with an optimization technique that utilizes the binding cache entry at the HA or LMA  20  and at the AGW or MAG  18 ,  26 ,  32 .  FIG. 3  illustrates the path or route optimization from MN 1   10  to MN 2   30 . Before the handover has taken place, MN 1   10  attaches to AGW 1  or PMA 1   18  which then sends a binding update (BU) to the HA  20  on behalf of MN 1   10 , creating a network attachment as PMIP tunnel  22 . Similarly, MN 2   30  creates a network attachment, connecting MN 2   30  to AGW 2  or PMA 2   26 , triggering the proxy-BU, or PMIP tunnel  28 , to the HA  20  on behalf of MN 2   30 . 
     The BCE optimization procedure is as follows. The initial packet from MN 1   10  to MN 2   30  is tunneled  22 ,  28  to the HA  20 . As soon as the HA  20  gets this packet, HA  20  knows how to forward the packet to AGW 2   26 , and at the same time, HA  20  also sends a proxy-BU to AGW 1   18  notifying that AGW 2   26  is the anchored PMA for MN 2   30 . AGW 1   18 , when obtaining this BU, establishes and maintains a cache that maps AGW 2   26  with MN 2   30 . Similarly, AGW 2   26  maintains in its cache that AGW 1   18  has been notified of AGW 2 &#39;s association with MN 2   30 . 
     Because of AGW 1 &#39;s cache, any subsequent packet from MN 1   10  destined to MN 2   30  gets intercepted by AGW 1   18  and is forwarded to AGW 2   26 , instead of being forwarded to the HA  20 . Hence, the trajectory of the packet becomes: MN 1 →AGW 1 →AGW 2 →MN 2  instead of MN 1 →AGW 1 →HA→AGW 2 →MN 2 . Accordingly, this new, shortened data path optimizes the route of the data packet from MN 1   10  to MN 2   30 . 
       FIG. 4  shows the optimized data path from MN 2   30  to MN 1   10  using the binding cache entry-based approach. In the situation illustrated in  FIG. 4 , during the BCE optimization procedure, the HA  20  sends the proxy-BU to AGW 2   26 , along with the parameters of MN 1   10  and AGW 1   18  to maintain the cache in AGW 2   26 . The result is an optimized data path from MN 2   30  destined to MN 1   10 . 
       FIG. 5  shows the BCE route optimization procedure and optimized route from MN 1   10  to MN 2   30  after MN 2   30  hands over to a new PMA such as AGW 3   32 . In this case, MN 2   30  attaches with AGW 3   32  and sends a proxy-BU to HA  20 . At that point, HA  20  immediately sends a proxy-BU to AGW 2   26 , since the HA  20  has the knowledge of AGW 2   26 . Using its cache, AGW 2   26  in turn sends a proxy-BU informing AGW 1   18  that MN 2   30  is under AGW 3   32 . Thus, both AGW 1   18  and AGW 2   26  are made aware of the fact that MN 2   30  is currently connected to AGW 3   32 . 
     During the initial hand off to the new PMA  32  for MN 2   30 , if any data from MN 1   10  destined to MN 2   30  arrives at AGW 1   18 , it forwards the data to AGW 2   26  which in turn forwards it to AGW 3   32 . AGW 3   32  then forwards it to MN 2   30 . But once the BCE route optimization procedure is completed, any data destined from MN 1   10  to MN 2   30  gets intercepted by AGW 1   18  and then gets directly forwarded to AGW 3   32  which forwards it to MN 2   30 . Hence, the optimized data path is MN 1 →AGW 1 →AGW 3 →MN 2 . 
       FIG. 6  shows the BCE route optimization procedure when the data is destined from MN 2   30  to MN 1   10  after the handover. During the establishment of the BCE route optimization, the first packet gets routed from MN 2   30  to MN 1   10  via HA  20  and is subjected to delay. However, after the BCE route optimization is completed, data from MN 2   30  destined to MN 1   10  gets picked up by AGW 3   32  which sends the data to AGW 1   18  to be delivered to MN 1   10 . Hence, the optimized data path is MN 2 →AGW 3 →AGW 1 →MN 1  instead of MN 2 →AGW 3 →HA→AGW 1 →MN 1 . 
     Below,  FIG. 11  shows how this specific approach can be applied to a scenario when the mobiles, e.g. MN 1   10  and MN 2   30 , are connected to MAGs that belong to two different LMAs in two different PMIP domains. 
     These BCE techniques thus avoid the extra route from HA  20  to AGWs  18 ,  26 ,  32  by forwarding the traffic from one AGW or PMA  18 ,  26 ,  32  to another AGW or PMA  18 ,  26 ,  32 . Nonetheless, because the binding cache entry must be established, the first packet is not subjected to route optimization. 
     Approach 2: Binding Query Approach 
       FIG. 7  shows a second approach of an optimization technique, a technique that utilizes a binding query approach. As with the first approach, a cache is created in the MAGs, and a packet gets diverted to the appropriate PMA (MAG/AGW)  18 ,  26 ,  32  associated with the destination node, instead of getting routed to the HA  20 . However, a querying approach is used for creating the cache. The example shown in  FIG. 7  illustrates how AGW 1   18  can query the neighboring AGWs  18 ,  26 ,  32  to find out if a specific target mobile is anchored at one of those AGWs  18 ,  26 ,  32 . 
     As shown in  FIG. 7 , when a packet or data from MN 1   10  destined to MN 2   30  is intercepted by AGW 1   18 , it sends a query to the neighboring AGWs  26 ,  32 , e.g., AGW 2   26  and AGW 3   32 . Since MN 2   30  is anchored at AGW 2   26 , it will send a binding reply that includes its address and the address of MN 2   30 . This reply information is stored in the cache of AGW 1   18 . Hence, AGW 1   18  can directly send the data to AGW 2   26  instead of forwarding the data to the HA  20 , although there will be some delay for the first packet because of the associated binding query and binding reply. However, for any subsequent data destined for MN 2   30 , AGW 1   18  does not need to send any queries, but rather examines its cache, finds MN 2   30  and its anchor, AGW 2   26 , and forwards the data to AGW 2   26  which in turn delivers it to MN 2   30 . As with BCE, AGW 2   26  maintains a cache including that AGW 1   18  has been notified of AGW 2 &#39;s association with MN 2   30 . In  FIG. 7 , AGW 1   18  unicasts its query to a list of AGWs  26 ,  32 ; however, the query could be multicast using a localized multicast address. 
     In this approach, a similar procedure will take place for the packets from MN 2   30  destined for MN 1   10 . This approach is also applicable to cases when the mobiles are under MAGs that belong to two different LMAs, as shown in  FIG. 11 . 
     Compared to the BCE approach described above, in the binding query approach, the first packet is route optimized, although it may be subjected to delay due to route look up or query. While the binding query method introduces more signaling between the AGWs, one can take advantage of localized multicast to reduce this number of signaling messages between the AGWs. This approach is also applicable to cases when the mobiles are under MAGs that belong to two different LMAs. 
     Approach 3: Mobile Ring-Based, Bus and Mesh-Based Solution 
       FIGS. 8 and 9  show a third approach of an optimization technique. This solution assumes that the data or packet transmitted from a sending mobile node to a receiving mobile node, for example, from MN 1   10  to MN 2   30 , can flow through each of the access gateways, e.g., MAGs or AGWs  18 ,  26 ,  32 , before it actually reaches the HA  20 . In this optimization technique, during the course of the flow, the data gets dropped at the specific AGW  18 ,  26 ,  32  to which the receiving mobile node  10 ,  30  is anchored, and then sent from this particular AGW  18 ,  26 ,  32  to the receiving mobile node  10 ,  30 . Accordingly, when the data flows through each of the AGWs  18 ,  26 ,  32  and HA  20  that are connected in either a ring, full mesh or bus fashion, the required data for a specific mobile node  10 ,  30  gets dropped at the anchor AGW  18 ,  26 ,  32  for that specific mobile node  10 ,  30 . 
       FIG. 8  shows three possible network configuration topologies, e.g., full mesh, ring, and bus topology, that, combined with add/drop technology, can provide PMIP route optimization. As shown in  FIG. 8 , data traffic destined from MN 1   10  to MN 2   30 , or from MN 2   30  to MN 1   10 , can take advantage of this add/drop technique while traveling via any one of these topologies. 
       FIG. 9  illustrates this approach, based on the ring topology of  FIG. 8  (upper right).  FIG. 9  shows that data transmitted from MN 1   10  to MN 2   30  will get dropped at AGW 2   26  which will forward it to MN 2   30 , bypassing HA  20 . Similarly, after MN 2   30  hands over to AGW 3   32 , it becomes the anchor AGW for MN 2   30 . Hence, any data destined to MN 2   30  now, i.e. after handoff, gets dropped at AGW 3   32  without being forwarded to HA  20 . AGW 3   32  forwards this packet to MN 2   30 , as AGW 3   32  is the current anchor for MN 2   30 . 
     As discussed above, various network configuration topologies in conjunction with add/drop technique can provide PMIP route optimization. This technique offers several advantages, such as no additional signaling traffic among AGWs and no signaling traffic during mobile node&#39;s handover or handoff is generated, and no Binding Cache Entries at the AGWs for other, non-associated mobiles are required. In order to take the best advantage of this technique, a network with broadcast or multicast capability should be used. A ring-based network that has the ability of using the resilient packet ring is an exemplary embodiment of this approach. 
     Approach 4: Multicasting Binding Cache to AGWs 
       FIG. 10  show an optimization technique that performs route optimization through the use of multicasting binding cache. As with approach 1 described above, in this approach when a mobile node gets anchored with the AGW or PMA  18 ,  26 ,  32 , it sends BU to the HA  20 . Thus, at any point in time, HA  20  maintains a binding cache with a mapping of each mobile node and its respective PMA  18 ,  26 ,  32 . Since the HA  20  is in the local domain, it can multicast its binding cache to all the PMAs (AGWs)  18 ,  26 ,  32  that act as anchors for the respective mobile nodes. HA  20  can use localized scope-based multicast to communicate with the PMAs  18 ,  26 ,  32  that are under the domain of HA  20 . This enables the neighboring AGWs  18 ,  26 ,  32  to have the binding cache entry before any data is transmitted. 
     As shown in  FIG. 10 , when a data from MN 1   10  for MN 2   30  arrives at AGW 1   18 , it can look up the local cache and forward the traffic to the respective anchor PMA, which is AGW 2   26  in this example. As with approach 1, this approach is also applicable to cases when the mobiles are under MAGs that belong to two different LMAs, as shown in  FIG. 11 . Unlike approach 1, however, the first data packet also gets routed through the optimized path, since the AGWs have been updated as part of the proxy binding updates that have been multicast to the AGWs. If additional mobile nodes connect to the AGWs, then binding cache at the HA  20  gets updated, which in turn updates the AGWs by way of localized multicasting. 
     Mobile Nodes in Different Domains 
       FIG. 11  illustrates the path optimization described in approach 1. In the scenario shown in  FIG. 11 , MN 1   10  is in PMIP domain  1   34  while MN 2   30  is in PMIP domain  2   36 . Before path optimization, illustrated by the dotted line, the initial packet from MN 1   10  to MN 2   30  goes to HA 1 /LMA 1   38  in PMIP domain  1   34 . As soon as this packet is received at HA 1   38 , it knows how to forward the packet to HA 2 /LMA 2   40  in PMIP domain  2   36 . HA 2   40  forwards the packet to the gateway associated with MN 2   30 , e.g., AGW 4   42 , and at the same time, HA 2   40  also notifies HA 1   38  who sends a proxy-BU to AGW 1   18  notifying it that AGW 4   42  is the anchored PMA for MN 2   30 . AGW 1   18 , when obtaining this BU, establishes and maintains a cache that maps AGW 4   42  with MN 2   30 . Similarly, AGW 4   42  maintains in its cache that AGW 1   18  has been notified of AGW 4 &#39;s association with MN 2   30 . 
     Because of AGW 1 &#39;s cache, any subsequent packet from MN 1   10  destined to MN 2   30  gets intercepted by AGW 1   18  and is forwarded to AGW 4   42 , instead of being forwarded to either HA 1   38  or HA 2   40 . Hence, the trajectory of the packet becomes: MN 1 →AGW 1 →AGW 4 →MN 2  instead of MN 1 →AGW 1 →HA 1 →HA 2 →AGW 4 →MN 2 . Accordingly, this new, shortened data path optimizes the route of the data packet from MN 1   10  in PMIP domain  1   34  to MN 2   30  in PMIP domain  2   36 . 
       FIG. 12  shows the two data paths, both non-optimized and optimized, from MN 2   30  in PMIP domain  2   36  to MN 1   10  in PMIP domain  2   34  using the binding cache entry-based approach. In the situation illustrated in  FIG. 12 , prior to the BCE optimization procedure, AGW 1   18  has a proxy-BU with HA 1   38 , and AGW 4   42  has a proxy-BU with HA 2   40 . During path optimization from MN 1   10  to MN 2   30 , HA 1   38  sends data to HA 2   40 , along with the parameters of MN 1   10  and AGW 1   18  to maintain the cache in AGW 4   42 . The result is an optimized data path from MN 2   30  destined to MN 1   10  in which the data travels from MN 1   10  to AGW 1   18  in PMIP domain  1   34 , and then the data travels directly from AGW 1   18  to AGW 4   42  and on to MN 2   30  in PMIP domain  2 . 
       FIG. 13  shows the BCE route optimization procedure and optimized route from MN 1   10  in PMIP domain  1   34  to MN 2   30  after MN 2   30  hands over to a new PMA such as AGW 5   44  in PMIP domain  2   36 . In this case, MN 2   30  attaches with AGW 5   44  and sends a proxy-BU to HA 2   40 . At that point, HA 2   40  immediately sends a proxy-BU to AGW 4   42 , since the HA 2   40  has the knowledge of AGW 4   42 . Using its cache, AGW 4   42  in turn sends a proxy-BU informing AGW 1   18  that MN 2   30  is under AGW 5   44 . Thus, both AGW 1   18  and AGW 4   42  are made aware of the fact that MN 2   30  is currently connected to AGW 5   44 . Hence, the optimized data path after handoff is MN 1 →AGW 1 →AGW 5 →MN 2 . 
     Accordingly, as discussed above, route optimization can be achieved for mobile nodes in two separate PMIP domains using approaches 1, 2 and 4 above. 
     While the present invention has been described in particular embodiments, it should be appreciated that the present invention should not be construed as limited by such embodiments, but rather construed according to the claims below.