Abstract:
Methods and apparatus for enhancing Mobile IP (MIP) signaling and to support the use of a novel proxy Co-located Care-of Address (PCCoA) are described. The enhanced MIP signaling adds the ability for the Mobile Node (MN) to acquire a MN specific Foreign Agent (FA) CoA that provides the MN with a topologically correct local address yet whose tunnel encapsulation/decapsulation is provided by the FA. This address is called a proxy CCoA (PCCoA) and the associated processing in the MN and FA is called Proxy CCoA tunneling. This capability is applicable to any access technology but is especially useful for wireless systems where the access bandwidth is expensive and when point-to-point link-layer connectivity exists between the MN and the FA. A method is supported for reverse tunneling and smooth hand-off extensions based on the PCCoA that enables inter-FA forwarding even for CCoAs.

Description:
RELATED APPLICATIONS 
     The present application claims the benefit of the filing date of U.S. Provisional Patent Application No. 60/372,655 filed Apr. 15, 2002 titled “Communications Methods and Apparatus”. 
    
    
     FIELD OF THE INVENTION 
     The present application relates to communications methods and, more particularly, to methods and apparatus for supporting encapsulation and tunnelling between network domains which use different address prefixes. 
     BACKGROUND 
     In Mobile Internet Protocol version 4 (MIPv4), when a Mobile Node (MN) registers with the ‘D’ bit, in the MIP Registration to a Home Agent (HA), then the MN wishes to use a Co-located Care-of address (CCoA) with a specific Home Address (HoA). Packets sent to the MN Home Address (HoA) will then be encapsulated in the CCoA by the HA and forwarded directly to the MN. Alternatively, a MN can obtain from the local Foreign Agent (FA) a shared FA CoA for inclusion in its MIP Registration to the FA/HA. In this case, the HA encapsulates to the FA CoA, and the Foreign Agent then decapsulates and delivers the HoA addressed packet unencapsulated to the MN. 
     Mobile IP (v4/v6), also indicated as MIPv4 [MIPv4] and MIPv6 [MIPv6], enables a mobile node (MN) to register its temporary location indicated by a care-of-address (CoA) to its Home Agent (HA). MIPv6 is described in D. Johnson, C. Perkins, “Mobility Support in IPv6”, Internet-Draft, draft-ietf-mobileip-ipv6-16.txt (work in progress), Mar. 22, 2002. The HA then keeps a mapping (also called a binding) between the MN&#39;s permanent address, otherwise called Home Address (HoA), and the registered CoA so that packets for that MN can be redirected to its current location using IP encapsulation techniques (tunneling). The CoA used by a MN can be an address that belongs to a Foreign Agent (FA) when MIPv4 is used or, in MIPv4 and MIPv6, it can be a temporarily allocated address to the MN itself in which case is called a collocated care-of-address (CCoA). 
     During MIP hand-off, the FAs are generally used to reroute traffic from the old FA (oFA) to the new FA (nFA). This however is only possible from the oFA if the MN was using a FA CoA at that oFA. The oFA can then change the CoA to either a CCoA of a MN or a FA CoA at the new FA. The oFA could also switch CCoAs if it has the necessary state and permissions, and the newFA could also deal with CCoAs if it is able to similarly deal with them correctly. 
     In MIPv4, when a MN registers with the ‘D’ bit, in the MIP Registration to a Home Agent through a Foreign Agent, then the MN wishes to use a Co-located Care-of address (CCoA) with a specific Home Address (HoA). Packets sent to the MN Home Address (HoA) will then be encapsulated in the CCoA by the HA and forwarded directly to the MN via the best route from any FA advertising the subnet of that address. In addition, the MN can use that CCoA as a topologically correct source/destination address for local access on the visited subnet. Different address prefixes are commonly used by different addressing domains. In CCoA based reverse tunneling, the MN can encapsulate the HoA itself into its Co-located Care of Address (CCoA) to cause the packet to be reverse tunneled to the HA. The MN can in addition leave the HoA unencapsulated so that the FA delivers the packet natively and unencapsulated to the destination address. This is known as selective reverse tunneling and is possible whether or not the MN registers via the local FA. 
     Alternatively, a MN can use a shared FA CoA advertised to it by the FA in an Agent Advertisement. In this case, the HA encapsulates to the FA CoA who then decapsulates and delivers the HoA addressed packet natively unencapsulated to the MN. When reverse tunneling, the MN can select during MIP registration between the default Direct Delivery Style and the optional Encapsulating Delivery Style. 
     In Direct Delivery Style, the MN sends packets unencapsulated via the FA using the HoA as a source address, and the FA undertakes the encapsulation of those packets towards the HA using the FA CoA as the source address of the tunnel. 
     In Encapsulating Delivery Style, the MN instead encapsulates packets with the HoA as a source address towards the FA, which after decapsulating, inspects the visitor list and then re-encapsulates into a tunnel with the FA CoA as the source address. In addition, once Encapsulating Delivery Style has been negotiated with the FA, then the MN can selectively bypass reverse tunneling by sending packets unencapsulated from the HoA. 
     MIPv6 has the use of a CCoA by the MN as the normal method of tunneling due to the better address availability and allocation mechanisms compared to IPv4. 
     The MN and the FA in existing MIP specs are therefore able to selectively send and receive packets, either unencapsulated, or encapsulated using the HoA as an inner source/destination address and a CoA as the outer address. When sending unencapsulated between each other, the MN and the FA avoid the additional bandwidth incurred by a tunnel header. By using a FA CoA, the MN is however deprived of a local topologically correct address (so preserving address space) but is able to selectively avoid tunneling over the access link, which is beneficial in cellular and other access systems. By using a CCoA, the MN gets a topologically correct address (where addresses are available) but then incurs the overhead of the additional tunnel header for incoming traffic and during any reverse tunneling operations. The use of a MN specific MIP tunnel address can also be useful for QoS support. What is missing in MIP is the ability for the MN to acquire a MN specific FA CoA that provides the MN with a topologically correct local address yet whose tunnel encaps/decaps is provided by the FA. 
     In view of the above discussion, it can be appreciated that it would be beneficial if a way could be found to provide MNs with an MN specific FA CoA and if ways of using tunnelling with such addresses could be developed which would allow tunnelling using such addresses even though ends of the created tunnels may be in addressing domains which use different address prefixes. 
     SUMMARY OF INVENTION(S) 
     The present invention is directed to methods and apparatus for enhancing mobile communications in the case where a mobile node (MN) is located in a visited network that is in a different addressing domain from the mobile node&#39;s home network. While in the visited network, the visited network&#39;s addressing prefix is used to route packets while packets are routed in the mobile node&#39;s home domain using a different address prefix. 
     The methods of the present invention may be used, and allow for, packets to be routed to/from a mobile node through multiple addressing domains. For example, the mobile node may be in a first addressing domain, the mobile node&#39;s home agent (HA) in a second addressing domain and a correspondence node (CN) with which the MN is communicating in still yet another addressing domain. 
     In accordance with one feature of the invention, MNs are assigned specific FA CoAs called herein Proxy CCoAs. A Proxy Colocated Care of Address (PCCoA), in accordance with the present invention, is a MN specific FA CoA, which provides the MN with a topologically correct local address yet whose tunnel encapsulation/decapsulation is provided by the FA. Proxy CCoAs are designed to enable the FA to manage state in cooperation with the MN so that it can handle the tunnelling for the MN and can deal correctly with forwarded traffic during a hand-off. The associated processing, relating to the PCCoAs, in the MN and FA, in accordance with the present invention, is called Proxy CCoA tunnelling for purposes of discussing the invention. Various features of the invention are also directed to reverse tunnelling and smooth hand-off extensions based on the PCCoA. 
     Use of PCCoAs avoids or reduces encapsulation overhead associated with potentially expensive access links, e.g., wireless links between a mobile node and access node operating as an FA. The negotiation of a PCCoA is a local matter between the MN and the FA and there is no need for a mobile node&#39;s HA to be informed of the optional configuration of the PCCoA capability by the MN on the local FA. The HA can simply detect a MIP request generated in accordance with the invention, via the FA, for CCoA tunnelling. According to Mobile IPv4 [MIPv4] and Reverse Tunneling [RevTun], the HA will expect the following tunneling to occur. MIPv4 is described in detail in C. E. Perkins, Ed., “IP Mobility Support for IPv4,” RFC3220, January 2002. Reverse Tunnelling as referred to in the current context is described in [RevTun] G. Montenegro, Ed., “Reverse Tunnelling for Mobile IP, revised,” Internet RFC 3024, January 2001. 
     The communications methods of the present invention may be applied to systems including a plurality of nodes, e.g., a first node, a second node, a third node and a fourth node. The first node may be, e.g., a mobile node (MN). The second node may be, e.g., the correspondence node (CN) with which said MN is communicating. The CN may be, e.g., another MN or some other network node. The third node may be, e.g., a node which servers as the MN&#39;s foreign agent (FA). The fourth node may be, e.g., a node which operates as the MN&#39;s home agent (HA). Packets communicated between the MN and CN may, in accordance with MIP be routed through the MN&#39;s FA and HA as part of the communication process. The various nodes may be located in different addressing domains, having different addressing prefixes associated with each of the different addressing domains and the nodes located therein. 
     Thus, as packets are communicated between the MN and CN they may pass through multiple addressing domains and, in accordance with the present invention, be subject to various encapsulation/tunnelling operations to overcome problems which can result from different address prefixes being used in the different addressing domains. 
     As part of one exemplary communication process between a mobile node (MN) and a correspondence node (CN), the mobile node transmits a packet towards the CN using a first address that corresponds to the MN as a source address and a second address associated with the CN as a destination address. The third node, e.g., MIP FA intercepts said packet, which not addressed to the FA, and encapsulates it into a tunnel using a third address which serves as the source address of the tunnel. The third address has a first prefix which is associated with the MIP FA, e.g., corresponds to the addressing domain in which the MIP FA is located. The third address is not however a shared FA CoA but has been assigned to the MN as an interface address which may therefore be used as a Colocated Care of Address (CCoA). As part of the encapsulation process, a fourth address corresponding to a fourth node, e.g., the MN&#39;s HA, is added to the packet being encapsulated. This fourth address serves as a destination address of the tunnel. Thus, packets may be tunnelled between the MN&#39;s FA and HA. In such an embodiment the first address corresponding to the MN includes an address prefix which corresponds to the HA, e.g., corresponds to the address prefix used by the addressing domain in which the HA is located. This address prefix may be called a second address prefix simply to distinguish it from the first address prefix associated with the addressing domain in which the FA is located. The first and second prefixes will be different in those cases where the FA and HA are located in different addressing domains as is often the case. Note that in this example the address used by the MN while in the first addressing domain as a source address when sending a packet to the CN is an address which included the address prefix corresponding to the HA&#39;s domain rather than the FA&#39;s domain. 
     The third address, i.e., the tunnel source address may be a co-located care of address (CCoA). In addition to forwarding packets towards the CN, the FA may receive and transmit packets to the MN. The packets may be unencapsulated packets originating from the CN but which were encapsulated by the HA for transmission to the MN&#39;s CCoA via the FA. Each encapsulated packet may include an inner packet having said second address as a source address and the first address associated with the MN as a destination address. The FA intercepts and decapsulates the inner packets and forwards them to the first node despite the fact that the first address includes an address prefix corresponding to the addressing domain of the HA. 
     An addressing table in the FA may be used to facilitate this decapsulation and forwarding process. The addressing table identifies the mac-layer address of the interface of each MN and the associated PCCoA address of each MN. The FA inspects the destination address of the tunnel to find the PCCoA, determines the mac-address of the MN, and forwards the decapsulated packets to that mac-address in point to point link layer frames. This addressing table can also assist with upstream traffic from the MN to the CN as the incoming mac_address of the MN can be used by the FA to determine the required PCCoA to be used as a source address for the tunnel to the HA. If the home address of the MN is also stored at the FA in this table, then this address can also be inspected to determine the correct PCCoA and mac_layer addresses. 
     In a further embodiment of the invention, the MN can send unencapsulated packets over the access link, with the home address as a source address and a multicast destination address, towards a group of CNs who are members of that group. The FA can then encapsulate into the PCCoA to HA tunnel by again using either the mac_address of the MN or the home address to identify the correct PCCoA. The packets over the access link must use a point to point link to the FA to avoid being received by members of that group on that access link. Similarly, the CN can send packets towards a multicast group of which the MN is a member at its HA, causing the HA to encapsulate these packets to the PCCoA of the MN which is intercepted and decapsualted by the FA. The FA uses the incoming PCCoA to identify the destination MN and its mac_layer address, before forwarding unencapsulated into a point to point link to the MN. The point to point link again avoids the multicast packets being received by other members of that group on the access link. 
     In a further embodiment of the invention, a MIP signal is used between the MN and the FA to request that the FA undertake tunnel management for the CCoA of the MN, which converts it into a PCCoA. The FA can agree to this request with a reply message, if it supports the PCCoA capabilities of the invention, and then the MN can safely send unencapsulated packets towards the CN via the FA, which will then undertake the tunnelling. In addition, the MN will expect to receive unencapsulated packets from the CN via the FA which will be undertaking the decapsulation on behalf of the MN. 
     In a further embodiment of the invention, the Mnc an decide to use CCoA forwarding in the FA (ie undertake tunnel management itself), but use a hand-off signal to the FA to cause it to temporarily move to PCCoA processing so that it, rather than the MN can undertake the forwarding of in-flight packets to the new CoA of the MN at the next FA. This new CoA is the fifth address of the invention from an access node that is the fifth node. During a hand-off, the table mapping no longer points to the mac_address of the MN but is instead populated with the fifth address so that the encapsulation can be triggered before sending the packet to the new CoA. The PCCoA processing enables the FA to decapsulate from the old PCCoA and then re-encapsulate into the new CoA, which could be either a FA CoA, a CCoA or a PCCoA. If the new CoA is a FA CoA then the old FA may use the old PCCoA as the source address for the tunnel towards the access node so that the access node can uniquely map that tunnel to the MN at the access node (the fifth node). Alternatively, the fifth node can use the Home address of the inner packet to identify the MN. 
     In the final embodiment of the invention, the MN has been assigned the CCoA as an interface address at the FA and so may use that as a source/destination address for communication with the CN which does not require the use of the home agent or associated tunnelling. For packets sent from the MN, the FA must detect that the PCCoA is associated with an unencapsulated packet and to therefore simply send it towards the CN rather than encapsulating it into a tunnel to the HA. For packets from the CN to the MN, the packets will arrive unencapsulated to the FA which must therefore not attempt to decapsulate the packet but should simply map between the PCCoA and the mac_address of the associated MN before forwarding to the packet via the link layer to that MN. 
     The concepts and solutions described here are applicable to both MIPv4 and MIPv6 unless otherwise mentioned. While IPv6 does not have the notion of a Foreign Agent, an access router could be modified in accordance with the invention to support a MIP Attendant or other Local Mobility Agent to undertake the PCCoA functionality defined of the present invention, described in the context of an FA. 
     In MIP v6 hand-off, the option of receiving a Binding Update (BU) including a new FA CoA is not possible and the new CoA can only be either a CCoA or a PCCoA. A MN in MIPv6 can selectively reverse tunnel simply by the use or absence of the CCoA encapsulation to the HA but this option is lost with a PCCoA because the FA will always encapsulate packets into the PCCoA for tunnelling to the HA, although a classifier could be used to select PCCoA processing in the FA for only a subset of packet flows. 
     The present summary describes some of the features, embodiments and benefits of the methods and apparatus of the present invention, numerous additional features, embodiments and benefits are discussed in the detailed description which follows. 
    
    
     
       DESCRIPTION OF THE FIGURES 
         FIG. 1  illustrates an exemplary access node implemented in accordance with the present invention. 
         FIG. 2  illustrates an exemplary end node implemented in accordance with the present invention. 
         FIG. 3  illustrates the contents of visitor list state which are exemplary of the visitor list state shown in  FIGS. 1 ,  2 , and  4 . 
         FIG. 4  illustrates an exemplary mobility agent node implemented in accordance with the present invention. 
         FIG. 5  illustrates a network diagram of an exemplary communications system in which the invention is applicable. 
         FIG. 6  illustrates exemplary signaling and packet flows for the network of  FIG. 5 . 
         FIGS. 7A through 7C , referred to collectively as  FIG. 7 , illustrate PCCoA processing and packet forwarding for unicast packet flows. 
         FIGS. 8A through 8C , referred to collectively as  FIG. 8 , illustrate PCCoA processing and packet forwarding for multicast traffic. 
         FIG. 9  illustrates PCCoA processing and packet forwarding for a hand-off between two foreign mobility agents. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an exemplary access node  12 , e.g., access router or base station, implemented in accordance with the invention. The access node  12  includes antennas  203 ,  205  and corresponding receiver, transmitter circuitry  202 ,  204 , respectively. The receiver circuitry  202  includes a decoder  233  while the transmitter circuitry  204  includes an encoder  235 . The circuitry  202 ,  204  is coupled by a bus  230  to an I/O interface  208 , a processor (e.g., CPU)  206  and memory  210 . The I/O interface  208  couples the access node  12 , e.g., base station, to the Internet. The memory  210  includes routines, which when executed by the processor  206 , cause the access node  12  to operate in accordance with the invention. Memory includes communications routines  223  used for controlling the access node  12  to perform various communications operations and implement various communications protocols. The memory  210  also includes an access node control routine  225  used to control the access node&#39;s  12 , e.g. base station&#39;s, operation and signaling to implement the steps of the method of the present invention. The access node control routine  225  includes a scheduler module  222  used to control transmission scheduling and/or communication resource allocation. Thus, module  222  may serve as a scheduler. The memory  210  also includes a mobility agent module  226  used to process and send mobility related signaling implementing the steps of the method of the present invention. Thus, module  226  may serve as a Mobile IP Foreign Agent. Memory  210  also includes information  212  used by communications routines  223 , control routine  225  and mobility agent module  226 . The information  212  includes an entry  213 ,  213 ′ for each active end node, which includes a list of the active sessions  243 ,  243 ′ being conducted by the end node and includes tunneling state associated with said end node. In particular, information for end node 1  213  includes active session list  243 , listing exemplary sessions A and B. Information for end node 1  213  also includes visitor list state  214 , shown in detail in  FIG. 3 . Information about end node N  213 ′ as depicted in  FIG. 1  includes exemplary session X  243 ′ and also includes visitor list state  214 ′, shown in detail in  FIG. 3 . 
       FIG. 2  illustrates an exemplary end node  14  implemented in accordance with the present invention. The end node  14  may be used by a user as a mobile terminal (MT). The end node  14  includes receiver and transmitter antennas  303 ,  305  which are coupled to receiver and transmitter circuitry  302 ,  304  respectively. The receiver circuitry  302  includes a decoder  333  while the transmitter circuitry  304  includes an encoder  335 . The receiver transmitter circuits  302 ,  304  are coupled by a bus  308  to a memory  310  and a processor  306 . Processor  306 , under control of one or more routines stored in memory  310 , causes the end node  14  to operate in accordance with the methods of the present invention. In order to control operation of the end node  14 , memory  310  includes communications routine  323  and end node control routine  325 . The end node communications routine  323  is used for controlling the end node  14  to perform various communications operations and implement various communications protocols. The end node control routine  325  is responsible for insuring that the end node operates in accordance with the methods of the present invention and performs the steps described in regard to end node operations and signaling. The memory  310  also includes user/device/session/resource information  312  which may be accessed and used to implement the methods of the present invention and/or data structures used to implement the invention. In particular, User/Device/Session/Resource information  312  includes MIP visitor state information  313  described in detail in  FIG. 3 . 
       FIG. 3  illustrates exemplary tunnel state  100 , associated with a given mobility agent. The exemplary tunnel state  100  may be used as visitor state  414  or  414 ′ of  FIG. 4 , the visitor list state  214 ,  214 ′ shown in  FIG. 1 , and visitor list state  313  shown in  FIG. 2 . The visitor list state  100  is sometimes called a visitor list table since it includes a plurality of visitor list entries that can be accessed using table access techniques. From the perspective of the access node  12  and the end node  14  of  FIGS. 1 and 2  respectively visitor list state  100  may include a number of tunnel state entries  110 ,  120 . 
     According to this invention Visitor state  100  includes entries for at least one MN  14 , each entry including state for the MN home address (HoA)  112 , a Home Agent address  115 , a CCoA  116 , a lifetime  113 , and mac-layer addresses  114  of the link between the MN  14  and the Access Node (e.g., Foreign Agent)  12 . The mac-layer addresses  114  are used for forwarding. The visitor list state  100  can also include information on the multicast group membership of the MN  14  so that multicast packets to and from the MN  14  can be policed and forwarded. 
     The visitor list entry also includes according to this invention a MN to FA tunnel state  110  which includes a PCCoA flag  118  and PCCoA configuration state  119 . The setting of the PCCoA flag indicates that the CCoA address  116  is converted to a PCCoA address for traffic from the MN  14 , and tunneling should be performed according to the PCCoA configuration  119 . The Foreign Agent (FA)  12  and not the MN  14  will then add the encapsulation to packets from the MN home address  112 , said encapsulation having a PCCoA source address  116  and a HA destination address  115 . Lifetime  113  is a timer associated with said visitor list state  100 . When lifetime  113  expires visitor state regarding MN  14  with home address  112  is removed. 
     The visitor list entry also includes according to this invention the FA to MN tunnel state  120  which includes a PCCoA flag  128  and PCCoA configuration state  129 . The setting of the PCCoA flag indicates that the CCoA address  116  is converted to a PCCoA address for traffic to the MN  14 , and detunneling should be performed according to the PCCoA configuration  129 . The FA  12  and not the MN  14  will then remove the encapsulation on packets to the MN home address  112 , said encapsulation having a PCCoA destination address  116  and a HA source address  115 . 
       FIG. 4  illustrates an exemplary home mobility agent node  15  implemented in accordance with the invention. The mobility agent node  15  includes a bus  430  that couples together an I/O interface  408 , a processor (e.g., CPU)  406  and memory  410 . The I/O interface  408  couples the mobility agent node  15  to the Internet. The memory  410  includes routines, which when executed by the processor  406 , cause the mobility agent node  15  to operate in accordance with the invention. Memory  410  includes communications routines  423  used for controlling the mobility agent node  15  to perform various communications operations and implement various communications protocols. The memory  410  also includes a mobility agent control routine  425  used to control the mobility agent node&#39;s  15  operation and signaling to implement the steps of the method of the present invention. The mobility agent node control routine  425  includes a scheduler module  422  used to control transmission scheduling and/or communication resource allocation. Thus, module  422  may serve as a scheduler. The memory  410  also includes a mobility agent module  426  used to process and send mobility related signaling implementing the steps of the method of the present invention. Thus, module  426  may serve as a Mobile IP Home Agent. Memory  410  also includes information  412  used by communications routines  423 , control routine  425  and mobility agent module  426 . The information  412  includes an entry  413 ,  413 ′ for each active end node (MN 1 ,MNn). In particular, information for end node 1  413  includes visitor state  414 , shown in detail in  FIG. 3 . Information about end node N  413 ′ includes visitor state  414 ′ also shown in detail in  FIG. 3 , with the exception that the presence of the PCCoA flags ( 118 ,  128 ) is optional. This is because the PCCoA functionality is provided between the End Node  14  and the Access Node  12 , does not need the assistance of the Home Agent  15  to invoke that functionality, and can be successfully implemented even when the Home Agent  15  otherwise believes that a traditional CCoA is being used by the End Node  14 . Knowledge of the implementation of the PCCoA functionality may however be provided to the Home Agent  15  for management and policy purposes. 
       FIG. 5  illustrates an exemplary system  500  comprising a plurality of access nodes  505 ,  505 ′,  505 ″ implemented in accordance with the present invention.  FIG. 5  also depicts communication cells  501 ,  501 ′,  501 ″ surrounding each access node  505 ,  505 ′,  505 ″, respectively, which represents the coverage area of corresponding access node  505 ,  505 ′,  505 ″, respectively. The same physical and functional elements are depicted in each of the communication cells ( 501 ,  501 ′,  501 ″), thus the following description of the elements in the cell  501  surrounding access node  505  is directly applicable to each of the cells  501 ,  501 ′,  501 ″. The depiction of the access node  505  is a simplified representation of the access node  12  depicted in  FIG. 1 . For simplicity access node  505  is shown to include a mobility agent module  507  (corresponding to mobility agent module  226  of  FIG. 1 ) responsible for the signaling implementing this present invention.  FIG. 5  illustrates the access node  505  providing connectivity to a plurality of N end nodes  502 ,  504  (EN1, ENn) via corresponding access link  506 ,  508 . End nodes  502 ,  504  are simplified versions of the end node  14  depicted in  FIG. 2 . End nodes  502 ,  504  may be, for example, mobile nodes (MNs) and links  506 ,  508  may be, for example, wireless links. 
     Interconnectivity between the access nodes  505 ,  505 ′,  505 ″ is provided through network links  510 ,  511 ,  512  and an intermediate network node  520 . Home network  530  in  FIG. 5  is coupled to the rest of the system  500  via link  522  and intermediate node  520 . Home Network  530  further includes a network node  536  also connected to link  522  and a mobility agent node  532 , connected to node  536  via link  538 . Mobility Agent node  532  operates as mobility agent of at least end node N  504 . Network  540  in  FIG. 5  is coupled to the rest of the system  500  via link  523  and node  520 . Network  530  further includes network node  546  also connected to link  523  and a correspondent node (CN)  542 , connected to node  546  via link  548 . CN  542  operates as corresponding node in a data session with at least end node N  504  for illustration of the methods of this present invention. 
       FIGS. 6-9  illustrate exemplary embodiments of the various methods of this present invention.  FIGS. 6-9  are simplified versions of the system  FIG. 5  showing elements of  FIG. 5 , as needed, to further explain the present invention.  FIG. 6  shows access nodes  505 ,  505 ′, including mobility agent modules  507 ,  507 ′, providing access to end node N  504 .  FIG. 6  also shows home mobility agent node  532  serving end node  504  and a CN node  542  being in a communication session with said end node  504 . In  FIG. 6 . solid thin arrows depict data traffic and the direction of the arrow points to the destination of said data traffic; thick solid lines depict tunnels and the direction of the arrow points to the destination of said tunnel; dashed lines depict signaling messages used for the registration of exemplary end node N  504  to the access node  505  with foreign mobility agent module  507  and the home mobility agent node  532 , and the direction of the arrow points to the destination of said signaling. 
     In  FIG. 6  end node  504  sends registration request signal  601 , including at least the address of the end node  504 , the address of the mobility agent node  532 , the address of the access node  505 , an indication that the MN  504  is using a CCoA, and an additional indication that forward and reverse tunneling is required using a PCCoA, between the access node  505  and the home mobility agent  532 . Access node  505  processes signal  601  via foreign mobility agent module  507 , accepting the request for PCCoA functionality, setting the PCCoA flags  118 ,  128 , and then forwarding registration request signal  602 , also including at least a portion of the information included in signal  601 , to mobility agent node  532 . This portion may optionally include an indication of the setting up of the PCCoA functionality between the end node  504  and the access node  505 . 
     Home Mobility agent node  532  receives signal  602  and sets up CCoA tunnel state associated with said end node  504  in its visitor state  414 ′ of  FIG. 4 . Said CCoA tunnel state includes state for outgoing tunnel  610  (forwarding direction) and state for incoming tunnel  611  (incoming direction) according to the contents of message  602 . Packets  610   p  move through tunnel  610 ; packets  611   p  move through tunnel  611 . Packets  610   p  originate from packets  616  which are sent from the CN  542  towards the home address of the end node N  504 . These are received at the home agent  532  which encapsulates them into tunnel  610 . Similarly, packets  611   p  arrive at the home agent  532  where they are decapsulated to produce packets  615  towards the CN  542 . 
     The source address of the outgoing tunnel  610  is set to the address of the mobility agent  532  and the destination address of the outgoing tunnel  610  is set to the CCoA of end node  504  while a lifetime  113  is associated with said state. The source address of the incoming tunnel  611  is set to the CCoA of the end node  504  and the destination address of the incoming tunnel  611  is set to the address of home mobility agent  532  while a lifetime  113  is associated with said state. Signal  603  is returned to the foreign mobility agent  507  to confirm the installation of the CCoA tunnel between the home mobility agent  532  and the CCoA of the end node  504 . Signal  604  is then sent between the foreign mobility agent  507  and the end node  504  to confirm the acceptance of the registration and the specific installation of PCCoA processing for the home address of the end node  504 , at the foreign mobility agent  507 . Note that CCoA tunneling should otherwise result in a tunnel between the end node  504  and the home mobility agent  532 . 
     The PCCoA processing at the foreign mobility agent  507 , for traffic from the foreign mobility agent  507  to the end node  504 , intercepts tunnel  610  that would normally terminate on the end node  504 , decapsulates the inner packet from the tunnel  610 , and then forwards the inner packet  617  within a point to point mac-layer link to the end node  504  that owns the CCoA from which the inner packet was decapsulated. 
     The PCCoA processing at the foreign mobility agent  507 , for traffic to the foreign mobility agent  507  from the end node  504 , receives the inner packet  614  within a point to point mac-layer link from the end node  504 , encapsulates the inner packet  614  in a tunnel  611  to the home mobility agent  532 , using the CCoA that matches the mac-layer address of the sending end node  504  as a source address, and the address of the home mobility agent  532  as a destination address. The PCCoA processing is described in detail in  FIGS. 7-8 . 
     Continuing with  FIG. 6 , during a hand-off between access nodes  505 ,  505 ′, the end node  504  can send signal  601  to the old access node  505  to trigger signal  624  to the new access node  505 ′, or can send signal  626  to the new access node  505 ′ to trigger signal  622  to the old access node  505 . Either sequence of signals can be used to redirect packets  614 ,  617  from the mac-layer link between the end node  505  and the old access router  505 , to the mac-layer link between the end node  504  and the new access node  505 ′, becoming packets  620   p  and then packets  621  for packets towards the MN  504 . The signals  601  or  622  include a request for PCCoA processing at the old access node (router)  505 , and therefore can cause the old access node  505  to temporarily invoke PCCoA processing, during the hand-off, for packets addressed to the CCoA of the end node  504 . This causes the old access node  505  to decapsulate packets addressed to the CCoA of the end node  504  that is undertaking the hand-off, and then re-encapsulate into the new CCoA of the end node  504  at the new access node  505 ′. If the end node  504  was already employing PCCoA functionality at the old access node  505  then the signals  601  or  622  simply redirect the forwarding of the unencapsulated packet, from the mac-layer link between the old access node  505  and the end node  504 , to an IP tunnel  620  between the old access node  505  and the new CCoA of the end node  504  via the new access node  505 ′. Note that either signal  624  (from old access node  505  to new access node  505 ′) or  626  (from EN  504  to new access node  505 ′) can, as part of this hand-off sequence, additionally invoke PCCoA processing in the new access node  505 ′, which will detunnel packets addressed to the new CCoA that arrive at the new access node  505 ′, such as packets  620   p , and forwarding them to the end node  504  over the mac-layer link that exists between the new access node  505 ′ and that end node  504 . 
       FIG. 7  shows the PCCoA processing in detail for unicast packets that are sent between the MN  504  and a CN  542 .  FIG. 7  shows the end node, e.g. Mobile Mode (MN)  504 , the Foreign Agent (FA) Node  505 , the home mobility agent (HA)  532  and the Correspondent Node (CN)  542 .  FIG. 7  is the composite of  FIGS. 7   a ,  7   b ,  7   c  showing exemplary cases A, B, C respectively. 
     In case A of  FIG. 7   a , a unicast packet flow is shown from the home address  112  of the MN  504  to CN address  542   a , the address of CN  542 . The packet flow is broken up into three sections. Between the MN  504  and the FA  505 , packets  614  are transmitted within mac-layer frames using point to point mac-layer addresses  114  (MN Mac address  114 ′, FA Mac address  114 ″) of the MN  504  and the FA  505 . The mobility agent module  507  maps the source address of the mac-link frames to the PCCoA of the MN  504  that owns that mac-layer source address, and then encapsulates the packet  614  into the tunnel  611   p . The HA  532  then decapsulates these packets and forwards them to the CN  542  as packets  615 . 
     In case B of  FIG. 7   b , a unicast packet flow is shown to the home address  112  of the MN  504  from the CN  542 . The packet flow is broken up into three sections. The HA  532  encapsulates packets  616  received from the CN  542  that are addressed to the home address  112 , in the CCoA that has been registered in the HA  532  for that home address  112 . The HA  532  then sends encapsulated packets  610   p  to the FA  505 . These are received by the mobility agent module  507  in the FA  505  which decapsulates the packets  610   p  and maps the PCCoA destination address  116  from the tunnel  610  into the destination mac-layer link address  114 ′ of the of the MN  504  that owns that PCCoA address. The FA  505  then sends the packets  617  to the MN  504  in point to point mac-layer frames using that destination mac-layer address  114 ′ of the MN  504 . 
     In case C of  FIG. 7   c , the MN  504  can use the PCCoA (from FA  505 )  116  as a normal CCoA source and destination address for communications with CN  542 , rather than using the home address  112  (from HA  532 ) as in  FIGS. 7   a  and  7   b . Packets  712  flow from MN  504  to FA  505 , while packets  713  flow between FA  505  and MN  504 . Between the MN  504  and the FA  505 , packets  712 ,  713  are transmitted within mac-layer frames using point to point mac-layer addresses  114  (MN Mac address  114 ′, FA Mac address  114 ″) of the MN  504  and the FA  507 . Packet flow  718  (from FA  505  to CN  542 ),  719  (from CN  542  to FA  507 ) does not visit the HA  532  as in  FIGS. 7   a  and  7   b , but only visits the mobility module  507  in FA  505  directly where it is mapped into and out of mac-frames as part of point to point link between the FA  505  and the MN  504  that has been assigned that PCCoA  116 . 
     Therefore, the mobility agent module  507  encapsulates and decapsulates into the PCCoA  116  for the MN  504 , when the MN  504  is using the home address  112  for communications with the CN  542  as in  FIGS. 7   a  and  7   b . In contrast, this encapsulation and decapsulation into the PCCoA  116  by the mobility agent module  507  of FA  505  is not required in case C of  FIG. 7   c  where the MN  504  is using the PCCoA address  116  for communications with CN  542 . 
     In  FIG. 8 , the PCCoA processing of the invention is further described for multicast traffic flows between the MN  504  and the CN  542 .  FIG. 8  is the composite of  FIG. 8   a ,  FIG. 8   b , and  FIG. 8   c  showing exemplary cases D, E, and F respectively. 
     In case D of  FIG. 8   a , a multicast packet flow is shown from the home address  112  of the MN  504  to the CN  542  that is a member of the multicast group whose multicast group address  117  is inserted into the destination address of packets in that flow. The packet flow is broken up into three sections. Between the MN  504  and the FA  5057814  are transmitted within mac-layer frames using point to point mac-layer addresses,  114  ( 114 ′,  114 ″) of the MN  504  and the FA  505 , rather than multicast addresses. The mobility agent module  507  maps the source address of the mac-link frames to the PCCoA of the MN  504  that owns that mac-layer source address, and then encapsulates the packet  814  into the tunnel from the PCCoA address  116  to the HA address  115  of the HA  532 , so producing packets  811   p . The HA  532  then decapsulates these packets  811   p  and forwards them to the CN  542  as packets  815  via multicast routing. 
     In case E of  FIG. 8   b , a multicast packet flow is shown being forwarded to the MN  504  from the CN  542 , when the MN  504  is a member of the multicast address  117  that the CN  542  inserts into the destination address of the packets in that packet flow. The packet flow is broken up into three sections. The HA  532  encapsulates packets  816  received from the CN  542  that are addressed to the multicast group address  117 , in the CCoA that has been registered in the HA  532  for the MN  504 . The HA  532  then sends encapsulated packets  810   p  to the FA  505 . These are received by the mobility agent module  507  in the FA  505  which decapsulates the packets  810   p  and maps the PCCoA destination address  116  from the tunnel into the destination mac-layer link address of the of the MN  504  that owns that PCCoA address  116 . The FA  505  then sends the multicast packets  817  to the MN  504  in point to point mac-layer frames, rather than multicast frames, using that destination mac-layer address  114 ′ of the MN  504 . The use of point to point mac-frames is required to ensure that only the target MN  504  from HA  532  with home address  112  can receive the multicast packet  817 . 
     In case F of  FIG. 8   c , the MN  504  can use the PCCoA  116  as a normal CCoA source address for multicast communications with a CN  542  that is the member of a multicast group whose multicast address  117  is inserted into the destination address of a packet  812  by the MN  504 . This packet flow  812  (from MN  504  to FA  505 ),  818  (from FA  505  to CN  542 ) does not visit the HA  532  but only visits the mobility module  507  in FA  505  directly where packets  812  are mapped out of mac-frames as part of point to point link between the MN  504  with MN Mac Address  114 ′, that has been assigned that PCCoA  116  and the FA  505  with FA Mac Address  114 ″. 
     Therefore, the mobility agent module  507  encapsulates packets into a tunnel with a PCCoA source address  116  for the MN  504 , when the MN  504  sends packets with a home address  112  as a source address as in case D of  FIG. 8   a . In contrast, this encapsulation of packets by module  507  of FA  505  is not required in case F of  FIG. 8   c  where the MN  504  is using the PCCoA address  116  for communications with CN  542 . 
       FIG. 9  shows the PCCoA processing and packet forwarding during a hand-off when the MN  504  moves between FA  505 , where the MN  504  is assigned CCoA1  116 , and FA  505 ′, where the MN  504  is assigned CCoA2  2116 . In case G of  FIG. 9 , the unicast packet flow is shown to the home address  112  of the MN  504  from the CN  542 . The packet flow is broken up into three sections. The HA  532  encapsulates packets  616  received from the CN  542  that are addressed to the home address  112 , in the CCoA1  116  that has been registered in the HA  532  for that home address  112 . The HA  532  then sends encapsulated packets  610   p  to the FA  505 . These are received by the mobility agent module  507  in the FA  505  which before the hand-off either forwards the packets directly to the MN  504  or applies PCCoA processing as described in case B. During the hand-off however, the MN  504  obtains a PCCoA1  116  from the FA  505  and a PCCoA2  2116  from the FA  505 ′. The FA  505  then decapsulates the packets  610   p  and maps the PCCoA1  116  destination address from the tunnel  610  into another tunnel  620  with PCCoA2  2116  as the destination address and the address of FA  505 ,  505   a , as a source address. This mapping is stored in the visitor list state in FA  505 . The FA  505  then sends the packets  620   p  to the FA  505 ′ where they are received by the mobility agent module  507 ′ in the FA  505 ′. The FA  505 ′ then decapsulates the packets  620   p  and maps the PCCoA2  2116  destination address from the tunnel  620  into the destination mac-layer link address of the MN  504  that owns that PCCoA2 address  2116 . The FA  505 ′ then sends the packets  621  to the MN  504  in point to point mac-layer frames using that destination mac-layer address  114 ′ of the MN  504 . The PCCoA processing in the FAs  505  and  505 ′ is installed using MIP hand-off signaling and lasts as long as the lifetime  113   5  avoids a double encapsulation wherein the FA  505  would further encapsulate the tunnel packet  610   p  destined to CCoA1  116  in a header with PCCoA2  2116  as a destination address. 
     Various modifications and additional signaling features are possible in accordance with the present invention. Some additional possible embodiments and signaling features will now be discussed. 
     In accordance with various embodiments of the invention, an HA will encapsulate permitted unicast, multicast and broadcast packets, intended for the MN HoA, with the CCoA included within the associated MIP Registrations. The HA then sends the packets to this CCoA from the source address of the HA. If reverse tunneling is enabled then the HA will decapsulate all permitted unicast, multicast and broadcast packets that are tunneled from the CCoA to the HA address, with the inner source address matching the HoA of the MN. 
     From the perspective of the HA, the CCoA is located at the MN and so requires the MIP signaling to have the ‘D’ bit set. However, as far as the FA is concerned the CoA is actually a PCCoA, which as far as Internet routing is concerned can be considered to be a MN specific FA CoA. The MN that is allocated this address is on a link-layer directly attached to the FA and so the FA can also enable the MN to make use of this MN specific FA CoA as a source/destination address for local communications. Therefore, the HA sees the PCCoA as a CCoA, the FA sees the PCCoA as a special MN specific FA CoA and the MN treats the PCCoA as an ordinary interface address. A specific implementation of the PCCoA process would be to simply move the tunnel/detunneling process to the other end of the link (from the MN to the FA) but in all other ways treat the address as a CCoA. This is then a link specific change in much the same way that header compression is a link specific function. 
     Proxy CCoA tunneling is therefore possible in MIP if the MN obtains a CCoA from the FA subnet, the MN then registers for PCCoA service via the FA, and that FA is able to support PCCoA processing for that CCoA. The HA forwarding and tunnel processing is unaffected by the changes proposed here. The availability of the PCCoA capability is advertised by the FA in a FAA, by setting the new ‘P’ bit, or could be triggered via an MIP extension, configuration, PPP, DHCP or other signaling. To request PCCoA service, the MN should register via the FA, whether or not this is mandated by the FAA ‘R’ bit, so that the FA can undertake correct PCCoA processing. The MN can be allocated a PCCoA either by a unicasted MIP FAA that includes a MN specific FA CoA, through a DHCP server with a FA specific prefix, or by any other means that can ensure the address is uniquely bound to a MN on the FA. 
     Proxy CCoA tunnelling is negotiated, in some embodiments, by the MN by including the Proxy CCoA extension in the MIP Registration as well as setting the ‘D’ flag used to signal the use of a CCoA. This structure is used so that the FA can remove the PCCoA extension whilst leaving the ‘D’ bit so that the HA will continue to treat the MN as if it had a CCoA. In the future, if HAs require knowledge of the PCCoA mechanism, and sufficient deployment has/will occur, then the extension mechanism could be replaced by instead assigning and setting a new ‘P’ flag bit (proxy CCoA) in the MIP Registration, as well as setting the ‘D’ bit (CCoA). Such implementations are to be considered within the scope of the invention. 
     The MIP CCoA Registration, is acknowledged by the HA and then the FA in the MIP Reply causes the FA to store both the HoA and the PCCoA in the visitor list for that MN. Both the HoA and the PCCoA can be used as source/destination addresses to/from the MN. The HoA is used for remote access to/from the HA whilst the PCCoA can be used for topologically correct local access whilst the MN remains at that FA. 
     Downlink Forwarding as implemented in various embodiments will now be discussed. 
     Downlink packets addressed to the HoA, arrive at the FA via the HA, encapsulated in the PCCoA of the MN. Downlink packets (local traffic using the PCCoA as a source/dest address) otherwise arrive directly, and unencapsulated, at the FA. The FA inspects the PCCoA and searches for it in a visitor list maintained by the FA. If the packet is unencapsulated then it is simply forwarded to the owning MN. If the packet is encapsulated then it is first decapsulated and the inner unicast destination header inspected to ensure it matches the HoA state for that MN. If the decapsulated packet is broadcast/multicast, and the MIP flags for that MN have requested broadcast traffic and/or the MN is a member of that multicast group, then the packet is forwarded unencapsulated to the MN over a point-to-point access medium but must be sent in its encapsulated form over a broadcast medium. 
     Uplink forwarding and reverse tunnelling will now be discussed. Uplink unicast packets from the HoA are sent unencapsulated via the FA and injected into the routing fabric unencapsulated. In the case of reverse tunneling, the FA encapsulates the permitted unicast, broadcast and multicast packets with the PCCoA of the MN as the tunnel source address, and HA as the tunnel destination address. This is so that the packets will match the registered binding in the HA. Broadcast/multicast packets sent over a broadcast access medium must be encapsulated in the HoA source address and sent to the shared FA CoA where they are decapsulated, the visitor list and group membership for that MN inspected, and permitted packets re-encapsulated to the HA as before using the PCCoA. Note that with proxy CCoA tunneling the option for selective reverse tunneling from the MN is lost. However, this ability can be re-instated if the MN provides the FA with a classifier that specifically defines which of the MNs uplink traffic should not be reverse tunneled. This is achieved by first selecting Reverse tunneling for a specific HoA by setting the ‘T’ bit as normal in the MIP Registration, and then including a set of excluded classifiers in the form of quintuples describing the uplink unicast header. 
     PCCoAs and smooth Hand-offs will now be discussed. Smooth hand-offs [RoutOp] enable a MN that was previously registered at the old Foreign Agent (oFA) with an oFA CoA, to request the forwarding of packets, sent to the MN HoA and decapsulated from the oFA HoA, to the MNs new CoA. RoutOp refers to C. Perkins, D. Johnson, “Route Optimization in Mobile IP”, Internet-Draft, draft-ietf-mobileip-optim-11.txt (work in progress), Sep. 6, 2001. 
     This means however, that smooth hand-offs are not supported for a MN with a CCoA that is either registered or unregistered at the oFA. This is because a FA is not allowed to decapsulate from the oCCoA and forward to the new CoA at the new point of attachment. Smooth forwarding could be supported by instead having the oFA additionally encapsulate the oCCoA to the nCoA but this clearly adds overhead and requires the nFA to have knowledge of the oCCoA to correctly forward in the case of the MN acquiring a nFA CoA. 
     The PCCoA capability in contrast brings the required functionality to the FA to support the smooth forwarding of CCoAs, if the MN registered via the oFA, irrespective of whether or not the MN is using a CCoA or a PCCoA. In the case of a normal CCoA, the FA can still transiently support the PCCoA capability and automatically transition the CCoA to a PCCoA when the BU is received from the nFA or directly from the MN. This is possible when the CCoA is uniquely advertised by that FA. The incoming BU that includes the nCoA will then create a binding between the HoA (and indirectly the oCCoA) and the nCCoA, such that the oFA can decapsulate everything from the oCCoA and re-encapsulate into the nCoA before forwarding. Broadcast/multicast traffic is handled by checking the MIP flags and the HoA group membership and re-encapsulating all permitted packets. The oFA will also encapsulate into the nCoA all packets that are received unencapsulated with a destination address equal to the oCCoA (local traffic using the oCCoA as a network address) during the shorter of the lifetime of the smooth hand-off or the delay until the oCCoA is re-allocated. The request to trigger transient PCCoA support is implicit at the oFA on the reception of a BU. In the case of a MN that was using a PCCoA at the oFA, the meaning of the BU is again implicit and the oFA simply proceeds as for the oCCoA after the PCCoA transition. 
     If the BU is from the MN then it is for a CCoA at a MN that is not registering via the nFA. This however does not affect this hand-off but will affect subsequent hand-offs because the PCCoA transient forwarding is only possible if a MN registers via a FA. If the BU is originated by the nFA then the nCoA in the BU is either a nFA CoA or a nPCCoA, which affects the processing at the oFA. This is because the sending of a nFA CoA implies that the nFA does not support PCCoAs and therefore the oFA (which does support PCCoAs) should undertake all processing required to convert the oCCoA or the oPCCoA received traffic into a format that will be correctly received and forwarded by the nFA. This means that any broadcast/multicast traffic should be first encapsulated into the HoA of the MN before encapsulating into the nFA CoA. It also means that the BU should specifically indicate whether it is for a FA CoA or a CCoA/PCCoA by setting the new ‘D’ bit. The ‘D’ bit is set in the BU if the MIP Registration via the nFA had either the ‘D’ or the ‘P’ bit set, or is set by the MN that is using a CCoA. The difference at the nFA between a CCoA and a PCCoA is kept within the nFA, and between the nFA and the MN that requested a PCCoA by including the PCCoA extension in its registration. 
     The BU is otherwise unchanged. In addition, the mandatory BUack and its status codes do not need to be extended because the failure of the BU for technical reasons at the oFA, for a CCoA, directly implies a PCCoA processing failure. 
     When considering reverse smooth tunneling, the mechanisms are unchanged for PCCoAs other than that the reverse smooth tunneling is now between MN specific and shared FA CoAs, rather than just between shared FA CoAs. The smooth BU will include both ‘T’ and ‘D’ bits set and the reverse tunneling will be from the nCCoA to the oFA CoA and then from the oCCoA/PCCoA to the GFA/HA. Broadcast/multicast must be reverse tunneled according to the required processing at the receiver for the CoA type. 
     PCCoA Advantages 
     These procedures avoid the CCoA encapsulation for remote access traffic over the access link. In addition, the FA is now in a position to police traffic addressed to a specific HoA from a specific gateway, via the PCCoA, before it is sent to the MN, and can also effectively support smooth hand-offs for all CCoAs. In the case of broadcast/multicast the FA is now in a position to avoid the additional encapsulation over the air in both directions when the access medium supports point to point link layer connectivity to/from the MN. Finally, the MN specific FA CoA (i.e. PCCoA) MIP encapsulation simplifies address-based QoS support in the network between the HA and the MN, when compared to a shared FA CoA, when the FA supports QoS aware address allocation, because the address QoS class can be used by network classifiers in scheduling decisions. 
     New Packet Formats 
     Mobility Agent Advertisement Extension 
     
       
         
               
               
             
           
               
                 0      1      2      3 
                   
               
               
                   
               
               
                 01234567890123456789012345678901 
               
               
                   
               
               
                 +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ 
               
               
                   
               
               
                 |   Type   |   Length   |    Sequence Number    | 
               
               
                   
               
               
                 +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ 
               
               
                   
               
               
                 |     Lifetime     |R|B|H|F|M|G|r|T|S|I|P|reserved| 
               
               
                   
               
               
                 +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ 
               
               
                   
               
               
                 |         zero or more Care-of Addresses         | 
               
               
                   
               
               
                 |                ...                | 
               
             
          
         
       
     
     The Mobility Agent Advertisement Extension described in [MIPv4] C. E. Perkins, Ed. “IP Mobility Support for IPv4”, RFC3220, January 2002, is changed by the addition of a ‘P’ bit:
         P Agent offers proxy CCoA tunneling.       

     A foreign agent that sets the ‘P’ bit SHOULD support the proxy CCoA tunneling for any CCoAs that are uniquely advertised into the routing system by that FA. Using this information, a mobile node is able to choose a foreign agent that supports proxy CCoA tunneling. Notice that if a mobile node does not understand this bit, it simply ignores it as per [MIPv4] and reverts to normal CCoA behaviour. The ordering of addresses in FAAs is according to the relevant MIP specs and is not altered by this draft. 
     Proxy CCoA Extension 
     The Proxy CCoA Extension should only be included if the ‘D’ bit is set and the MN is registering via the FA. If this extension is absent, and the ‘D’ bit is set, then normal CCoA behaviour from Mobile IP [MIPv4] and RevTun is undertaken. RevTun refers to G. Montenegro, Ed. “Reverse Tunneling for Mobile IP”, revised, Internet RFC 3024, January 2001. The Encapsulating Delivery Style extension and the Proxy CCoA extension should not be in the same registration. Mobile Nodes and Foreign agents should support the Proxy CCoA Extension. 
                         0      1                   0123456789012345               +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+               |   Type   |   Length   |    Type: TBA, Length 0.               +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+            
New Registration Reply Codes
 
     Foreign agent registration replies SHOULD convey if the PCCoA request failed. These new reply codes are defined: 
     Service denied by the foreign agent:
         X1 PCCoA capability is mandatory   X2 PCCoA capability is administratively barred   X3 submitted PCCoA is not routable at the FA   X4 submitted PCCoA unavailable       

     In response to a Registration Request with the ‘D’ bit set, and accompanied by the PCCoA extension, mobile nodes may receive (and should accept) code  70  (poorly formed request) from foreign agents. However, foreign agents that support PCCoA capability should use the appropriate new code. 
     If the MN registers via the FA with the ‘D’ bit set, and does not include the PCCoA extension, then code X1 should be returned to the MN to cause the MN to include the extension in any new request. If the MN does include the PCCoA extension and it is either administratively barred from using this capability (through either foreign or home AAA policy state), then code X2 should be returned to cause the MN to modify the Registration. Code X3 should be used if the MN attempts to use as a CCoA an address that is not routable at the FA, and code X4 should be used if the included address is already being used by another MN. In either case, the MN should attempt to get a new PCCoA for the local FA, either from the FA or via some other method. 
     Binding Update Message 
     In various exemplary emobodiments, the known binding Update message of MIPv4 is modified as described below in accordance with the various embodiments of the invention. A new BU flag, the ‘D’ flag, is added to indicate a request for smooth forwarding of the oCoA to the nCCoA/nPCCoA. The BU ‘D’ flag is only set if the MIP Registration to the nFA, that generated the BU also has the ‘D’ bit set. 
     
       
         
               
               
             
           
               
                 0      1      2      3 
                   
               
               
                   
               
               
                 01234567890123456789012345678901 
               
               
                   
               
               
                 +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ 
               
               
                   
               
               
                 |   Type   |A|I|M|G|D|Rsv|     Lifetime     | 
               
               
                   
               
               
                 +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ 
               
               
                   
               
               
                 |          Mobile Node Home Address          | 
               
               
                   
               
               
                 +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ 
               
               
                   
               
               
                 |             Care-of Address             | 
               
               
                   
               
               
                 +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ 
               
               
                   
               
               
                 |                                  | 
               
               
                   
               
               
                 +              Identification              + 
               
               
                   
               
               
                 |                                  | 
               
               
                   
               
               
                 +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ 
               
               
                   
               
               
                 |Extensions... 
               
               
                   
               
               
                 +−+−+−+−+−+−+−+− 
               
             
          
         
       
     
     It is generally preferable that a BU with the ‘D’ bit set should also have the ‘A’ bit set so that the BU sender has confirmation that the forwarding will occur. The absence of this flag indicates that the CoA in the BU is a nFA CoA. If the oCoA is either a CCoA or a PCCoA, then the absence of this flag causes the oFA to try to convert any arriving flows so that they are compatible with the destination nFA CoA. This specifically means that any permitted broadcast/multicast traffic, and any packets with the oCCoA/PCCoA as an unencapsulated destination address (local traffic), should first be encapsulated into the HoA before being additionally encapsulated into the nFA CoA in the BU. 
     Binding Acknowledge Message 
     The format of the MIPv4 Binding Acknowledge message is unchanged, apart from extending the allowed values of the status field to cover the same cases as identified for the MIP Reg. The processing is such that if a BU is sent with the ‘D’ bit set that does not also have the ‘A’ bit set, then the oFA should still accept the request, if in all other ways correct, and return an acknowledgement. 
     The present application hereby expressly incorporates the U.S. Provisional Patent Application listed in the Related Application section of this patent application. However, it is to be understood that any mandatory language such as, e.g., must, is required, and necessary, found the provisional application is to be interpreted as applying to the examples and embodiments described in the particular provisional application and in no way limits the scope of the claims or invention described in the text of this application which is not incorporated by reference. 
     In various embodiments nodes described herein are implemented using one or more modules to perform the steps corresponding to one or more methods of the present invention, for example, signal processing, message generation and/or transmission steps. Thus, in some embodiments various features of the present invention are implemented using modules. Such modules may be implemented using software, hardware or a combination of software and hardware. Many of the above described methods or method steps can be implemented using machine executable instructions, such as software, included in a machine readable medium such as a memory device, e.g., RAM, floppy disk, etc. to control a machine, e.g., general purpose computer with or without additional hardware, to implement all or portions of the above described methods, e.g., in one or more nodes. Accordingly, among other things, the present invention is directed to a machine-readable medium including machine executable instructions for causing a machine, e.g., processor and associated hardware, to perform one or more of the steps of the above-described method(s). The methods and apparatus of the present invention are applicable to a wide range of communications systems including many OFDM, CDMA and other non-OFDM systems. 
     The methods and apparatus of the present invention may be, and in various embodiments are, used with CDMA, orthogonal frequency division multiplexing (OFDM), and/or various other types of communications techniques which may be used to provide wireless communications links between access nodes and mobile nodes. In some embodiments the access nodes are implemented as base stations which establish communications links with mobile nodes using OFDM and/or CDMA. In various embodiments the mobile nodes are implemented as notebook computers, personal data assistants (PDAs), or other portable devices including receiver/transmitter circuits and logic and/or routines, for implementing the methods of the present invention. 
     Numerous additional variations on the methods and apparatus of the present invention described above will be apparent to those skilled in the art in view of the above description of the invention. Such variations are to be considered within the scope of the invention.