WO2006048608A1

WO2006048608A1 - Managing node mobility in a ip network

Info

Publication number: WO2006048608A1
Application number: PCT/GB2005/004101
Authority: WO
Inventors: Matthew Wilkinson
Original assignee: Matsushita Electric Industrial Co., Ltd.
Priority date: 2004-10-30
Filing date: 2005-10-25
Publication date: 2006-05-11
Also published as: GB0424107D0; GB2419778A

Abstract

A system for managing mobility of a mobile network that includes and a mobile router and one or more mobile network nodes, the system being operable to receive from the mobile router mobile network node address information (38); store the mobile network node address information in memory (42); receive subsequent messages indicative of the current address of the mobile router, but without any mobile network node address information (46); use information in the subsequent messages and the stored information, so that packets arriving at the home network and addressed to the mobile network can be intercepted and routed via the mobile router at its current address, and update the mobile network address information in response to an update message from the mobile router.

Description

Managing Node Mobility in an IP Network

The present invention relates to a system and method for managing mobility in an internet protocol (IP) network. In particular, the invention is an enhancement to

'network mobility' (or NEMO) which, in itself, is an extension to Mobile IP.

Both NEMO and mobile IP are internet protocols that work transparently at the IP layer. By transparent, it is meant that protocols operating above and below the IP layer (transport and network protocols) are able to operate as if no mobility was taking place and do not need to support mobility in any way themselves.

Mobile IP is concerned with allowing mobile enabled nodes (mobile devices such as laptops or PDAs) to seamlessly move within the internet topology without having to interrupt and restart any internet sessions taking place. From a user's point of view, they can, for example, constantly stream content from a website while moving between Internet access points. Mobile IP employs a Home Agent to work on behalf of the user. This intercepts any packets destined for the Mobile Network Node and forwards it on to wherever it currently may be.

Network Mobility (or NEMO) extends Mobile IP to allow for a network of nodes to move position within the Internet topology. One example of such a network of nodes is a Personal Area Network made up of a user's devices such as their mobile phone, PDA, laptop, media player etc. Instead of making each device Mobile IP enabled, Network Mobility enables mobility through the use of one or more Mobile Routers.

This. Mobile Router then provides the internet connection for the rest of the network and routes packets to and from the other nodes. When the Home Agent intercepts a packet addressed to one of the nodes, it forwards it on to the Mobile Router which then, in turn, routes the packet to the node.

Figure 1 shows a Mobile Network. This has a single Mobile Router and two nodes, A and B, attached to a Mobile Sub-net. The functionality of the Mobile Router of Figure 1 will be described with reference to the IP protocol/standard IPv6. In Network Mobility, each Mobile Network is associated with a Home Network, which as shown in Figure 1 is connectable to the Mobile Network. A Home Agent is also connected at the Home Network, but this does not play a role until the Mobile Network leaves home. When the Mobile Network is at home, normal routing of packets can take place. The Correspondent Node of Figure 1 represents any address with which the Mobile Network is communicating. For example, the Correspondent Node may be a website from which packets of audio data are being streamed to one of the nodes within the Mobile Network. Each Node in the Mobile Network has an address made up of a prefix (corresponding to the sub-net) and a unique identifier for that node. This prefix is referred to as the Mobile Network Prefix. When packets addressed to one of the nodes arrives at the Home Network, the Home Network knows to route the packets to the Mobile Router, which in turn can route the packet to the correct node.

At some point the Mobile Network may change its connection point to the Internet. For example a user may take their Mobile Network away from the home network's Wi-Fi and go outside where their Mobile Network makes a connection via a Cellular network. Figure 2 shows the Mobile Network away from home. The Access Point represents the point of attachment to the Internet. Through this, the Mobile Router is now connected to a Foreign Network. Under Network Mobility (and Mobile IP), the Mobile Router's IP address is known as the Home Address, because this is its address on the Home Network. Away from home, the Home Address is no longer a routable address. Packets addressed to either the Mobile Router or any of the Mobile Network's nodes arrive at the Home Network, but the Home Network has no way of routing the packet to the Foreign Network. To accommodate this, when the Mobile Router arrives at the Foreign Network it is given a new IP address, which is a routable address on the Foreign Network. Under Network Mobility (and Mobile IP), this address is referred to as the Care of Address. The Home Network must be notified of this address in order to know where the Mobile Network is within the Internet topology. When the Mobile Router detects that it has moved connection, it must send a message known as a Binding Update to the Home Agent. This message contains the Home Address and the new Care of Address. The Home Agent stores the Home Address and Care of Address in a table that is normally referred to as the Binding Cache. This association forms the binding between the two addresses.

Figure 3 shows the sending and storing of the Binding Update containing the Mobile Router's Home Address (HoA) and newly acquired Care of Address (CoA). The Home Agent stores the binding information in its Binding Cache. In practice, on receiving and storing a valid binding, the Home Agent sends a Binding Acknowledgement (BAck) to the Mobile Router. In Mobile IP the Binding Update sent by a node to the Home Agent has the information that allows the Home Agent to intercept packets addressed to the node and forward it on to that node. The packets are redirected through a tunnel. In Network Mobility, the Mobile Router sends the Binding Update on behalf of itself (as in Mobile IP), but also on behalf of the other nodes within the Mobile Network. In other words, it identifies where the Mobile

Router is and, in turn, where the whole Mobile Network is. However, there also needs to be a way for the Home Agent to know to intercept and forward packets to all the nodes in the Mobile Network, and not just the Mobile Router itself.

One method for ensuring that the Home Agent knows to intercept and forward packets for all nodes in the Mobile Network is to operate in what is normally referred to as an Explicit Mode. In this mode, the Binding Update sent by the Mobile Router contains the Mobile Network Prefix information, in addition to the Home and Care of Addresses. The Home Agent stores this information with the Home Address and the Care of Address in its Binding Cache. This is illustrated in Figure 4, which shows an

Explicit Mode Binding Update containing the Mobile Network Prefix (being the prefix for all nodes on the Mobile Sub-net). The Home Agent stores the Mobile Network Prefix with the other binding information.

Figure 5 shows the arrival of a packet from the Correspondent Node (src=CN). The packet is addressed to Node B (dst = Node B). Because Node B is on the Mobile Sub- Net, its address has the Mobile Network Prefix (MNP). The Home Agent can find this prefix information in the entry in the Binding Cache. From the entry, the Care of Address can be identified and used to redirect the packet down the tunnel (shown by dotted lines) to the Mobile Router. The Mobile Router can then route the packet on to Node B

Another method for ensuring that the Home Agent knows to intercept and forward packets for all nodes in the Mobile Network is to operate in what is normally referred to as an Implicit Mode. In this mode, a Pre-configured Table is stored for use by the Home Agent. This table includes all the Mobile Network Prefix information for the Mobile Network associated with a given Mobile Router, and associates it with the

Mobile Router's Home Address.

Figure 6 shows an Implicit Binding Update that the Home Agent is able to use to obtain and store the Home Address (HoA) and Care of Address (CoA). This information is stored in the Binding Cache. Also shown is the Pre-Configured table that has the Home Address (HoA) associated with the Mobile Network Prefix (MNP). When the Home Agent sees packets with the Mobile Network Prefix, instead of identifying the MNP in the Binding Cache, the Home Agent finds it in the Pre- Configured Table. From the corresponding entry, the Home Address is found. With this Home Address, the Home Agent can get the Mobile Router's Care of Address from the Binding Cache and redirect the packet down the tunnel to the Mobile Router, which can then route the packet on to the destination node.

A Mobile Router operating in Explicit Mode appends Mobile Sub-net address information, typically in the form of the Mobile Network Prefixes, each time it moves away from home, and each time it moves between Foreign Networks - even when, in most cases, the information has not changed. In contrast a Mobile Router operating in

Implicit Mode does not need to append this Mobile Sub-net address information.

However, it relies on the Home Agent having a pre-configured table. If for any reason the Mobile Sub-nets are changed, enabled or disabled, then the pre-configured table needs to be updated. This involves some form of downtime and administration. An object of the present invention is to overcome one or more problems associated with the prior art.

Various aspects of the invention are defined in the accompanying independent claims. Some preferred features are defined in the dependent claims.

According to one aspect of the invention, there is provided a method for managing mobility of one or more mobile network nodes using a home agent and a mobile router, the method involving: sending to the home agent an address message from the mobile router, the address message including mobile network node address information; storing the mobile network node address information in memory, and sending subsequent messages to the home agent indicative of the current address of the mobile router, but without any mobile network node address information, unless or until a change to the mobile network node address information occurs, in which case an update message is sent from the mobile router to the home agent with updated mobile network node address information.

The address message may also include information indicative of the current address of the mobile router. The message may be an explicit binding update, which is typically sent if and when the mobile network moves its connection. The subsequent messages may comprise implicit binding update messages.

The method may further involve sending a message from the home agent to the mobile router confirming receipt of the mobile network node address information. Additionally or alternatively, the method may involve determining whether an update of the mobile network nodes addresses is permissible before storing any new or updated addresses. The step of determining whether the update is permissible may involve checking a permissions table. In the event that the address update is deemed to be impermissible, the method may further involve sending a message to the mobile router confirming this. The method may further involve maintaining the stored mobile network node address information unless or until changes to the mobile network node addresses or network occur.

The mobile network node address information may be stored in a table, together with the home address of the mobile router.

The memory may be a binding cache memory in which is also stored the mobile router's home address and current address and the method may involve including a de-registered indicator in the binding cache memory in the event that the mobile router returns to its home network, so that the current address is de-registered, but the mobile network node address information remains available for re-use.

Preferably, the mobile network node address information is provided in the form of one or more mobile network pre-fixes (MNP).

According to another aspect of the invention, there is provided a method for managing mobility of one or more mobile network nodes using a home agent and a mobile router, the method involving: sending to the home agent an explicit binding update message from the mobile router, the explicit binding up-date message including mobile network node address information; storing the mobile network node address information in a memory in or associated with the home agent; subsequently sending implicit binding update messages from the mobile router to the home agent indicative of the current address of the mobile router unless or until a change to the mobile network node address information occurs, in which case an explicit binding update message is sent to the home agent with updated mobile network node address information.

According to yet another aspect of the invention, there is provided a mobile router for use in an IP network, the mobile router being associated with a home network, a home agent within that network, and one or more mobile network nodes, the mobile router being operable to send an address message to the home agent, the address message including mobile network node address information, and send subsequent messages to the home agent indicative of its current address, but without any mobile network node address information, unless or until a change to the mobile network node address information is detected, in which case the mobile router is operable to send a message to the home agent with updated mobile network node address information.

The address message may also include information indicative of the mobile router's home address and its current address. For example, the message may be an explicit binding update. In this case, the subsequent messages are preferably implicit binding update messages.

Preferably, the mobile network node address information is provided in the form of one or more mobile network pre-fixes.

According to still another aspect of the present invention, there is provided a home agent for managing mobility of a mobile router and one or more nodes of a mobile network that is associated with the mobile router, the home agent being operable to receive an address message from the mobile router, the address message including mobile network node address information; store the mobile network node address information in memory; receive subsequent messages from the mobile router indicative of its current address, but without any mobile network node address information; use information in the subsequent messages and the stored information, so that packets arriving at the home network and addressed to the mobile network are intercepted by the home agent and routed via the mobile router at its current address; and update the stored mobile network node information in response to an update message from the mobile router.

The address message may also include information indicative of the mobile router's home address and its current address. For example, the message may be an explicit binding update. In this case, the subsequent messages are preferably implicit binding update messages. The home agent may be operable to determine whether an update of the mobile network node address information is permissible before storing any new or updated information. The home agent may be operable to determine whether the update is permissible by checking a permissions table. The home agent may be operable to send to the mobile router a failed message in the event that the update is deemed to be impermissible.

The home agent may be operable to maintain the stored address information in the memory unless or until changes to the mobile network node addresses or network occur, even if the mobile router returns to the home network.

The home address of the mobile router and the mobile network node address information may be stored in a table. The table may be dynamically updatable as and when new address information is received.

The memory may be a binding cache memory in which is also stored the mobile router's home address and current address. The home agent may be operable to include a de-registered indicator in the binding cache memory in the event that the mobile router returns to its home network, so that the current address in the cache memory is de-registered, but the mobile network node address information remains available for re-use.

Various aspects of the present invention will now be described by way of example only and with reference to the accompanying drawings, of which:

Figure 7 is a block diagram of a Home Agent;

Figure 8 is a flow diagram of the steps taken by the Home Agent of Figure 7; Figure 9 is a flow diagram of a binding update of a dynamic memory of the Home Agent of Figure 7;

Figure 10 is a flow diagram of a binding process using the dynamic memory of Figure 7; Figure 11 is a flow diagram of a binding process; Figure 12 is a flow diagram for a prior art home agent, and Figure 13 is the corresponding flow diagram for a home agent of the present invention.

Figure 7 shows a Home Agent in accordance with the present invention. This includes a dynamic store that stores Mobile Network Prefix Information for the Mobile Network Nodes of a Mobile Router, which information is sent from the Mobile Router when the Router initially leaves the home network and then subsequently only if and when the Mobile Network Prefix Information changes. This dynamic store can be in addition to or as an alternative to the Preconfigured Table of the prior art.

The Home Agent of Figure 7 includes a binding update receiver 10 for receiving binding updates and forwarding them to a Validator 12. This determines whether a received update is an Implicit Update or an Explicit Update and validates the message, e.g. checks it is in the correct format, checks checksums etc. The Validator 12 is connected to two Binding Update Handlers, one for handling Explicit Binding Updates 14 and one for handling Implicit Binding Updates 16. The Explicit Binding Updates Handler 14 is operable to communicate with both a Dynamic Store Controller

18, which is able to update information in a Dynamic Store 20, and a Binding Cache 22, in which the Explicit Update information is stored. The Implicit Binding Updates Handler 16 is operable to communicate with a Pre-configured Store 24, as well as the Dynamic Store 20 and the Binding Cache 22. As with the prior art arrangement, the Pre-Configured Store 24 has to be manually filled with relevant data prior to any

Mobile Network movements and subsequently manually up-dated as and when new Mobile Network Prefix information is received. Each of the Handlers 14 and 16 is also able to communicate with a Tunnel Configuration Manager 26 that is operable to configure a suitable communication tunnel or path with the Mobile Router. The Tunnel Manager 26 is connected to a Binding Update Acknowledge message sender

28, which is operable to send an acknowledgement message to the Mobile Router. To route packets addressed to Mobile Routers and/or Mobile Network Nodes, the Home Agent also includes a Receiver 30 for forwarding a packet to a redirection Controller 32. This Controller 32 is operable to check whether a packet has to be re¬ directed. In the event that redirection is necessary, the Controller 32 checks the Binding Cache 22 and the Preconfigured Table 24 and/or the Dynamic Store 20 to identify the correct destination address for the packet. Once this is found, the packet can be re-directed to the appropriate Mobile Router and from there to the appropriate Mobile Network Node.

Figure 8 shows the steps that are taken when the Mobile Router sends its first Binding

Update, and indeed subsequent implicit Binding Updates. When leaving the Home Network for the first time, the first message sent by the Mobile Router includes Mobile Network Prefix Information together with the Binding Update, i.e. the first message is an Explicit Binding Update. The Home Agent at the Home Network receives this Binding Update 34 and checks 36 for validity using the Binding Update

Validator. Assuming the Binding Update is successfully validated, and the Binding Update is identified as being an Explicit Binding Update 38, then the dynamic controller takes 40 the Home Address HoA and Mobile Network Prefix information MNPl, MNP2 etc from the Explicit Binding Update 41 and places them into the Dynamic Store 42, as shown in Figure 9. The Home Agent then processes the

Binding as with the prior art, and sets up a tunnel and route to the Mobile Router and so the Mobile Network Nodes 44. This involves updating the Binding Cache and setting the Home Agent to intercept and redirect packets addressed to the Mobile Network and the Mobile Router itself.

Having sent its first Binding Update, the Mobile Router sends any subsequent Binding Updates as Implicit Binding Updates 43 (containing only Home Address and Care of Address). The Home Agent receives these subsequent Binding Updates each time the Mobile Network moves and determines that they are Implicit Binding Updates, as shown in Figure 8. In the event that the home network includes a Preconfigured table, the Home Agent checks 48 any pre-configured information for Mobile Network Prefix Information stored in association with the Home Address as seen in the received Binding Update 43. In the event that there is Mobile Network Prefix information in the Pre-Configured Table 50 then this is extracted 52. In the absence of any pre-configured data, the Home Agent then checks the dynamic store 20 for Mobile Network Prefix Information; as shown in Figure 10. Of course, in the absence of a Preconfigured Table, the Home Agent would merely check the dynamic store and extract information from that 56. In either case, having extracted the Mobile Network Prefix Information, the Home Agent can complete the binding 44 as would happen in the prior art system described previously.

Under normal operating conditions, the Mobile Network Prefix Information is not expected to change often. Consequently, the Mobile Router can continue to send Implicit Binding Updates. However, it may occur that some prefix information will change. For example, if a link on the Mobile Network comes up or goes down. This would be detected by the Mobile Router. After this event, when the Mobile Router next sends a Binding Update, it must be explicit 41, i.e. it must contain the Mobile

Network Prefix Information with the Home Address and the Care of Address. The Home Agent, upon receiving the latest Explicit Binding Update 41, will already have an entry in its dynamic store. Consequently, the Home Agent must find the existing entry and update it with the new Mobile Network Prefix Information. Once this is done the Home Agent sends an acknowledgement message to the Mobile Router.

Receipt of this causes the Mobile Router to go back to sending Implicit Binding Updates 43. In this way, the Home Agent can be reliably and dynamically up-dated of changes to the Mobile Network Node information via messages from the Mobile Router, without the need for separately providing information to a Preconfigured Table.

It should be noted that whilst Explicit Binding Updates 41 are generally only sent when the Mobile Router moves and its Care of Address changes, the Mobile Router could be configured/operable also to send an Explicit Binding Update 41 in the event that a change to the Mobile Network Prefix(es) is detected. The method described above utilises an Explicit Binding Update 41 to obtain the

Mobile Network Prefix Information in preparation for the subsequent Implicit Binding Updates 43. A variation on this is to use a dedicated message to inform the Home Agent of the Mobile Network Prefixes and Implicit Binding Updates to inform the Home Agent of the Care of Address, in the event that the Mobile Router moves into a new network. In this case, the Mobile Router would send to the Home Agent the dedicated message containing the Mobile Router's Home Address and its associated Mobile Network Prefix Information. When the Home Agent receives the dedicated message sent by the Mobile Router, it stores the Home Address and Mobile Network Prefix Information into the Dynamic Store 20. The Home Agent sends a dedicated acknowledgement message to the Mobile Router to indicate that the message has successfully been processed and that the Mobile Router is now able to send Implicit Binding Update messages 43. In this scenario, all Binding Updates are implicit Binding Updates 43. If, for whatever reason, the Mobile Network Prefix Information changes, then the Mobile Router must resend the dedicated message with the new information and then await the acknowledgement before sending any more Implicit Binding Updates 43.

In some circumstances, it may be necessary to disallow attempts made by certain updates, for example, for security reasons. To allow this, the Home Agent may have a set of permissions whereby it allows certain operations for its associated Mobile

Routers. In particular, the Home Agent may store details of all the Mobile Routers that are permitted to operate according to the invention, but prevent other Mobile Routers for doing so. To do this, the Home Agent may store a Permissions Table that has the Home Address of each allowed Mobile Router. In another implementation, a flag could be added to any existing general-purpose permissions table that stores all permissions against all Mobile associated with the Home Agent. In either case, when receiving the Explicit Binding Update 41, the Home Agent would firstly check the

Permissions Table. Only if the Home Address in the Binding Update corresponds to an entry in the Permissions Table would the Home Agent allow for the Dynamic Store to be updated. If there is no entry within the Permissions Table then, assuming the Binding Update itself is still valid, the Home Agent sends a message to the Mobile Router with a special code that indicates that the updating of the Dynamic Store 20 has not been successful. This means that although the Mobile Router is able to treat the binding as successful, it must not assume that it can start sending Implicit Binding Updates 43.

Because of this, the mobile router has to continue to send Explicit Binding Updates

41. Alternatively, a dynamic store update may have to be rejected due to certain conditions. For example, the dynamic store may need to be administered and, during that period, disable any new updates. In such a case, the Home Agent will check its conditions before attempting to update the dynamic store.

Yet another variation is to extend the Home Agent's Binding Cache with a 'Deregistered' flag, instead of using a dynamic store, thereby to use the Binding Cache itself to store Mobile Network Prefix Information. The steps for doing this are shown in Figure 11. When first sending a Binding Update 58, the Mobile Router sends an Explicit Binding Update 43 as described previously. The Home Agent determines whether the Binding Update is valid 60. If yes, then the Home Agent amasses whether the Binding Update is an Implicit Binding Update 62. When the Binding Update is Explicit, the Home Agent extracts and stores 66 the Binding Update' s information in the Binding Cache as with the prior art, but with a new

'Deregistered' flag. Initially, this flag would be set to 0. This indicates that the entry is registered and valid in accordance with the prior art. As with the prior art, upon successful registration of the binding, the Home Agent sets itself up to intercept/redirect packets to the Mobile Router 60 and packets addressed to devices that match the Mobile Network Prefix Information, and sends an acknowledgement to the Mobile Router to indicate this success 70. This allows the Mobile Router to subsequently send Implicit Binding Updates 43 until the Mobile Network Prefix information changes. When the Mobile Router moves between foreign networks, implicit Binding Updates are sent to the Home Agent, these Updates including the Mobile Router's Home Address and Care or Address. Upon receiving such Implicit

Binding Updates 43, the Home Agent looks up the corresponding entry in the Binding Cache and updates the Care of Address with the new one stored in the Binding Update. It can also obtain the Mobile Network Prefix Information in order to set itself up to intercept/redirect packets for the mobile network 74.

In a conventional arrangement, when the Mobile Router returns home, its Binding Cache entry is deleted, as shown in Figure 12. In contrast, in the present invention, the Binding Cache entry is not deleted. Instead, the Deregistered flag is set to 1, as shown at step 78 in Figure 13. This flag records the fact that the binding is no longer valid - the Home Agent no longer intercepts and redirects packets for the mobile network. However, by not deleting the entry, the association of the Home Address with the Mobile Network Prefix Information is preserved without the need for a separate dynamic store. Hence, when the mobile network leaves home again, there is no need for the Mobile Router to send an Explicit Binding Update 41, but instead it merely needs to send an Implicit Binding Update 43. The Home Agent receives this and looks up the existing entry in the Binding Cache and replaces the Care of Address as with conventional arrangements, but additionally extracts the Mobile Network

Prefix Information. In this case, the Deregistered flag is set to 0 as this entry is valid again.

A skilled person will appreciate that variations of the disclosed arrangements are possible without departing from the invention. For example, the Mobile Router may be modified to take action in the event that it discovers there are no longer any prefixes to route for, eg when the Mobile Router's ingress interfaces are shut down for reconfiguring. To do this, advantage can be taken of the Router Flag (called 'R' flag) in the Binding Update messages, which indicates that a Device wants to operate as a router. This is a standard flag that is included in all Network Mobility Binding

Updates. Unless this flag is set, the Home Agent only routes packets addressed to the

Mobile Router itself. If the flag is set, then the Home Agent knows to also route packets addressed to the Mobile Network Nodes via the Mobile Router. In the context of the present invention, if the Mobile Router discovers there are no longer any prefixes to route for, the Mobile Router is adapted to send any subsequent Binding

Updates with the router flag to zero until there are any prefixes to be routed for again. Whilst the term home agent has been used throughout, it will be appreciated that any suitable control system or software could be used, provided it is able to carry out the required functionality. Also, whilst the invention has been described primarily with reference to a mobile router having a single mobile sub-network, it will be appreciated that a plurality of such sub-networks could be provided, each having its own prefix or other suitable identifier. Equally, whilst only a single mobile router has been described it will be appreciated that in practice a plurality of such mobile routers would exist. In addition, although the invention has been described primarily with reference to the IP standard IPv6, the principles of the invention could be applied to IPv4. In this case, however, rather than the mobile router sending care of address information directly to the Home Agent, a Binding Update is generated and sent by a Foreign Agent that is active in the foreign network. This Binding Update is sent when the Mobile Router leaves its home network and moves into the foreign network. In this case, if the Mobile Network has left the Home Network for the first time or the Mobile Network node address information has changed since the last Binding Update, the Foreign Agent is notified by the Router of the Mobile Network node address information, and an Explicit Binding Update is sent. Otherwise, the Binding Updates are implicit. Alternatively, all Binding Updates are implicit, and any new Mobile Network address information is sent as a dedicated message from the Mobile Router.

Although the invention is described as an add-on to an implicit mode arrangement, the pre-configured implicit mode table could be omitted, and instead all mobile routers associated with the home agent could communicate by sending an initial explicit binding update message and subsequently using implicit binding updates until a change in the prefix information for the mobile network nodes is detected.

Accordingly, the above description of a specific embodiment is made by way of example only and not for the purposes of limitations. It will be clear to the skilled person that minor modifications may be made without significant changes to the operation described.

Claims

1. A method for managing mobility of one or more mobile network nodes using a home agent and a mobile router, the method involving: sending mobile network node address information from the mobile router to the home agent; storing the mobile network node address information in memory, and sending subsequent messages to the home agent indicative of the current address of the mobile router, but without any mobile network node address information, unless or until the mobile network node address information changes, in which case an update message is sent from the mobile router to the home agent with updated mobile network node address information.

2. A method as claimed in claim 1 wherein the mobile network node address information is included in an address message that also includes information indicative of the router's home address and its current address.

3. A method as claimed in claim 2 wherein the address message is an explicit binding update.

4. A method as claimed in claim 2 or claim 3 wherein the address message is sent from the mobile router.

5. A method as claimed in any of the preceding claims wherein the subsequent messages are implicit binding updates.

6. A method as claimed in any of the preceding claims further involving determining whether an update of the mobile network node address information is permissible before storing any new or updated addresses.

7. A method as claimed in claim 6 wherein the step of determining whether the update is permissible involves checking a permissions table.

8. A method as claimed in claim 6 or claim 7 involving sending to the mobile router a failed message in the event that the address update is deemed to be impermissible.

9. A method as claimed in any of claims 1 to 8 wherein the home address of the mobile router and the mobile network node address information are stored in a table in memory, and the method further involves dynamically updating the table in the event that updated mobile network node address information is received from the mobile router.

10. A method as claimed in any of claims 1 to 9 wherein the memory is a binding cache memory in which is also stored the mobile router's home address and current address, and the method further involves including a de-registered indicator in the binding cache memory in the event that the mobile router returns to its home network, so that the current address is de-registered, but the mobile network node address information remains available for re-use.

11. A method as claimed in any of the preceding claims wherein the mobile network node address information comprises one or more mobile network pre¬ fixes.

12. A method for managing mobility of a mobile network using a home agent, the mobile network having a mobile router and one or more mobile network nodes, the method involving: sending to the home agent an explicit binding update message that includes mobile network node address information; storing the explicit binding update message in memory; subsequently sending implicit binding update messages to the home agent indicative of the current address of the mobile router, unless or until a change occurs to the mobile network node address information, in which case an explicit binding update message is sent to the home agent with updated mobile network node address information.

13. A mobile router for use in an IP network, the router being associated with a home agent and a mobile network, the router being operable to send to the home agent mobile network node address information, and send or cause to be sent subsequent messages indicative of its own current address, but without any mobile network node address information, unless or until a change to the mobile network node address information is detected, in which case the router is operable to send a message to the home agent with updated mobile network node address information.

14. A router as claimed in claim 13 wherein the mobile network address information is included in an address message that also includes home address and current address information for the mobile router.

15. A router as claimed in claim 14 wherein the message is an explicit binding update.

16. A router as claimed in claim 14 or claim 15 wherein the address message is sent from the mobile router.

17. A router as claimed in any of claims 13 to 16 wherein the subsequent messages are implicit binding updates.

18. A router as claimed in any of claims 13 to 17 wherein the mobile network node address information is one or more mobile network pre-fixes.

19. A home agent for managing mobility of a mobile network that includes and a mobile router and one or more mobile network nodes, the home agent being operable to: receive from the mobile router mobile network node address information; store the mobile network node address information in memory; receive subsequent messages indicative of the current address of the mobile router, but without any mobile network node address information; use information in the subsequent messages and the stored information, so that packets arriving at the home network and addressed to the mobile network are intercepted and routed via the mobile router at its current address, and update the mobile network address information in response to an update message from the mobile router.

20. A home agent as claimed in claim 19 wherein the mobile network node address information also includes information indicative of the mobile router's home address and its current address.

21. An agent as claimed in claim 20 wherein the message is an explicit binding update.

22. An agent as claimed in any of claims 19 to 21 wherein the subsequent messages are implicit binding updates.

23. An agent as claimed in any of claims 19 to 22 being operable to determine whether an update of the mobile network node address information is permissible before storing any new or updated addresses.

24. An agent as claimed in claim 23 wherein the node is operable to determine whether the update is permissible by checking a permissions table.

25. An agent as claimed in claim 23 or claim 24 being operable to send to the mobile router a failed message in the event that the address update is deemed to be impermissible.

26. An agent as claimed in any of claims 19 to 25 wherein mobile network node address information is stored in a table, together with the home address of the mobile router, and the home agent is operable to dynamically update the table in the event that updated mobile network node address information is received from the mobile router.

27. An agent as claimed in any of claims 19 to 26 wherein the memory is a binding cache memory in which is also stored the mobile router's home address and current address, and the agent is operable to include a de- registered indicator in the binding cache memory in the event that the mobile router returns to its home network, so that the current address in the cache memory is de-registered, but the mobile network node address information remains available for re-use.

28. An agent as claimed in any of claims 19 to 27 wherein the mobile network node address information comprises one or more mobile network pre-fixes.

29. A system for managing mobility of one or more mobile network nodes using a home agent and a mobile router, the system comprising means for sending mobile network node address information to the home agent from the mobile router; means for storing the mobile network node address information in memory; means for sending subsequent messages to the home agent indicative of the current address of the mobile router, but without any mobile network node address information; means in the mobile router for determining/identifying changes to the mobile network node address information and in the event that such changes are detected sending an update message from the mobile router to the home agent with updated mobile network node address information.

30. A system for managing mobility of one or more mobile network nodes using a home agent and a mobile router, the system being configured to send mobile network node address information to the home agent from the mobile router; store the mobile network node address information in memory, and send subsequent messages to the home agent indicative of the current address of the mobile router, but without any mobile network node address information, unless or until the mobile network node address information changes, in which case an update message is sent from the mobile router to the home agent with updated mobile network node address information.