WO2006088614A1

WO2006088614A1 - Multicast routing

Info

Publication number: WO2006088614A1
Application number: PCT/US2006/002514
Authority: WO
Inventors: Imed Romdhani; Hon-Yon Lach; Christophe Jacques Philippe Janneteau
Original assignee: Motorola, Inc.
Priority date: 2005-02-17
Filing date: 2006-01-19
Publication date: 2006-08-24
Also published as: GB0503307D0; GB2423438B; GB2423438A

Abstract

A method, and system for routing multicast data traffic to a mobile node (48), e.g. a mobile receiver or a Mobile Router, in a packet data network (41), for example IP multicast in an IPv4 or an IPv6 network, comprising: a home agent (52) receiving multicast group membership information from a mobile node (48) located outside the home network (50) of the mobile node (48); the home agent (52) forwarding the multicast group membership information to a router chosen to serve as a multicast router proxy (56); the multicast router proxy (56) joining a multicast group based on the multicast group membership information from the mobile node (48); and the multicast router proxy (56) forwarding multicast data traffic to the mobile node (48). The choice of the router to serve as the multicast router proxy (56) may be determined by the home agent (52).

Description

MULTICAST ROUTING

Field of the Invention

The present invention relates to group communication over packet data networks. The present invention relates in particular, but not exclusively, to multicast according to the Internet Protocol, i.e. IP multicast, to a mobile receiver.

Background of the Invention

Internet Protocol (IP) is a well established protocol for routing of data packets over packet data networks, for example the Internet. Examples of specific versions of IP are IPversion4 (IPv4) and IPversionβ (IPv6).

Multicast is a process whereby groups of users are formed, usually temporarily, and then each user in the group may send common data to some or all of the other members of the group. Protocols for multicast, i.e. broadcast of given data from one provider to plural receivers are included in, or added to, the general IP protocols, and such multicast may be referred to as IP Multicast. Typical applications are multimedia conferences, video games and so on.

A protocol for supporting mobile nodes, e.g. mobile receivers such as mobile telephones, portable computers with wireless connection functionality, and so on, under IP, is known as Mobile IP, in particular MobileIPv4 based on IPv4, and Mobile IPv6 based on IPv6. CML01679N

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The IP, IP Multicast and Mobile IP protocols are standardised by the Internet Engineering Task Force (IETF).

A mobile node, e.g. a mobile receiver or a Mobile Router, can change location, e.g. change from being attached to one network or sub-network to being attached to another network or sub-network without changing its IP address. The mobile node continues, although at different locations, to communicate with other network receivers using its constant IP address. This is, broadly speaking, achieved in IPv4 networks as follows. The mobile node is associated with a home agent on a home network, e.g. a home intranet network, where the mobile node is given a long-term IP address. When the mobile node is roaming, i.e. away from its home network, routing services are provided to the mobile node by a foreign agent at a network where the mobile node is temporarily located, say. The foreign agent detunnels and delivers, to the mobile node, datagrams that were tunnelled by the mobile node's home agent. For datagrams sent by the mobile node, the foreign agent may serve as a default router for registered mobile nodes.

When away from its home network, a care-of address is associated with the mobile node and reflects the mobile node's current point of attachment. Broadly speaking the IETF has defined two approaches for a mobile node to continue receiving multicast traffic when roaming from one network to another. One approach is called "remote subscription" and the other approach is called "home subscription".

To join a multicast group under the remote subscription approach, the mobile node sends a membership request in the form of a membership report message to a local multicast router located in the visited network. The router CML01679N - 3 -

joins the multicast group and the mobile node is treated like a stationary local member.

To join a multicast group under the home subscription approach, the mobile node tunnels a membership request in the form of a multicast group membership report message to its own home agent. The home agent receives, decapsulates and forwards the tunnelled multicast report message to the local multicast router, i.e. a multicast router on the home network. The local multicast router intercepts the multicast report message and sends a "join" message to the nearest router forming part of a network connection for the multicast (i.e. the nearest "on-tree" router). Once a multicast branch is established between the home network and the multicast tree, the home agent intercepts and forwards incoming multicast packets to the mobile node.

FIG. 1 shows a typical prior art multicast network 1 for multicast to a mobile receiver. The prior art network 1 comprises a multicast source 2, coupled to various nodes 4 which together form a multicast delivery tree 6. The prior art network 1 further comprises a mobile receiver 8 and a home network 10. In this example the mobile receiver 8 is a mobile telephone, but the invention is applicable also to other types of mobile receiver or node, for example portable computers with wireless connection functionality. The home network 10 comprises a home agent 12 for the mobile receiver 8. The home network 10 comprises various routers and other nodes. Of these only two specific routers are shown, namely an ingress router 14 and an egress router 16. The ingress router 14 is a router, at the boundary of the home network 10, that receives incoming data traffic into the home network 10. The egress router 16 is a router, at the boundary of the home network 10, that transmits outgoing data traffic away from the home network 10. CML01679N

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According to conventional operation of the prior art network 1, multicast data traffic is routed from the multicast source 2 to the mobile receiver 8 as follows. The multicast data traffic is sent from the multicast source 2 to the ingress router 14 via some of the nodes 4 of the multicast delivery tree; in particular the ingress router 14 receives the multicast data traffic from a node 4 of the multicast delivery tree 6 over a link 18 that may for convenience be called the "multicast delivery tree-to-ingress router link 18". The ingress router 14 forwards the multicast data traffic to the home agent 12 over a link 20 that may for convenience be called the "ingress router-to-home agent link 20". The home agent 2 forwards the multicast data traffic to the egress router 16 over a link 22 that may for convenience be called the "home agent-to-egress router link 24". The egress router 16 forwards the multicast data traffic to the mobile receiver 8 over a link 24 that may for convenience be called the "egress router-to-mobile receiver" link 24. A further link 26, which may for convenience be called the "multicast membership control messages link 26", is provided between the home agent 12 and the mobile receiver 8 for sending multicast membership control messages in both directions between the home agent 12 and the mobile receiver 8.

Ye Min-hua, Yang Lv-yun, Liu Yu, and Hui-min Zhang, "The Implementation of Multicast in Mobile IP", Wireless Communications and Networking, 2003. WCNC 2003. Volume: 3, Page(s): 1796 -1800, 16-20 March 2003, discloses a modification of the home subscription approach. Multicast data traffic from the home agent is intercepted by a so-called "Mobile Multicast Gateway". The Mobile Multicast Gateway uses this multicast data traffic to serve other mobile receivers within the foreign network, independently of the way the other mobile receivers have joined. The Mobile CML01679N - 5 -

Multicast Gateway manages multicast operation in a given region of a network, and all multicast data traffic to mobile receivers passes through the Mobile Multicast Gateway. However, the following limitations arise:

• The Mobile Multicast Gateway requires advance knowledge of all the remote mobile receivers.

• It is necessary to intercept and filter membership report messages between mobile receivers and their home agents.

• A multicast session may be disrupted if particular mobile receivers leave the region covered by the Mobile Multicast Gateway. • Mobile Multicast Gateway entities need to be provided in the home network and the foreign network.

• The Mobile Multicast Gateway is required to be a multicast router with Mobile IP functions.

A Mcauley, E. Bommaiah, A. Misra, et al, "Mobile Multicast Proxy", Proceedings of IEEE MILCOM, November 1999, discloses an approach using a new entity called a Multicast Proxy which forwards multicast messages using unicast, multicast or limited scope broadcast. When a mobile receiver changes it point of attachment, it needs to send a "Binding" message containing its new location to the Multicast Proxy. However, the following limitations arise:

• The mobile receiver needs to locate the Multicast Proxy.

• A Binding signalling mechanism between the Multicast Proxies and mobile receivers is required.

• The Multicast Proxy s required to implement Mobile IP functions. • Since a new form of membership control messages is introduced for mobile members, non-interoperability arises between present protocols. CML01679N - 6 -

Summary of the Invention

The present inventors have realised that the above described conventional approaches, in particular the prior art arrangement shown in FIG. 1, result in an inefficient route for data through the home network, in particular requiring multicast data traffic to be passed via the home agent. The present inventors have also realised that the above described conventional approaches incur significant tunnelling overhead by virtue of such routing through the home agent, because the home agent needs to separately duplicate and forward a given individual multicast packet to each mobile receiver receiving that packet in a given multicast.

In a first aspect, the present invention provides a method of routing multicast data traffic to a mobile node, e.g. a mobile receiver or a mobile router, in a packet data network, the method comprising: a home agent receiving multicast group membership information from a mobile node located outside the home network of the mobile node; the home agent forwarding the multicast group membership information to a router chosen to serve as a multicast router proxy; the multicast router proxy joining a multicast group based on the multicast group membership information from the mobile node; and the multicast router proxy forwarding multicast data traffic to the mobile node.

The choice of the router to serve as the multicast router proxy may be determined by the home agent. CML01679N

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In a further aspect, the present invention provides a method of operating a home agent in a packet data network, the method comprising: receiving multicast group membership information from a mobile node located outside the home network of the mobile node; and forwarding the multicast group membership information to a router chosen to serve as a multicast router proxy.

The home agent may determine the choice of the router to serve as the multicast router proxy.

In a further aspect, the present invention provides a method of operating a router in a home network of a packet data network, the method comprising: receiving, from a home agent, multicast group membership information originating from a mobile node located outside the home network; joining a multicast group based on the multicast group membership information; and forwarding multicast data traffic to the mobile node. In a further aspect, the present invention provides a storage medium storing processor-implementable instructions for controlling a processor to carry out the method of any of the above aspects.

In a further aspect, the present invention provides a system for routing multicast data traffic to a mobile node in a packet data network, the system comprising: a home agent arranged to receive multicast group membership information from a mobile node located outside the home network of the mobile node; the home agent further arranged to forward the multicast group membership information to a router chosen to serve as a multicast router proxy; a router arranged to perform as a multicast router proxy including joining a multicast group based on the multicast group membership CML01679N - 8 -

information from the mobile node; and the router further arranged to forward multicast data traffic to the mobile node.

The home agent may further be arranged to determine the choice of the router to serve as the multicast router proxy. In a further aspect, the present invention provides a home agent for a packet data network, comprising: means for receiving multicast group membership information from a mobile node located outside the home network of the mobile node; and means for forwarding the multicast group membership information to a router chosen to serve as a multicast router proxy.

The home agent may further comprise means for determining the choice of the router to serve as the multicast router proxy.

In a further aspect, the present invention provides a router for a home network of a packet data network, comprising: means for receiving, from a home agent, multicast group membership information originating from a mobile node located outside the home network; means for joining a multicast group based on the multicast group membership information; and means for forwarding multicast data traffic to the mobile node.

In any of the above aspects, the packet data network may be an IP network, for example an IPv4 network or an IPv6 network.

Brief Description of the Drawings

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: CML01679N - 9 -

FIG. 1 shows a typical prior art multicast network for multicast to a mobile receiver;

FIG. 2 is a schematic illustration of an embodiment of a multicast network for multicast to a mobile receiver; FIG. 3 is a flowchart showing process steps of an embodiment; and

FIG. 4 is a schematic illustration of an embodiment of a multicast network for multicast to a mobile receiver.

Description of Preferred Embodiments

FIG. 2 is a schematic illustration of an embodiment of a multicast network 41 for multicast to a mobile receiver. The network 41 comprises a multicast source 42, coupled to various nodes 44 which together form a multicast delivery tree 46. The network 41 further comprises a mobile receiver 48 and a home network 50. In this embodiment the home network 50 is an Intranet, i.e. may be called a home Intranet network, but in other embodiments may be other types of network which serve as a home network for a mobile receiver. The home network 50 comprises a home agent 52 for the mobile receiver 48. The home network 50 comprises various routers and other nodes. Of these only two specific routers are shown, namely an ingress router 54 and a router 56 whose operation will be described below and which is hereinafter referred to as a Multicast Router Proxy (MRP) 56. The ingress router 54 is a router, at the boundary of the home network 50, that receives incoming data traffic into the home network 50. The MRP 56 is a router that forwards multicast data traffic to the mobile receiver 48, as will be described in more detail below. In this embodiment the MRP 56 is at the boundary of CML01679N - 10 -

the home network 50, but this need not be the case, and in other embodiments the MRP 56 may be located elsewhere in the home network 50, as will be described in more detail below.

According to an embodiment of the invention, the multicast network 41 routes multicast data traffic from the multicast source 42 to the mobile receiver 48 as follows. The multicast data traffic is sent from the multicast source 42 to the ingress router 54 via some of the nodes 44 of the multicast delivery tree; in particular the ingress router 54 receives the multicast data traffic from a node 44 of the multicast delivery tree 46 over a link 58 that may for convenience be called the "multicast delivery tree-to-ingress router link 58". The ingress router 54 forwards the multicast data traffic to the MRP 56 over a link 60 that may for convenience be called the "ingress router-to-MRP link 60". The MRP 56 forwards the multicast data traffic to the mobile receiver 48 over a link 62 that may for convenience be called the "MRP-to-mobile receiver" link 62.

A further link 64, which may for convenience be called the "MRP multicast membership control messages link 64", is provided between the home agent 52 and the MRP 56 for sending multicast membership set-up messages in both directions between the home agent 52 and the MRP 56. A further link 66, which may for convenience be called the "mobile receiver multicast membership control messages link 66", is provided between the home agent 52 and the mobile receiver 48 for sending multicast membership control messages in both directions between the home agent 52 and the mobile receiver 48. In overview, in this embodiment, the IP multicast routing processes and multicast data traffic forwarding processes conventionally carried out by CML01679N - li ¬

the home agent 52 are instead carried out at the MRP 56. Usually the path from the MRP 56 to the mobile receiver 48 is shorter than the path from the home agent 52 to the mobile receiver 48, thus making the multicast data traffic flow more efficient. FIG. 3 is a flowchart showing process steps of this embodiment. At step s2, the home agent 52 intercepts the multicast membership report messages from mobile receivers associated with it, which here includes the mobile receiver 48.

At step s4, the home agent 52 determines, for each mobile receiver it has a membership report message for, a multicast router within the home network 50 to serve as an MRP for that mobile receiver. Different multicast router may be selected to act as respective MRPs for different mobile receivers, or the same multicast router may be selected for two or more mobile receivers. Any suitable criterion may be used for determining which router in the home network 50 is to be used as the MRP. For example, the home agent 52 may choose the best MRP based on path attributes. Other characteristics such as delay, bandwidth or latency may be used. If two or more routers are equal according to a first criterion, then a further criterion may be considered, and so on. Furthermore, the criteria to be used may be varied in a time-dependent or other adaptive manner. Another possibility is that the router to be used as the MRP is predetermined. Possible selection approaches will be described in more detail below. Returning to the present example, for the mobile receiver 48 the home agent determined to serve as the MRP is shown as MRP 56 in FIG. 2. At step s6 the home agent 52 redirects the membership information and the membership reports messages to the MRP 56 via the MRP multicast CML01679N - 12 -

membership control messages link 64. This is carried out without notifying the mobile receiver 48 about such redirection.

The MRP 56 maintains a multicast forwarding table. At step s8 the MRP 56 updates the multicast forwarding table with the information of the new or updated multicast group membership of its associated mobile receivers.

At step slO the MRP 56 joins the requested multicast groups, i.e. in this example joins the multicast group requested by or for the mobile receiver 48.

At step sl2 the MRP 56 forwards multicast data traffic pertaining to the joined multicast group to the mobile receivers, i.e. in this example mobile receiver 48 over the MRP-to-mobile receiver link 62, i.e. multicast service is provided to the mobile receiver without the multicast data traffic passing through the home agent 52.

If a mobile receiver performs either a position update or joins/leaves a multicast group, the home agent 52 notifies the relevant MRP, e.g. MRP 56. The MRP, e.g. MRP 56, then updates the entries in its multicast forwarding table, thereby reflecting the dynamic variation of mobile multicast receivers in the multicast group or groups.

In conventional operation, for those mobile receivers of a given home network, one or more designated routers in the multicast tree serve those receivers, i.e. route multicast data to the home network for those receivers. An option that may be applied is that if according to the process described above with reference to FIG. 3, or the process of any other implementation or embodiment, all mobile receivers that may potentially be served by such a designated router become allocated to one or more MRPs, then the designated router of the home network removes itself from the multicast tree. CML01679N - 13 -

A further possibility is that the MRP does not need to process joining the same multicast group if it has already joined this group based on the membership of a given mobile node. The join, process need not be repeated for the same multicast group information, thereby reducing the processing load of the MRP. For example, in the case of the embodiment described with reference to FIGS. 2 and 3, if a further mobile node is to be served by the MRP 48, then the MRP 48 can be used as described above without the need to carry out the process steps relating to joining the multicast group.

FIG. 4 is a is a schematic illustration of a further embodiment of a multicast network 41 for multicast to a mobile receiver 48, showing details of one way in which the embodiment of FIG. 2 may be adapted. Those parts of the multicast network 41 corresponding to like parts in the arrangement of FIG. 2 are indicated by the same reference numerals. The home network 50 comprises an additional router, referred to hereinafter as a home network router 68. The ingress router 54 forwards multicast data traffic to the home network router 68 over a link 70 that may for convenience be called the "ingress router-to-home network router link 70". A link 72, which may for convenience be called the "home network router-to-MRP link 72", is provided between the home network router 68 and the MRP 56. A link 74, which may for convenience be called the ""home network router-to-home agent link 74", is provided between the home network router 68 and the home agent 74. In operation, multicast traffic reaches the home agent 52 before being tunnelled to the MRP 56, the home network router 68 being traversed twice by multicast traffic: a first time by native multicast from the multicast delivery tree and to the home agent 52, and a second time by tunnelled multicast from the home agent 52 to the mobile receiver 48. CML01679N - 14 -

Further details of the above, and other, embodiments, will now be described with specific reference to the functions performed by the MRP 56. The MRP 56 joins and leaves the multicast group(s) requested by the home agent 50. The MRP 56 does not need to exchange membership control messages

(e.g. Internet Group Management Protocol (IGMP) messages in the case of IP version 4 or Multicast Listener Discovery (MLD) in the case of IP version 6) with the mobile receiver 48, this is instead performed by the home agent 52.

The MRP 56 does not need to implement Mobile IP functions. A further option, if security is desired, is for the MRP 56 to maintain a

Security Association with the home agent 52 for including, updating or excluding mobile receivers.

The MRP 56 may register and cache the current care-of-address of the mobile receiver and the related multicast group membership information. The MRP 56 forwards multicast data traffic to the mobile receiver 48.

This can be carried out in any suitable manner. Two implementations are as follows.

In the first implementation, which is fully compliant with the Mobile IP specification, the MRP transparently uses the IP address of the home agent as the source address to send multicast traffic to a care-of-address of a given mobile receiver. This does not require any change to the mobile receiver specification.

In the second implementation, an optional extension is used, and a security enhancement is achieved. With this extension, the MRP uses its own IP address to send multicast traffic to the mobile receiver. In this case, the home agent notifies the mobile receiver in advance about the IP address and CML01679N - 15 -

the identity of the MRP. A Security Association is established between the mobile receiver and the MRP with the help of the home agent. This extension involves the following modifications being made to conventional operation of a mobile receiver: the mobile receiver receives protocol messages from the home agent that indicate the IP address of the MRP, and the mobile receiver accepts multicast data traffic from the MRP.

Further details of the above, and other, embodiments, will now be described with specific reference to the functions performed by the home agent 52. The home agent 52 determines whether a mobile receiver, e.g. mobile receiver 48, has moved outside the home network 50 or not (although in other embodiments this may be determined by some other suitable entity). The home agent 52 may rely on the knowledge of the prefixes of the care-of- address of the mobile receiver 48 and the scope of the home network 50. The home agent 52 forwards multicast membership control message to the remote mobile receiver. One optional way to implement the process is for the home agent to be 52 programmed or otherwise arranged to only forward membership control messages to mobile receivers not yet in the multicast group. The home agent 52 may maintain a cache for mobile receivers that wish to join a multicast group.

In certain embodiments the home agent 52 may determine which is the optimal tunnel to use for transmitting membership control messages to the mobile receiver: i.e. the home agent may use the tunnel from the MRP 56 to the mobile receiver 48 rather than the conventional tunnel from the home agent 52 to the mobile receiver or its proper tunnel. Another option is for the CML01679N - 16 -

home agent 52 to always use the tunnel from the MRP 56 to the mobile receiver 48 for transmitting membership control messages to the mobile receiver.

The home agent 52 requests or instructs the MRP 56 to join multicast groups and forwards multicast data to remote mobile receivers. In certain embodiments the home agent 52 formulates this request by redirecting the membership report message received from a remote mobile receiver to the MRP 56. In other embodiments, the MRP 56 may sometimes or always use other extensions of the current IGML/MLD protocols instead, or indeed any other appropriate process or means.

The home agent 52 updates information specifying or otherwise relating to the location of the mobile receivers, e.g. the mobile receiver 48, in the MRP 56. This update is transparent to the mobile receivers.

In the above embodiment, at step s4, the home agent 52 determines, for each mobile receiver it has a membership report message for, a multicast router within the home network 50 to serve as an MRP for that mobile receiver. The determination of a suitable router to serve as the MRP can be carried out in any appropriate manner according to one or more suitable criteria or other aspects. Different examples of this are as follows: The home agent 52 uses a pre-configuration method where it knows in advance the IP address of one or more routers it can use as an MRP.

In those cases where the home agent runs an Shortest Path First (SPF)- based routing protocol such as Open Shortest Path First OSPF (as described in J. Moy, "OSPF Version 2", IETF RFC 1583, which reference is incorporated herein by reference), the home agent maintains a database describing the home network topology. CML01679N - 17 -

In those cases where the Border Gateway Protocol (BGP) (as described in Y. Rekhter, T. Li, S. Hares, "A Border Gateway Protocol 4 (BGP-4)", IETF Internet Draft, draft-ietf-idr-bgp4-26.txt, 22 October 2004, which reference is incorporated herein by reference) is used, the home agent 52 can locate and identify the internal and the external BGP peers, known as I-BGP and E-BGP.

By following an approach described in US 6,611,528 incorporated herein by reference), a multicast router can maintain routing information regarding the Upstream Border Router (UBR) and the Downstream Border Routers (DBRs) of a given multicast group. The UBR router is defined as the border router of a network subnet (IP domain or Autonomous System), which routes the multicast packet from outside the network subnet. The DBR routers are defined as one or more routers of the network subnet, which route the packet outside the network subnet (IP domain or Autonomous System). The home agent 52 may choose the router to be used as the MRP 56 based on some prior knowledge of the home network topology, for example the placement of existing Egress Routers, or from a derived knowledge of the network prefixes of the care-of-addresses of remote mobile receivers. In this respect, it is noted that the MRP 56 in FIG. 2 may be an egress router such as the egress router 16 shown in FIG. 1, but this need not be the case. In a further embodiment, where the home network has more than one home agent, the home agents may choose one or more strategically positioned MRPs.

In further embodiments the home network may be a Virtual Private Network (VPN), in which case the multicast data traffic may be forwarded from the home network in VPN tunnels. Furthermore, the MRP and the VPN Gateway may be collocated. CML01679N - 18 -

In the above embodiments, the choice of which router is to serve as the MPR is determined by the home agent. However, this need not be the case, and in other embodiments one or more other entities may perform this determination either in isolation or in conjunction with the home agent. In the above embodiments the multicast source is positioned outside the home network, but this need not be the case, and the invention may still be applied when the multicast source is positioned inside the home network.

The above embodiments show the invention applied to routing to a mobile receiver 48, e.g. an end-user mobile receiver, which may be, for example, a mobile telephone, or a portable computers with wireless connection functionality, and so on. In further embodiments the invention may be applied instead, or in addition, to a mobile router, e.g. according to the Mobile Router definition of the Mobile IP specification, as described for example in T. Ernst, H-Y. Lach, "Network Mobility Support Terminology", draft-ietf-nemo-terminology-02.txt, October 25, 2004, which reference is incorporated herein by reference. Generally, each of the above described embodiments (and further embodiments mentioned below) may be applied to either, or both, end-user mobile receivers and mobile routers, which together may be termed mobile nodes. By comparing the links required in the embodiment of FIG. 2 with the links required in the prior art arrangement of FIG. 1, it will be appreciated that the present invention tends to provide a more efficient routing of the multicast data traffic. Furthermore, the data does not have to be separately extracted for each mobile receiver, as is the case in the prior art arrangement. The present invention also provides a potential for join latency to be reduced, since the multicast path from the MRP to the mobile receiver will CML01679N - 19 -

usually be a shorter path than the conventional path from the home agent to the mobile receiver.

In most embodiments there is no requirement to modify the mobile receiver. It is advantageous that the present invention may be applied to multicast under both the Mobile IPv4 and the Mobile IPv6 protocols. However, the invention may be applied to other versions of IP. The invention may also be applied to other packet data networks with data packet switching protocols that support mobility and multicast. The above described embodiments may be implemented by configuring or adapting any suitable apparatus, for example conventional equipment and software providing a conventional home agent, and conventional equipment and software providing a conventional router, and other hosts, nodes, receivers etc. such as mobile telephones and portable computers. Alternatively, or in addition, the processes described may be implemented by processor-implementable instructions implemented by a processor and/or stored on a suitable storage medium, such as computer memory, hard disk, floppy disk, ROM, PROM etc.

Claims

CML01679N - 20 -CLAIMS

1. A method of routing multicast data traffic to a mobile node in a packet data network, the method comprising: a home agent receiving multicast group membership information from a mobile node located outside the home network of the mobile node; the home agent forwarding the multicast group membership information to a router chosen to serve as a multicast router proxy; the multicast router proxy joining a multicast group based on the multicast group membership information from the mobile node; and the multicast router proxy forwarding multicast data traffic to the mobile node.

2. A method according to claim 1, wherein the choice of the router to serve as the multicast router proxy is determined by the home agent.

3. A method of operating a home agent in a packet data network, the method comprising: receiving multicast group membership information from a mobile node located outside the home network of the mobile node; and forwarding the multicast group membership information to a router chosen to serve as a multicast router proxy.

4. A method according to claim 3, further comprising determining the choice of the router to serve as the multicast router proxy. CML01679N - 21 -

5. A method of operating a router in a home network of a packet data network, the method comprising: receiving, from a home agent, multicast group membership information originating from a mobile node located outside the home network; joining a multicast group based on the multicast group membership information; and forwarding multicast data traffic to the mobile node.

6. A method according to any of claims 1 to 5, wherein the packet data network is an IP network.

7. A storage medium storing processor-implementable instructions for controlling a processor to carry out the method of any of claims 1 to 6.

8. A system for routing multicast data traffic to a mobile node in a packet data network, the system comprising: a home agent arranged to receive multicast group membership information from a mobile node located outside the home network of the mobile node; the home agent further arranged to forward the multicast group membership information to a router chosen to serve as a multicast router proxy; a router arranged to perform as a multicast router proxy including joining a multicast group based on the multicast group membership information from the mobile node; and CML01679N - 22 -

the router further arranged to forward multicast data traffic to the mobile node.

9. A system according to claim 8, wherein home agent is further arranged to determine the choice of the router to serve as the multicast router proxy.

10. A home agent for a packet data network, comprising: means for receiving multicast group membership information from a mobile node located outside the home network of the mobile node; and means for forwarding the multicast group membership information to a router chosen to serve as a multicast router proxy.

11. A home agent according to claim 10, further comprising means for determining the choice of the router to serve as the multicast router proxy.

12. A router for a home network of a packet data network, comprising: means for receiving, from a home agent, multicast group membership information originating from a mobile node located outside the home network; means for joining a multicast group based on the multicast group membership information; and means for forwarding multicast data traffic to the mobile node.

13. A system or apparatus according to any of claims 8 to 12, wherein the packet data network is an IP network.