GB2436664A

GB2436664A - Establishing communication between mobile station and unidirectional network

Info

Publication number: GB2436664A
Application number: GB0606564A
Authority: GB
Inventors: Nima Sattari; Paul Anthony Pangalos; Abdol Hamid Aghvami
Original assignee: Kings College London
Current assignee: Kings College London
Priority date: 2006-03-31
Filing date: 2006-03-31
Publication date: 2007-10-03
Anticipated expiration: 2026-03-31
Also published as: GB0606564D0; GB2436664B

Abstract

A method of establishing communication between a unidirectional network (DVB) and a mobile station (MR) comprises the steps of (a) sending a message from the mobile station to a home agent (Ext-MR-HA) of the mobile station via a bidirectional network (UMTS), the message containing a care-of-address of the mobile station and an identification of the unidirectional network; (b) sending the message from the home agent (Ext-MR-HA) of the mobile station (MR) to the unidirectional network (DVB); (c) sending an acknowledgement of the message from the unidirectional network to the home agent (Ext-MR-HA); and (d) sending the acknowledgement from the home agent to the mobile station (MR) via the bidirectional network (UMTS). A mobile station comprising a mobile router and nodes of a mobile network, a home agent therefor and a gateway for the unidirectional network are also disclosed.

Description

MOBILE NETWORKS

Background to the Invention

f0001]This invention relates to a method of operating a mobile communication device. The device may be a mobile router, for use with a network of mobile nodes, each comprising a communication device such as a portable computer. If so,the invention provides a novel extension to the conventional IETF-proposed basic NEMO (NEtwork MObility) solutions, enabling NEMO to work in the heterogeneous environments which consists of unidirectional networks such as DVB (Digital Video Broadcasting).

Single Handover (Mobile IP) [0002]Jn order for a mobile node (MN) to remain in continuous communication throughout dynamic changes to its point of attachment to the Internet, the Internet Engineering Task Force (IETF) has standardized Mobile IF (MIP) protocol. Using this protocol, a new IF address is allocated to a Mobile Node (MN) when it is being handed over to a different Access Network (AN). This new IF address is termed as "Care-of-Address" (CoA). Using conventional Mobile IF (MIP) solutions, such as MIFV4 (C.Perkins, "IP Mobility Support for IPv4, Revised," draft-ietfmjp4rfc33bis..OOt June 2004) and MIPv6 (D.

Johnson, C. Perkins, J. Arkko, "mobility Support in IPv6," IETF RFC 3775, June 2004) all traffic is routed via the MN's Home Agent (HA), which keeps a record of the CoAs allocated to the MN at any one time. The HA then forwards all packets to the MN's most recent CoA, termed current CoA, using IP-in-IP encapsulation, in order to ensure that traffic reaches the MN in the visited network. As implied, conventional MI? solutions work only on a per-terminal basis.

[0003JIn Figure la, 1 designates a data path between the MN and a Correspondent Node (CN), when the MN is at its home network. When the MN moves to a foreign network, as shown by dotted arrow 2, the MN's HA receives and intercepts at 3 packets that are destined for the MN. This HA then tunnels packets to the MN's CoA via 4. Subsequently the MN and the CN communicate directly via 5 and 6.

Group Handover (Network in Motion) [0004]Consider a public transportation vehicle (such as a train) with a large number of MNs onboard. Many of these MNs would undergo the same handover between ANs at approximately the same time. Using conventional MIP solutions, we need separate signalling for the handover for each of the terminals, causing excess signalling traffic potentially leading to phenomena such as a so-called Binding Update (BU) storm. However, if all the terminals in the moving vehicle were made a part of the same network and the network were handed over between ANs as one, then the handover process would be vastly more efficient. That is the solution, which is considered by the NEtworks in MOtion (NEMO) working group of IETF nemo-charter.h,J) This mobility solution is performed by deploying a gateway router (termed a Mobile Router (MR)) in a typical moving network such as a train or a bus, which changes its point of attachment to the outside Internet. See Figure lb. [0005] The basic NEMO solution is described by V. Devarapalli, R. Wakikawa, A. Petrescu, P. Thubert "Network Mobility Basic Support Protocol" IETF RFC January 2005. This provides session continuity by creating a bi-directional tunnel between the Mobile Router (MR) and its home network. Furthermore, the mobile nodes within the MR's subnet might also be connected through a tunnel to their respective home networks. As a result, all traffic between the nodes in the mobile network and their correspondent nodes passes through multiple tunnels, as shown in Figure 2. In the basic NEMO solution, we consider three different kinds of nodes in the moving network: * Local Fixed Nodes (LFNs): Those nodes downstream of the MR, which are unable to change their point of attachment to the MR's network. LFNs are mobility unaware nodes, meaning that they do not have any mobility software running on them.

* Local Mobile Nodes (LMNs): Those nodes downstream of the MR, which are able to change their point of attachment to the MR's network, but are unable to leave the MR's network * Visiting MNs (VMNs): Those nodes downstream of the MR which are capable of joining/leaving the MR's network when necessary. VMNs are mobility aware nodes, meaning that they must have mobility software such as MIPv6 installed and running.

[0006]In the MR-HA bidirectional tunnelling approach, which is essential to the functioning of the NEMO Basic Support solution, the MR acquires one or more IPv6 prefixes from its home network. Then the MR assigns IF addresses to LFN5/LMN5 from its IPv6 prefixes. LMNs/LFN5 use these IF addresses as their permanent IF addresses and register them with the MR's HA. These global routable IF addresses stay the same and will not change during the movement of network.

[0007] When a VMN joins the MR's network, the MR assigns an IF address (based on the prefix) to the VMN, which the VMN uses as its CoA. The VMN then sends a BU to its home network via the MR. On receiving the BU, the user's HA updates its binding cache and replies with an acknowledgement. This CoA will stay the same as long as the VMN is in the MR's network.

[0008] When the MR is away from its home network, it obtains a new address (primary CoA) and registers this new CoA with its home agent. When the new MR CoA registrations with its home agent finished, all traffic to visiting nodes within the mobile network is routed to the MR's home agent and then double tunnelled, using the encapsulation described by C. Perkins, "IF enclapsulation within IP," IETF RFC 2003, October 1996, to the MR. The double tunnel is formed of: * Outer tunnel: from MR's home agent to MR * Inner Tunnel: from user's home agent to VMN [0009] Figure 2 illustrates the data path from a Correspondent Node (CN) to a VMN node in the mobile network.

[0010]The traffic to local fixed/mobile nodes within the mobile network is routed to the MR's home agent directly and then gets tunnelled (using IP-IP encapsulation) to the MR. Figure 3 illustrates the data path from a CN to a LFN/LMN node in the mobile network.

[001 1]The IETF-proposed mobile IP as well as NEMO support single as well as group handovers (using a mobile router) using bidirectional networks. These solutions do not work with unidirectional networks such as the DVB (digital video broadcasting) networks. It is one objective of this invention to provide new mechanisms to support both of these mechanisms in unidirectional networks.

Summary of the Invention

[0012] Consider a situation where the MR should initiate a handover to a unidirectional network (e.g. a DVB network) for downlink and a UMTS network for uplink (for instance, the MR, using WLAN hot spot to connect to the outside world, is going out of the coverage of the WLAN and, therefore it could handover to UMTS/DVB for uplink/downjink connectivity respectively). In order to do so, the MR needs to obtain a new CoA from a UMTS network, the DVB network ID and cell ID as well as the network information table (NIT) from the DVB network it intends to handover to.

[0013] It is an aim of the invention to provide a novel mobile network solution which can work by utilising both bidirectional and unidirectional access networks.

[0014] The invention provides a method of establishing communication between a unidirectional network and a mobile station, according to claim 1. The invention also provides a mobile station according to claim 9, a home agent according to claim 13 and a gateway according to claim 17. Preferred or optional features of the invention are defined in the dependent claims.

Brief Description of the Drawings

(0015]The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which: [OOI6]Figure la schematically shows a known single node handover arrangement; [O017]Figure lb schematically shows a known group node handover arrangement; [0018] Figure 2 shows a known data path for a VMN; [001 9] Figure 3 shows a known data path for a LFN/LMN; [0020]Figure 4 schematically shows the heterogeneous environment in which the invention is required to operate; [O021]Figure 5 shows a known VMN data path; [OO22]Figure 6 shows the encapsulation of a packet used in the data path of Figure 5; [OO23]Figure 7 shows a known LFN/LMN data path; [0024] Figure 8 shows the encapsulation of a packet used in the data path of Figure 7; [0025] Figure 9 shows the signalling procedure for a binding update used in an embodiment of the invention;

] Figure 10 shows the procedure of Figure 9 in schematic graphical form; [O027]Figure 11 shows the structure of a NEMO binding update used in an embodiment of the invention; [0028] Figure 12 shows the structure of an Inter Network Binding Update; [O029]Figure 13 shows the structure of an Inter Network Binding Update Acknowledgement; [0030] Figure 14 shows the structure of a NEMO Binding Update acknowledgment; and [0031] Figure 15 shows a data path for a VMN after the handover.

Detailed Description of Particular Embodiment

[0032]The invention introduces a novel "Enhanced Basic NEMO Support Protocol". In this new solution, we introduce extended Binding Updates, which enable the MR to perform the handover utilising both unidirectional and bidirectional networks. We consider a heterogeneous environment that consists of WLAN, DVB and UMTS as illustrated in Figure 4.

[0033] Consider a mobile network, which could be any public transport vehicle such as a train, a bus or a ship, in the heterogeneous environment of Figure 4.

The mobile network connectivity to the outside world is provided by its MR, and the mobile network's WLAN network provides internal connectivity to the MR for all nodes in the mobile network. We suppose that the mobile network is within the coverage of a WLAN hot spot, which could be provided in a rail station, bus station or pier. As long as the mobile network is within the coverage of this WLAN hot spot, the MR stays connected to this hot spot as it provides high bandwidth at low cost.

[0034]For users joining the mobile network, one of the following cases may apply. Some users might not have any computational devices to hand, thus could use the wireless enabled devices provided within the train (i.e. LFNs/LMN5).

Other users might have their own wireless enabled devices when they join the train (i.e. their VMNs). However, for present purposes, we assume that all users have already subscribed to the mobile network and informed their own home networks, via the MR, about their new CoAs.

[0035J To send information to the nodes inside the mobile network, the packets should be sent to the user's home network first by either the user's Content Provider or the Service Provider, labelled source in Figures 5 and 7, to fulfil the NEMO requirements, as mentioned by T. Ernest at tNetwork Mobility Support Goals and Requirements", IETF Internet Draft (work in progress), draft-ietf-nemorequirements45.j-,<t, October 2005. If the user uses a VMN, the packets are encapsulated for the MR at the user's home network. These packets go to the MR home network and are encapsulated again and sent to the MR care-of-address, as illustrated in Figure 5. When the MR receives the packets, it decapsulates the packets once and sends them over to the destination node. The destination node decapsulates the packets again and retrieves the original data.

[0036] Details of the encapsulation of a packet destined for a VMN are illustrated in Figure 6. The inner tunnel is shown by the four boxes on the right hand side.

The source address field, for the tunnel entry-point node, contains the user's HA address. The destination address field, for the tunnel exit-point node, contains the user's CoA. The IPv6 routing extension header contains the extended MR-HA address. The outer tunnel is shown by the two boxes on the left hand side.

The source address field of the outer tunnel contains the extended MR-HA address. The destination address field contains the MR's CoA. The IPv6 routing extension header of the outer tunnel contains the WLAN-AR address.

[0037]If the receiving node is a LFN/LMN, the packets are sent to the MR home network directly. In the MR home network, the packets are encapsulated and sent to the MR's CoA. When the MR receives the packets, it decapsulates the packets and sends them over to the destination node. As illustrated in Figure 7, there is only one tunnelling because there is no user's home network in this case (the user's home network is the same as the MR's home network).

[0038] Details of the encapsulation of a packet destined for a LFN/LMN are illustrated in Figure 8. In the tunnel headers, the source address field contains the extended MR-HA address, the destination address field contains the MR's CoA and the IPv6 routing extension header of that tunnel contains the WLAN-AR address.

[0039] When the mobile network moves, it gradually goes out of the coverage of the WLAN hot spot network. In order to continue supporting users with their current services and connections, users should be handed over to other available access networks, such as DVB and UMTS.

[0040] When the MR initiates the handover, it obtains a CoA from the chosen UMTS network using existing procedures, such as MIPv6. Once the MR has obtained its CoA from the UMTS network, it sends a BU to the Extended Mobile Router Home Agent (Ext-MR-HA) to register its new CoA with Ext-MR-HA and to send the necessary information to the chosen DVB network. In order to do so, the MR will use an extended NEMO Binding Update message containing extra information transmitted for the DVB network. This information includes the MAC address of the mobile router as well as the DVB network ID, cell ID and network table. Figures 9 and 10 illustrate the signalling procedure.

[0041] A DVB network operator has an Original Network ID (ONETID) that serves as unique identification codes for DVB networks. Each DVB network transmits a Network Information Table (NIT) that carries dynamically updated network and transponder specific information (network name ID, frequencies, code rates etc.) for all transponders of the network. A NIT is transmitted every lOs or less. For example if the network is a broadcast network that uses MPEG encoding (such as a DVB network) the MR may receive and store the entire Network Information Table (NIT) and/or Program Association Table (PAT) and/or Program Map Tables broadcast with each transport stream used for carrying packet data; some or all of the NIT, PAT and/or PMTs may be included in the extended binding update. In one aspect the foreign network indicator may comprise a Network Information Table (NIT); a Service List Descriptor; a Terrestrial Delivery System Descriptor; or a Frequency List Descriptor for

example.

[0042] As shown at 11 and 12, the MR sends a NEMO Binding Update Extension message to its HA through a GGSN (Gateway GPRS Support Node) in the chosen UMTS network to register its UMTS CoA with its HA. The details of this message are illustrated in Figure 11. Apart from the required fields in standard Mobile IP and standard NEMO Basic support, new Mobility Options are required. A new flag (E) is included in the NEMO Binding Update Extension to indicate to the Ext-MR-HA that the Binding Update contains extra information relating to a unidirectional network.

[0043] As shown in Figure 9 at 13, the Ext-MR-HA sends an Inter Network (IN) Binding Update to the DVB-GW in the selected DVB network to provide the necessary information about the MR's DVB interface (MR's MAC address) as well as to establish a tunnel that will be used to forward future packets to the MR. On receiving this information, the DVB-GW maps the MR interface address, which is a UMTS CoA, with MR MAC address. Figure 12 illustrates the details of the IN BU message. A new flag (I) is included in the IN Binding Update to indicate to the DVB-GW that the Binding Update is coming from a Ext-MR-HA.

[0044] As shown in Figure 9 at 14, when the DVB-GW finishes its mapping procedure, it sends an acknowledgement to the Ext-MR-HA. This message is illustrated in Figure 13. A new flag (I) is included in the IN Binding Update Acknowledgment to indicate that the DVB-GW which processed the IN Binding Update Supports this functionality. A tunnel is established between the DVB and UMTS network for sending signalling messages such as the IN Binding Update and the IN Binding Update Acknowledgment. This tunnel may also be used for forwarding the data streams.

[0045] As shown in Figure 9 at 15 and 16, on receiving the IN BU Ack message from the DVB-GW, the Ext-MR-HA sends a NEMO BU Ext Ack message to the MR. Figure 14 illustrates the NEMO BU Ext Ack message. The new flag (E) is included in this Binding Acknowledgement to confirm that Ext-MR-HA received the NEMO BU Extension and that the DVB-GW has successfully been configured.

Claims

CLAIMS

1. A method of establishing communication between a unidirectional network and a mobile station, the method comprising the steps of: a. sending a message from the mobile station to a home agent of the mobile station via a bidirectional network, the message containing a care-of-address of the mobile station and an identification of the unidirectional network; b. sending the message from the home agent of the mobile station to the unidirectional network; c. sending an acknowledgement of the message from the unidirectional network to said home agent; and d. sending the acknowledgement from said home agent to the mobile station via the bidirectional network.

2. A method according to claim 1, wherein the home agent of the mobile station is part of the bidirectional network.

3. A method according to claim 1, wherein the home agent of the mobile station is not part of the bidirectional network.

4. A method according to claim 1, 2 or 3, wherein the identification of the unidirectional network comprises the network identity, the cell identity and the Network Information Table (NIT) and/or Program Association Table (PAT) and/or Program Map.

5. A method according to any preceding claim, wherein the message includes the media access control (MAC) address of a unidirectional interface of the mobile station.

6. A method according to any preceding claim, comprising establishing a tunnel for forwarding signalling messages from the home agent to the unidirectional network and vice versa.

7. A method according to any preceding claim, wherein the unidirectional network is a DVB (digital video broadcasting) network.

8. A method according to any preceding claim, wherein the mobile station is a mobile router for use in a mobile network comprising a plurality of nodes arranged to move substantially together with the mobile router.

9. A mobile station comprising a unidirectional interface configured to send to a bidirectional network a message containing a care-of-address of the mobile station and an identification of a unidirectional network in order to establish communication between the unidirectional network and the mobile station.

10. A mobile station according to claim 9, wherein the identification of the unidirectional network comprises the network identity, the cell identity and the network identification table of the unidirectional network network identity, the cell identity and the Network Information Table (NIT) and/or Program Association Table (PAT) and/or Program Map.

11. A mobile station according to claim 9 or 10, wherein the message includes the media access control (MAC) address of the unidirectional interface of the mobile router.

12. A mobile station according to claim 9, 10 or 11, consisting of a mobile router for use in a mobile network comprising nodes arranged to move substantially together with the mobile router 13. A home agent for a mobile station, the home agent being configured to send a message from the mobile router to a unidirectional network, the message containing a care-of-address of the mobile station and an identification of a unidirectional network in order to establish communication between the unidirectional network and the mobile station.

14. A home agent according to claim 13, including means for establishing a tunnel for forwarding signalling messages from the home agent to the unidirectional network and vice versa.

15. A home agent according to claim 13 or 14, wherein the identification of the unidirectional network comprises the network identity, the cell identity and the Network Information Table (NIT) and/or Program Association Table (PAT) and/or Program Map.

16. A home agent according to claim 13, 14 or 15, wherein the message includes the media access control (MAC) address of the unidirectional interface of the mobile station.

17. A gateway for a unidirectional network, the gateway being configured to receive a message from a home agent of a mobile station, the message containing a care-of-address of the mobile router and an identification of the unidirectional network, and to send an acknowledgement of the message to said home agent in order to establish communication between the unidirectional network and the mobile station.

18. A gateway according to claim 17, wherein the identification of the unidirectional network comprises the network identity, the cell identity and the Network Information Table (NIT) and/or Program Association Table (PAT) and/or Program Map.

19. A gateway according to claim 17 or 18, wherein the message includes the media access control (MAC) address of the unidirectional interface of the mobile station.