GB2438666A

GB2438666A - Simultaneous support of multiple mobility protocols in a flexible reconfigurable mobile terminal

Info

Publication number: GB2438666A
Application number: GB0610849A
Authority: GB
Inventors: Nikolaos Georganopoulos; Konstantinos Boukis
Original assignee: Toshiba Research Europe Ltd
Current assignee: Toshiba Europe Ltd
Priority date: 2006-06-01
Filing date: 2006-06-01
Publication date: 2007-12-05
Anticipated expiration: 2026-06-01
Also published as: GB2438666B; GB0610849D0

Abstract

A method to enhance the design of flexible network protocol stack to concurrently support multiple modular mobility protocols is based on the derived framework enabling the design of such a flexible reconfigurable terminal. It can further control at run time the mobility protocols and thus transparently operate more than one protocol simultaneously, for example, both macro and micro mobility protocols. A dynamic protocol database 180 stores the location of the various protocol modules in the memory 150. A single reconfiguration element is maintained in a Generic Mobility Components 130 and is controlled by an Event Identifier in the Generic Mobility Component Manager 110. The Event Identifier 114 is enhanced to process all incoming events and reconfigure the elements to the related part of the Protocol Database according to the relevant protocol the event is associated with. The resulting flexible architecture employs an enhanced protocol component design and may be implemented in numerous manners and platforms. A mobile terminal 100 with this architecture may move around and transparently connect to different access networks. It is further enabled to operate concurrently more than one protocol to fulfil various application scenarios and their requirements. This enables mobile terminals to become more intelligent and operate flexibly in a heterogeneous multi-access network environment with multiple protocol support.

Description

METHOD TO SUPPORT MULTIPLE MOBILITY PROTOCOLS iN A FLEXIBLE

RECONFIGUIRABLE MOBILE TERMiNAL The present invention relates to a method to support multiple mobility protocols in a flexible reconfigurable mobile terminal. More particularly it relates to a method to support concurrent multiple TIP mobility protocols in a flexible terminal enabled with a modular reconfigurable protocol stack. It further relates to corresponding mobile terminals.

It is envisaged that in the future, communication systems, including wireless, will employ pure Internet Protocol (IP) as the solution for packet transport between nodes, with the mobile terminal normally being the last node or sink of the data flow. A Mobile Terminal (MT) could be equipped with one ore more wired network interfaces, thus enabling it to move and cormect to different fixed networks. In a wireless communication scenario a MT with one or more wireless interfaces coimects to the fixed network, through one or more Access Points (AP) or Base Station (BS).

In the Internet, different protocols are employed to solve issues like [P mobility management, Quality of Service, security, routing. These solutions are proposed and standardised in the Internet Engineering Task Force (IETF). Fixed network protocol solutions are often adapted, or new protocols are designed to cater for the specific requirements of MTs. As a result, a plethora of protocols is proposed to solve these problems, some for specific communication scenarios and applications and some for general cases.

In addition, advances in software radio technologies will enable terminals to be equipped with reconfigurable RF front ends. This will enable a wireless MT to modify its wireless properties and connect to different Access Networks (AN).

In US6172980 a network bridge/router for identifying a data unit to be routed by a network bridge/router is described.

In W00124458 wireless communication of concurrent voice and data is disclosed, using overlapping protocols.

In EP097 1289, an apparatus and a method for concurrently executing multiple instructions are disclosed.

In US 2004/022095 8 a multiple protocol database is proposed.

A system and a method for enabling multi-protocol database transaction processing has been described in US2004078377.

In co-pending patent application GB0606002.8 a terminal architecture to support a reconfigurable modular mobility protocol stack was designed. This framework was also applied to the family of mobility management protocols and a Generic Mobility Component (GMC) has been developed, which is included in co-pending patent application GBO5 10738.8. This GMC enables a flexible and reconfigurable mobile terminal operation in the presence of multiple access networks with support for different mobility management protocols.

The designed mobile terminal can reconfigure the protocol modules it supports and change the relevant mobility protocol operation. There are cases though where more than one protocol needs to be supported at the same time. In the case of mobility protocols and as has already been discussed above, micro and macro mobility often need to be addressed at the same time. A mobile terminal thus needs to be able to support one protocol (e.g. MIPv6 D. Johnson, C. Perkins, J. Arkko, "Mobility Support for IPv6", IETF Request for Comments 3775, June 2004) for macro mobility, i.e. movement between large networks or administrative domains, where the IP address of the terminal changes and another protocol (e.g. HMIPv6 H Soliman, C. Castelluccia, El Malki, K., and L. Bellier, "Hierarchical Mobile lPv6 mobility management (HIMIPv6)", IETF, draft-ietf-mipshop-hmipV6-O4.tXt (work in progress), December 2005; BCMPv6 Costas Boukis, Nikos Georganopoulos, Hamid Aghvami, "A Hardware Implementation of BCMP Mobility Protocol for IPv6 Networks", GLOBECOM 2003, San Francisco; B. Stiller, C. Class, M. Waldvogel, 0. Caronni, D. Bauer, B. Plattne, "The Design and Implementation of a Flexible Middleware for Multimedia Communications Comprising Usage Experience", 1998, http://olymp.org/-caronni/work/papers/TIK-Report54.pdf) for micro mobility, i.e. frequent handovers between different APs inside the same network, where the IP address of the terminal does not change. In the case of combined macro/micro mobility management the protocols must interoperate. Further it is envisaged in more scenarios that other multiple network protocols like quality of service or routing could be supported for different data streams over the same interface in the access network. In these cases protocol interoperation might also be needed.

In conventional implementations where every protocol runs independently in a different system process information exchange can be achieved through signalling which raises performance and synchronization concerns. Copying data from a process to another is a time consuming task and there is no guarantee that notifications between protocols will be timely. For instance, in the case of mobility protocols, when the micro mobility protocol detects the presence of an access network it will generate a signal to inform the macro, however, in the meantime, and prior to receiving and processing this signal the macro mobility protocol could have detected the new network as well and initiated a registration. These interoperation procedures are not part of the standard protocol design and are extra functionalities that need to be specified.

The limitation of the current GMC design according to co-pending patent application GB0606002.8 is that only one protocol can be supported at any time. Protocol modules are loaded in the system memory at rim time and their memory location is lost once the new protocol modules are loaded.

It is therefore desirable to enhance the mobile terminal operation to support concurrent multiple protocol operation and in the case of mobility management protocols it would be advantageous to support macro/micro mobility protocol cooperation.

Accordingly, aspects of the present invention seek to mitigate, alleviate or eliminate the above-mentioned problem.

In a first aspect of the present invention, a method of communication comprises the steps of processing an incoming data control packet by means of data control packet processing means; storing one or more sets of communication protocols for simultaneous use in a plurality of reconfigurable modules; configuring and controlling said data control packet processing means such that in use said plurality of reconfigurable modules are simultaneously implemented by means of said communications protocols to receive said incoming data control packet; and obtaining said incoming data control packet and arranging said incoming data control packet such that in use said incoming data control packet corresponds with said communications protocols simultaneously implemented in said reconfigurable modules.

In a first configuration of the above aspect, multiple protocols are flexibly supported.

In another configuration of the above aspect, a dynamic protocol database is provided.

In a further configuration of the above aspect, the dynamic protocol database is adapted to store the various protocol modules in memory.

In a configuration of the above aspect, a single RE is maintained in the generic mobility component.

In one more configuration of the above aspect, the RE is controlled by the event identifier in the generic mobility component.

In a further configuration of the above aspect, the event identifier is adapted to support multiple protocols.

In a configuration of the above aspect, the event identifier is further adapted to process all incoming events and to adjust the elements to the related parts of the protocol DB according to the relevant protocol the event is associated with.

In one more configuration of the above aspect micro and macro mobility protocols are supported at the same time In another aspect of the present invention, a mobile terminal comprises a data control packet processing means operable to process an incoming data control packet, said data control packet processing means further comprising a plurality of functional modules and a plurality of reconfigurable modules; a memory means operable to store one or more sets of communications protocols for simultaneous use in said plurality of reconfigurable modules; a control means operable to configure and control said data control packet processing means such that in use said plurality of reconfigurable modules are simultaneously implemented by means of said communications protocols to receive said incoming data control packet; and an input terminal operable to receive said incoming data control packet, said input terminal further comprising a queuing means such that in use said incoming data control packet corresponds with said communications protocols simultaneously implemented in said reconfigurable modules.

In a first configuration of the above aspect, the mobile terminal is further adapted to flexibly support multiple protocols.

In a further configuration of the above aspect, the mobile terminal further comprises a dynamic protocol database.

In another configuration of the above aspect, the dynamic protocol database is adapted to store the various protocol modules in memory.

In another configuration of the above aspect, the the event identifier is adapted to support multiple protocols.

In a further configuration of the above aspect, the event identifier is further adapted to process all incoming events and to adjust the elements to the related parts of the protocol DB according to the relevant protocol the event is associated with.

In one more configuration of the above aspect, the mobile terminal is further adapted to support micro and macro mobility protocols at the same time In another aspect of the present invention, a computer program comprises data processing device program code means adapted to perform the method of the first aspect, when said program is run on a data processing device In a further aspect of the present invention, a computer-readable medium comprises computer-executable instructions for performing the method of the first aspect, when said instructions are executed on a data processing device According to the present invention a method is provided for enhancing the terminal flexible reconfigurable network protocol stack with a method to support multiple protocols in the same family and thus protocol cooperation.

The use of the method according to the invention in the context of the flexible reconfigurable terminal protocol stack facilitates transparent and secure protocol cooperation.

In order to provide a mobility service that takes advantage of fast handovers provided by micro mobility and global IP address mobility provided by macro mobility, these protocols must interoperate. This interoperation is not achieved simply by installing the protocols and by operating them simultaneously, since numerous aspects should be considered.

These and other aspects of the invention will now be further described, by way of example only, with reference to the accompanying figure in which Figure 1 depicts an embodiment of the enhanced flexible architecture according to the present invention.

Referring now to Figure 1, in an embodiment of the present invention, the modules, collectively referred to as reconfigurable mobility protocol architecture 100 are described as follows.

A Generic Mobility Component Manager (GMCM) 110 is a terminal module responsible for controlling the flexible reconfigurable process. Input events 120 are passed to the GMCM 110 which identifies whether a related mobility protocol is currently supported (loaded) by a Generic Mobility Component (GMC) 130. If a mobility protocol is currently installed, the event is then pushed to the GMC 130 for processing. If the protocol is not installed, but the protocol modules are stored in the mobile terminal, it loads the modules through instructing the Dynamic Loader 112, and modifies the GMC's individual components to deploy the newly installed protocol modules. The operation of the GMC's individual components is described in the following paragraph. If the relevant protocol modules are not stored in the mobile terminal, it initiates a new procedure to acquire the modules from external entities. This procedure is not specified here, as it is a different work area.

The Generic Mobility Component (GMC) 130 behaves according to the protocol currently installed. Initially the message is passed to the packet verification component 131 so as to verify the packet's consistency and to discard bogus messages. Valid protocol messages are then passed to the movement detection component 132 for identification of mobile terminal network movements and then the packet is pushed to a handler 133 for processing. The behaviour of the handler 133 varies from one protocol to another and also from one input message to another. This component 133 is responsible for initiating the appropriate procedures in the event of MT registration, MT handover, or simple reception of acknowledgement messages. The handler 133 is responsible for identifying when a network related reconfiguration is required. Thus it instructs the network configuration component 136 to perform the desired operation according to the specifications of the mobility protocol.

Additionally the handler sets timers 135 and is also responsible for initiating procedures that are triggered from the timers 135. Mobility protocols define functionalities that are triggered from the timers 135 and aim to enhance protocol reliability. One such example is the retransmission of handover messages if an acknowledgement is not received within a specified time period. In the GMC 130 the timer 135 is responsible for generating these events. The handler 133 sets the timer 135 after the transmission of the protocol control message and the timer 135 on its behalf notifies the handler 133 when the time period from the transmission of the message has elapsed. The handler 133 then passes information to the packet constructor, who generates the relevant protocol message to be transmitted.

Various mobility protocols can be modelled with the above abstractions, independent from the type of mobility which they address. The internal behaviour of the abstractions can either vary significantly or not vary at all from one protocol to another.

In the latter case, the behaviour of the network configuration 136 together with the timer components is specific to the underlying Operating System and thus in the specific design those components do not need to be modified. On the other hand, the remaining components operate according to the intrinsic characteristic of the mobility protocols and thus those components need to be replaced when the terminal reconfigures from one mobility protocol to another. As a result, packet verification 131, movement detection 132, handler 133 and packet construction 134 components include a Reconfigurable Element (RE), to enable them to dynamically change to different protocol modules. On the other hand network configuration 136 and the timers 135 are common and fixed in the GMC 130, and therefore do not need to comprise REs.

The architecture of the described embodiment consists of a selection of module components that interact. These components include the components of the GMC 130 as described above and a Generic Mobility Component Manager (GMCM) 110.

Following the design framework the most appropriate Model of Computation (MoC) is chosen and adapted to exactly fit the operation requirements of the GMC 130. In the case of mobility protocol family Component Interaction (CI) MoC is used (see David Clark, "Structuring of systems using upcalls", ACM Symposium on Operating System Principles, December 1985). CI is a model which is specifically designed for network protocols and specifies data being pushed or pulled between components. In both cases communication is data driven. Input messages are pushed to the GMCM 110. Message prncessing occurs in the GMCM 110 according to the procedures described later. The message is then pushed to the GMC 130 for processing. Inside the GMC 130, messages are pushed to the internal components according to the procedure described above.

However, a more thorough insight about the handler-timer interaction raises a significant issue in the system design. Although no message is passed from handler 133 to the timer 135, the timer 135 generates events (notifications) that must be passed back to the handler 133 for processing. Since these events are time varied and can happen in the future, there is a chance that a reconfiguration procedure might have happened and the GMC 130 components have changed to an entirely different protocol. This would result in system instability and erroneous operation since the wrong handler protocol component would be notified. Similarly there are other system events, generated randomly, and not network layer3 events, which need to be passed to protocol modules to enhance protocol performance. For example, link layer-2 changes (channel, network id), can be passed to the movement detection 132 component to instruct the handler 133 to initiate a handover. It has to be ensured that such events are passed to the correct module component and the GMC 130 is not in the process of reconfiguring to a new protocol operation.

As a result, to ensure that the right events are processed from the correctly installed module components and the system operation remains linear, an input queue 140 is included in the architecture. Every input event, i.e. message, timer event, system event, which is to be processed from the GMC 130 is placed into the input queue 140 and from there the events are retrieved (pulled) by the GMCM 110 in order to be processed, and if needed, passed to the GMC 130. This procedure adds a slight delay in input events processing, but on the other hand secure linear operation of the system is ensured, an important requirement for reliable dynamic reconfiguration. Furthermore, the use of the CI MoC, enables implementation of the architecture in a single thread using a single programming language such as C, Java, or C++. This attribute enables dynamic modification of the architecture, by employing the software techniques described below.

The maimer in which dynamic reconfiguration is performed in the system will now be described. This is implementation related and therefore does not have a major effect on the architecture design. A platform specific method for loading and unloading at run-time the various reconfigurable modules is provided. These include the GMC 130 and GMCM 110, which are represented as kernel modules in Figure 1, and the various supported protocols 152-1, 152-2, 152-3 loaded in the system memory (as are the kernel modules as well). An example of such a method is the Dynamic Linking facility available in all operating system platforms, including Windows and Linux. This requires that platform specific binaries are available in the terminal and loaded in the memory. Furthermore these modules need to be compliant to the GMC 130 specifications and ensure interoperability between the components. This again is implementation specific and thus is resolved at realisation time.

A method for the GMCM 110 to access at run-time the relevant protocol modules by modifying the Generic Component Manager. Reconfigurable Elements (RE) in Generic Components 131, 132, 133, 134 can be dynamically changed via the entries 182-1, 182- 2, 182-3 in the protocol DB 180 to point to the appropriate place in the memory 150 where modules 152-1, 152-2, 152-3 are loaded. REs can be pointers to functions in the case of programming languages like C, or overridden parent/child classes in the case of object oriented classes (C++, Java). Again this is an implementation specific issue.

Changes to the mobile terminal's operating system (kernel) have to be made to support the GMC 130. Kernel modifications are needed that specifically intercept mobility protocol related messages, or protocol messages and passed to the GMCM 110 for processing. In the case that other system process could pass events to the GMC 1 30 they also need to be altered to support that. Interception of some messages (e.g. lPv6 router advertisements) also requires some system control functions of the kernel to be disabled, since they bypass IP input and directly call relevant system processes. This will enable all relative messages to reach the IP input and then be intercepted and pushed to the input queue.

In the GMC 130 a single process is responsible for simultaneously managing mobility protocols, which facilitates information exchange and synchronicity issues. To further enable the mobile terminal to support multiple protocol cooperation the design needs to be enhanced by enhancing the intelligence of the GMCM: Multiple protocols are flexibly and simultaneously supported by adding a dynamic Protocol Database (DB) 180 that stores the location 1 82-1, 182-2, 182-3 of the various protocol modules 152-1, 152-2, 152-3 in the memory 150. A single RE is maintained in the GMC components and is again controlled by the Event Identifier 114 in the GMCM.

The Event Identifier in the original single protocol support case only processes new incoming events to initiate a reconfiguration event and calls the Dynamic Loader to load the new protocol modules. In order to support multiple protocols of any protocol family the Event Identifier 114 is further enhanced to continuously process all incoming events and adjust the elements to the related part of the Protocol DB 180 according to the relevant protocol the event is associated with.

The resulting protocol component design and Protocol DB can be implemented in numerous manners and platforms. The enhanced design is also backward compatible and can still support a single protocol. (A practical implementation of the described design has been realised as a proof of concept and for performance evaluation.) In the foregoing, the details of the enhancements needed for a flexible reconfigurable terminal to support multiple mobility protocol components have been described. This enables the terminal to transparently support concurrent protocols, when connected to an access network, and change at run-time the supported mobility management protocol.

By employing the Protocol DB, protocol components' place in the memory is stored and GMC reconfiguration of REs takes place to link to the appropriate DB entries. The Protocol DB can also be dynamically extended to add and remove protocols and their details on demand. DB entries are fixed and pointing to the system memory where protocol modules are initially loaded by the Dynamic Loader.

By enhancing the operation of the Event Identifier, all incoming events are processed, the relevant protocol is identified and the REs are changed to link to the operation of the specific protocol.

According to the present invention, the design of a flexible reconfigurable terminal mobility protocol component has been enhanced to concurrently support multiple protocols.

The main benefit of the present invention is that a single system process is still responsible for operating multiple protocols, thus avoiding Inter Process Communication. Hence security and terminal resource utilisation can be increased.

Moreover, the present invention facilitates protocol interoperation with this being centrally controlled with the GMCM.

Further, by applying the present invention backward compatibility with the single protocol is maintained and there is no performance overhead.

Overall, the benefit of the enhanced design according to the present invention is that a secure, efficient, fast and smooth reconfiguration process is achieved to support concurrent multiple protocol operation.

The terminal designed in accordance with the present invention can support micro and macro mobility protocols at the same time. Micro mobility protocols can be categorized in two groups depending on the interoperation with a macro mobility protocol needed: Group A: Macro protocol mobility registration message is needed to set up also the micro mobility registration. In this case, from the mobile terminal perspective the proposed functionality is just an extension to the macro protocol functionality. In this group since both registrations are managed from the same handler no protocol interoperation is required.

Group B: Separate independent micro protocol registration is necessary. These protocols require a micro protocol registration to be accomplished before initiating a macro protocol registration. Thus the micro mobility protocol, after accomplishing the registration, it must notify the macro mobility protocol and also pass to it the locally acquired address (care-of address) necessary for the latter to perform its registration.

Initially the macro mobility protocol must be alerted that the mobile terminal has access to an access network which offers micro mobility service and thus from this point on movement detection, routing table manipulation and IP address acquisition will be handled from another protocol. After the micro protocol has accomplished its registration, the macro protocol must be triggered so as to update the link between mobile terminal's permanent IP address arid the temporary care-of address attained from the micro mobility protocol. It is obvious thus that protocol module modification is needed to support this interoperation.

MIPv6 is considered the main macro mobility protocol according to the invention.

HMIPv6 and BCMPv6 are micro mobility protocol that may also be considered. In the implementation two protocols may be concurrently installed in the terminal and the reconfiguration managed by the GMCM. Incoming events are processed in the Event Identifier and the relevant protocol is accessed. Evaluation results showed that the terminal's network perfonnance may be attained in the same standards as if a single mobility protocol was operating. Thus the extra processing of managing the DB and adjusting the GMC for every event did not deteriorate the performance.

Although the examples described in the present invention refer to IPv6, it is evident to the person skilled in the art that the present invention may equally well be employed under other Internet protocols, e.g. IPv4. Moreover, other suitable communications protocols may also be employed.

According to the present invention a method to enhance the design of flexible network protocol stack to concurrently support multiple modular mobility protocols is based on the derived framework enabling the design of such a flexible reconfigurable terminal. It may further control at run time the mobility protocols and thus transparently operate more than one protocol.

A dynamic protocol database stores the location of the various protocol modules in the memory. A single reconfiguration element is maintained in a Generic Mobility Components and is controlled by an Event Identifier in the Generic Mobility Component Manager. The Event Identifier is enhanced to process all incoming events and reconfigure the elements to the related part of the Protocol Database according to the relevant protocol the event is associated with.

The resulting flexible architecture employs an enhanced protocolcomponent design and may be implemented in numerous manners and platforms. A mobile terminal with this architecture may move around and transparently connect to different access networks. It is further enabled to operate concurrently more than one protocol to fulfil various application scenarios and their requirements. This could enable mobile terminals to become more intelligent and operate flexibly in a heterogeneous multi-access network environment with multiple protocol support.

No doubt many other effective alternatives will occur to the skilled person. It will be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the spirit and scope of the claims appended hereto.

Claims

CLAIMS

1. A method of communication comprising the steps of: processing an incoming data control packet by means of data control packet processing means; storing one or more sets of communications protocols for simultaneous use in a plurality of reconfigurable modules; configuring and controlling said data control packet processing means such that in use said plurality of reconfigurable modules are simultaneously implemented by means of said communications protocols to receive said incoming data control packet, and; obtaining said incoming data control packet and arranging said incoming data control packet such that in use said incoming data control packet corresponds with said communications protocols simultaneously implemented in said reconfigurable modules.

2. The method of claim 1, wherein multiple protocols are flexibly supported.

3. The method of claim 2, wherein a dynamic protocol database is provided.

4. The method of claim 3, wherein the dynamic protocol database is adapted to store the various protocol modules in memory.

5. The method according to any of the preceding claims wherein a single RE is maintained in the generic mobility component.

6. The method according to claim 5, wherein the RE is controlled by the event identifier in the generic mobility component.

7. The method according to any of the preceding claims, wherein the event identifier is adapted to support multiple protocols.

8. The method according to claim 7, wherein the event identifier is further adapted to process all incoming events and to adjust the elements to the related parts of the protocol DB according to the relevant protocol the event is associated with.

9. A method according to any of the preceding claims, further comprising the steps of supporting micro and macro mobility protocols at the same time.

10. A mobile terminal comprising: a data control packet processing means operable to process an incoming data control packet, said data control packet processing means further comprising a plurality of functional modules and a plurality of reconfigurable modules; a memory means operable to store one or more sets of communications protocols for simultaneous use in said plurality of reconfigurable modules; a control means operable to configure and control said data control packet processing means such that in use said plurality of reconfigurable modules are simultaneously implemented by means of said communications protocols to receive said incoming data control packet, and; an input terminal operable to receive said incoming data control packet, said input terminal further comprising a queuing means such that in use said incoming data control packet corresponds with said communications protocols simultaneously implemented in said reconfigurable modules.

11. The mobile terminal of claim 10, further adapted to flexibly support multiple protocols.

12. The mobile terminal of claim 10 or 11, further comprising a dynamic protocol database.

13. The mobile terminal of claim 12, wherein the dynamic protocol database is adapted to store the various protocol modules in memory.

14. The mobile terminal according to any of claims 10-13, wherein a single RE is maintained in the generic mobility component.

15. The mobile terminal according to claim 14, wherein the RE is controlled by the event identifier in the generic mobility component.

16. The mobile terminal according to any of claims 10 to 15, wherein the event identifier is adapted to support multiple protocols.

17. The mobile terminal according to claim 16, wherein the event identifier is further adapted to process all incoming events and to adjust the elements to the related parts of the protocol DB according to the relevant protocol the event is associated with.

18. A mobile terminal according to any of claims 10 to 17, further adapted to support micro and macro mobility protocols at the same time 19. A computer program comprising data processing device program code means adapted to perform the method of any of claims 1 to 8, when said program is run on a data processing device 20. A computer-readable medium comprising computer-executable instructions for performing the method of any of claims 1 to 8, when said instructions are executed on a data processing device