FIELD OF INVENTION

The present invention relates to a method of secure handover and related devices, in particular a method of operating an access point in a wireless communication environment for secure handover, a related access point, and a mobile terminal for executing handover between different access points.

BACKGROUND ART

In a mobile communication environment, when a mobile terminal MT having established a communication session with an access point moves and becomes able to attach to a new access point AP, the new access point AP will require an authorization of the mobile terminal MT before accepting the handover. Therefore, while moving a mobile terminal attached to the access point it reaches the coverage area of the new access point. If the new access point AP spans an overlapping coverage area, a handover is one solution to maintain seamless connectivity for the mobile terminal MT.

However, before a new access point AP accepts the handover thereto, an authorization of the mobile terminal MT is necessary. Such an authorization typically requires that the mobile terminal MT supports the authorization procedure by providing information. This information allows the new access point to validate identity and authorization credentials, both referred to as credentials, or handover secret in short in the following, of the mobile terminal MT. When the new access point successfully verifies this information, it accepts handover of the mobile terminal from the previous access point.

In view of the above, performance related to authorization, which in fact contributes to total latency of the handover process or the fraction of time, a mobile terminal MT actually lacks connectivity to any access point, depends on the effort for distributing credentials to mobile terminals, the use of credentials within handover procedures, and the verification of credentials at the access point whereto handover is executed. Therefore, handover solutions according to prior art assume that credentials and/or handover secrets are generated at the old access point, used during the handover procedures, and, once the mobile terminal MT presents the credentials to the new access point, then the new access point will have access to the old access point for verification purposes. However, this leads to significant delay of handover procedure execution.

Yet another disadvantage of those solutions is that a mobile terminal is allowed during handover to be attached to the new access point, and only then the related handover credentials are verified. Considering the case that the verification process shows that the mobile terminal is not allowed to execute handover, significant signaling load between the- mobile terminal and the new access point occurs without eventual handover of the mobile terminal to the new access point. In other words, the approach according to prior art leads to a waste of scarce radio resources for control signaling, should the mobile terminal not be authorized to execute handover. It should be noted that the above deficiencies occur irrespective of different fields of mobile communication environments, e.g., according to 802.IX, mobile IP/Seamoby, hierarchical mobile IP, fast mobile IP, and/or any other type of second and third mobile communication systems according to any type of communication standards. SUMMARY OF INVENTION

In view of the above, the object of the present invention is to provide a handover framework increasing performance efficiency while reducing software managerial effort, in particular for authorization security services in secure handover procedures.

As will be explained in the following, to achieve this object, the present invention relates to the operation structure of three operation subunits of the mobile communication environment, i.e. a mobile terminal for which secure handover is executed, a new access point to which secure handover is executed, and a previous access point to which the mobile terminal establishes a communication session prior to secure handover.

In more detail, the operation of the new access point in the wireless communication environment comprises the steps of generating handover secrets for secure handover and distributing the handover secrets to neighborhood access points for forwarding to mobile terminals being handover candidates prior to secure handover.

Further, the operation at the previous access points supporting secure handover of a candidate mobile terminal to the new access point comprises the steps of receiving the handover secrets from the new access point and forwarding the handover secrets to a handover candidate mobile terminal having a communication session established with the previous access prior to secure handover of the candidate mobile terminal.

Still further, the operation of the mobile terminal during secure handover from the previous access point to the new access point in the wireless communication environment comprises the steps of receiving the handover secrets prior to secure handover from the previous access point having the communication session established to the mobile terminal and forwarding the received handover secrets to the. new access point at the time of secure handover for mobile terminal authorization.

In view of the above, the present invention is based in the insight that the distribution and application of handover secrets involves closely related activities at a new access point at the previous access point and at the mobile terminal executing secure handover. In particular, the present invention uses an approach which is fully opposite to the principles applied in the prior art in that it is the new access point that generates handover secrets and not the previous access point.

Yet another important advantage of delivery of handover secrets to the previous access point and related forwarding thereof to the mobile terminals is that according to the present invention, handover attempts are only accepted at the new access point from authorized mobile terminals, so as to avoid unnecessary control signaling load in the mobile communication environment.

Further solution properties of the invention are the applicability of existing security associations between access points, e.g., a plurality of previous access points and a new access point, the reduction of interactions/round trips of handover secrets for speed- up of handover procedure. Further, as the new access point verifies the handover secret that was reduced by the new access point itself, the inventive secure handover framework is independent of the quality of secret, applicable to any type of L2/L3 combination and available in support of any services on higher layers of the OSI-model.

The reason for this is that the previous access point and the new access point know each other via the security association and that the previous access point has authorized the mobile terminal which authorization may be trusted by the new access point during re- authorization of the mobile terminal at the new access point during handover.

Further preferred embodiments of the present invention are related to the operation of the new access point.

In particular, according to a corresponding preferred embodiment, the generation and distribution of handover secrets is executed on the condition that the new access point accepts new secure handovers.

According to this preferred embodiment, it is possible to avoid unnecessary signaling traffic in the mobile communication network. In other words, e.g., should the new access point be already operated at the capacity limit, no further handovers thereto would be acceptable, so that related distribution of handover secrets is avoided at all. Therefore, not only traffic in the core network with respect to a handover would finally be rejected by the new access point. The same advantage also applies with respect to the signaling traffic between the previous access point and the mobile terminal and the mobile terminal and the new access point before rejection of the handover by the new access point.

According to yet another preferred embodiment being related to the operation of the new access point, it is suggested that the distributed handover secret is used for authorization of the mobile terminal for secure handover at the new access point.

Therefore, contrary to the prior art, the present invention suggests that the new access point generating the handover secret actually verifies the handover secret it has previously distributed so as to achieve local operation of the new access point for verification of handover secrets without interaction with other mobile communication network elements. This improves the time period used to verify handover secrets at the new access point.

Further, according to yet another preferred embodiment of operation of the new access point, it is suggested to generate handover secrets and distribute these handover secrets regularly and frequently, e.g., according to a predetermined handover secret generation timing.

As the new access point sends the handover secrets frequently to interested previous access points in its neighborhood, there may be achieved an improvement for the time period until a handover secret for the handover is available at the previous access points. Further, timestamps to prevent reply attacks are not required, as they are superseded by the regularly sent handover secrets.

In view of the above, with respect to the operation of the new access point, the present invention allows for an improvement of deployment of handover secret generation and handover secret verification software. Further, the operator of the new access point has full freedom to decide on how stringent the handover secret shall be. All this may be achieved by one and only one network element, i.e. the new access point, or in or close to the new access point. Further preferred embodiments are related to the operation of previous access points.

According to a first such preferred embodiment, it is suggested that any previous access point executes an authorization at the new access point prior to handover. Upon successful authorization, preferably there follows a step of registration of the previous access point at the new access point for subsequent handover secret delivery.

The important advantage of this preferred embodiment is the establishment of trust between the previous access point and the new access point prior to actual execution of secure handover so as to achieve a further acceleration of handover authorization execution.

Another important advantage of this preferred embodiment, in particular in view of the registration of previous access points at the new access point, is that the operator of the new access point may decide on which type, category, or class of previous access points is willing to accept for execution of secure handover. This is of particular importance, should the secure handover be executed across different types of mobile communication environments or across boundaries of network communication environments run by different operators. According to a further preferred embodiment of operation of the previous access points, it is suggested to authorize the mobile terminal at the previous access point.

The advantage of this preferred embodiment is that, in view of forwarding of handover secrets, not only an authorization is executed between previous access points and new access points, but also between previous access points and the mobile terminal for setup of an authorized communication channel from the handover target, i.e. the new access point, down to the mobile terminal in preparing a secure handover.

According to a further preferred embodiment of operation of previous access points, it is the previous access point which indicates secure handover. Alternatively, it may also be the mobile terminal which indicates secure handover.

In other words, advantageously according to the present invention, there is no restriction on which network element actually indicates handover, i.e. either the previous access point or mobile terminal, so that secure handover of the present invention may be applied to any type of network-assisted or mobile-assisted handover or any hybrid form thereof. Further preferred embodiments of operation of previous access points are related to the type of forwarding of handover secrets to the mobile terminal.

According to first preferred embodiment, this forwarding of handover secrets is executed in an event-driven way, where handover secrets are forwarded to the mobile terminal only upon indication of the handover. This approach has the advantage of minimized communication traffic for forwarding of handover secrets.

Alternatively, according to the present invention, it is also considered that handover secrets are forwarded frequently from previous access points to the mobile terminal, so that at the time of handover indication no further signaling must take place for forwarding of handover secrets and the mobile terminal may directly proceed to authorization at the new access point to further reduce the secure handover time period.

According to another preferred embodiment of the present invention there is provided a computer program product directly loadable into the internal memory of an access point of a mobile communication environment and/or mobile terminal comprising software code portions for performing the inventive method steps when the product is run on a processor of the access point and/or mobile terminal. Therefore, the present invention is also provided to achieve an implementation of the inventive method steps on computer or processor systems. In conclusion, such implementation leads to the provision of computer program products for use with a computer system or more specifically a processor comprised in e.g., an access point of a mobile communication environment or a related mobile terminal.

This programs defining the functions of the present invention can be delivered to a computer/processor in many forms, including, but not limited to information permanently stored on non-writable storage media, e.g., read only memory devices such as ROM or CD ROM discs readable by processors or computer I/O attachments; information stored on writable storage media, i.e. floppy discs and harddrives,- or information convey to a computer/processor through communication media such as network and/or Internet and/or telephone networks via modems or other interface devices. It should be understood that such media, when carrying processor readable instructions implementing the inventive concept represent alternate embodiments of the present invention. DESCRIPTION OF DRAWING

In the following, the best mode and preferred embodiments of the present invention will be described with respect to the drawing, in which:

Fig. 1 shows a basic principle underlying the technical teaching of the present invention;

Fig. 2 shows the operational context for secure handover of a mobile terminal between a previous access point and the new access point according to the present invention;

Fig. 3 shows a schematic diagram of an access point according to the present invention;

Fig. 4 shows a flowchart of operation for the access point shown in Fig. 3 operated as new access point;

Fig. 5 shows a first flowchart of operation for the access point shown in Fig. 3 operated as previous access point;

Fig. 6 shows a second flowchart of operation for the access point shown in Fig. 3 operated as previous access point; Fig. 7 shows a schematic diagram of the mobile terminal;

Fig. 8 shows a first flowchart of operation for the mobile terminal shown in Fig. 7; and

Fig. 9 shows a second flowchart of operation for the mobile terminal shown in Fig. 7.

DESCRIPTION OF BEST MODE AND PREFERRED EMBODIMENTS

In the following, the best mode of operating the present invention and preferred embodiments thereof will be explained with reference to the drawing. Insofar as functionality according to the present invention is explained, it should be noted that this functionality may be implemented either in hardware and/or software and/or any combination thereof. Further, it should be noted that the present invention is applicable to any type of mobile communication environment wherein secure handover is applied, e.g., WLAM, mobile communication standards GSM, 3G mobile communication standards, mobile IP, etc.

In view of the above, access point in the sense of the present invention may be understood as any type of core network and radio network for establishment of the communication session between mobile terminals and the core network. Further, the handover secret or handover credential to be referred to in the following is to be understood as an item of information that is protected and used for authentication. The term 'handover secret' implies, e.g., symmetric and private keys and passwords, see IETF RFC 2828. Therefore, handover secret is any type of secret information, e.g., a token that the new access point expects to receive from a mobile terminal and that fulfils the requirements of the new access point for a mobile terminal authorization.

Fig. 1 shows the basic principle underlying the technical teachings of the present invention as outlined in the following.

As shown in Fig. 1, according to the present invention it is proposed to execute a secure handover for a mobile terminal from a previous access point 12 to a new access point 14 in that the new access point generates handover secret for secure handover and distributes the handover secrets to neighborhood access points 12, 16, 18, for forwarding thereof to the mobile terminal 10 prior to secure handover to the new access point 14. Therefore, the previous access point 12 receives the handover secret from the new access point 14 and forwards the handover secret to the mobile terminal having a communication session established with the previous access point 12 prior to secure handover. Then, the mobile terminal will forward the handover secret to the new access point 14 at the time of secure handover for mobile terminal authorization at the new access point through local operation at the new access point 14.

Fig. 2 shows the overall operational context for executing secure handover from a previous access point 12 to a new access point 14 for a mobile terminal 10.

As shown in Fig. 2, a first aspect of the operational context according to the present invention relates to the authorization of the previous access point 12 at the new access point 14. Therefore, the new access point 14 has the option to selectively admit different access points for execution of secure handover thereto according to the desires of the operator of the new access point.

As shown in Fig. 2, assuming that the previous access point 12 is authorized for handover to the new access point 14, what follows is registration of the previous access point 12 at the new access point 14 for delivery of handover secrets from the new access point 14 to the previous access point 12.

As shown in Fig. 2, such distribution of handover secrets may be executed frequently from the new access point 14 to the previous access point 12, e.g., according to a regular timing scheme, so that almost the most recent handover secret generated at the new access point 14 will be available at the previous access point 12. As shown in Fig. 2, a further aspect of secure handover according to the present invention is related to interoperation between the previous. access point 12 and the mobile terminal 10. Here, one may assume that there is established a communication session for access of the mobile terminal 10 at the previous access point. The establishment of such a communication session preferably requires an authorization of the mobile terminal 10 at the previous access point 12 for generation of trust between the previous access point 12 and the mobile terminal. The new access point 14 may then rely on the established trust between the previous access point 12 and the mobile terminal 10 for forwarding of handover secrets during execution of secure handover.

As shown in Fig. 2, subsequent to establishment of a communication session between the previous access point 12 and the mobile terminal 10, there may follow the initiation of a handover, either from the previous access point 12 or from the mobile terminal 10. This is the event that triggers the forwarding of a handover secret available at the previous access point 12 to the mobile terminal 10. On receipt of the handover secret, the mobile terminal 10 will then forward the received handover secret to the new access point 14 for subsequent authorization of the mobile terminal 10 at the new access point 14. Therefore, the new access point 14 will again receive the handover secret previously generated and distributed therefrom for local processing of the handover secret at the new access point. Then, after authorization, follows establishment of a communication link between the mobile terminal 10 and the new access point 14.

Further details of the present invention will be explained in the following with reference to Figs. 3 to 9. In particular, the explanations given with respect to Figs. 3 to 6 relate to the operation of access points, while the further Figs. 7 to 9 are related to the operation of a mobile terminal.

Fig. 3 shows a schematic diagram of an access point according to the present invention. The schematic diagram shown in Fig. 3 applies to both the structure of the previous access point 12 and a new access point 14, respectively.

As shown in Fig. 3, each access point comprises a control unit 20, a registration and authorization unit 22, a handover secret processing unit 24, a handover unit 26, and a communication unit 28.

Fig. 4 shows a flowchart of operation for the new access point 14, wherein handover secrets are generated and executed according to a regular timing.

As shown in Fig. 4, operatively the handover secret processing unit 24 will continuously determine whether a time is given for generation of a new handover secret in a step SlO and generate and distribute a handover secret to neighboring access points in a step S12 accordingly.

As shown in Fig. 4, operatively the control unit 20 of the new access point 14 will determine whether new handovers are accepted at all in a step S14. If this is not the case, the procedure will branch back to step SlO for, e.g., periodic generation and distribution of handover secrets.

As shown in Fig. 4, if new handovers are accepted, the process proceeds to Step S16 to identify neighboring access points from which handovers are accepted. This step is executed by the registration and authorization unit 22 of the new access point 14. The registration and authorization unit 22 also executes registration of authorized neighboring access points at the new access point for secure handover in a step S18.

As shown in Fig. 4, operatively the handover unit 26 will evaluate submission of a new handover request from a mobile terminal in a step S20 and authorize the mobile terminal in a step S22. Upon successful authorization in step S22, there follows the actual execution of the handover for subsequent establishment of a communication session through operation of the communication unit 28.

Fig. 5 shows a flowchart ,of operation for the previous access point 12 shown in Figs. 1 and 2 in the event- driven mode, wherein a handover secret is forwarded to a mobile terminal on an indication of a handover.

As shown in Fig. 5, operatively in a step S24 the registration and authorization unit 22, now in the mode for operation as previous access point, will register and authorize the previous access point at the new access point.

As shown in Fig. 5, operatively the handover secret processing unit, in the mode for operating the previous access point, will continuously evaluate provision of new handover secrets according to step S26 and receive related handover secrets in a step S28, accordingly.

As shown in Fig. 5, at any time during operation of the previous access point the communication unit 28 is adapted to evaluate a request for establishment of a new communication session from a mobile terminal in a step S30 and for establishment of the new communication session upon successful authorization of the mobile terminal at the previous access point in a step S32. It should be understood that also step S30 and step S32 as shown in Fig. 5 are in relation to preceding and succeeding steps, that the establishment of a communication session may be achieved at any time, i.e. preceding the receipt of handover secrets also subsequent to forwarding of handover secrets to mobile stations that have pre-established a communication session. As shown in Fig. 5, a further step of operation of the previous access point relates to evaluation of initiation of a new handover through the handover unit 26 in a step S34. Should a new handover be initiated, then in a step S36 the handover secret processing unit 24 will forward the current handover secrets to a mobile terminal for which a secure handover is executed. Subsequent thereto, the handover unit 26 will execute handover-related functionality in a step S38.

Fig. 6 shows a further flowchart of operation of the previous access point. While according to the flowchart shown in Fig. 5 the forwarding of a handover secret is event-driven, i.e. triggered by indication of a •handover, according to the operation shown in Fig. 6, a handover is forwarded regularly independent of indication of a handover. Therefore, one may assume that a handover secret is immediately available at the mobile terminal for secure handover. This allows for accelerated handover at the cost of slightly increased signaling load for repeated forwarding of the handover secret.

As shown in Fig. 6, the steps S24 to S32 are similar to those explained with respect to Fig. 5 and will therefore not be explained again. The operation of the previous access point according to Fig. 6 is modified with respect to operation of the handover secret processing unit 24 and the handover unit 26. As shown in Fig. 6, according to this modified operation of the previous access point, the handover secret processing unit will continuously evaluate the timing for forwarding of a handover secret according to a predetermined timing in step S40 and then forward the current handover secret in a step S42, accordingly. Therefore, forwarding of handover secrets is not triggered through handover application but determined according to a predetermined timing, e.g., a regular timing.

As shown in Fig. 6, the handover unit 26, upon indication of a handover in a step S44, will then immediately proceed to execution of handover in a step S46 assuming that the mobile terminal has been successfully authorized at the new access point. In other words, the handover unit 26 will immediately proceed to handover without waiting for forwarding of the handover secrets for an even more accelerated secure handover.

In the following, different aspects of operation of the mobile terminal for secure handover according to the present invention will be explained with respect to Fig. 7 to Fig. 9.

Fig. 7 shows a schematic diagram of the mobile terminal, and Fig. 8 and Fig. 9 show two flowcharts of operation for the mobile terminal according to the present invention.

As shown in Fig. 7, the mobile terminal, which may be any type of mobile terminal according to the present invention, e.g., a mobile telephone, a laptop computer, a PDA, a mobile organizer, an ITC, comprises a control unit 30, an authorization unit 32, a handover unit 34, and a communication unit 36.

Fig. 8 shows a flowchart of operation of the mobile terminal as shown in Fig. 7.

As shown in Fig. 8, initially the authorization unit 32 will execute an authorization of a mobile terminal at the access point that is commonly supporting communication for the mobile terminal in a step S48. Upon successful authorization, the communication unit will establish a communication session with the current access point in a step S50.

As shown in Fig. 8, during communication between the mobile terminal and the current access point, there may be executed a step S52 by the handover unit 34 for forwarding handover-related information to the current access point. This information may be related to determination whether a secure handover is to be executed or not. It should be noted that this step S52 is optional, as it may be omitted when determination and secure handover is determined exclusively, e.g., by the mobile terminal itself.

As shown in Fig. 8, what follows is an indication of a handover unit in a step S54 being executed by the handover unit 34. Upon such indication, the communication unit 36 will receive a handover secret from a current access point in a step S56. This received handover secret will then be used by the authorization unit 32 for authorization of the mobile terminal at the new access point in a step S58. Upon successful authorization in step S58, the handover unit 34 will then execute handover to the new access point in a step S60, followed by establishment of a communication session to the new access point through the communication unit 36 in a step S62. It should be noted that for the purpose of explanation of the mobile terminal subsequent to handover, the new access"point will become the current access point for subsequent operation of the mobile terminal, as explained with respect to Fig. 8.

Fig. 8 shows the operation of the mobile terminal with forwarding of handover secrets to the mobile terminal in an event-driven manner, i.e. on indication of a handover. However, according to the present invention, also the forwarding of handover secrets using a regular timing is covered, as will be explained in the following with respect to Fig. 9. As shown in Fig. 9, the step of authorization of the mobile terminal S48 of establishing communication session, the step S50 in forwarding of handover-related information, and step S52 are similar to those explained with respect to Fig. 8 and will not be explained again. The operation according to Fig. 9 is different with respect to the reception of the handover secret by the authorization unit 32, which is not triggered by- indication of a handover but through interrogation whether a new handover secret is forwarded to the mobile terminal in a step S64 and subsequent reception of the new handover secret in a step S66 upon affirmative interrogation in step S64.

As shown in Fig. 9, subsequent to step S66, the handover unit 34 will interrogate on indication of a handover in a step S68. In case no handover is indicated, the procedure will branch back to step S52. Otherwise, the authorization unit 32 will forward the current handover segment to the new access point in a step S70 for authorization of the mobile terminal at the new access point. Then, the handover unit 34 will execute handover in a step S72, followed by establishment of a communication session in a step S74 by the communication unit 36.

While above different embodiments and the best mode of operating the present invention has been described with reference to the drawing, it should be noted that the different aspects and functionalities described with respect to embodiments may easily be verified and modified by a person skilled in the art for achieving even further ways for implementing the present invention. Any such variation and modification is to be considered as well covered by the scope of the present invention as outlined in the appended claims.