Telecommunications – Radiotelephone system – Security or fraud prevention
Reexamination Certificate
1999-11-23
2003-07-01
Le, Thanh Cong (Department: 2684)
Telecommunications
Radiotelephone system
Security or fraud prevention
C455S435100, C455S437000, C455S438000, C380S248000, C380S270000, C380S272000
Reexamination Certificate
active
06587680
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to radio communications systems of which a wireless local area network (WLAN) is a non-limiting example. More specifically this invention relates to providing information security when a mobile terminal is handed-over from a first base station or access point (AP) to a second base station or access point (AP).
BACKGROUND OF THE INVENTION
In a minimum configuration, a communication system is formed by a transmitting station and a receiving station that are interconnected by a communication channel. Communication signals generated by the transmitting station are transmitted upon the communication channel and received by the receiving station.
In a radio communication system at least a portion of the communication channel is formed by a portion of the electromagnetic spectrum. Increased mobility of communications is permitted in a radio communication system because a fixed or a hard-wired connection is not required between the transmitting and receiving stations.
A cellular communication system, of which a cellular telephone system is an example, is an example of a radio communication system. When the mobile terminal of a subscriber to a cellular communication system is physically positioned at almost any location throughout an area that is encompassed by the network infrastructure of the cellular communication system, the mobile terminal is able to communicate by way of the cellular communication system with another mobile terminal.
The network infrastructure of an exemplary wireless communication system includes physically spaced-apart base stations or access points (APs) which each include a transceiver. In such an exemplary system, each base station or AP defines a geographic area or cell of the communications system. As a first mobile terminal is used to communicate with a second mobile terminal, and as the first mobile terminal travels or moves between the cells of the system, uninterrupted communication is possible by handing-over communications from one base station to another base station. Such a communication handover is provided by a handover process.
A High Performance radio Local Area Network such as HIPERLAN type-2supports three kinds of handover. HIPERLAN/2 PROVIDES HIGH SPEED (typically 25 Mb/s data rate) communications between portable devices and broadband IP, ATM and UMTS networks, and is capable of supporting multiple media applications, with the typical application being indoors.
HIPERLAN/2 provides local wireless access to different infrastructure networks (e.g. IP, ATM and UMTS) by moving and stationary terminals that interact with access points which, in turn, usually are connected to an IP, ATM, or UMTS backbone. A number of access points are required to service the network. The wireless network as a whole supports handovers of connections between access points to provide mobility. Typical operating environments include business networks and domestic premises networks. An overview of HIPERLAN/2 access networks is provided by the European Telecommunications Standards Institute (ETSI) document DTR/BRAN-00230002, 1998, incorporated herein by reference.
Depending upon the mobile terminal's handover decision, sector handover (inter-sector), radio handover (inter access point transceiver/inter access point handover), network handover (inter access point/inter network handover) or forced handover may occur in accordance with HIPERLAN/2.
Prior to the execution of a handover, the mobile terminal must gather relevant measurements on the frequency that is used by the current access point, as well as on the frequencies that are used by access points that are candidates for a handover. Measurements on the serving frequency can be carried out by the mobile terminal while it is synchronized to the current access point. However, in order to measure the frequency of neighboring access points, the mobile terminal must be temporarily absent from the current access point.
During a mobile terminal absent procedure the mobile terminal is temporarily disconnected from the current access point, in order that the mobile terminal can perform measurements on neighboring access points. During this time, no communication between the mobile terminal and the current access point is possible. As part of this absent procedure, the mobile terminal tells the current access point that it will be absent for n-frames. During this absent period, the mobile terminal cannot be reached by the current access point. After the absent period, the current access point may trigger a mobile terminal alive sequence to check if the mobile terminal is available.
During a sector handover the antenna sector of the access point is changed, and the same access point controls the entire handover. After a successful sector handover, the mobile terminal communicates via the new sector. A radio handover relates to access points having more than one transceiver per access point, for example two access point transceivers and one access point controller. Radio handover is performed when a mobile terminal moves from a coverage area of one access point to another coverage area that is served by the same access point. Since radio handover can be performed within the data link control (DLC) layer, higher layer protocols (HL) are not involved. When the mobile terminal detects the need for a handover to another access point controller, the mobile terminal may still synchronize to the current access point. In this case the mobile terminal may notify its access point controller that the mobile terminal will perform a handover to another access point controller. In the case of a radio handover all relevant information about on-going connections, security parameters, etc. are available in the access point, so that this information is not re-negotiated.
A network handover is carried out when a mobile terminal moves from one access point to another access point. Since the mobile terminal leaves the serving area of a radio control link (RLC) instance, a network handover involves the convergence layer (CL) and the HL (as may be needed), as well as DLCI. To maintain HL association and connections, specific signaling via the backbone may be needed. When the mobile terminal detects the need for handover to another (target) access point, the mobile terminal may still be synchronized to the current access point. In this case, the mobile terminal may notify the current access point that it will perform a handover to another access point. The notified access point shall then stop transmitting to that mobile terminal, but shall maintain association for a specified time, when indicated.
Forced handover gives a current access point the opportunity to order a certain mobile terminal to leave the current access point's cell. A forced handover is initiated by the access point sending a Force_Handover signal to the mobile terminal. In one procedure the mobile terminal performs a normal handover and leaves its old cell, regardless of whether it finds a new cell. In a second procedure the mobile terminal has the opportunity to come back to the old access point if handover fails.
For further discussion of HIPLERLAN/2 features see the Broadband Radio Access Networks (BRAN); HIPERLAN type 2 Functional Specification; Radio Link Control (RLC) that are provided by the ETSI standardization organization, incorporated herein by reference.
Several types of wireless communication systems have been implemented, and others have been proposed, to encompass limited geographic areas, for example a limited area that is encompassed by a building or by an office workplace within a building. Wireless communication systems such as microcellular networks, private networks, and WLANs are exemplary of such systems.
Wireless communication systems are typically constructed pursuant to standards that are promulgated by a regulatory or a quasi-regulatory body. For instance, the IEEE 802.11 standard promulgated by the IEEE (Institute of Electrical and Electronic Engineering) is a wireless local area network (LAN) stand
Ala-Laurila Juha
Hansen Harri
Salvela Juha
Cong Le Thanh
Nokia Corporation
Tran Tuan
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