Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2000-11-13
2003-11-18
Nguyen, Lee (Department: 2682)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S426100
Reexamination Certificate
active
06650899
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to a mobile communication system; and, more particularly, to a method, a switching node and a program for the handover of user equipment from a first base station subsystem controlled by a first switching node to a second base station subsystem controlled by a second switching node, and which provides the second base station subsystem with the required parameters for the handover.
BACKGROUND OF THE INVENTION
When a user moves through a cellular communication system or requests a connection with different parameters it is often necessary to perform a handover of user equipment from a first base station subsystem in the communication system to a second base station subsystem. In the handover, a connection of the user equipment, e.g. a mobile phone, to the second base station subsystem is established and the connection to the first base station subsystem is generally released. Customary base station subsystems comprise one or several base stations for the wireless connection to the user equipment and a base station controller which controls the base stations and connects them to the core network of the communication system. The controller can be for example a base station controller (BSC) as defined in GSM or a radio network controller (RNC) for a base station subsystem according to the UMTS standard.
A base station subsystem, i.e. the controller, is in turn controlled by a switching node, e. g. a mobile switching center (MSC). A switching node is connectable or permanently connected to a base station subsystem with a protocol corresponding to the connection specification used between the base station subsystem and the user equipment. For a connection according to the UMTS standard, the RANAP (Radio Access Network Application Protocol) protocol is exchanged over the lu interface between the switching node and the controller in the base station subsystem while GSM subsystems use the BSSMAP (Base Station System Management Application Part) protocol over the A interface to the switching node. Correspondingly, an MSC in a GSM system generally exchanges only BSSMAP messages with a BSC while a 3G MSC in a UMTS system processes RANAP messages. A 3G MSC can normally also process BSSMAP messages and can be connected to a BSC according to GSM specifications over an A interface.
Frequently, a handover is necessary between base station subsystems which are controlled by different switching nodes. In this case, the switching nodes exchange messages to perform the handover procedure of the user equipment from the first base station subsystem to the second base station subsystem which is controlled by a second switching node. The messages are described in 3GPP technical specification 3G TS 29.010 V 3.0.0. They encapsulate a set of parameters used in the protocol between the switching nodes and the base station subsystem. The set is necessary to perform the handover and comprises an identification of the connection for which the handover is to be executed and parameters which are required to provide defined services to the user. The necessary parameters for different types of connections, especially speech and data connections can differ.
For communication between switching nodes and transfer of the parameter set, MAP (Mobile Application Part) messages as described in 3GPP Technical Specification 29.002 V 3.2.0 are suitable which allow to encapsulate BSSMAP messages. The parameter set is generated in the first switching node. serving the user equipment from a message which is transmitted from the user equipment to the first switching node. The latter message which is generally in the DTAP (Direct Transfer Application Part) protocol is forwarded by the first base station subsystem without evaluation.
On the interface to the base station subsystem, user equipment is often capable of a connection according to at least two connection specifications, e.g. according to the standards for the GSM and UMTS air interfaces. User equipment which can set up connections according to further standards, e.g. DECT (Digital European Cordless Telecommunications) or WLAN (Wireless Local Area Network), in addition to at least one of these or other connection specifications is also possible. Correspondingly, many communication systems comprise base station subsystems for connection to the user equipment wherein different subsystems use different connection specifications on the interface to the user equipment.
The necessary parameters in the set used in the protocol between a switching node and a base station subsystem are dependent on the connection specification between the user equipment and the base station subsystem because the protocol is adapted to the connection specification, i.e. the interface between base station and user equipment. The messages over a specific interface comprise mandatory fields which have to be filled in from the parameter set. Parameter sets for different protocols comprise different mandatory parameters. Consequently, the connection will be lost in an intersystem handover if the parameters necessary for the handover are not provided. This problem is aggravated if the movements of the user require a repeated handover between connections of different specifications. An additional problem is that the handover between different switching nodes requires a considerable time which can also lead to a disruption of the connection.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to obviate these disadvantages and provide a method for the handover between base station subsystems controlled by different switching nodes which provides the target subsystem with the required parameters for the handover. It is a further object, to provide a method which is simple and easy to implement. It is still another object to provide a method which performs the handover in a short time.
According to the invention, a method is provided for a handover of user equipment in a mobile communication system from a first base station subsystem controlled by a first switching node to a second base station subsystem controlled by a second switching node. The user equipment is capable of connections to base stations according to at least two connection specifications, and the communication system comprises different base station subsystems for connection to the user equipment using one of the at least two connection specifications. The second switching node controls the second base station subsystem using a protocol corresponding to the connection specification used on an interface between the base station subsystem and the user equipment. The switching nodes exchange messages in the handover which encapsulates a parameter set for one of the protocols, the parameter set is generated in the first switching node from a message which is transmitted from the user equipment to the first switching node, the first switching node detects out of a message transmitted from the user equipment whether the user equipment is capable of connection according to different specifications, and the first switching node selects the parameter set encapsulated in the message to the second switching node according to the protocol for the connection of the second switching node to the second base station subsystem.
In the proposed method, the first switching node determines from a message transmitted from the user equipment whether the user equipment is capable of connections according to different specifications. The user equipment can be for example a mobile phone, a personal digital assistant (PDA) or a palmtop computer which is connectable to the communication network according to different specifications, e.g. with a GSM or UTRAN (UMTS Terrestrial Radio Access Network) and a WLAN connection. Preferably, the evaluated message is a DTAP message from the user equipment to the first switching node during the idle mode of the user equipment before a connection or during the establishment of the connection. The evaluated message can be the message w
Nguyen Lee
Telefonaktiebolaget LM Ericsson (publ)
LandOfFree
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