Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-04-16
2001-12-11
Trost, William (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S437000, C455S439000, C455S555000
Reexamination Certificate
active
06330448
ABSTRACT:
BACKGBOUND OF THE INVENTION
1. Field of the invention
The present invention relates generally to cellular mobile communications systems, and more specifically to a communications network in which a number of private branch exchanges (PBXs) are interconnected and each PBX accommodates a number of wireless cell-site stations for serving handheld personal mobile stations.
2. Description of the Related Art
In conventional PBX networks where wireless cell-site stations are provided, mobile stations are allowed to establish communication within the area of a PBX if their system identifiers are verified. Handover operation is effected when a communicating mobile station moves from one cell site to another only if the mobile station remains within the area of the PBX in which it is verified. When a mobile station belonging to a first PBX moves to the area of a second PBX where it is not verified, the mobile station is required to use the system identifier of the second PBX if it establishes a communication. Therefore, if a communicating mobile station of the first PBX moves around and enters the area of the second PBX and wishes to continue the communication, the mobile station is required to interrupt the communication by sending an on-hook signal to the first PBX and re-originate a call through the second PBX to the first PBX by sending an off hook signed to the second PBX containing the system identifier of the second PBX.
Therefore, a need exists to provide a handover operation that allows a communicating mobile station of a PBX node to continue communication without interruption when it enters the area of an adjacent PBX node.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a network of interconnected private branch exchanges having celi-site stations, wherein each PBX provides handover operation for a communicating mobile station moving from one PBX cell-site station to another PBX cell-site station.
According to a first aspect of the present invention, there is provided a communication network comprising a plurality of a plurality of private branch exchange (PBX) nodes, each having a database for storing shared data for verification of authorized mobile stations when accessing the network, a plurality of wireless cell-site stations connected to the PBX nodes, and a mobile station for monitoring a downlink signal from a first cell-site station of a first PBX node, detecting a strong signal if the strength of the downlink signal falls below a threshold, transmitting a handover request message to a second cell-site station transmitting the strong signal. A second PBX node of the plurality of nodes, when receiving the message via the second cell-site station, establishes mobile's verification using data stored in the database of the second PBX node, transmits a handover grant message to the second cell-site station, transmits a command message to the first PBX node for a switchover to a link between the first and second PBX nodes, and connects the link to the second cell-site station.
According to a second aspect, the present invention provides a communications network comprising a plurality of private branch exchange (PBX) nodes each having a local database for storing data associated with mobile stations and a global database for storing verification data commonly shared by the PBX nodes, a plurality of wireless cell-site stations connected to the PBX nodes, and a mobile station having a mobile's address for operating in a wireless mode and a PBX extension number of one of the PBX nodes for operating in a PBX extension mode, the mobile station detecting a strong signal after the strength of a downlink signal falls below a predefined threshold during a wireless mode with a talking party of a first one of the PBX nodes via a first cell-site station and transmitting a handover request message containing a mobile's address to a second cell-site station which is transmitting the strong signal. A second one of the PBX nodes, when receiving the handover request message via the second cell-site station, determines a home PBX node of the mobile station from the mobile's address contained in the handover request message, acquires data associated with the mobile station from the local database of the home PBX node, identifies the first PBX node from the acquired data as a node from which the mobile station is moving, test the acquired data against verification data stored in the global database of the second PBX node to determine whether the mobile station is an authorized user, transmit a handover grant message to the second cell-site station if the mobile station is verified as an authorized user, transmit a command message to the first PBX node for a switchover from an old connection between the first cell-site station and the mobile's talking party to a new path from the mobile's talking party to a communication link between the first and second PBX nodes, and establish a path In the second PBX node between the communication link and the second cell-site station.
Preferably, the data stored in the local database includes data concerning identifications of the cell-site stations, and the second PBX node is arranged to acquire from the local data base of the home PBX node the identification of a cell-site station with which the mobile station is currently associated, transmit the acquired Identification of the cell-site station to the first PBX node with the command message, and update the local database of the home PBX node with an indication that the mobile station is served by the second cell-site station, rather than with the first cell-site station, when the path is established in the second PBX node.
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Itagaki Yoshio
Otsuka Kiyokazu
NEC Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
Tran Congvan
Trost William
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