Cordless key telephone system having zone switching function

Claim 2

A cordless key telephone system as claimed in claim 1, wherein said main controller is responsive to said zone switching signal for transmitting a disconnect signal to the access unit of the first service zone (3₁) and transmitting an alert signal to the given cordless station via the access unit of said second service zone to elicit an acknowledgment signal from said given cordless station, and wherein the access unit of the first service zone is responsive to the disconnect signal for clearing the channel to the given cordless station for readying to receive signals in a standby mode, and wherein the access unit of the second service zone is responsive to the acknowledgment signal for transmitting to said given cordless station a channel assignment signal indicating an idle speech channel to be assigned to said given cordless station.

Claim 3

A cordless key telephone system as claimed in claim 1 or 2, wherein said given cordless stations includes means for transmitting a call request signal to the access unit of said second service zone (3₂) following the transmission of said zone switching signal, wherein the access unit of said second service zone (3₂) is responsive to said call request signal for transmitting to said given cordless station a channel assignment signal indicating an idle speech channel to be assigned to said given cordless station, and wherein the main controller (2) is responsive to said call request signal via the access unit of the second service zone (3₂) for transmitting a disconnect signal to the access unit of the first service zone for clearing the channel established therefrom to the given cordless station for readying to receive signals in a standby mode.

Claim 4

A cordless key telephone system for covering a plurality of service zones each having a uniquely assigned two-way control channel and a plurality of two-way speech channels, comprising: a plurality of access units (4₁∼4₄) respectively located in said service zones (3₁, 3₂); a plurality of cordless stations (5) movable across boundaries of said service zones, each of the cordless stations establishing a first control connection to the access unit of a first service zone (3₁), in which the cordless station is located, through the control channel of said first service zone and subsequently establishing a speech connection to said access unit through one of the speech channels of the first service zone instead of the first control connection, and including means (26) for constantly monitoring field intensity of the established speech connection, reestablishing the first control connection and transmitting a zone switching signal when the field intensity is below a specified level as an indication that the cordless station is leaving said first service zone (3₁) and entering a second service zone (3₂), and establishing a second control connection to the access unit of the second service zone through the control channel of the second service zone; and a main controller (2) for establishing a switched connection between exchange lines (6₁-6₃) and said access units and responsive to said zone switching signal from a given cordless station via the access unit of the first service zone for holding an exchange line which is connected to the access unit of the first service zone through a first switched connection, and establishing a second switched connection between said exchange line and the access unit of the second service zone instead of the first switched connection.

Claim 5

A cordless key telephone system as claimed in claim 4, wherein said main controller (2) is responsive to said zone switching signal for transmitting a disconnect signal to the access unit of the first service zone (3₁) and transmitting an alert signal to the given cordless station via said second control connection to elicit an acknowledgment signal from the given cordless station, and wherein the access unit of the first service zone (3₁) is responsive to the disconnect signal for clearing the second control connection for readying to receive signals in a standby mode, and wherein the access unit of the second service zone (3₂) is responsive to the acknowledgment signal for transmitting to said given cordless station a channel assignment signal indicating an idle speech channel to be assigned to said given cordless station.

Claim 6

A cordless key telephone system as claimed in claim 4 or 5, wherein said given cordless stations includes means for transmitting a call request signal through said second control connection to the access unit of said second service zone (3₂) following the transmission of said zone switching signal, wherein the access unit (3₂) of said second service zone is responsive to said call request signal for transmitting to said given cordless station a channel assignment signal indicating an idle speech channel to be assigned to said given cordless station, and wherein the main controller (2) is responsive to said call request signal via the access unit of the second service zone (3₂) for transmitting a disconnect signal to the access unit of the first service zone for clearing the second control connection for readying to receive signals in a standby mode.