Nec Corporation

Nippon Telegraph and Telephone Corporation

Ichiro Tamura

Noboru Saegusa

Shinji Kumataka

Kosuke Hashimoto

Yukihiro Shimura

Toshihiro Hara

Hirokazu Adachi

Naoyasu Nishimura

In a cordless key telephone system for servicing separate service zones (3.sub.1, 3.sub.2), a cordless station (5) establishes a two-way radio channel with an access unit (4) of the service zone in which it is located, and constantly monitors the field intensity of the established channel and transmits a zone switching signal when the field intensity is below a specified level as an indication that the cordless station is leaving a first zone (3.sub.1) and entering a second zone (3.sub.2). A main controller (2) establishes a switched connection between exchange lines (6) and the access units (4). In response to the zone switching signal from a given cordless station via the access unit of the first zone, the main controller holds an exchange line (6.sub.i) that is connected to the access unit (4.sub.j) of the first zone through a first switched connection, and establishes a second switched connection between the exchange line (6.sub.i) and the access unit (4.sub.j) of the second zone, instead of the first switched connection. A vocal announcement is applied to the exchange line indicating to a communicating party that the cordless station is switching zones.

Cordless key telephone system having zone switching function

In a cordless key telephone system in which radio-frequency connections are established between exchange lines and cordless stations in response to a call request, a ringing signal is transmitted in response to an incoming call by containing in it the identification of the line at which the call is terminated. Each cordless station has an array of line keys associated respectively with the exchange lines and an array of line indicators associated respectively with the line keys, and a memory for storing tenant data indicating the lines to which the cordless station is authorized to access. The cordless station examines the tenant data in response to receipt of the ringing signal, and activates one of the line indicators if the indicated line is found in the tenant data, or examines the tenant data in response to an outgoing call originated from the cordless station operating a line key, and allows a connection to be established from that station to an exchange line when the line associated with the operated line key is found in the tenant data.

Cordless key telephone system with multiple tenant facility

In a cordless key telephone system where adjacent service zones having the same control channel are overlapped, forming an unavoidable interference-affected overlapping zone, a main unit initially selects an access unit from each service zone in response to an incoming call from a network and transmits a first alert signal to that unit where it is broadcast to elicit an acknowledgement (ACK) signal from cordless stations. On receiving it, the access unit selects a speech channel, broadcasts a first channel assignment signal on the control channel, and then a first ringing signal on the selected speech channel. The main unit determines whether there is a cordless station falling to respond to the first alert signal. If such a station exists, the main unit selects a first, idle access unit which is located in one of the adjacent service zones. A second alert signal is then broadcast on a control channel from the first access unit. Following receipt of an ACK signal from a cordless station, a second channel assignment signal is broadcast from the first access unit, signalling the identification of a speech channel previously selected by a second, initially selected access unit located in the adjacent service zones. A second ringing signal is broadcast from the second access unit on the previously selected speech channel.

Cordless key telephone system for repeating attempts to alert stations

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Tokyo, Japan

Ichiro Tamura