Cordless key telephone system having zone switching function

• US 5,454,028 A
• Filed: 01/27/1994
• Issued: 09/26/1995
• Est. Priority Date: 09/11/1990
• Status: Expired due to Fees

• Current Assignee: NEC Corporation, Nippon Telegraph and Telephone Corporation
• Original Assignee: NEC Corporation, Nippon Telegraph and Telephone Corporation
• Inventors: Tamura, Ichiro, Hashimoto, Kosuke, Kumataka, Shinji, Hara, Toshihiro
• Primary Examiner(s): Kuntz, Curtis
• Assistant Examiner(s): OEHLING, GEORGE J
• Application Number:
  US08/187,315
• Time in Patent Office: 607 Days
• Field of Search: 379/58-61, 379/63, 455/33.1, 455/33.2, 455/33.4, 455/34.2, 455/53.1, 455/54.1, 455/54.27, 455/56.1
• US Class Current: 455/437
• CPC Class Codes: H04W 36/0055 Transmission or use of information for re-establishing the radio link
• CPC Class Codes: H04W 36/30 by measured or perceived connection quality data
• CPC Class Codes: H04W 84/16 WPBX [Wireless Private Branch Exchange]

Abstract

In a cordless key telephone system for servicing separate service zones (3₁, 3₂), 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 (3₁) and entering a second zone (3₂). 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_i) that is connected to the access unit (4_j) of the first zone through a first switched connection, and establishes a second switched connection between the exchange line (6_i) and the access unit (4_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.

Claims

1. A method for switching zones in a cordless key telephone system serving at least first and second zones, the system comprising first and second access units respectively located in the first and second zones, and a main controller for selectively establishing one of a first switched connection between an exchange line and the first access unit and a second switched connection between the exchange line and said second access unit, the method comprising the steps of:

a) establishing a first speech channel between a cordless station and the first access unit and coupling the first speech channel via said first switched connection to said exchange line;

b) constantly monitoring a field intensity of the first speech channel at said cordless station;

c) transmitting a zone switching signal from the cordless station to the first access unit when the field intensity falls below a specified level;

d) relaying the zone switching signal via the first access unit to the main controller;

e) responsive to the relayed zone switching signal, holding said exchange line at said main controller, applying a vocal announcement to said exchange line indicating to a communicating party that the cordless station is switching zones, transmitting a disconnect signal from the main controller to the first access unit to clear said first-speech channel, and transmitting an alert signal from the main controller via said second access unit to the cordless station to cause the cordless station to return an acknowledgement signal;

f) responsive to the acknowledgement signal from the cordless station, transmitting a channel assignment signal from the second access unit to the cordless station, and relaying the acknowledgement signal via the second access unit to the main controller;

g) responsive to the channel assignment signal, establishing a second speech channel between the cordless station and the second access unit and returning a switching complete signal from the cordless station to the second access unit;

h) relaying the switching complete signal via the second access unit to the main controller; and

i) responsive to the relayed acknowledgement signal and the relayed switching complete signal, establishing said second switched connection and coupling the second speech channel to the exchange line via said second switched connection.

2. A method for switching zones in a cordless key telephone system serving at least first and second zones, the system comprising first and second access units respectively located in the first and second zones, and a main controller for selectively establishing one of a first switched connection between an exchange line and said first access unit and a second switched connection between said exchange line and said second access unit, the method comprising the steps of:

a) establishing a first speech channel between a cordless station and the first access unit and coupling the first speech channel via said first switched connection to said exchange line;

b) constantly monitoring a field intensity of the first speech channel at said cordless station;

c) transmitting a zone switching signal from the cordless station to the first access unit when the field intensity falls below a specified level, and transmitting a call request signal from the cordless station to the second access unit;

d) relaying the zone switching signal via the first access unit to the main controller;

e) responsive to the relayed zone switching signal, holding said exchange line at said main controller, and applying a vocal announcement to said exchange line indicating to a communicating party that the cordless station is switching zones;

f) relaying the call request via the second access unit to the main controller and transmitting a channel assignment signal for the second access unit to the cordless station;

g) responsive to the relayed call request signal, transmitting a disconnect signal from the main controller to the first access unit to clear said first speech channel, and responsive to the channel assignment signal, establishing a second speech channel between the cordless station and the second access unit and transmitting a switching complete signal from the cordless station to the second access unit;

h) relaying the switching complete signal via the second access unit to the main controller; and

i) responsive to the relayed switching complete signal, establishing said second switched connection and coupling the second speech channel to the exchange line via said second switched connection.