A cordless communication system includes a plurality of cordless communication devices, a plurality of connection units which couple the cordless communication devices and communication lines, and a control unit which controls connections between the connection units and the cordless communication devices....http://www.google.com.hk/patents/US5329575?utm_source=gb-gplus-share專利 US5329575 - Idle channel retrieving method and cordless communications system using the same
