The locations of a plurality of devices are tracked using a network of communication links, each of which corresponds to a location. Each device is given a tag that identifies the device with respect to other devices and that is connectable to a communication link when the device is disposed at the location...http://www.google.com.hk/patents/US5434775?utm_source=gb-gplus-share專利 US5434775 - Managing an inventory of devices
