In conventional computer networks where a plurality of appliances are connected via the network, each appliance has a network address which enables information to be routed to it over the network. The network address has no correlation with the physical location of the appliance.
Providing network appliances with location awareness has many potential applications. These range from relatively simple applications such as inventory control so that for example an office manager would be able to identify the presence of each piece of equipment in an office or building, to more advanced applications such as providing information tailored to a user's physical location, such as the Hewlett Packard Cooltown project which aims to produce a connection between the physical and virtual worlds. A service location method for locating devices on a network could include the physical location of a network appliance as part of a search parameter.
A number of techniques for providing location awareness for networked devices have been proposed. For example, each device can be manually programmed with location information or provided with the location using a network bootstrap protocol such as BOOTP. However, when a device's location is changed, the change must be manually recorded in the device or the configuration database. Radio frequency identification (RFID) is a technique in which transducers, commonly known as tags, carry data and suitable readers can read a tag to retrieve the data. The data held in the tag may comprise any information as desired, and the distance at which a tag can be read depends in part on the power available to the reader and may be adapted to match the particular application required. To provide location awareness for a network appliance, it might be envisaged that, for example, a physical location may be provided with a tag and network appliances supplied with a reader to read the location information contained in the tag. Alternatively, a network appliance could be provided with a tag and a suitably powerful reader could be located in each physical location to read the tag of a network appliance placed in the that location.
A further system which uses radio frequency transmissions and which may be adapted to provide location information is Bluetooth, a protocol whereby devices may communicate over an ad hoc local network using radio communications. It is known to provide a “beacon” which transmits a location signal using a Bluetooth link to all devices in its range. A related technique is infra red beacons which transmit location information over an infrared link to devices equipped with suitable detectors, for example using the IrDA protocol.
These techniques are however disadvantageous in providing location awareness for network appliances in that they each require a relative complex infrastructure to provide location signals.
A simple protocol for enabling devices to communicate via a mains electricity power supply network in a building is the X10 protocol. X10 provides a robust system for signalling between devices by superimposing a high-frequency modulation on the relatively low frequency alternating current mains supply. Using X10, a control unit is connected to a device to be controlled, for example a light switch or power outlet and has an address set to one of 256 addresses using a manually settable switch. The control unit only responds to messages sent to that address. It is a feature of the X10 protocol that several control units can be provided with the same address such for example, a number of lights may be turned on or off with a single message.
The X10 protocol is disadvantageous in that an X10 control unit does not provide its address to a device connected to it, nor is the address necessarily correlated to the physical location.
An aim of the invention is to provide a new or improved location device for a network appliance which overcomes or reduces one or more of the above disadvantages.