Bluetooth has been attracting attention as means for achieving short-distance wireless communication. Various devices compliant with Bluetooth have been developed and on the market.
Systems for wireless communication by means of Bluetooth have no directivity and high transmissivity. They are therefore advantages over the conventional infrared communication system such as IrDA (Infrared Data Association). To use high-directivity communication by means of, for example, IrDA, the devices between which to accomplished communication should be appropriately positioned to face each other. Such positioning is unnecessary in any communication system that employs Bluetooth.
Bluetooth SIG Inc. controls the standards of Bluetooth. The details of the standards are available to any person. In any communication utilizing Bluetooth, a device called “master” that controls the communication transmits, by broadcasting, a device detection message for detecting the devices that exist around the master.
The master can detect any device (slave) that exists around it and has received the device-detecting message, when it receives a response message transmitted from the device that can communicate with it.
To establish communication with the device thus detected, the master identifies the device on the basis of the ID information that is contained in the response message. The communication with this device is thereby established.
In Bluetooth, each device is assigned with ID information called “Bluetooth-device address,” which is used to identify the device. Since the ID information is unique to the device, it is utilized in various processes such as the management of the device.
In Bluetooth, a network composed of a master and slaves is called “piconets.” In the piconet, up to seven slaves can belong to one master. All devices of the piconet are synchronized in terms of frequency axis (frequency hopping pattern) and time axis (time slot).
A plurality of piconets may be connected to one another, thus constituting a larger network, which is called “scatter net.”
In Bluetooth, specification which is called “profile” is defined for each service item, in connection with the data to be transmitted and received by wireless communication and the procedure of wireless communication. The service that each device can provide is described according to the profile.
PAN (Personal Area Network) profile describes the method of communication between the slaves of a piconet. Any device of the piconet configured on the basis of the PAN profile can transmit and receive various data items in the piconet, which is one network. It is planned that, in a scatter net, too, any device can transmit and receive various data items because the scatter net is also a network. This network can be a network based on IP (Internet Protocol).
In the process of constructing such a network, it is necessary to determine which device should be the master, which device should be a slave, and which service should be used to achieve communication. It is the master that determines these, by acquiring the information about the devices existing around it, from the above-mentioned response message or the like, and in accordance with the instructions of the user.
When the master is removed from the piconet, the slaves can no longer communicate with one another through the master in the piconet. The communication must be stopped, and it is necessary to set one of the slaves as master, thereby constructing a new piconet.
At present, one of the devices is not automatically set as master. It needs to be set as such manually by the user. Hence, the user is bothered to set a new master when the piconet ceases to exist due to the removal of the master from the network, the power running-out of the master battery, or the like. Unless the user set a slave as new master, no communication can be accomplished between the other slaves in the network. The communication may be interrupted for a long time.
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