Bluetooth-working

[vaibhavbhati]

Bluetooth is implemented in a variety of new products such as phones, printers, modems, and headsets. Bluetooth is acceptable for situations when two or more devices are in proximity to each other and don't require high bandwidth. Bluetooth is most commonly used with phones and hand-held computing devices, either using a Bluetooth headset or transferring files from phones/PDAs to computers.
Bluetooth also simplifies the discovery and setup of services. Bluetooth devices advertise all services they provide. This makes the utility of the service that much more accessible, without the need to worry about network addresses, permissions and all the other considerations that go with typical networks.

Communication and connection
A master Bluetooth device can communicate with up to seven devices. This network group of up to eight devices is called a piconet.
A piconet is an ad-hoc computer network, using Bluetooth technology protocols to allow one master device to interconnect with up to seven active devices. Up to 255 further devices can be inactive, or parked, which the master device can bring into active status at any time.
At any given time, data can be transferred between the master and one other device, however, the devices can switch roles and the slave can become the master at any time. The master switches rapidly from one device to another in a round-robin fashion. (Simultaneous transmission from the master to multiple other devices is possible, but not used much.)
Bluetooth specification allows connecting two or more piconets together to form a scatternet, with some devices acting as a bridge by simultaneously playing the master role and the slave role in one piconet. These devices are planned for 2007.



Air interface
The protocol operates in the license-free ISM band at 2.4-2.4835 GHz. To avoid interfering with other protocols that use the 2.45 GHz band, the Bluetooth protocol divides the band into 79 channels (each 1 MHz wide) and changes channels up to 1600 times per second. Implementations with versions 1.1 and 1.2 reach speeds of 723.1 kbit/s. Version 2.0 implementations feature Bluetooth Enhanced Data Rate (EDR) and reach 2.1 Mbit/s. Technically, version 2.0 devices have a higher power consumption, but the three times faster rate reduces the transmission times, effectively reducing power consumption to half that of 1.x devices (assuming equal traffic load

Health concerns
Bluetooth uses the microwave radio frequency spectrum in the 2.4 GHz to 2.4835 GHz range. Maximum power output from a Bluetooth radio is 1 mW, 2.5 mW, and 100 mW for Class 3, Class 2, and Class 1 devices respectively, which puts Class 1 at roughly the same level as cell phones, and the other two classes much lower.

[greetal]

Bluetooth was the brainchild of the SIG (Special Interest Group). This SIG included Intel, Toshiba, Nokia, IBM, Compaq, Dell, Motorola, HP, Lucent, and Samsung to name a few. They all came together to set up a short frequency wireless technology for transferring data.

Bluetooth is a communication protocol. It is a like a language that devices use to wirelessly communicate between each other. It is in fact based on a Master/Slave operation format. Pico net is a term used to describe a network formed by one device and all other devices detected in its range. In single coverage are around 10 Pico nets can co-exist. A master can connect to more than one slave simultaneously. In reality, the master keeps switching between slaves. Bluetooth links two Pico nets to form a larger network. This works over a short range and can be used to establish connections between PDAs, mobile phones, laptops, digital cameras, printers, scanner, and many other electronic gadgets.

Establishing a connection using Bluetooth is a complicated process. Initially, the device stays in a "Passive state", i.e. it is just in contact with the network, but not performing any activity. Next the connection establishment process begins with the inquiry process. "Inquiry" is a request sent by the master to all the devices found in its range. Whichever devices receive this inquiry send a response with their respective addresses. Now the master chooses one address and synchronises with its access point. This process known as the "Paging technique" involves alignment of its clock and frequency with that of the access point.

Next in line is the "Service Discovery" phase, wherein a link is established and the master device enters the access point using the Service Discovery Protocol. As a result of linking, a "Communication Channel" is to be created. Sometimes the access point may include a security mechanism and you may need to know the encryption key or in common terms the PIN. Once the PIN is sent and received and confirmed a communication is established. Finally the master and slave can use the communication channel to transfer data and information.

Thus Bluetooth is neither a broadband nor a long distance networking technique. It is a Personal Area Networking technology that can be used in a number of important applications. First of all, Bluetooth technology uses the same frequency range as the Wi-Fi system. It only requires a careful coordination of the various frequencies with the perfect transmit and receive timings between various devices. Finally, the enhanced version of Bluetooth is expected to use Ultra-Wide Band frequencies that contributes increased data rate and improved signal strength.

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