| Bluetooth devices will normally operate at 2.4 GHZ | | | | frequency the Bluetooth devices will use next. |
| in the license free, globally available ISM radio band. | | | | Go here and see the newest Bluetooth Headsets: |
| The advantage to this band includes worldwide | | | | The connected devices however, must agree |
| availability and compatibility. A disadvantage to this | | | | upon the frequency they will use next. The |
| however, is that the devices must share this | | | | specification in Bluetooth ensures this in two ways. |
| band with other RF emitters. This includes | | | | First, it defines a master and slave type |
| automobile security systems, other wireless | | | | relationship between Bluetooth devices. Next, it |
| devices, and other noise sources, such as | | | | specifies an algorithm that uses device specific |
| microwaves. | | | | information when calculating the frequency hop |
| To overcome this challenge, Bluetooth employs a | | | | sequences. |
| fast frequency hopping scheme and therefore | | | | A Bluetooth device that operates in master mode |
| uses shorter packets than other standards within | | | | can communicate with up to seven devices that |
| the ISM band. This scheme helps to make | | | | are set in slave mode. To each of the slaves, the |
| Bluetooth communication more robust and more | | | | master Bluetooth device will send its own unique |
| secure. | | | | address and the value of its own internal clock. |
| Frequency hopping | | | | The information sent is then used to calculate the |
| Frequency hopping is basically jumping from | | | | frequency hop sequences. |
| frequency to frequency within the ISM radio band. | | | | Because the master device and each of the slave |
| After a Bluetooth device sends or receives a | | | | devices use the same algorithm with the same |
| packet, it and the device (or devices) it's | | | | initial input, the connected devices will always |
| communicating with hop to another frequency | | | | arrive together at the next frequency that they |
| before the next packet is sent. | | | | have agreed upon. |
| This scheme offers three advantages: | | | | As a replacement for cable technology, it's no |
| 1. Allows Bluetooth devices to use the entirety of | | | | wonder that Bluetooth devices are usually battery |
| the available ISM band, while never transmitting | | | | powered, such as wireless mice and battery |
| from a fixed frequency for more than a short | | | | powered cell phones. To conserve the power, |
| period of time. This helps insure that Bluetooth | | | | most devices operate in low power. This helps to |
| conforms to the ISM restrictions on the | | | | give Bluetooth devices a range of around 5 - 10 |
| transmission quantity per frequency. | | | | meters. |
| 2. Ensures that any interference won't last long. | | | | This range is far enough for wireless |
| Any packet that doesn't arrive safely to its | | | | communication but close enough to avoid drawing |
| destination can be resent to the next frequency. | | | | too much power from the power source of the |
| 3. Provides a base level of security as it's very | | | | device. |
| hard for an eavesdropping device to predict which | | | | |