Bluetooth technology is motivated by the desire to provide a universal interface to battery-driven portable devices. As such, the technology makes several provisions for effective power management in order to conserve power. Some of the key power management features are implemented at the micro level. The first such feature is identified with respect to frequency hopping. The mechanism for frequency hopping is defined such that no dummy data has to be exchanged in order to keep the master and slave devices synchronized to each other. This obviates the need for the transceivers on both the master and slave devices to periodically wake up and transmit dummy packets. The second feature is inherent in the packet format. Because Bluetooth packets begin with the access code of the piconet for which they are intended, a device that is listening on the piconet's hop frequency during its receive slot can quickly ascertain whether the packet carried on the current hop frequency is intended for its piconet. If the device determines that the packet was not intended for its piconet, the device's receiver can go to sleep for the remainder of the time slot. Moreover, the packet header contains information about the length of the payload. So, if the payload is very small, the device does not have to keep its receiver on for the entire duration of the time slot. It can put its receiver to sleep as soon as the entire payload has been received. Aside from the micro-level power management features discussed here, Bluetooth provides support for macro-level power management in that it allows devices to be put in any one of three power saving modes: hold, sniff, and park (see Section 13.3.3).
Because Bluetooth is an RF-based wireless technology, data exchanged between Bluetooth devices can be easily intercepted. Clearly, there is a need to protect personal and private data from would-be eavesdroppers. The Bluetooth SIG has made a conscious effort to provide various security mechanisms at many different levels of the specification. To begin with, the fact that the technology employs a frequency hopping spread spectrum technique to establish a channel for communication itself provides a certain degree of security. Consider that without knowing the hop sequence of the piconet, the eavesdropper will not know which 1-MHz channel to listen to during the next 625-μs time slot. But there are other intentional security mechanisms provided in the Bluetooth specification.
At a macro level, the specifications provide three security modes for a Bluetooth device. Devices in security mode 1 never initiate any security procedures. Additionally, devices in this mode are not required to support device authentication. In security mode 2, devices do not need to initiate security procedures until an L2CAP channel is established. Once the L2CAP link is established, the device can decide which security procedures to enforce. Security mode 3 is the most stringent of the three security modes. In this mode, security procedures are initiated at the link level, i.e., before any link is established between devices.
There are two key security procedures defined in the specification: device authentication and link encryption (see Section 13.3). In addition to the security mechanisms provided by Bluetooth at the lowest levels, more-advanced security mechanisms can be employed at higher layers. , , 
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