Wireless
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Bluetooth
Bluetooth-equipped devices can communicate without wires, using frequency-hopping spread spectrum (FHSS)
radio frequency (RF) to transmit and receive data in the 2.4 GHz Industry Scientific and Medical (ISM) band
(802.15.1). Bluetooth wireless technology is specifically designed for short-range (10 meters (32.8 feet))
communication and low power consumption.
Devices with Bluetooth capabilities can exchange information (e.g., files, appointments, and tasks) with other
Bluetooth enabled devices such as printers, access points, and other mobile devices.
Adaptive Frequency Hopping
Adaptive Frequency Hopping (AFH) is a method of avoiding fixed frequency interferers, and can be used with
Bluetooth voice. All devices in the piconet (Bluetooth network) must be AFH-capable in order for AFH to work.
There is no AFH when connecting and discovering devices. Avoid making Bluetooth connections and discoveries
during critical 802.11b communications. AFH for Bluetooth consists of four main sections:
• Channel Classification - A method of detecting an interference on a channel-by-channel basis, or
pre-defined channel mask.
• Link Management - Coordinates and distributes the AFH information to the rest of the Bluetooth network.
• Hop Sequence Modification - Avoids interference by selectively reducing the number of hopping
channels.
• Channel Maintenance - A method for periodically re-evaluating the channels.
When AFH is enabled, the Bluetooth radio “hops around” (instead of through) the 802.11b high-rate channels. AFH
coexistence allows Enterprise devices to operate in any infrastructure.
The Bluetooth radio in this device operates as a Class 2 device power class. The maximum output power is 2.5
mW and the expected range is 10 meters (32.8 ft.). A definition of ranges based on power class is difficult to obtain
due to power and device differences, and whether one measures open space or closed office space.
Security
The current Bluetooth specification defines security at the link level. Application-level security is not specified. This
allows application developers to define security mechanisms tailored to their specific need. Link-level security
occurs between devices, not users, while application-level security can be implemented on a per-user basis. The
Bluetooth specification defines security algorithms and procedures required to authenticate devices, and if needed,
encrypt the data flowing on the link between the devices. Device authentication is a mandatory feature of Bluetooth
while link encryption is optional.
Pairing of Bluetooth devices is accomplished by creating an initialization key used to authenticate the devices and
create a link key for them. Entering a common personal identification number (PIN) in the devices being paired
generates the initialization key. The PIN is never sent over the air. By default, the Bluetooth stack responds with no
key when a key is requested (it is up to user to respond to the key request event). Authentication of Bluetooth
devices is based-upon a challenge-response transaction. Bluetooth allows for a PIN or passkey used to create
other 128-bit keys used for security and encryption. The encryption key is derived from the link key used to
authenticate the pairing devices. Also worthy of note is the limited range and fast frequency hopping of the
Bluetooth radios that makes long-distance eavesdropping difficult.
NOTE: It is not recommended to perform Bluetooth wireless technology inquiry when high rate 802.11b
operation is required.
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