Wireless
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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 1 device power class. The maximum output power
is 7.5 mW and the expected range is 30 m (98.4 ft). A definition of ranges based on power class is difficult
to obtain due to power and device differences, and whether in open space or closed office space.
NOTE: It is not recommended to perform Bluetooth wireless technology inquiry when high rate 802.11b
operation is required.
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.
Recommendations are:
• Perform pairing in a secure environment
• Keep PIN codes private and do not store the PIN codes in the device
• Implement application-level security.
Bluetooth Profiles
The device supports the Bluetooth services listed.
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