Dynamic Frequency Selection; Understanding Dynamic Frequency Selection - Cisco C3201FESMIC-TP= - 3201 Fast EN Switch Mobile Interface Card Expansion Module Software Configuration Manual

Dynamic Frequency Selection

At startup and by default, wireless devices passively scan for and select the least-congested channel. The
channel settings on wireless devices correspond to the frequencies available in your regulatory domain.
For example, in the European Telecommunications Standards Institute (ETSI) domain, the regulatory
agencies do not allow the channel to be set on 5.0 GHz (802.11a/h) radios by the users. However, channel
groups can be blocked on wireless devices running ETSI images. When a wireless device boots from an
ETSI image, it automatically selects the least congested channel where radar is not detected by using
Dynamic Frequency Selection (DFS).
Transmission Power Control (TPC) is used to automatically adjust the transmission power level on
5.0-GHz radios, also to avoid interfering with radar.

Understanding Dynamic Frequency Selection

TPC is used to automatically adjust the transmission power level on 5.0-GHz radios, also to avoid
interfering with radar. 5.0 GHz (802.11a/h) radios in wireless devices running Cisco IOS version
12.4(6)T and later shipped to Europe and Japan are required to use DFS to detect and avoid interfering
with radar signals to comply with those regulatory domains.
DFS is the process of detecting radar signals that must be protected against interference from 5.0 GHz
(802.11a/h) radios, and upon detection switching the operating frequency of the 5.0 GHz (802.11a/h)
radio to one that is not interfering with the radar systems. TPC is used to adapt the transmission power
of a radio based on regulatory requirements and range information.
The wireless device automatically sets the frequency on a DFS-enabled 5.0 GHz (802.11a/h) radio
operating in a regulatory domain where DFS is required for compliance with the rules of that regulatory
agency.
For the ETSI regulatory domain, 5.0-GHz radios support the DFS 1.3.1 compliance requirement.
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