Table of Contents
Advertisement
Dynamic Frequency Selection
The maximum legal transmit power is greater for some 5 GHz channels than for others. When the
wireless device randomly selects a 5 GHz channel on which power is restricted, the wireless device
automatically reduces transmit power to comply with power limits for that channel in that regulatory
domain.
Configuring a Preferred Channel
By default, a WMIC in the root mode randomly selects its operating channel to meet the uniform channel
distribution requirement for standalone deployments. However, the random selection of the operating
channel can result in adjacent and co-channel interference in deployments with multiple overlapping
access points.
To minimize this type of interference, specify the channel of operation (prefer channel) of each access
point. The user is then responsible for ensuring that the selected channels are uniformly distributed
across the network.
To configure a prefer channel for the C3205 WMIC 12.3(2)JL release, use the following command:
spacing {5 | 10 | 20} channel prefer_channel [return-time <1-48>]
To configure a prefer channel for the C3205 WMIC 12.4(3g)JK release, use the following command:
channel prefer_channel [return-time <1-48>]
These commands let you specify a prefer channel for the WMIC to use as its operating channel. The
commands mark the specified channel with the highest priority to be chosen, but not the only channel
that can be used.
After the prefer channel is configured, the WMIC resets its radio and selects the configured prefer
channel to go through the channel availability check (60 seconds of scanning for radar signals) prior to
enabling transmission on the channel.
However, if a radar signal is detected on the prefer channel, a new operating channel is randomly
selected, which again can result in interchannel interference.
To resolve this issue, you can use the return-time option to specify a timeout period. This forces the
WMIC to periodically try to return to the configured prefer channel after the timeout period expires,
provided no radar is operating on the channel. If radar is operating on the prefer channel, the WMIC tries
again after another timeout period expires. The WMIC keeps trying until it finds no radar on the prefer
channel, at which point the WMIC switches back to the prefer channel.
To specify a prefer channel and configure a timeout period do the following.
Command
Step 1
configure terminal
Step 2
interface dot11radio port
Step 3
channel prefer_channel
[return-time timeout_period]
Step 4
end
OL-11491-03
Understanding Dynamic Frequency Selection
Purpose
Enters global configuration mode.
Enters interface configuration mode for the radio interface.
Specifies the prefer channel.
(Optional) Specifies in 30-minute time units how long to wait
before trying to return to the prefer channel after radar has been
detected on the operating prefer channel.
The minimum value is 1 time unit (30 minutes). The maximum
value is 48 time units (1,440 minutes or 24 hours). The default
value is 1 (30 minutes).
Returns to privileged EXEC mode.
Radio Channels and Transmit Frequencies
3
Hide quick links:
Advertisement
Table of Contents
