Wireless
Radio
Cisco Small Business WAP371 Wireless Access Point Administration Guide
60
5
DFS is a feature that requires wireless devices to share spectrum and avoid co-channel
operation with radar systems in the 5 GHz band. DFS requirements vary based on the
regulatory domain, which is determined by the country code setting of the AP.
When using the 802.11h Wireless Mode, there are a number of key points about the
IEEE 802.11h standard:
-
802.11h only works for the 5 GHz band. It is not required for the 2.4 GHz band.
-
If you are operating in an 802.11h enabled domain, the AP attempts to use the
channel you assign. If the channel has been blocked by a previous radar detection,
or if the AP detects a radar on the channel, then the AP automatically selects a
different channel.
-
When 802.11h is enabled, the AP will not be operational in the 5 GHz band for at
least 60 seconds due to radar scanning.
-
Setting up WDS links may be difficult when 802.11h is operational. This is because
the operating channels of the two APs on the WDS link may keep changing
depending on channel usage and radar interference. WDS will only work if both the
APs operate on the same channel. For more information on WDS, see
WDS Bridge,
page 85
.
•
Short Guard Interval Supported—This field is available only if the selected radio mode
includes 802.11n.
The guard interval is the dead time, in nanoseconds, between OFDM symbols. The
guard interval prevents Inter-Symbol and Inter-Carrier Interference (ISI, ICI). The
802.11n mode allows for a reduction in this guard interval from the a and g definition
of 800 nanoseconds to 400 nanoseconds. Reducing the guard interval can yield a 10
percent improvement in data throughput.
The client with which the WAP device is communicating must also support the short
guard interval.
Select one of these options:
-
Yes—The WAP device transmits data using a 400-nanosecond guard Interval when
communicating with clients that also support the short guard interval. Yes is the
default selection.
-
No—The WAP device transmits data using an 800-nanosecond guard interval.
•
Protection—The protection feature contains rules to guarantee that 802.11
transmissions do not cause interference with legacy stations or applications. By default,
protection is enabled (Auto). With protection enabled, protection is invoked if legacy
devices are within range of the WAP device.
