DFS is a mechanism 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.
•
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.
Choose 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. This 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 the legacy devices are within the range of the WAP device.
You can disable the protection (Off); however, the legacy clients or the WAP devices within the range can be affected
by 802.11n transmissions. Protection is also available when the mode is 802.11b/g. When protection is enabled in
this mode, it protects 802.11b clients and the WAP devices from 802.11g transmissions.
This setting does not affect the ability of the client to associate with the WAP device.
Note
•
Beacon Interval
— The interval between the transmission of beacon frames. The WAP device transmits these
frames at regular intervals to announce the existence of the wireless network. The default behavior is to send a
beacon frame once every 100 milliseconds (or 10 per second). Enter an integer from 20 to 2000 milliseconds. The
default is 100 milliseconds.
•
DTIM Period
— The Delivery Traffic Information Map (DTIM) period. Enter an integer from 1 to 255 beacons.
The default is 2 beacons.
The DTIM message is an element included in some beacon frames. It indicates which client stations, currently
sleeping in low-power mode, have data buffered on the WAP device awaiting pickup.
The DTIM period indicates how often the clients served by this WAP device should check for buffered data awaiting
pickup.
Cisco WAP581 Wireless-AC/N Dual Radio Access Point with 2.5GbE LAN Administration Guide
47
Wireless
Radio
