How does 802.1h (DFS) help 802.11 devices avoid interference?
A.
The standard ensures that 802.11 devices do mil interfere with other, non-802 11, devices that
use the 2.4 GHz range.
B.
The standard enables APs to switch channels when they encounter any interference in the 5.0
GHz range.
C.
The standard ensures that 802.11n devices do not interface with radar in the 5 GHz frequency
range.
D.
The standard enables 802.11g and 802.11n devices to switch channels when interference
causes the SNR to drop below the minimum level.
Explanation:
Student Guide Book 1 – Implementing and Troubleshooting HP Wireless Networks – Page 3-9
Because military radar devices and satellites operate in the 5 GHz frequency band,it is more
tightly regulated than the 2.4 GHz band. To prevent 802.11 devices frominterfering with military
radar or satellites, the 802.11 standard was amended toinclude 802.11h.
This amendment defines two mechanisms for meeting regulations:
-Dynamic Frequency Selection (DFS)
-Transmit Power Control (TPC)
Both mechanisms help an AP adapt to changing circumstances, such as significantinterference.
They also ensure that your wireless network meets the regulationsenforced in your country.
DFS
To prevent APs from interfering with military radar, DFS is designed to help APsdetect radar and
then select its channel dynamically.
-The AP solicits reports from stations to monitor the channel.
-The AP determines when to change the channel.
Soliciting ReportsWhen advertising its presence, the AP also advertises its support for DFS.
Afterconnecting to the AP, a station must send the AP the channels it supports. Thisinformation
helps the AP to choose the best channel if it must change channels.
At any time, the AP can request that a station monitor various channels forinterference and send
information about interference to the AP. This information helpsthe AP to determine when it must
change channels.
Changing ChannelsIf a station‘s report indicates that the wireless network is experiencing undueinterference, the AP
decides to change the channel. Before changing the channel, theAP first informs all connected
stations of the change and when it will take place. TheAP can also suppress transmissions until
the change is final.