![]() ![]() For the FCC domain: there are 9 non-DFS channels (36-48,149-165).Use 20MHz channel width, which also allows better reuse of non-DFS channels.In order to mitigate/reduce the impact of these events, we can: In general, if DFS channels are used with dense client populations, one must prepare to handle up to four false DFS events per AP radio, as well as, of course, real radar events. If there are multiple AP radios on the same DFS channel in the same location, then we can assume, as a rule of thumb, that if a single AP detects radar at a given time, then it is probably false detection, while if multiple radios detect radar at the same time, it is likely "real" radar.Ĭisco has numerous improvements to our access points' ability to distinguish between real and false radar signals however, it is not possible entirely to eliminate all false radar detection. It is very difficult to determine whether or not radar detection events are "false". ![]() It sees an energy pattern that it believes is radar, even though it is not (it is possibly a signal from a nearby client radio). wcp/dfs :: RadarDetection: sending packet out to capwapd, slotId=1, msgLen=386, chanCnt=1 -100įor IOS APs Feb 10 17:15:55: %DOT11-6-DFS_TRIGGERED: DFS: triggered on frequency 5320 MHzįeb 10 17:15:55: %DOT11-6-FREQ_USED: Interface Dot11Radio1, frequency 5520 selectedįeb 10 17:15:55: %DOT11-5-EXPECTED_RADIO_RESET: Restarting Radio interface Dot11Radio1 due to channel change from 64 to 104 False Events with DFS channelsĪ "false DFS event" is when a radio falsely detects radar. wcp/dfs :: RadarDetection: radar detected When we examine the AP logs, we can see messages similar to the following:įor COS APs Radar detected: cf=5496 bw=4 evt='DFS Radar Detection Chan = 100' If a radar signal is detected, the AP selects a different channelĭFS triggered channel changes impact client connectivity. If there are no radar signals on the new channel, the AP enables beacons and accepts client associations. If the AP selects a DFS-required channel, it scans the new channel for radar signals for 60 seconds.If the selected channel is not DFS then AP enables beacons and accepts client associations.Selects a different channel from the DCA (Dynamic Channel Assignment) list.Broadcasts an 802.11h channel-switch announcement.Stops transmission of data frames on that channel.When an access point (AP) uses a DFS channel and a radar signal is detected, the AP then: Thus, if a radio detects radar in its serving channel, then switch to another DFS channel, this then imposes (at least) a one-minute outage. And, if an 802.11 radio detects radar while the DFS channel is used, it must vacate that channel quickly. (Consult the applicable Channels and Maximum Power spreadsheets to see the specific channels that require DFS for a given access point / domain.)Ĩ02.11 stations, before they transmit in a DFS channel, must validate (listen for 60 seconds) that there is no radar activity on it. In most regulatory domains, 802.11 stations are required to use Dynamic Frequency Selection (DFS) when used with some or all of the channels in the 5GHz band. The only thing missing is a portable version to take it with you.This document describes radar detection in Dynamic Frequency Selection (DFS) channels theory, and how to mitigate its impacts on wireless networks. NoVirusThanks Driver Radar Pro is a serious time-saver for anyone investigating a possible infection by speeding up the time it takes to research a loaded file. Lightweight in the memory and CPU usage. ![]()
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