Specifications

About Rogues and RF Detection
22-4 Rogue Detection and Countermeasures
RF Detection Scans
AllradioscontinuallyscanforotherRFtransmitters. Ra dios performpassivescansandactive
scans:
• Passivescans—Theradiolistensforbeaconsandproberesponses.
•Activescans—Theradiosendsprobeanyrequests(proberequestswithanullSSIDname)to
solicitproberesponsesfromotheraccesspoints.
Passivescansarealwaysenabledand
cannotbedisabled.Activescansareenabledbydefaultbut
canbedisabledonaradio‐profilebasis.
Radiosperformbothtypesofscansonallchannelsallowedforthecountryofoperation.(Thisis
theregulatorydomainsetbythesetsystemcountrycodecommand.)802.11b/gradiosscaninthe
2.4
GHzto2.4835GHzspectrum.802.11aradiosscaninthe5.15GHzto5.85GHzspectrum.
Bothenabledradiosanddisabledradiosperformthesescans.
Theactive‐scanalgorithmissensitivetohigh‐priority(voiceorvideo)trafficorheavydatatraffic.
Active‐scanscansfor30mseconceevery
second,unlesseitherofthefollowingconditionsistrue:
•High‐prioritytraffic(voiceorvideo)ispresentat64Kbpsorhigher.Inthiscase,active‐scan
scansfor30 msecevery60seconds.
•Heavydatatrafficispresentat4Mbpsorhigher.Inthi scase,active‐scanscansfor30
msec
every5 seconds.
Onadisabledradio,theradioisdedicatedtoroguedetectionandscansoneachchannelinround‐
robinfashion.
Dynamic Frequency Selection (DFS)
SomeregulatorydomainsrequireconformancetoETSIdocumentEN 301 893.Section4.6ofthat
documentspecifiesrequirementsforDynamicFrequencySelection(DFS).Theserequirements
applytoradiosoperatinginthe5 GHzband(802.11aradios).
IncountrieswhereDynamicFrequencySelection(DF S)isrequired,MSSperformstheappropriate
checkforradar.If
radarisdetectedonachannel,theAPradiostopsperformingactivescanson
thatchannelinaccordancewithDFS.However,theradiocontinuestopassivelyscanforbeacons
fromroguedevices.
WhenanAPradiodetectsradaronachannel,theradioswitchestoanotherchannelanddoesnot
attempt
tousethechannelwheretheradarwasdetectedfor30minutes.MSSalsogeneratesa
message.
Note: The RF Auto-tuning feature must be enabled. Otherwise MSS cannot change the channel.