3com WX1200 3CRWX120695A Manuel D’Utilisation

All radios continually scan for other RF transmitters. Radios 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 this 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.

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 (DFS) is required, MSS 
performs the appropriate check for radar. If radar is detected on a 
channel, the MAP radio stops performing active scans on that channel in 
accordance with DFS. However, the radio continues to passively scan for 
beacons from rogue devices.