Wireless LAN – WLAN
BAT54-Rail/F..
Release
7.54
06/08
3.4
Configuration of WLAN parameters
67
D Has a radar signal been found on the channel?
D How many other networks have been found on the channel?
With the help of this data base a WLAN device can select a radar free
channel with the least number of networks. As soon as a channel has
been selected the data transfer can begin with no further waiting time.
D The “blacklist” in the data base saves the channels which are blocked
due to found radar signals. To keep the blacklist up to date every entry
is deleted automatically after 30 minutes.
D The “whitelist” contains the channels where no radar signals were
found. As long as no radar signals occur on a channel an entry re-
mains valid for the next 24 hours. If a radar signal is found, then the
entry is directly deleted out of the list and saved in the blacklist.
The 60 second scanning procedure is only necessary under following cir-
cumstances:
D The device is switched on or a coldstart is done. In this case the data
base is empty, the device cannot select a channel out of the whitelist.
D If the device has been operating for 24 hours, the whitelist entries are
deleted. In this case the data base has to be refilled.
Note: To prevent the 60 second scanning procedure initiating to an unsuit-
able time, the time when the database is deleted can be adjusted with
WEBconfig or Telnet under the menu
/setup/Interfaces/WLAN/Radio-
Settings
. The cron commands can be used for defining the time, e.g.
'1,6,13' for a DFS scan at 1 a.m., 6 a.m. and 1 p.m, or '0-23/4' for a DFS
scan every four hours from 0 a.m. to 11 p.m.. Precondition is the correct
program time of the device.
Note: As of LCOS 7.20, the limitation requiring 5-GHz operations with DFS
to be interrupted for one minute every 24 hours (as required for outdoor
radio paths, for example) no longer applies. The connection can now be
operated for any length of time on the channel selected by the DFS algo-
rithm until either a radar signal is detected or the radio cell is restarted
(e.g. by changing the device configuration, firmware upload, or restart).
The validity of the result of the one-minute scan is still limited to 24
hours. For this reason, restarting the radio cell or the detection of a
radar signal can cause a one-minute interruption if the last scan was
more than 24 hours ago, because the device is not aware of channels
identified as "free" and available for immediate use. As with earlier
versions of LCOS, the configuration item 'DFS rescan hours' makes it
possible to force the one-minute scan to take place at a time of day
when the wireless network is not being used.
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