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WifiPROBE
The WifiPROBE function traverses each channel, measuring its available transmit (TX) time. This is reported as ‘%
Available TX’, compared to a baseline reference. This metric —
% Available TX
—
is a measure of a channel’s
“health”. The higher this
value then the more bandwidth is available for transmitting data packets. Using this
metric, WifiPROBE can be used to rank channels from best-to-worst. However, a few more points should be
clarified:
•
Should you always use the channel with the highest ‘% Available TX’? For example, suppose your 802.11N
channel has a theoretical bandwidth of 100 Mbps, but because of interference and congestion that has
decreased to 40 Mbps
—
i.e. the ‘%
Available TX’ is 40%. Should you avoid using that channel at all costs? The answer is ‘not necessarily’. If
your current bandwidth needs are only 5 Mbps
—
which is much less than the available 40 Mbps
—
then
it is perfectly fine to continue using that channel because it still has plenty of capacity to handle your
current traffic load. Only when your traffic load begins to approach the bandwidth ceiling is it then
necessary to consider a different channel. WifiPROBE can tell you what that ceiling is, but it does not tell
you the current traffic load.
•
When monitoring the 2.4x GHz band you should always choose either channel 1, 6, or 11
—
even if other
channels have a higher ‘% Available TX’ value. There are few exceptions to this rule —
The image above shows the results of WifiPROBE scanning all the 2.4x GHz channels in a typical office
environment. As WifiPROBE cycles through all the channels, the channel currently being measured is filled-in
(e.g. channel 2 in this example). We see that some channels are higher than others
—
but all are greater than
50%. Since this is the 2.4x GHz band, we really should focus just on channels 1, 6, and 11. We would interpret
this result to mean it is okay to use channels 1, 6, 11 for your AP.
