Technical Reference - ZyXEL Communications NWA Series User Manual

Chapter 10 Wireless

10.6 Technical Reference

The following section contains additional technical information about the features described in this
chapter.
Dynamic Channel Selection
When numerous APs broadcast within a given area, they introduce the possibility of heightened radio
interference, especially if some or all of them are broadcasting on the same radio channel. If the
interference becomes too great, then the network administrator must open his AP configuration options
and manually change the channel to one that no other AP is using (or at least a channel that has a
lower level of interference) in order to give the connected stations a minimum degree of interference.
Dynamic channel selection frees the network administrator from this task by letting the AP do it
automatically. The AP can scan the area around it looking for the channel with the least amount of
interference.
In the 2.4 GHz spectrum, each channel from 1 to 13 is broken up into discrete 22 MHz segments that are
spaced 5 MHz apart. Channel 1 is centered on 2.412 GHz while channel 13 is centered on 2.472 GHz.
Figure 69 An Example Three-Channel Deployment
Three channels are situated in such a way as to create almost no interference with one another if used
exclusively: 1, 6 and 11. When an AP broadcasts on any of these 3 channels, it should not interfere with
neighboring APs as long as they are also limited to same trio.
Figure 70 An Example Four-Channel Deployment
However, some regions require the use of other channels and often use a safety scheme with the
following four channels: 1, 4, 7 and 11. While they are situated sufficiently close to both each other and
the three so-called "safe" channels (1,6 and 11) that interference becomes inevitable, the severity of it is
dependent upon other factors: proximity to the affected AP, signal strength, activity, and so on.
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