MSM7xx Controllers Configuration Guide v6.4.0

Selecting channels in the 2.4 GHz band
In the 2.4 GHz band, the center frequency of each channel is spaced 5 MHz apart (except for
channel 14). Each 802.11 channel uses 20 MHz of bandwidth (10 MHz above and 10 MHz
below the center frequency), which means that adjacent channels overlap and interfere with each
other as follows:
Overlaps channelsCenter frequencyChannelOverlaps channelsCenter frequencyChannel
6, 7, 9, 10244782, 324121
7, 8, 10, 11245291, 3, 424172
8, 9, 11, 122457101, 2, 4, 524223
9, 10, 12, 132462112, 3, 5, 624274
10, 11, 132467123, 4, 6, 724325
11, 122472134, 5, 7, 824376
2484145, 6, 8, 924427
To avoid interference, APs in the same area must use channels that are separated by at least 25
MHz (5 channels). For example, if an AP is operating on channel 3, and a second AP is operating
on channel 7, interference occurs on channel 5. For optimal performance, the second AP should
be moved to channel 8 (or higher).
With the proliferation of wireless networks, it is possible that the wireless cells of APs outside your
control overlap your intended area of coverage. To choose the best operating frequency, select
Controlled APs >> Security > Neighborhood to view a list of all APs that are operating nearby and
their operating frequencies.
The number of channels available for use in a particular country are determined by the regulations
defined by the local governing body and are automatically configured by the AP based on the
Country setting you define. (See “Assigning country settings to a group” (page 170)). This means
that the number of non-overlapping channels available to you varies by geographical location.
The following table shows the number of channels that are available in North America, Japan,
and Europe.
Available channelsRegion
1 to 11North America
1 to 14Japan
1 to 13Europe
Since the minimum recommended separation between overlapping channels is 25 MHz (five
channels) the recommended maximum number of overlapping cells you can have in most regions
is three. The following table gives examples relevant to North America, Japan, and Europe (applies
to 22 MHz channels in the 2.4 GHz band).
EuropeJapanNorth America
cell 1 on channel 1cell 1 on channel 1cell 1 on channel 1
cell 2 on channel 7cell 2 on channel 7cell 2 on channel 6
cell 3 on channel 13cell 3 on channel 14cell 3 on channel 11
In North America you can create an installation as shown in the following figure.
82 Wireless configuration