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Chapter 8: Channel Management
How It Works In A Nutshell
74
Psion Teklogix 9160 G2 Wireless Gateway User Manual
8.2.1 How It Works In A Nutshell
At a specified interval (the default is 1 hour) or on demand (click Update), the
Channel Manager maps APs to channel use and measures interference levels in the
cluster. If significant channel interference is detected, the Channel Manager auto-
matically re-assigns some or all of the APs to new channels per an efficiency algo-
rithm (or automated channel plan).
8.2.2 For The Curious: More About Overlapping Channels
The radio frequency (RF) broadcast Channel defines the portion of the radio spec-
trum that the radio on the access point uses for transmitting and receiving. The range
of available channels for an access point is determined by the IEEE 802.11 mode
(also referred to as band) of the access point.
IEEE 802.11b/802.11g modes (802.11 b/g) support use of channels 1 through 11
inclusive, while IEEE 802.11a mode supports a larger set of non-consecutive chan-
nels (36, 40, 44, 48, 52, 56, 60, 64, 149, 153, 157, 161, 165).
Interference can occur when multiple access points within range of each other are
broadcasting on the same or overlapping channels. The impact of this interference
on network performance can intensify during busy times when a large amount of
data and media traffic are competing for bandwidth.
The Channel Manager detects which bands (b/g or a) clustered APs are on, and uses a
predetermined collection of channels that will not mutually interfere. For the “b/g”
radio band, the classical set of non-interfering channels is 1, 6, 11. Channels 1, 4, 8, 11
produce minimal overlap. A similar set of non-interfering channels is used for the “a”
radio band, which includes all channels for that mode since they are not overlapping.
8.2.3 Example: A Network Before And After Channel Management
Without automated channel management, channel assignments to clustered APs
might be made on consecutive channels, which would overlap and cause interfer-
ence. For example, AP1 could be assigned to channel 6, AP2 to channel 6, and AP3
to channel 5 as shown in Figure 8.1 on page 75.