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Chapter 8: Channel Management
For The Curious: More About Overlapping Channels
76 Psion Teklogix 9160 G2 Wireless Gateway User Manual
8.2.2 For The Curious: More About Overlapping Channels
The radio frequency (RF) broadcast Channel defines the portion of the radio spectrum 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 channels (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 broadcast-
ing 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 prede-
termined 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 in-
cludes 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 interference. For example,
AP1 could be assigned to channel 6, AP2 to channel 6, and AP3 to channel 5 as shown in
Figure 8.2.
Figure 8.2 Without Automatic Channel Management
AP3
AP1
Channel 6
(802.11b)
AP2
Channel 6
(802.11b)
Channel 5
(802.11b)
Channel 6
(802.11b)
AP5
Channel 7
(802.11b)
AP4
Client Station
Client Station
Interference from APs
on same channel (6)
Interference from
APs on adjacent channels
(5,6,7)