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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

Interference from APs

on same channel (6)

Interference from

APs on adjacent channels

(5,6,7)

1 2 ... 95 96 97 98 99 100 101 102 103 104 105 ... 435 436

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