Performance Degradation And Channel Separation - Colubris Networks CN3000 Administrator's Manual

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Performance degradation and channel separation

When two wireless cells operating on the same frequency overlap, it can cause a
reduction in throughput in both cells. This occurs because a wireless station that is
attempting to transmit will defer (delay) its transmission if another station is currently
transmitting. On a network with many clients and a lot of traffic, this can severely affect
performance as stations defer multiple times before the channel becomes available. If a
station is forced to delay its transmission too many times, data may be lost.
Delays and lost transmissions can severely reduce throughput on a network. Use the
Wireless option on the Status menu to view this information on your network.
The following example shows two overlapping wireless cells operating on the same
frequency. Since both access points are within range of each other, the number of
deferred transmissions will be large.
cell 1 cell 2
Overlapping wireless cells can cause transmission delays.
The solution to this problem is to set the two networks to different channels with as great
a separation as possible in their operating frequencies. This reduces cross-talk, and
enables client stations connected to each access point to transmit at the same time.
Choosing non-overlapping channels
For optimum performance when operating in 802.11b or 802.11g modes, choose a
frequency that differs from other wireless access points operating in neighboring cells
by at least 25 MHz.
Two channels with the minimum 25 MHz frequency separation will always perform
worse than two channels using the maximum separation. So, it is always best to use the
greatest separation possible between overlapping networks.)
Note: When operating in 802.11a mode, all channels are non-overlapping.
With the proliferation of wireless networks, it is very possible that the wireless cells of
access points outside your control may overlap your intended area of coverage. To
choose the best operating frequency, use the Wireless > Neighborhood page to
generate a list of all access points operating near you and their operating frequencies.
The set of available channels is automatically determined by the CN3000 based on the
Country setting you define on the Wi-Fi page, which means that the number of non-
overlapping channels available to you will also vary. This will affect how you setup your
multi-cell network.
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