802.11N Channel Widths - Cisco M10-RM Software Manual

Chapter 6 Configuring Radio Settings
In places where RF interferrence might be causing clients to occassionally get disconnected from the
Note
wirless network, setting the wireless interface to run on a different channel, such as channel 1 (2412),
might avoid the interference.
Note Cisco Aironet CB20A client radios sometimes fail to associate to the AIR-RM21A radio module because
the CB20A client does not support all the channels supported by the AIR-RM21A radio module. The
default channel setting for the AIR-RM21A radio module, least congested, often results in the access
point settling on one of these frequencies that the CB20A client radio does not support: channel 149
(5745 GHz), channel 153 (5765 GHz), channel 157 (5785 GHz), and channel 161 (5805 GHz). To avoid
this problem, set the channel on the AIR-RM21A radio module to one of the channels supported by the
CB20A client.
Each 2.4-GHz channel covers 22 MHz. The bandwidth for channels 1, 6, and 11 does not overlap, so you
can set up multiple access points in the same vicinity without causing interference. Both 802.11b and
802.11g 2.4-GHz radios use the same channels and frequencies.
The 5-GHz radio operates on eight channels from 5180 to 5320 MHzup to 27 channels from 5170 to 5850
MHz depending on regulatory domain. Each channel covers 20 MHz, and the bandwidth for the channels
overlaps slightly. For best performance, use channels that are not adjacent (44 and 46, for example) for
radios that are close to each other.
Too many access points in the same vicinity creates radio congestion that can reduce throughput. A
Note
careful site survey can determine the best placement of access points for maximum radio coverage and
throughput.
Because they change frequently, channel settings are not included in this document. For up-to-date
information on channel settings for your access point or bridge, see the Channels and Maximium Power
Settings for Cisco Aironet Autonomous Access Points and Bridges. This document is available on
cisco.com at the following URL:
http://www.cisco.com/en/US/products/ps6521/tsd_products_support_install_and_upgrade.html

802.11n Channel Widths

802.11n allows both 20-MHz and 40-Mhz channel widths conisting of 2 contiguous non-overlapping
channels (for example, 2.4-GHz channels 1 and 6)
One of the 20-MHz channels is called the control channel. Legacy clients and 20-MHz high throughput
clients use the control channel. Beacons can only be sent on this channel. The second 20-MHz channel
is called the extension channel. 40-MHz stations may use this channel and the control channel
simultaneously.
A 40-MHz channel is specified as a channel and extension, such as 1,1. In this example, the control
channel is channel 1 and the extension channel is above it.
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Cisco IOS Software Configuration Guide for Cisco Aironet Access Points
Configuring Radio Channel Settings
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