Cisco WAP121 Administration Manual page 61

Wireless Settings
Radio
STEP 4
Cisco Small Business WAP121 and WAP321 Wireless-N Access Point with PoE
• Channel Bandwidth (802. 1 1n modes only)—The 802. 1 1n specification
allows a 40 MHz-wide channel in addition to the legacy 20 MHz channel
available with other modes. The 40 MHz channel enables higher data rates
but leaves fewer channels available for use by other 2.4 GHz and 5 GHz
devices.
Set the field to 20 MHz to restrict the use of the channel bandwidth to a
20 MHz channel.
• Primary Channel (802. 1 1n modes with 40 MHz bandwidth only)—A 40 MHz
channel can be considered to consist of two 20 MHz channels that are
contiguous in the frequency domain. These two 20 MHz channels are often
referred to as the Primary and Secondary channels. The Primary Channel is
used for 802. 1 1n clients that support only a 20 MHz channel bandwidth and
for legacy clients.
Select one of these options:
- Upper—Set the Primary Channel as the upper 20 MHz channel in the
40 MHz band.
- Lower—Set the Primary Channel as the lower 20 MHz channel in the
40 MHz band.
• Channel—The portion of the radio spectrum the radio uses for transmitting
and receiving.
The range of available channels is determined by the mode of the radio
interface and the country code setting. If you select Auto for the channel
setting, the WAP device scans available channels and selects a channel
where no traffic is detected.
Each mode offers a number of channels, depending on how the spectrum is
licensed by national and transnational authorities such as the Federal
Communications Commission (FCC) or the International Telecommunication
Union (ITU-R).
In the Advanced Settings area, configure these settings:
• Short Guard Interval Supported—This field is available only if the selected
radio mode includes 802. 1 1n.
The guard interval is the dead time, in nanoseconds, between OFDM
symbols. The guard interval prevents Inter-Symbol and Inter-Carrier
Interference (ISI, ICI). The 802. 1 1n mode allows for a reduction in this guard
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