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Cisco Small Business WAP551 and WAP561 Wireless-N Access Point 60
5
By default, when the radio mode includes 802.11n, the channel bandwidth is
set to 20/40 MHz to enable both channel widths. Set the field to 20 MHz to
restrict the use of the channel bandwidth to a 20 MHz channel.
• Primary Channel (802.11n modes with 20/40 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 802.11n clients that support only a 20 MHz channel
bandwidth and for legacy clients.
Select one of these options:
- Upper—Sets the Primary Channel as the upper 20 MHz channel in the
40 MHz band.
- Lower—Sets the Primary Channel as the lower 20 MHz channel in the
40 MHz band. Lower is the default selection.
• 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 the least amount of 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).
STEP 5 In the Advanced Settings area, configure these settings:
• Short Guard Interval Supported—This field is available only if the selected
radio mode includes 802.11n.
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 802.11n mode allows for a reduction in this guard
interval from the a and g definition of 800 nanoseconds to 400 nanoseconds.
Reducing the guard interval can yield a 10 percent improvement in data
throughput.
The client with which the WAP device is communicating must also support
the short guard interval.
Select one of these options: