HP MSM7xx Management And Configuration Manual page 125

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Guard interval
Supported on: MSM410, MSM422 (radio 1), E-MSM430, E-MSM460, E-MSM466
Not available in Monitor or Sensor modes.
This parameter is only configurable when Wireless mode is set to support an 802.11n option.
On the MSM410 and MSM422, Guard interval is automatically set to Long when Channel
width is set to 20 MHz.
To enhance performance in 802.11n modes, the guard interval can be reduced from its default
of 800 nanoseconds to 400.
The guard interval is the intersymbol time period that is used to prevent symbol interference
when multiple data streams are used (MIMO). However, symbol interference reduces the
effective SNR of the link, so reducing the guard interval may not improve performance under
all conditions.
The following settings are available:
 Short: Sets the guard interval to 400 nanoseconds which can provide improved
throughput (up to 10%) in some environments. The AP remains compatible with clients
that only support a long guard interval. Use this setting when Channel width is set to
Auto 20/40 MHz to get the best throughput.
 Long: Sets the guard interval to the standard of 800 nanoseconds.
Maximum range (ack timeout)
Only available in modes that support Local Mesh.
Fine tunes internal timeout settings to account for the distance that a link spans. For normal
operation, timeout is optimized for links of less than 1 km.
Note
This is a global setting that applies to all wireless connection made with the radio. Therefore,
adjusting this setting may lower the performance for users with marginal signal strength or
when interference is present. (Essentially, it means that if a frame needs to be retransmitted
it will take longer before the actual retransmit takes place.)
No MAC protection: This setting gives the best performance for 802.11n clients in
the presence of 802.11g or 802.11a legacy clients or APs. No protection frames (CTS-
to-self or RTS/CTS) are sent at the MAC layer by the AP. PHY-based protection
remains active, which alerts legacy clients to stay off the air while the AP is
transmitting data to 802.11n clients. This method of protection is supported by most
802.11g or 802.11a clients, but is not supported for 802.11b-only clients and should
not be used if such clients are expected on the network.
Wireless configuration
Radio configuration
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