MSM7xx Controllers Configuration Guide v6.4.0

Tx protection
Supported on: MSM410, HP 425, MSM430, MSM460, MSM466, MSM466-R
Not available in Monitor or Sensor modes.
When an AP is operating in an 802.11n mode, and legacy (a/b/g) traffic is present on the same
channel as 802.11n traffic, this feature can be used to ensure maximum 802.11n throughput.
The following options are available:
• CTS-to-self: 802.11n transmissions are protected by sending a Clear To Send (CTS) frame
that blocks other wireless clients from accessing the wireless network.
• RTS/CTS: 802.11n transmissions are protected by sending a Request To Send (RTS) frame
followed by a CTS frame. This is a more robust, but slower, solution than CTS-to-self. However,
this method resolves the hidden station problem (where certain legacy stations may not see
only a CTS frame).
• 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.
Guard interval
Supported on: MSM410, MSM422 (radio 1), HP 425, MSM430, MSM460, MSM466, MSM466-R
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. Guard interval is not configurable on the HP 517. It is always set to Short, but
will downgrade to Long based on the capability of connected clients or the wireless environment.
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.)
98 Wireless configuration