Cisco Cisco Aironet 350 Mini-PCI Wireless LAN Client Adapter Guia Do Desenho
3-31
Enterprise Mobility 4.1 Design Guide
OL-14435-01
Chapter 3 WLAN Radio Frequency Design Considerations
Radio Resource Management (Auto-RF)
When neighboring APs receive neighbor messages, they validate them before forwarding them to the
controller. If they can validate the message hash and confirm that it belongs to the same RF group, the
packet is sent to the controller; otherwise, the AP drops the neighbor packet. The APs then forward the
validated messages to the controller, filling in the LWAPP packet status field with the SNR and RSSI of
the received neighbor packet.
controller. If they can validate the message hash and confirm that it belongs to the same RF group, the
packet is sent to the controller; otherwise, the AP drops the neighbor packet. The APs then forward the
validated messages to the controller, filling in the LWAPP packet status field with the SNR and RSSI of
the received neighbor packet.
provides a summary of the various functions of the devices in the system.
Note
TPC performs only downward power level adjustments. Coverage hole detection and correction increases
power levels on APs.
power levels on APs.
Auto-RF should not be confused with Rogue Detection (channel scanning), which is done separately
from the auto-RF algorithm. APs perform rogue detection by periodically monitoring all
country-specific channels (channel scanning). The APs goes “off-channel” for a period not greater than
60 ms to listen to the other channels. Packet headers collected during this time are sent to the controller,
where they are analyzed to detect rogue access points, whether service set identifiers (SSIDs) are
broadcast or not, rogue clients, ad-hoc clients, and interfering access points.
from the auto-RF algorithm. APs perform rogue detection by periodically monitoring all
country-specific channels (channel scanning). The APs goes “off-channel” for a period not greater than
60 ms to listen to the other channels. Packet headers collected during this time are sent to the controller,
where they are analyzed to detect rogue access points, whether service set identifiers (SSIDs) are
broadcast or not, rogue clients, ad-hoc clients, and interfering access points.
By default, each access point spends approximately 0.2 percent of its time off-channel. This is
statistically distributed across all access points so that no two adjacent access points are scanning at the
same time, which can adversely affect WLAN performance. Packets received by the AP from clients are
forwarded to the controller with the LWAPP status field filled in, which provides the controller with
radio information including RSSI and signal-to-noise ratio (SNR) for all packets received by the AP
during reception of the packet.
statistically distributed across all access points so that no two adjacent access points are scanning at the
same time, which can adversely affect WLAN performance. Packets received by the AP from clients are
forwarded to the controller with the LWAPP status field filled in, which provides the controller with
radio information including RSSI and signal-to-noise ratio (SNR) for all packets received by the AP
during reception of the packet.
Auto-RF Variables and Settings
Auto-RF can be turned on and off via the global setting on the Channel Selection (Wireless >
802.11b/g/n > Configure) web page (see
802.11b/g/n > Configure) web page (see
). You can manually set the channel and transmit
level for the AP from this web page. Additionally, it can be turned off and on from the global Auto-RF
web page. Remember that Auto-RF is per band and RF group computations are done for both the
802.11b/g band and another set of computations for 802.11a. The two radios do not have to share to have
the same configuration. But these configurations are applied to every AP associated to the controller.
Auto-RF configuration variables are shown on the global parameters Auto-RF configuration page (see
web page. Remember that Auto-RF is per band and RF group computations are done for both the
802.11b/g band and another set of computations for 802.11a. The two radios do not have to share to have
the same configuration. But these configurations are applied to every AP associated to the controller.
Auto-RF configuration variables are shown on the global parameters Auto-RF configuration page (see
Table 3-7
Device Function
Device
Functions
RF Group Leader
Collects data from WLCs in the RF group and analyzes it for TX Power
Control (TPC) and Dynamic Channel Assignment (DCA) system-wide. TPC
adjusts power levels only downward.
Control (TPC) and Dynamic Channel Assignment (DCA) system-wide. TPC
adjusts power levels only downward.
Local WLC
Collects data and runs the Coverage Hole Detection and Correction algorithm.
Adjusts power levels upward if necessary for clients
Adjusts power levels upward if necessary for clients
Light-weight access
point
point
•
Sends neighbor messages on all channels at full power at configured
interval
interval
•
Verifies neighbor hash on received neighbor messages
•
Scans configured channels for noise, interference, and IDS/rogue
detection and alerts if profile fails
detection and alerts if profile fails